Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: Simulation and experimental validation

Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: Simulation and experimental validation | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: Simulation and experimental validation Meng Guo, Shilin Xia This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8814992/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Selective laser melting of pure tungsten has always been a challenge due to its intrinsic properties such as high melting point, high surface tension and dynamic viscosity. In order to reveal the physical phenomenon during SLM-processed pure tungsten, a transient mesoscale model was developed by finite volume method (FVM). The temperature evolution and thermodynamic behavior within the molten pool were investigated. The simulation results demonstrated that the peak temperature and cooling rate were enhanced as the laser power increased. The peaking temperature and cooling rate reached 5742 K and 4.66 \(\:\times\:\) 10 7 K/s using a high laser power of 350 W, respectively. Accordingly, the long liquid lifetime of 182 µs was obtained. At a high laser power of 350 W, the velocity vectors within the molten pool were intensified obviously, generating a strong mass transfer. A regular molten pool with a large width of 62 µm was obtained, which was favorable to metallurgical bonding with adjacent scanning tracks. The laser power played an important role in influencing the surface morphologies of SLM-processed tungsten parts. At a relatively low laser power of 200 W, the scanning track was discontinuous with a large number of unmelted particles. Simultaneously, the corresponding SLM-processed tungsten parts were observed with large pores. However, as a high laser power of 350 W was applied, the top surface of scanning track was continuous with regular liquid flow. Under this situation, the corresponding SLM-processed tungsten part was nearly free of pores. Moreover, the cracks were inevitable regardless of the applied laser powers and the formation mechanism of cracks was revealed. Based on the simulation results of SLM-processed tungsten, the available methods used to reduce the cracks were proposed. Selective laser melting Tungsten Temperature evolution Thermodynamic behavior Defects formation Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Introduction As an important part of additive manufacturing (AM) technology, selective laser melting (SLM) is considered as the most promising technology owing to its unique characteristics such as high forming accuracy and high design freedom [ 1 – 3 ]. During SLM, a moving laser beam with high energy selectively irradiates the powder layer and the powder particles are fused to form metallurgical bonding with each other. Subsequently, the continuous scanning tracks are shaped with the movement of the laser beam based on the computer-aided design (CAD) data [ 4 ]. Through the metallurgical bonding of powder between layer and layer, a component is finally built. The layer-by-layer construction method allows the rapid production of complex parts without the limitation of geometric shape. Therefore, SLM is widely used in many special manufacturing fields such as aerospace engineering and biological tissue engineering [ 5 , 6 ]. So far, a large number of studies have been conducted on various metal materials, including Al-based alloys, Ti-based alloys, Ni-based alloys, stainless steels and so on [ 7 – 12 ]. The mapping relationships among defects formation, phase transition, microstructure evolution and ultimate mechanical properties of these materials during SLM process have been revealed to take full advantage of SLM-processed metal materials. With the continuous development of SLM technology in high-power laser and high-speed galvanometer, the metal materials applicable to SLM become very extensive from the low melting point materials to the high melting point materials. Recently, the researches on SLM-processed the refractory metals such as tungsten (W), Tantalum (Ta), molybdenum (Mo) and niobium (Nb) have been reported one after another [ 13 – 17 ]. Among these refractory metals, tungsten is the most popular material due to its high melting point, high thermal conductivity and high strength. Moreover, tungsten is widely regarded as the most promising candidate material for plasma facing materials (PFMs) owing to its high sputtering threshold and low tritium retention [ 18 , 19 ]. Therefore, a number of researches have been conducted to demonstrate the possibility of SLM-processed tungsten. However, selective laser melting of tungsten parts remains a challenge due to its intrinsic characteristics. Zhang et al. [ 20 ] successfully fabricated tungsten parts with a novel nanocrystalline structure by SLM. It was found that the solid forces by laser could result in the formation of nanocrystalline tungsten. Moreover, the novel nanocrystalline showed a fine grain structure, which was beneficial to the performance of final SLM-processed parts. K. Enneti et al. [ 21 ] conducted a study to understand the effect of process parameters such as hatch spacing and scanning speed on the densification of SLM-processed tungsten. He found that the densification of SLM-processed tungsten increased with energy density and porosity was the main reason accounting for the decrease in densification. Zhou et al. [ 22 ] pointed out that there existed a process where melt spreading and solidification competed with each other in SLM of tungsten. Furthermore, the densification behavior was determined by intrinsic properties of tungsten and the laser processing parameters. Previous works on SLM-processed tungsten demonstrated that formation of porosity and cracks were the main defects influencing the forming quality of SLM-processed tungsten [ 23 , 24 ]. As a result, understanding the formation mechanism of defects like porosity and cracks was significantly effective to control the performances of final tungsten components. Generally, the necessary trial and error tests should be conducted to make the SLM-processed tungsten parts meet the engineering quality standards. However, this process tends to be costly and time-consuming. As a result, the numerical modeling and simulation method rises in response to the proper time and conditions. The numerical modeling and simulation method could offer an effective approach to further figure out the physical phenomenon, which serves as a precursor to optimize the experimental processing parameters for SLM-processed metal parts [ 25 ]. Recently, simulations of physical phenomenon such as the formation and evolution of porosity during SLM process have been demonstrated to be a promising method to effectively control the defects formation. Xia et al. [ 26 ] proposed a transient mesoscale model with a randomly packed powder-bed to understand the porosity evolution during SLM-processed Inconel 718 alloy. In this model, the phase transition, variation of thermos-physical properties and interfacial force were taken into consideration. Through this model, the influence of scanning speed on porosity formation was revealed. A. Khairallah et al. [ 27 ] developed a three-dimensional high-fidelity powder-scale model to understand the formation mechanism of pore defects, material spattering and denudation zones. It was found that there existed different pore formation mechanisms on a melt track. Moreover, measures for eliminating the undesirable were proposed. Qiu et al. [ 28 ] utilized a computational fluid dynamics (CFD) calculation to predict the development of porosity and surface defects of SLM-processed Ti-6Al-4V under different laser scanning speed and powder layer thickness. The results demonstrated that the unstable melt flow could result in increased porosity and surface roughness. Furthermore, the porosity was more sensitive to powder layer thickness and a thick powder layer could lead to significant porosity. The above-mentioned works demonstrated that numerical modeling and simulation method was applicable to predict the defects evolution during SLM. In view of the difficulties in selective laser melting of pure tungsten, the numerical simulation method was introduced to simulate the SLM process of pure tungsten. In order to reveal the porosity evolution and cracks formation during SLM of pure tungsten, a random stacking model of powder bed was established, which was close to the actual situation. The commercial fluent finite volume method (FVM) software was employed to calculate the mesoscale model of random packed powder-bed. The transition of solid to liquid, surface tension, recoil force, thermo-capillary force, gravity and buoyancy force were taken into consideration to obtain more accurate simulation results [ 29 ]. Furthermore, the experimental results of top and cross-section surface of SLM-processed tungsten were obtained to further prove the accuracy of the random packed model of powder bed. Experimental procedure Numerical simulation During SLM, a high energy laser beam selectively irradiates the powder bed and resultant the fusion of powder particles. A series of complex physical phenomenon such as heat conduction and convection, evaporation of elements, recoil pressure of laser and spatters of powder particles are involved, as depicted in Fig. 1 (a). In order to reveal the heat transfer and thermodynamic behavior during the fabrication of tungsten parts by SLM, a three-dimensional model with a size of 300 µm \(\:\times\:\) 200 µm \(\:\times\:\) 80 µm was established using the FLUENT software (Fig. 1 (b)). Table 1 described the material properties and processing parameters used in this simulation. Other material properties such as thermal conductivity and specific heat capacity were classified in reference [ 30 ]. In this model, the molten metal was considered as the incompressible fluid in high temperature. The motion of molten metal fluid was described by energy, mass, momentum conservation, which was detailed in our previous work [ 26 , 31 , 32 ]. Based on the volume of fluid model, the volume fraction equation for different phase was described as: $$\:\frac{\partial\:{a}_{i}}{\partial\:t}+\overrightarrow{v}\bullet\:\nabla\:{a}_{i}=\frac{{S}_{i}}{{\rho\:}_{i}}$$ 1 Where \(\:\:{\sum\:}_{i=1}^{n}{a}_{i}=1\) , \(\:{a}_{i}\) represented the volume fraction of i phase, n was the total number of phases. At the interface of the gas phase and tungsten phase, the mixed material properties were calculated as: $$\:\phi\:=\eta\:{\phi\:}_{gas}+(1-\eta\:){\phi\:}_{tungsten}$$ 2 Where \(\:\phi\:\) represented a certain material property like density, thermal conductivity and so on, \(\:\eta\:\) was the volume fraction of the gas phase in mesh. The boundaries satisfied the following equation: $$\:K\frac{\partial\:T}{\partial\:n}+{h}_{c}\left(T-{T}_{0}\right)+\sigma\:\epsilon\:\left({T}^{4}-{T}_{0}^{4}\right)=Q$$ 3 Where n was the normal vector of the surface, \(\:{h}_{c}\) was the heat transfer coefficient of thermal convection, \(\:\epsilon\:\) was the emissivity and \(\:\sigma\:\) was the Stefan-Boltzmann constant. The laser source was considered as a volumetric Gaussian distributed circular heat source, which could be defined as: $$\:q=\frac{6PA}{{R}^{2}\pi\:H\left(1-\frac{1}{{e}^{3}}\right)}exp\left(\frac{-9\left({x}^{2}+{y}^{2}\right)}{{R}^{2}log\left(\frac{H}{z}\right)}\right)$$ 4 Where P was the laser power, R represented the radius of laser beam, H was the penetrated depth of heat source, and A was the effective laser energy absorption of the material. The value of A was calculated as 0.68 [ 33 ]. Table 1 The as-used material properties and processing parameters during SLM. Parameters Value Density, \(\:\rho\:\) 19350 kg/m 3 Ambient temperature, T 0 (K) 293 Layer thickness, d (µm) 30 Diameter of laser beam, D (µm) 70 Hatch spacing, s (µm) 50 Absorption of tungsten powder, A 0.68 Scanning speed, v (mm/s) 200 Laser power, P (W) 200, 250, 300, 350 Experimental methods To verify the accuracy of the physical model, the corresponding processing parameters were applied to fabricate scanning tracks and cubic samples of pure tungsten. As shown in Fig. 2 , the tungsten powder with a spherical shape was used in this work. The tungsten powder had a diameter ranging from 5 µm to 25 µm. The SLM system used in this study was equipped with a YLR-500 ytterbium fiber laser, an automatic spreading device for spreading powder, an inert gas system for providing protective atmosphere and a computer control system. The fiber laser had a maximum laser power of 500 W and a laser spot size of 70 µm (IPG Laser GmbH, Germany). The scanning tracks and cuboid samples were fabricated on the stainless-steel substrate, respectively. The surface morphologies of the SLM-processed scanning tracks were characterized by FEI Quanta 200 scanning electron microscope (SEM). The cuboid samples were cut, ground and then polished for the observation of the morphologies from the building direction. A MDS400 optical microscopy (Chongqing Optec Instrument Co., Ltd., China) was used to observe the polished surface of SLM-processed tungsten. Results and discussions Temperature evolution It is known to all that laser processing is an extremely nonequilibrium process with the rapid heating and fast cooling. In this case, the fast-cooling rate (10 3 – 10 8 K/s) can result in special structure with fine grains and novel properties [ 34 ]. Therefore, having a good understanding of temperature evolution and resultant variation of cooling rate during SLM is favorable to better fabricate a component. Figure 3 shows the temperature distribution profiles and attendant cooling rate versus processing time at the monitor point ( X = 150 µm, Y = 0 µm and Z = 10 µm) with different laser powers. It was obviously observed that the maximum temperature and cooling rate were significantly different as the various laser powers were applied. When a low laser power of 200 W was used, a peak temperature of 4260 K and a maximum cooling rate of 2.10 \(\:\times\:\) 10 7 K/s were obtained, respectively (Fig. 3 (a)). In this case, the liquid lifetime was 136 µs. As the laser power was increased to 250 W, the obtained maximum temperature and cooling rate were increased correspondingly. As shown in Fig. 3 (b), the maximum temperature and cooling rate reached a value of 5132 K and 2.77 \(\:\times\:\) 10 7 K/s, respectively. In this case, the liquid lifetime was enhanced to 176 µs. With the laser power increased to 300 W, the energy input was increased, resulting in a peak temperature and cooling rate of 5558 K and 3.88 \(\:\times\:\) 10 7 K/s, respectively (Fig. 3 (c)). The lifetime was prolonged to 182 µs. While a high laser power of 350 W was applied, the maximum temperature and cooling rate was 5742 K and 4.66 \(\:\times\:\) 10 7 K/s, respectively (Fig. 3 (d)). Moreover, the high laser power could facilitate a longer lifetime of 184 µs. Generally, increasing laser power consequentially resulted in an enhancement of energy input and resultant high temperature in molten pool. In this case, the melting flow could be generated vastly due to the elevated operating temperature within the molten pool, which could facilitate the spreading of the liquid tungsten to wet the surrounding powder particles. Moreover, the viscosity of liquid tungsten was inversely proportional to temperature [ 35 ], indicating that the viscosity of molten liquid could be obviously reduced with the elevated operating temperature within the molten pool, which was favorable to form good metallurgical bonding between the melt and obtain high dense parts. Simultaneously, an elevated laser power could bring more energy input, prompting longer liquid lifetime of liquid tungsten and resulting in a higher peaking temperature. It was worth noting that the cooling rate curves showed a fluctuation when the temperature of solid tungsten reached its melting point or liquid tungsten arrived its solidifying point. This was due to the effect of latent heat of fusion during melting or solidification. During SLM, the rapid melting and solidification would happen in an instant. In this process, huge latent heat of fusion could be released and resultant the fluctuation of cooling rate curves [ 36 ].Generally, during the melting process, the cooling rate was a negative value. While the cooling rate changed to a positive value during the solidification process. The calculated maximum cooling rate increased from 2.10 \(\:\times\:\) 10 7 K/s to 4.66 \(\:\times\:\) 10 7 K/s as the laser power increased from 200 W to 350 W. This was because the increased energy input could cause the peak temperature to rise at a given scanning speed. Thus, the cooling rate could be increased in unit time. In this case, the novel microstructure and unprecedented mechanical properties of final SLM-processed parts could be obtained. Moreover, it was clearly noted that the liquid lifetime of the molten pool increased as the elevated laser power was applied. When the laser power was 200 W, the liquid lifetime was only 136 µs, which was unable to produce sufficient liquid to wet the surrounding powder particles and form sound scanning tracks. While the laser power was increased to 350 W, the liquid lifetime was prolonged to 184 µs. In this case, the wettability of liquid-solid could be improved, promoting the melt spreading and resultant sound scanning tracks. Thermodynamic behavior of molten pool Typically, the calculated temperature distribution contours and velocity profiles of the top surface ( X - Y plane) of scanning tracks under different laser powers are clearly depicted in Fig. 4 . It was obvious that the contours and dynamics of molten pool exhibited a significant difference at various laser powers. The temperature line of 3695 K represented the liquid line of tungsten. When a low laser power of 200 W was applied, the top surface of molten pool presented an ellipse shape with a narrow dimension, as shown in Fig. 4 (a). The calculated velocity of vector was below 0.3 m/s and its distribution was narrow, indicating that the mass transfer process was weak. In this situation, the molten liquid of tungsten generated in the molten pool was considerably less. As the laser power increased to 250 W, the dimension of top surface of molten pool was significantly enlarged (Fig. 4 (b)). Moreover, the velocity of vector was increased and its distribution range was expanded. At a higher laser power of 300 W, the ellipse-shaped pool exhibited with an increased dimension in comparison to those of 200 W and 250 W (Fig. 4 (c)). Meanwhile, the range of mass transfer was enlarged with more velocity vector. When an elevated laser power of 350 W was used, the ellipse-shaped pool was observed with intense velocity of vector and increased size. The maximum velocity of vector reached 0.6 m/s, demonstrating that there existed strong mass and heat transfer within the molten pool (Fig. 4 (d)). Figure 5 illustrates the typical temperature distribution contours and corresponding velocity vector plots of the cross section ( Y - Z plane) of scanning tracks under various laser powers. It was obviously observed that the width and dynamic behavior of the molten pool presented significant differences. At a low laser power of 200 W, the energy input was insufficient to promote the interaction between laser and powder. Thus, the power particles cannot be melted and form good wetting. Accordingly, a small width of 25 µm was formed, as shown in Fig. 5 (a), which was detrimental to the metallurgical bonding between neighboring scanning tracks. Moreover, the operating temperature within the molten pool was below 3800 K. In this situation, the thermal convection and mass transfer was weak. With increasing the applied laser power to 250 W, the width of molten pool was enlarged to 45 µm and the maximum operating temperature of molten pool was enhanced to 4000 K (Fig. 5 (b)). To some extent, an elevated laser power could bring high operating temperature within molten pool, promoting the mass transfer and melt flow. Consequently, it was beneficial to form a sound bonding with the adjacent tracks. When a laser power of 300 W was used, the energy input was sufficient to facilitate the melt flow and mass transfer, obtaining a molten pool with a width of 52.5 µm (Fig. 5 (c)). Meanwhile, the operating temperature within molten pool was increased to 4600 K, which could facilitate the motion and transfer of substance and resultant good metallurgical bonding. As an even higher laser power of 350 W was applied, the high energy input could bring sufficient operating temperature, resulting in abundant molten liquid and reducing the viscosity of melt. Correspondingly, a molten pool with a large width of 62 µm was formed, as clearly depicted in Fig. 5 (d). Meanwhile, the Marangoni convection with a symmetric shape was generated. In this case, the mass transfer within the molten pool was considerably intense, which was favorable to the motion and escape of bubbles. Therefore, it was demonstrated that the width of molten pool was significantly influenced by laser power. A relatively high laser power could contribute to the formation of the molten pool and achieve a well metallurgical bonding between adjacent tracks. Surface morphology evolution and defects formation The simulated evolution of surface morphology of the scanning tracks on the top surface at different laser powers is shown in Fig. 6 . It was visibly observed that the surface morphology exhibited with big differences as the laser power increased. When a low laser power of 200 W was applied, the top surface appeared to be discontinuous with a mass of unmelted powder particles (Fig. 6 (a)). Meanwhile, the maximum temperature of the molten pool surface reached 3500 K, which was insufficient to melt the tungsten powder to form continuous scanning tracks. As the laser power was increased to 250 W, the energy input was increased accordingly, promoting some powder particles to melt. Thus, some continuous melting areas appeared. However, the operating temperature was limited to reduce the viscosity. The melting areas was unable to form continuous tracks, as clearly depicted in Fig. 6 (b). Nevertheless, at a high laser power of 300 W, the maximum operating temperature within the molten pool reached to 4250 K. Under this situation, the powder particles were melted largely to form molten liquid. Simultaneously, the elevated temperature could reduce the viscosity of molten liquid and facilitate the wetting and spreading of melt. Finally, a continuous track was formed (Fig. 6 (c)). As the laser power was enhanced to 350 W, the maximum operating temperature in the molten pool was further improved to 4500 K. Correspondingly, the powder particles were melted more thoroughly and resultant more molten liquid. Meanwhile, the viscosity of molten liquid was reduced, promoting the melt flowing. As a result, a continuous scanning track was obtained (Fig. 6 (d)). Figure 7 illustrates the corresponding experimental results of scanning tracks of SLM-processed tungsten. The surface morphology presented huge differences as the laser power increased. When a low laser power of 200 W was used, it could be obviously observed that the tungsten powder particles were unmelted due to the limited laser power (Fig. 7 (a)). Moreover, the laser power was unable to penetrate into the substrate to form good metallurgical bonding. Thus, a scanning track with a large number of unmelted particles was generated. As the laser power increased to 250 W, the energy input was increased, bringing elevated operating temperature within molten pool. To some extent, the elevated temperature could melt most tungsten powder and resultant abundant molten liquid. However, the viscosity and surface tension of liquid tungsten were very large, impeding the wetting and spreading of liquid tungsten. Thus, the obtained scanning track was discontinuous with unstable melt flow, as shown in Fig. 7 (b). At a high laser power of 300 W, the operating temperature was further increased, reducing the viscosity of molten liquid. Simultaneously, the powder particles were well melted and resultant melt flow. Due to the elevated energy input, the penetration depth was sufficient to forming a good metallurgical bonding between powder layer and substrate. Finally, a continuous scanning track with stable melt flow was formed (Fig. 7 (c)). When an even high laser power of 350 W was used. The surface morphology exhibited with a good surface quality. The sufficient energy input could result in adequate penetration depth to facilitate the metallurgical bonding [ 37 , 38 ]. Meanwhile, the intense Marangoni flow induced by the high laser power could disturb the molten pool and promote the flow of molten liquid. In this case, both the melting behavior and the spreading ability were strengthened. As a result, a continuous scanning track with regular shape and stable melt flow was obtained, as clearly shown in Fig. 7 (d). The typical evolution of simulated porosity at different laser powers from the X - Z plane is illustrated in Fig. 8 . It could be understood that the porosity on the cross section reflected the interlayer bonding. The distribution of the porosity showed a big difference as the laser power increased. As the laser power of 200 W was applied, the morphology of the cross section was porous with a considerable number of large pores (Fig. 8 (a)). Due to the insufficient energy input caused by the low laser power, the powder particles were incompletely melted and became the source of pores. Furthermore, the number of molten liquids in the pool was limited and the lifetime of molten pool was short, which could hinder the molten liquid to migrate and fill into the porosity. When the laser power was increased to 250 W, the number of pores was reduced. Meanwhile, the dimensions of the pores were diminished, as depicted in Fig. 8 (b). Due to the enhancement of laser power, the energy input was increased to fuse most powder particles and generate more molten liquid. Moreover, the dynamic viscosity of molten pool could be reduced and resultant sufficient melt flow. In this case, the preformed pores could be filled up. However, the energy input was limited to eliminate the pores. When the laser was settled as 300 W, the number of pores was further decreased. Some large pores merged and formed small pores (Fig. 8 (c)). Owing to the enhanced laser power, the tungsten powder could be completely melted. Simultaneously, the elevated operating temperature could reduce the dynamic viscosity of molten pool, facilitating the wetting and spreading of molten liquid. Thus, the preformed large pores were further filled with molten liquid. At an elevated laser power of 350 W, the surface morphology was almost free of pores (Fig. 8 (d)). On one hand, the elevated laser power could provide sufficient energy to penetrate the powder layer and fuse the powder particles. On the other hand, the operating temperature could be enhanced, reducing the dynamic viscosity and resultant regular melt flow. Furthermore, the intensified Marangoni flow could promote some gas bubbles to escape from the molten pool, which was favorable to the densification behavior. In order to further verify the accuracy of simulation results, the corresponding processing parameters was employed to fabricate the tungsten cuboid parts by SLM. The OM images of SLM-processed tungsten parts using various laser powers are depicted in Fig. 9 . It could be visibly observed that pores and cracks were the main defects in SLM-processed pure tungsten parts. When the laser power was 200 W, a mass of inter-layer pores with large dimensions were clearly observed (Fig. 9 (a)). These pores clustered with irregular shapes and some unmelted particles could be observed in pores. Moreover, some microcracks were found along the building direction. As the laser power increased to 250 W, it was obvious that the number of pores was largely reduced (Fig. 9 (b)). Meanwhile, the dimension of pores was decreased and the cluster phenomenon was weakened. However, the microcracks were remained on the surface. At an elevated laser power of 300 W, the pores were further reduced both in size and numbers. Moreover, the microcracks were obvious with large length, as shown in Fig. 9 (c). When an even high laser power was employed, only small pores could be observed (Fig. 9 (d)). Furthermore, the long microcracks were more remarkable. As mentioned above, the pores appeared at the low laser power were due to the incomplete melting of powder particles. There existed a competitive of melt spreading and solidification during SLM. Due to the high surface tension and viscosity of liquid tungsten, the wetting and spreading speeds of liquid tungsten were relatively low. In this situation, the tungsten liquid was unable to form melt flow. Finally, the obtained scanning tracks were discontinuous and the SLM-processed tungsten parts were porous at a low laser power. Fortunately, the pores could be eliminated by adjusting the laser power. While the microcracks seemed to be inevitable. Previous experimental works on SLM-processed tungsten demonstrated that the thermal stresses were prone to arise during rapid solidification or recrystallization [ 39 , 40 ]. Moreover, the high ductile-brittle transition temperature (DBTT), typically between 200 ℃ and 400 ℃, accounted for the generation of cracks [ 41 ]. SLM process would inevitably experience the fast cooling, as the temperature was below the DBTT, the yield strength was low than the residual stress, causing the cracks [ 42 – 44 ]. In order to reveal the influence of temperature on cracks formation. The temperature under different laser powers and the corresponding temperature gradient were calculated, respectively. Figure 10 illustrates the temperature variation and distribution of temperature gradient along the Z -axis at different laser powers. It was observed that the temperature increased at first and decreased subsequently along the Z -axis direction (Fig. 10 (a)). Meanwhile, the temperature was enhanced with the elevated laser power. The calculated temperature gradient was depicted in Fig. 10 (b). When the laser power increased from 200 W to 350 W, the calculated maximum temperature gradient was 336.8 \(\:\times\:\) 10 6 K/m, 290.1 \(\:\times\:\) 10 6 K/m, 285.1 \(\:\times\:\) 10 6 K/m and 234.8 \(\:\times\:\) 10 6 K/m, respectively. It was demonstrated that thermal shrinkage caused by the change in temperature would generate during laser processing [ 45 ]. In this situation, the larger the temperature gradient was, the more the thermal shrinkage would generate. Furthermore, due to the low coefficient of thermal expansion of tungsten, the shrinkage was prone to result in cracks. When the laser power was low, the cracks were not obvious in comparison of the high laser power. This was because the pores could serve as the source of stress relief in some degree [ 46 ]. Thus, the cracks were more obvious at an even higher laser power. Based on the simulation results, it was concluded that decreasing the temperature gradient was able to reduce the cracks during SLM-processed tungsten parts. Thus, a higher laser power was favorable. Furthermore, the alloying elements with low melting could result in the reduction of the temperature gradient. As a result, alloying design was another effective way to reduce the cracks. Conclusions In the present study, a random stacking model of powder particles was established to study the influence of laser power on SLM-processed pure tungsten parts. The temperature evolution, thermodynamic behavior of molten pool, surface morphology and defects evolution during SLM of pure tungsten were analyzed in detail. Meanwhile, the corresponding experiments were conducted. The main conclusions were drawn as follows: (1) The laser power had a huge influence on the temperature during SLM-processed tungsten parts. The peak temperature and relevant cooling rate were increased with the elevated laser power. Meanwhile, the lifetime of molten pool was prolonged as the laser power increased. (2) At a high laser power, the resultant velocity of vector was intensified, indicating a strong mass transfer in the molten pool. Simultaneously, the high laser power resulted in an increased width of pool, which was favorable to the metallurgical bonding with adjacent scanning tracks. (3) Laser power played a crucial role in influencing the surface morphologies of scanning tracks. As the laser power increased, the powder particles were melted completely and resultant good wetting and spreading of molten liquid, promoting a continuous scanning track. Meanwhile, the pores were obviously reduced with enhancing the laser power, which was beneficial to the densification behavior. However, the cracks induced by the high DBTT and large temperature gradient were inevitable in SLM-processed tungsten parts. (4) The top surface morphologies of scanning tracks and cross section morphologies of tungsten parts by SLM were obtained, respectively. According to the simulation and experimental results, it was proposed that enhancing the laser power and alloying design were feasible methods to reduce the cracks. Declarations Acknowledgements The authors gratefully acknowledge the financial support from the Basic Research Program of Jiangsu (No. BK20250521) and Jiangsu Funding Program for Excellent Postdoctoral Talent. Compliance with ethical standards Conflict of interest The authors declare that they have no conflict of interest. References Gu DD, Meiners W, Wissenbach K, Poprawe R (2012) Laser additive manufacturing of metallic components: materials, processes and mechanisms. Int Mater Rev 57:133–164. https://doi.org/10.1179/1743280411Y.0000000014 Yap CY, Chua CK, Dong ZL et al (2015) Review of selective laser melting: Materials and applications. Appl Phys Rev 2. https://doi.org/10.1063/1.4935926 Aboulkhair NT, Simonelli M, Parry L et al (2019) 3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting. Prog Mater Sci 106:100578. https://doi.org/10.1016/j.pmatsci.2019.100578 Dogu MN, McCarthy E, McCann R et al (2022) Digitisation of metal AM for part microstructure and property control. IntJ Mater Form 15:30. https://doi.org/10.1007/s12289-022-01686-4 Martin JH, Yahata BD, Hundley JM et al (2017) 3D printing of high-strength aluminium alloys. Nature 549:365–369. https://doi.org/10.1038/nature23894 Meng L, Zhao J, Lan X et al (2019) Multi-objective optimisation of bio-inspired lightweight sandwich structures based on selective laser melting. Virtual Phys Prototyp 2759:1–14. https://doi.org/10.1080/17452759.2019.1692673 Olakanmi EO, Cochrane RF, Dalgarno KW (2015) A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties. Prog Mater Sci 74:401–477. https://doi.org/10.1016/j.pmatsci.2015.03.002 Herzog D, Seyda V, Wycisk E, Emmelmann C (2016) Additive manufacturing of metals. Acta Mater 117:371–392. https://doi.org/10.1016/j.actamat.2016.07.019 Wang D, Wu S, Fu F et al (2017) Mechanisms and characteristics of spatter generation in SLM processing and its effect on the properties. Mater Des 117:121–130. https://doi.org/10.1016/j.matdes.2016.12.060 Li R, Wang M, Yuan T et al (2017) Selective laser melting of a novel Sc and Zr modified Al-6.2 Mg alloy: Processing, microstructure, and properties. Powder Technol 319:117–128. https://doi.org/10.1016/j.powtec.2017.06.050 Zhang L, Song B, Liu R et al (2020) Effects of Structural Parameters on the Poisson’s Ratio and Compressive Modulus of 2D Pentamode Structures Fabricated by Selective Laser Melting. Engineering 6:56–67. https://doi.org/10.1016/j.eng.2019.06.009 Sghaier TAM, Sahlaoui H, Mabrouki T et al (2023) Selective Laser Melting of Stainless-Steel: A Review of Process, Microstructure, Mechanical Properties and Post-Processing treatments. IntJ Mater Form 16:41 Braun J, Kaserer L, Stajkovic J et al (2019) Molybdenum and tungsten manufactured by selective laser melting: Analysis of defect structure and solidification mechanisms. Int J Refract Met Hard Mater 84:104999. https://doi.org/10.1016/j.ijrmhm.2019.104999 Kaserer L, Braun J, Stajkovic J et al (2019) Fully dense and crack free molybdenum manufactured by Selective Laser Melting through alloying with carbon. Int J Refract Met Hard Mater 84:105000. https://doi.org/10.1016/j.ijrmhm.2019.105000 Zhang S, Cheng X, Yao Y et al (2015) Porous niobium coatings fabricated with selective laser melting on titanium substrates: Preparation, characterization, and cell behavior. Mater Sci Eng C 53:50–59. https://doi.org/10.1016/j.msec.2015.04.005 Zhou L, Yuan T, Li R et al (2017) Selective laser melting of pure tantalum: Densification, microstructure and mechanical behaviors. Mater Sci Eng A 707:443–451. https://doi.org/10.1016/j.msea.2017.09.083 Zhang J, Gu D, Yang Y et al (2019) Influence of Particle Size on Laser Absorption and Scanning Track Formation Mechanisms of Pure Tungsten Powder During Selective Laser Melting. Engineering 5:736–745. https://doi.org/10.1016/j.eng.2019.07.003 Butler BG, Paramore JD, Ligda JP et al (2018) Mechanisms of deformation and ductility in tungsten – A review. Int J Refract Met Hard Mater 75:248–261 Neu R, Riesch J, Coenen JW et al (2016) Advanced tungsten materials for plasma-facing components of DEMO and fusion power plants. Fusion Eng Des 109–111:1046–1052. https://doi.org/10.1016/j.fusengdes.2016.01.027 Zhang D, Cai Q, Liu J (2012) Formation of nanocrystalline tungsten by selective laser melting of tungsten powder. Mater Manuf Processes 27:1267–1270. https://doi.org/10.1080/10426914.2012.663119 Enneti RK, Morgan R, Atre SV (2018) Effect of process parameters on the Selective Laser Melting (SLM) of tungsten. Int J Refract Met Hard Mater 71:315–319. https://doi.org/10.1016/j.ijrmhm.2017.11.035 Zhou X, Liu X, Zhang D et al (2015) Balling phenomena in selective laser melted tungsten. J Mater Process Technol 222:33–42. https://doi.org/10.1016/j.jmatprotec.2015.02.032 Wen S, Wang C, Zhou Y et al (2019) High-density tungsten fabricated by selective laser melting: Densification, microstructure, mechanical and thermal performance. Opt Laser Technol 116:128–138. https://doi.org/10.1016/j.optlastec.2019.03.018 Guo M, Gu D, Xi L et al (2019) Selective laser melting additive manufacturing of pure tungsten: Role of volumetric energy density on densification, microstructure and mechanical properties. Int J Refract Met Hard Mater 84:105025. https://doi.org/10.1016/j.ijrmhm.2019.105025 Wu YC, Hwang WS, San CH et al (2018) Parametric study of surface morphology for selective laser melting on Ti6Al4V powder bed with numerical and experimental methods. IntJ Mater Form 11:807–813. https://doi.org/10.1007/s12289-017-1391-2 Xia M, Gu D, Yu G et al (2017) Porosity evolution and its thermodynamic mechanism of randomly packed powder-bed during selective laser melting of Inconel 718 alloy. Int J Mach Tools Manuf 116:96–106. https://doi.org/10.1016/j.ijmachtools.2017.01.005 Khairallah SA, Anderson AT, Rubenchik A, King WE (2016) Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones. Acta Mater 108:36–45. https://doi.org/10.1016/j.actamat.2016.02.014 Qiu C, Panwisawas C, Ward M et al (2015) On the role of melt flow into the surface structure and porosity development during selective laser melting. Acta Mater 96:72–79. https://doi.org/10.1016/j.actamat.2015.06.004 Khairallah SA, Anderson A (2014) Mesoscopic simulation model of selective laser melting of stainless steel powder. J Mater Process Technol 214:2627–2636. https://doi.org/10.1016/j.jmatprotec.2014.06.001 Guo M, Gu D, Xi L et al (2019) Formation of scanning tracks during Selective Laser Melting (SLM) of pure tungsten powder: Morphology, geometric features and forming mechanisms. Int J Refract Met Hard Mater 79:37–46. https://doi.org/10.1016/j.ijrmhm.2018.11.003 Yuan P, Gu D (2015) Molten pool behaviour and its physical mechanism during selective laser melting of TiC/AlSi10Mg nanocomposites: Simulation and experiments. J Phys D Appl Phys 48:35303. https://doi.org/10.1088/0022-3727/48/3/035303 Xia M, Gu D, Yu G et al (2016) Selective laser melting 3D printing of Ni-based superalloy: understanding thermodynamic mechanisms. Sci Bull (Beijing) 61:1013–1022. https://doi.org/10.1007/s11434-016-1098-7 Wang D, Yu C, Zhou X et al (2017) Dense Pure Tungsten Fabricated by Selective Laser Melting. Appl Sci 7:430. https://doi.org/10.3390/app7040430 Das M, Balla VK, Basu D et al (2010) Laser processing of SiC-particle-reinforced coating on titanium. Scr Mater 63:438–441. https://doi.org/10.1016/j.scriptamat.2010.04.044 Paradis PF, Ishikawa T, Yoda S (2005) Viscosity of liquid undercooled tungsten. J Appl Phys 97. https://doi.org/10.1063/1.1896432 Romano J, Ladani L, Razmi J, Sadowski M (2015) Temperature distribution and melt geometry in laser and electron-beam melting processes - A comparison among common materials. Addit Manuf 8:1–11. https://doi.org/10.1016/j.addma.2015.07.003 Le KQ, Tang C, Wong CH (2019) On the study of keyhole-mode melting in selective laser melting process. Int J Therm Sci 145. https://doi.org/10.1016/j.ijthermalsci.2019.105992 Yu G, Gu D, Dai D et al (2016) Influence of processing parameters on laser penetration depth and melting/re-melting densification during selective laser melting of aluminum alloy. Appl Phys Mater Sci Process 122:1–12. https://doi.org/10.1007/s00339-016-0428-6 Wang DZ, Li KL, Yu CF et al (2019) Cracking Behavior in Additively Manufactured Pure Tungsten. Acta Metall Sinica (English Letters) 32:127–135. https://doi.org/10.1007/s40195-018-0752-2 Wang D, Wang Z, Li K et al (2019) Cracking in laser additively manufactured W: Initiation mechanism and a suppression approach by alloying. Mater Des 162:384–393. https://doi.org/10.1016/j.matdes.2018.12.010 Németh AAN, Reiser J, Armstrong DEJ, Rieth M (2015) The nature of the brittle-to-ductile transition of ultra fine grained tungsten (W) foil. Int J Refract Met Hard Mater 50:9–15. https://doi.org/10.1016/j.ijrmhm.2014.11.005 Arakcheev AS, Huber A, Wirtz M et al (2015) Theoretical investigation of crack formation in tungsten after heat loads. J Nucl Mater 463:246–249. https://doi.org/10.1016/j.jnucmat.2014.10.090 Li C, Zhu D, Li X et al (2017) Thermal–stress analysis on the crack formation of tungsten during fusion relevant transient heat loads. Nuclear Mater Energy 13:68–73. https://doi.org/10.1016/j.nme.2017.06.008 Budaev VP, Martynenko YV, Karpov AV et al (2015) Tungsten recrystallization and cracking under ITER-relevant heat loads. J Nucl Mater 463:237–240. https://doi.org/10.1016/j.jnucmat.2014.11.129 Zheng B, Zhou Y, Smugeresky JE et al (2008) Thermal behavior and microstructural evolution during laser deposition with laser-engineered net shaping: Part I. Numerical calculations. Metall Mater Trans Phys Metall Mater Sci 39:2228–2236. https://doi.org/10.1007/s11661-008-9557-7 Xia Z, Wang H, Xu Q (2012) The stress relief mechanism in laser irradiating on porous films. Opt Commun 285:70–76. https://doi.org/10.1016/j.optcom.2011.09.012 Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8814992","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":593294730,"identity":"8a7edf59-f29d-43a0-b867-52e2f29d8d1c","order_by":0,"name":"Meng Guo","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAuklEQVRIiWNgGAWjYLCCDwwMMgwSpOhgnMHAwEOaFmYekrTIRyQf3Wzzp46Hf3YD44cfDHZ5BLUY3khLu53bxsYjcecAs2QPQ3IxYS0zcsxu5zbw8DDcSGCQZmA4kNhAlBaLPxI88jcSmH8TpUVeAqiFgc2Ax+BGAhtxthjwPEu72duWwGN452CbZY9BMhG2tCcfu/HjT52c3O3mwzd+VNgRYcsBOJMRqNiAkHqQLQQNHQWjYBSMglEAAL/LOUwS93IGAAAAAElFTkSuQmCC","orcid":"","institution":"Suzhou Laboratory","correspondingAuthor":true,"prefix":"","firstName":"Meng","middleName":"","lastName":"Guo","suffix":""},{"id":593294731,"identity":"07204ed8-4760-423d-90a9-dcf674c2ee21","order_by":1,"name":"Shilin Xia","email":"","orcid":"","institution":"Suzhou Laboratory","correspondingAuthor":false,"prefix":"","firstName":"Shilin","middleName":"","lastName":"Xia","suffix":""}],"badges":[],"createdAt":"2026-02-07 11:23:14","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8814992/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8814992/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":103125189,"identity":"bb4ccaa4-0da2-40a1-b90d-6211c1f1114d","added_by":"auto","created_at":"2026-02-21 10:42:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":211911,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ea\u003c/strong\u003e) Schematic diagram of physical phenomenon during SLM and (\u003cstrong\u003eb\u003c/strong\u003e) model of random packed powder bed\u003c/p\u003e","description":"","filename":"floatimage1.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/b760864f022a7d5e2ea541fa.png"},{"id":103125192,"identity":"ab0742aa-8f03-471b-9776-977ef5697350","added_by":"auto","created_at":"2026-02-21 10:42:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":176471,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image showing the surface morphology of pure tungsten powder in this work\u003c/p\u003e","description":"","filename":"floatimage2.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/db068b21fc4f7919c4d155bc.png"},{"id":103125190,"identity":"67478d47-9b22-475c-acdb-0e450d66a3de","added_by":"auto","created_at":"2026-02-21 10:42:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":592181,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution profiles and cooling rate versus time at the monitor point (\u003cem\u003eX\u003c/em\u003e = 150 μm, \u003cem\u003eY\u003c/em\u003e = 0 μm and \u003cem\u003eZ\u003c/em\u003e = 10 μm) under different laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage3.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/1e316a50fc75aca10e089892.png"},{"id":103504659,"identity":"d2ca3df7-e6ed-4a45-bee3-d0dbf7ede169","added_by":"auto","created_at":"2026-02-26 13:20:56","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":420219,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution contours and velocity profiles of the top surface (\u003cem\u003eX\u003c/em\u003e-\u003cem\u003eY\u003c/em\u003eplane) of scanning tracks under different laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage4.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/bcf43c2829712d4ffdea75a1.png"},{"id":103125194,"identity":"a52cd0b2-db1a-4485-ab87-8ced2dd5ba90","added_by":"auto","created_at":"2026-02-21 10:42:34","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":585674,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature distribution contours and velocity vector plots of the cross section (\u003cem\u003eY\u003c/em\u003e-\u003cem\u003eZ\u003c/em\u003e plane) of scanning tracks under various laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage5.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/946d14906b57009f9c5b7f01.png"},{"id":103504762,"identity":"f4d3c8fd-1346-4622-8281-374638d2d5a2","added_by":"auto","created_at":"2026-02-26 13:21:18","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":735477,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of the simulated surface morphologies of scanning tracks at various laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage6.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/5c3977bacd77f491f7119c7e.png"},{"id":103125195,"identity":"a74d93bf-933b-41c7-99ae-c276d629c32b","added_by":"auto","created_at":"2026-02-21 10:42:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":771797,"visible":true,"origin":"","legend":"\u003cp\u003eTop surface SEM morphologies of SLM-processed scanning tracks of pure tungsten powder at different laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage7.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/ff9027810077bd908fd2eba0.png"},{"id":103125197,"identity":"96c714d4-c3c1-47a6-ac69-2b7f5a384555","added_by":"auto","created_at":"2026-02-21 10:42:35","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":581385,"visible":true,"origin":"","legend":"\u003cp\u003eEvolution of simulated porosity at different laser powers from the \u003cem\u003eX\u003c/em\u003e-\u003cem\u003eZ\u003c/em\u003e plane: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage8.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/863a19b2699ebb5473f94dfa.png"},{"id":103504563,"identity":"b8fe544c-8409-4c01-b790-b9bd27b4817b","added_by":"auto","created_at":"2026-02-26 13:20:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":594292,"visible":true,"origin":"","legend":"\u003cp\u003eOM images of SLM-processed tungsten parts under various laser powers from the building direction: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage9.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/69f7409dc486155235e99f7d.png"},{"id":103125198,"identity":"c7cfc3e2-d147-4970-8de0-2b1c59e31097","added_by":"auto","created_at":"2026-02-21 10:42:36","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":260610,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature variation and distribution of temperature gradient along the \u003cem\u003eZ\u003c/em\u003e-axis direction at different laser powers: (\u003cstrong\u003ea\u003c/strong\u003e) 200 W, (\u003cstrong\u003eb\u003c/strong\u003e) 250 W, (\u003cstrong\u003ec\u003c/strong\u003e) 300 W, (\u003cstrong\u003ed\u003c/strong\u003e) 350 W\u003c/p\u003e","description":"","filename":"floatimage10.png","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/3e546dfd09588cd643e2a322.png"},{"id":103509164,"identity":"ccbb7634-6a5d-4ee7-acf3-348359c91f27","added_by":"auto","created_at":"2026-02-26 13:56:54","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5561996,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8814992/v1/d6a453a1-c9b5-4843-b708-c2ecc7a1237d.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: Simulation and experimental validation","fulltext":[{"header":"Introduction","content":"\u003cp\u003eAs an important part of additive manufacturing (AM) technology, selective laser melting (SLM) is considered as the most promising technology owing to its unique characteristics such as high forming accuracy and high design freedom [\u003cspan additionalcitationids=\"CR2\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. During SLM, a moving laser beam with high energy selectively irradiates the powder layer and the powder particles are fused to form metallurgical bonding with each other. Subsequently, the continuous scanning tracks are shaped with the movement of the laser beam based on the computer-aided design (CAD) data [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. Through the metallurgical bonding of powder between layer and layer, a component is finally built. The layer-by-layer construction method allows the rapid production of complex parts without the limitation of geometric shape. Therefore, SLM is widely used in many special manufacturing fields such as aerospace engineering and biological tissue engineering [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. So far, a large number of studies have been conducted on various metal materials, including Al-based alloys, Ti-based alloys, Ni-based alloys, stainless steels and so on [\u003cspan additionalcitationids=\"CR8 CR9 CR10 CR11\" citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. The mapping relationships among defects formation, phase transition, microstructure evolution and ultimate mechanical properties of these materials during SLM process have been revealed to take full advantage of SLM-processed metal materials. With the continuous development of SLM technology in high-power laser and high-speed galvanometer, the metal materials applicable to SLM become very extensive from the low melting point materials to the high melting point materials. Recently, the researches on SLM-processed the refractory metals such as tungsten (W), Tantalum (Ta), molybdenum (Mo) and niobium (Nb) have been reported one after another [\u003cspan additionalcitationids=\"CR14 CR15 CR16\" citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Among these refractory metals, tungsten is the most popular material due to its high melting point, high thermal conductivity and high strength. Moreover, tungsten is widely regarded as the most promising candidate material for plasma facing materials (PFMs) owing to its high sputtering threshold and low tritium retention [\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Therefore, a number of researches have been conducted to demonstrate the possibility of SLM-processed tungsten. However, selective laser melting of tungsten parts remains a challenge due to its intrinsic characteristics. Zhang et al. [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e] successfully fabricated tungsten parts with a novel nanocrystalline structure by SLM. It was found that the solid forces by laser could result in the formation of nanocrystalline tungsten. Moreover, the novel nanocrystalline showed a fine grain structure, which was beneficial to the performance of final SLM-processed parts. K. Enneti et al. [\u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e] conducted a study to understand the effect of process parameters such as hatch spacing and scanning speed on the densification of SLM-processed tungsten. He found that the densification of SLM-processed tungsten increased with energy density and porosity was the main reason accounting for the decrease in densification. Zhou et al. [\u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e] pointed out that there existed a process where melt spreading and solidification competed with each other in SLM of tungsten. Furthermore, the densification behavior was determined by intrinsic properties of tungsten and the laser processing parameters. Previous works on SLM-processed tungsten demonstrated that formation of porosity and cracks were the main defects influencing the forming quality of SLM-processed tungsten [\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. As a result, understanding the formation mechanism of defects like porosity and cracks was significantly effective to control the performances of final tungsten components.\u003c/p\u003e \u003cp\u003eGenerally, the necessary trial and error tests should be conducted to make the SLM-processed tungsten parts meet the engineering quality standards. However, this process tends to be costly and time-consuming. As a result, the numerical modeling and simulation method rises in response to the proper time and conditions. The numerical modeling and simulation method could offer an effective approach to further figure out the physical phenomenon, which serves as a precursor to optimize the experimental processing parameters for SLM-processed metal parts [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. Recently, simulations of physical phenomenon such as the formation and evolution of porosity during SLM process have been demonstrated to be a promising method to effectively control the defects formation. Xia et al. [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e] proposed a transient mesoscale model with a randomly packed powder-bed to understand the porosity evolution during SLM-processed Inconel 718 alloy. In this model, the phase transition, variation of thermos-physical properties and interfacial force were taken into consideration. Through this model, the influence of scanning speed on porosity formation was revealed. A. Khairallah et al. [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e] developed a three-dimensional high-fidelity powder-scale model to understand the formation mechanism of pore defects, material spattering and denudation zones. It was found that there existed different pore formation mechanisms on a melt track. Moreover, measures for eliminating the undesirable were proposed. Qiu et al. [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e] utilized a computational fluid dynamics (CFD) calculation to predict the development of porosity and surface defects of SLM-processed Ti-6Al-4V under different laser scanning speed and powder layer thickness. The results demonstrated that the unstable melt flow could result in increased porosity and surface roughness. Furthermore, the porosity was more sensitive to powder layer thickness and a thick powder layer could lead to significant porosity. The above-mentioned works demonstrated that numerical modeling and simulation method was applicable to predict the defects evolution during SLM. In view of the difficulties in selective laser melting of pure tungsten, the numerical simulation method was introduced to simulate the SLM process of pure tungsten. In order to reveal the porosity evolution and cracks formation during SLM of pure tungsten, a random stacking model of powder bed was established, which was close to the actual situation. The commercial fluent finite volume method (FVM) software was employed to calculate the mesoscale model of random packed powder-bed. The transition of solid to liquid, surface tension, recoil force, thermo-capillary force, gravity and buoyancy force were taken into consideration to obtain more accurate simulation results [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Furthermore, the experimental results of top and cross-section surface of SLM-processed tungsten were obtained to further prove the accuracy of the random packed model of powder bed.\u003c/p\u003e"},{"header":"Experimental procedure","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003eNumerical simulation\u003c/h2\u003e \u003cp\u003eDuring SLM, a high energy laser beam selectively irradiates the powder bed and resultant the fusion of powder particles. A series of complex physical phenomenon such as heat conduction and convection, evaporation of elements, recoil pressure of laser and spatters of powder particles are involved, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a). In order to reveal the heat transfer and thermodynamic behavior during the fabrication of tungsten parts by SLM, a three-dimensional model with a size of 300 \u0026micro;m \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 200 \u0026micro;m \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e80 \u0026micro;m was established using the FLUENT software (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b)). Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e described the material properties and processing parameters used in this simulation. Other material properties such as thermal conductivity and specific heat capacity were classified in reference [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn this model, the molten metal was considered as the incompressible fluid in high temperature. The motion of molten metal fluid was described by energy, mass, momentum conservation, which was detailed in our previous work [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e, \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Based on the volume of fluid model, the volume fraction equation for different phase was described as:\u003cdiv id=\"Equ1\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ1\" name=\"EquationSource\"\u003e\n$$\\:\\frac{\\partial\\:{a}_{i}}{\\partial\\:t}+\\overrightarrow{v}\\bullet\\:\\nabla\\:{a}_{i}=\\frac{{S}_{i}}{{\\rho\\:}_{i}}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e1\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\:{\\sum\\:}_{i=1}^{n}{a}_{i}=1\\)\u003c/span\u003e\u003c/span\u003e, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{a}_{i}\\)\u003c/span\u003e\u003c/span\u003e represented the volume fraction of \u003cem\u003ei\u003c/em\u003e phase, \u003cem\u003en\u003c/em\u003e was the total number of phases. At the interface of the gas phase and tungsten phase, the mixed material properties were calculated as:\u003cdiv id=\"Equ2\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ2\" name=\"EquationSource\"\u003e\n$$\\:\\phi\\:=\\eta\\:{\\phi\\:}_{gas}+(1-\\eta\\:){\\phi\\:}_{tungsten}$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e2\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\phi\\:\\)\u003c/span\u003e\u003c/span\u003e represented a certain material property like density, thermal conductivity and so on, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\eta\\:\\)\u003c/span\u003e\u003c/span\u003e was the volume fraction of the gas phase in mesh.\u003c/p\u003e \u003cp\u003eThe boundaries satisfied the following equation:\u003cdiv id=\"Equ3\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ3\" name=\"EquationSource\"\u003e\n$$\\:K\\frac{\\partial\\:T}{\\partial\\:n}+{h}_{c}\\left(T-{T}_{0}\\right)+\\sigma\\:\\epsilon\\:\\left({T}^{4}-{T}_{0}^{4}\\right)=Q$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e3\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003en\u003c/em\u003e was the normal vector of the surface, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:{h}_{c}\\)\u003c/span\u003e\u003c/span\u003e was the heat transfer coefficient of thermal convection, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\epsilon\\:\\)\u003c/span\u003e\u003c/span\u003e was the emissivity and \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\sigma\\:\\)\u003c/span\u003e\u003c/span\u003e was the Stefan-Boltzmann constant.\u003c/p\u003e \u003cp\u003eThe laser source was considered as a volumetric Gaussian distributed circular heat source, which could be defined as:\u003cdiv id=\"Equ4\" class=\"Equation\"\u003e\u003cdiv format=\"TEX\" class=\"mathdisplay\" id=\"FileID_Equ4\" name=\"EquationSource\"\u003e\n$$\\:q=\\frac{6PA}{{R}^{2}\\pi\\:H\\left(1-\\frac{1}{{e}^{3}}\\right)}exp\\left(\\frac{-9\\left({x}^{2}+{y}^{2}\\right)}{{R}^{2}log\\left(\\frac{H}{z}\\right)}\\right)$$\u003c/div\u003e\u003cdiv class=\"EquationNumber\"\u003e4\u003c/div\u003e\u003c/div\u003e\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eP\u003c/em\u003e was the laser power, \u003cem\u003eR\u003c/em\u003e represented the radius of laser beam, \u003cem\u003eH\u003c/em\u003e was the penetrated depth of heat source, and \u003cem\u003eA\u003c/em\u003e was the effective laser energy absorption of the material. The value of \u003cem\u003eA\u003c/em\u003e was calculated as 0.68 [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eThe as-used material properties and processing parameters during SLM.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eParameters\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDensity, \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\rho\\:\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e19350 kg/m\u003csup\u003e3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAmbient temperature, \u003cem\u003eT\u003c/em\u003e\u003csub\u003e\u003cem\u003e0\u003c/em\u003e\u003c/sub\u003e (K)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e293\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLayer thickness, \u003cem\u003ed\u003c/em\u003e (\u0026micro;m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e30\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eDiameter of laser beam, \u003cem\u003eD\u003c/em\u003e (\u0026micro;m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eHatch spacing, \u003cem\u003es\u003c/em\u003e (\u0026micro;m)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eAbsorption of tungsten powder, \u003cem\u003eA\u003c/em\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.68\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eScanning speed, \u003cem\u003ev\u003c/em\u003e (mm/s)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLaser power, \u003cem\u003eP\u003c/em\u003e (W)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e200, 250, 300, 350\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"Experimental methods","content":"\u003cp\u003eTo verify the accuracy of the physical model, the corresponding processing parameters were applied to fabricate scanning tracks and cubic samples of pure tungsten. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the tungsten powder with a spherical shape was used in this work. The tungsten powder had a diameter ranging from 5 \u0026micro;m to 25 \u0026micro;m. The SLM system used in this study was equipped with a YLR-500 ytterbium fiber laser, an automatic spreading device for spreading powder, an inert gas system for providing protective atmosphere and a computer control system. The fiber laser had a maximum laser power of 500 W and a laser spot size of 70 \u0026micro;m (IPG Laser GmbH, Germany). The scanning tracks and cuboid samples were fabricated on the stainless-steel substrate, respectively. The surface morphologies of the SLM-processed scanning tracks were characterized by FEI Quanta 200 scanning electron microscope (SEM). The cuboid samples were cut, ground and then polished for the observation of the morphologies from the building direction. A MDS400 optical microscopy (Chongqing Optec Instrument Co., Ltd., China) was used to observe the polished surface of SLM-processed tungsten.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results and discussions","content":"\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003eTemperature evolution\u003c/h2\u003e \u003cp\u003eIt is known to all that laser processing is an extremely nonequilibrium process with the rapid heating and fast cooling. In this case, the fast-cooling rate (10\u003csup\u003e3\u003c/sup\u003e \u0026ndash; 10\u003csup\u003e8\u003c/sup\u003e K/s) can result in special structure with fine grains and novel properties [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Therefore, having a good understanding of temperature evolution and resultant variation of cooling rate during SLM is favorable to better fabricate a component. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e shows the temperature distribution profiles and attendant cooling rate versus processing time at the monitor point (\u003cem\u003eX\u003c/em\u003e\u0026thinsp;=\u0026thinsp;150 \u0026micro;m, \u003cem\u003eY\u003c/em\u003e\u0026thinsp;=\u0026thinsp;0 \u0026micro;m and \u003cem\u003eZ\u003c/em\u003e\u0026thinsp;=\u0026thinsp;10 \u0026micro;m) with different laser powers. It was obviously observed that the maximum temperature and cooling rate were significantly different as the various laser powers were applied. When a low laser power of 200 W was used, a peak temperature of 4260 K and a maximum cooling rate of 2.10 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s were obtained, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a)). In this case, the liquid lifetime was 136 \u0026micro;s. As the laser power was increased to 250 W, the obtained maximum temperature and cooling rate were increased correspondingly. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b), the maximum temperature and cooling rate reached a value of 5132 K and 2.77 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s, respectively. In this case, the liquid lifetime was enhanced to 176 \u0026micro;s. With the laser power increased to 300 W, the energy input was increased, resulting in a peak temperature and cooling rate of 5558 K and 3.88 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c)). The lifetime was prolonged to 182 \u0026micro;s. While a high laser power of 350 W was applied, the maximum temperature and cooling rate was 5742 K and 4.66 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s, respectively (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d)). Moreover, the high laser power could facilitate a longer lifetime of 184 \u0026micro;s.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eGenerally, increasing laser power consequentially resulted in an enhancement of energy input and resultant high temperature in molten pool. In this case, the melting flow could be generated vastly due to the elevated operating temperature within the molten pool, which could facilitate the spreading of the liquid tungsten to wet the surrounding powder particles. Moreover, the viscosity of liquid tungsten was inversely proportional to temperature [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e], indicating that the viscosity of molten liquid could be obviously reduced with the elevated operating temperature within the molten pool, which was favorable to form good metallurgical bonding between the melt and obtain high dense parts. Simultaneously, an elevated laser power could bring more energy input, prompting longer liquid lifetime of liquid tungsten and resulting in a higher peaking temperature.\u003c/p\u003e \u003cp\u003eIt was worth noting that the cooling rate curves showed a fluctuation when the temperature of solid tungsten reached its melting point or liquid tungsten arrived its solidifying point. This was due to the effect of latent heat of fusion during melting or solidification. During SLM, the rapid melting and solidification would happen in an instant. In this process, huge latent heat of fusion could be released and resultant the fluctuation of cooling rate curves [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].Generally, during the melting process, the cooling rate was a negative value. While the cooling rate changed to a positive value during the solidification process. The calculated maximum cooling rate increased from 2.10 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s to 4.66 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s as the laser power increased from 200 W to 350 W. This was because the increased energy input could cause the peak temperature to rise at a given scanning speed. Thus, the cooling rate could be increased in unit time. In this case, the novel microstructure and unprecedented mechanical properties of final SLM-processed parts could be obtained. Moreover, it was clearly noted that the liquid lifetime of the molten pool increased as the elevated laser power was applied. When the laser power was 200 W, the liquid lifetime was only 136 \u0026micro;s, which was unable to produce sufficient liquid to wet the surrounding powder particles and form sound scanning tracks. While the laser power was increased to 350 W, the liquid lifetime was prolonged to 184 \u0026micro;s. In this case, the wettability of liquid-solid could be improved, promoting the melt spreading and resultant sound scanning tracks.\u003c/p\u003e \u003c/div\u003e\n\u003ch3\u003eThermodynamic behavior of molten pool\u003c/h3\u003e\n\u003cp\u003eTypically, the calculated temperature distribution contours and velocity profiles of the top surface (\u003cem\u003eX\u003c/em\u003e-\u003cem\u003eY\u003c/em\u003e plane) of scanning tracks under different laser powers are clearly depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e. It was obvious that the contours and dynamics of molten pool exhibited a significant difference at various laser powers. The temperature line of 3695 K represented the liquid line of tungsten. When a low laser power of 200 W was applied, the top surface of molten pool presented an ellipse shape with a narrow dimension, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a). The calculated velocity of vector was below 0.3 m/s and its distribution was narrow, indicating that the mass transfer process was weak. In this situation, the molten liquid of tungsten generated in the molten pool was considerably less. As the laser power increased to 250 W, the dimension of top surface of molten pool was significantly enlarged (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(b)). Moreover, the velocity of vector was increased and its distribution range was expanded. At a higher laser power of 300 W, the ellipse-shaped pool exhibited with an increased dimension in comparison to those of 200 W and 250 W (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c)). Meanwhile, the range of mass transfer was enlarged with more velocity vector. When an elevated laser power of 350 W was used, the ellipse-shaped pool was observed with intense velocity of vector and increased size. The maximum velocity of vector reached 0.6 m/s, demonstrating that there existed strong mass and heat transfer within the molten pool (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(d)).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e illustrates the typical temperature distribution contours and corresponding velocity vector plots of the cross section (\u003cem\u003eY\u003c/em\u003e-\u003cem\u003eZ\u003c/em\u003e plane) of scanning tracks under various laser powers. It was obviously observed that the width and dynamic behavior of the molten pool presented significant differences. At a low laser power of 200 W, the energy input was insufficient to promote the interaction between laser and powder. Thus, the power particles cannot be melted and form good wetting. Accordingly, a small width of 25 \u0026micro;m was formed, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(a), which was detrimental to the metallurgical bonding between neighboring scanning tracks. Moreover, the operating temperature within the molten pool was below 3800 K. In this situation, the thermal convection and mass transfer was weak. With increasing the applied laser power to 250 W, the width of molten pool was enlarged to 45 \u0026micro;m and the maximum operating temperature of molten pool was enhanced to 4000 K (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(b)). To some extent, an elevated laser power could bring high operating temperature within molten pool, promoting the mass transfer and melt flow. Consequently, it was beneficial to form a sound bonding with the adjacent tracks. When a laser power of 300 W was used, the energy input was sufficient to facilitate the melt flow and mass transfer, obtaining a molten pool with a width of 52.5 \u0026micro;m (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(c)). Meanwhile, the operating temperature within molten pool was increased to 4600 K, which could facilitate the motion and transfer of substance and resultant good metallurgical bonding. As an even higher laser power of 350 W was applied, the high energy input could bring sufficient operating temperature, resulting in abundant molten liquid and reducing the viscosity of melt. Correspondingly, a molten pool with a large width of 62 \u0026micro;m was formed, as clearly depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e(d). Meanwhile, the Marangoni convection with a symmetric shape was generated. In this case, the mass transfer within the molten pool was considerably intense, which was favorable to the motion and escape of bubbles. Therefore, it was demonstrated that the width of molten pool was significantly influenced by laser power. A relatively high laser power could contribute to the formation of the molten pool and achieve a well metallurgical bonding between adjacent tracks.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003eSurface morphology evolution and defects formation\u003c/h2\u003e \u003cp\u003eThe simulated evolution of surface morphology of the scanning tracks on the top surface at different laser powers is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e. It was visibly observed that the surface morphology exhibited with big differences as the laser power increased. When a low laser power of 200 W was applied, the top surface appeared to be discontinuous with a mass of unmelted powder particles (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(a)). Meanwhile, the maximum temperature of the molten pool surface reached 3500 K, which was insufficient to melt the tungsten powder to form continuous scanning tracks. As the laser power was increased to 250 W, the energy input was increased accordingly, promoting some powder particles to melt. Thus, some continuous melting areas appeared. However, the operating temperature was limited to reduce the viscosity. The melting areas was unable to form continuous tracks, as clearly depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(b). Nevertheless, at a high laser power of 300 W, the maximum operating temperature within the molten pool reached to 4250 K. Under this situation, the powder particles were melted largely to form molten liquid. Simultaneously, the elevated temperature could reduce the viscosity of molten liquid and facilitate the wetting and spreading of melt. Finally, a continuous track was formed (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(c)). As the laser power was enhanced to 350 W, the maximum operating temperature in the molten pool was further improved to 4500 K. Correspondingly, the powder particles were melted more thoroughly and resultant more molten liquid. Meanwhile, the viscosity of molten liquid was reduced, promoting the melt flowing. As a result, a continuous scanning track was obtained (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e(d)).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eFigure\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e illustrates the corresponding experimental results of scanning tracks of SLM-processed tungsten. The surface morphology presented huge differences as the laser power increased. When a low laser power of 200 W was used, it could be obviously observed that the tungsten powder particles were unmelted due to the limited laser power (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(a)). Moreover, the laser power was unable to penetrate into the substrate to form good metallurgical bonding. Thus, a scanning track with a large number of unmelted particles was generated. As the laser power increased to 250 W, the energy input was increased, bringing elevated operating temperature within molten pool. To some extent, the elevated temperature could melt most tungsten powder and resultant abundant molten liquid. However, the viscosity and surface tension of liquid tungsten were very large, impeding the wetting and spreading of liquid tungsten. Thus, the obtained scanning track was discontinuous with unstable melt flow, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(b). At a high laser power of 300 W, the operating temperature was further increased, reducing the viscosity of molten liquid. Simultaneously, the powder particles were well melted and resultant melt flow. Due to the elevated energy input, the penetration depth was sufficient to forming a good metallurgical bonding between powder layer and substrate. Finally, a continuous scanning track with stable melt flow was formed (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(c)). When an even high laser power of 350 W was used. The surface morphology exhibited with a good surface quality. The sufficient energy input could result in adequate penetration depth to facilitate the metallurgical bonding [\u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e]. Meanwhile, the intense Marangoni flow induced by the high laser power could disturb the molten pool and promote the flow of molten liquid. In this case, both the melting behavior and the spreading ability were strengthened. As a result, a continuous scanning track with regular shape and stable melt flow was obtained, as clearly shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e(d).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe typical evolution of simulated porosity at different laser powers from the \u003cem\u003eX\u003c/em\u003e-\u003cem\u003eZ\u003c/em\u003e plane is illustrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e. It could be understood that the porosity on the cross section reflected the interlayer bonding. The distribution of the porosity showed a big difference as the laser power increased. As the laser power of 200 W was applied, the morphology of the cross section was porous with a considerable number of large pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(a)). Due to the insufficient energy input caused by the low laser power, the powder particles were incompletely melted and became the source of pores. Furthermore, the number of molten liquids in the pool was limited and the lifetime of molten pool was short, which could hinder the molten liquid to migrate and fill into the porosity. When the laser power was increased to 250 W, the number of pores was reduced. Meanwhile, the dimensions of the pores were diminished, as depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(b). Due to the enhancement of laser power, the energy input was increased to fuse most powder particles and generate more molten liquid. Moreover, the dynamic viscosity of molten pool could be reduced and resultant sufficient melt flow. In this case, the preformed pores could be filled up. However, the energy input was limited to eliminate the pores. When the laser was settled as 300 W, the number of pores was further decreased. Some large pores merged and formed small pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(c)). Owing to the enhanced laser power, the tungsten powder could be completely melted. Simultaneously, the elevated operating temperature could reduce the dynamic viscosity of molten pool, facilitating the wetting and spreading of molten liquid. Thus, the preformed large pores were further filled with molten liquid. At an elevated laser power of 350 W, the surface morphology was almost free of pores (Fig.\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e(d)). On one hand, the elevated laser power could provide sufficient energy to penetrate the powder layer and fuse the powder particles. On the other hand, the operating temperature could be enhanced, reducing the dynamic viscosity and resultant regular melt flow. Furthermore, the intensified Marangoni flow could promote some gas bubbles to escape from the molten pool, which was favorable to the densification behavior.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to further verify the accuracy of simulation results, the corresponding processing parameters was employed to fabricate the tungsten cuboid parts by SLM. The OM images of SLM-processed tungsten parts using various laser powers are depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e. It could be visibly observed that pores and cracks were the main defects in SLM-processed pure tungsten parts. When the laser power was 200 W, a mass of inter-layer pores with large dimensions were clearly observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(a)). These pores clustered with irregular shapes and some unmelted particles could be observed in pores. Moreover, some microcracks were found along the building direction. As the laser power increased to 250 W, it was obvious that the number of pores was largely reduced (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(b)). Meanwhile, the dimension of pores was decreased and the cluster phenomenon was weakened. However, the microcracks were remained on the surface. At an elevated laser power of 300 W, the pores were further reduced both in size and numbers. Moreover, the microcracks were obvious with large length, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(c). When an even high laser power was employed, only small pores could be observed (Fig.\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e(d)). Furthermore, the long microcracks were more remarkable.\u003c/p\u003e \u003cp\u003eAs mentioned above, the pores appeared at the low laser power were due to the incomplete melting of powder particles. There existed a competitive of melt spreading and solidification during SLM. Due to the high surface tension and viscosity of liquid tungsten, the wetting and spreading speeds of liquid tungsten were relatively low. In this situation, the tungsten liquid was unable to form melt flow. Finally, the obtained scanning tracks were discontinuous and the SLM-processed tungsten parts were porous at a low laser power. Fortunately, the pores could be eliminated by adjusting the laser power. While the microcracks seemed to be inevitable. Previous experimental works on SLM-processed tungsten demonstrated that the thermal stresses were prone to arise during rapid solidification or recrystallization [\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e]. Moreover, the high ductile-brittle transition temperature (DBTT), typically between 200 ℃ and 400 ℃, accounted for the generation of cracks [\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e]. SLM process would inevitably experience the fast cooling, as the temperature was below the DBTT, the yield strength was low than the residual stress, causing the cracks [\u003cspan additionalcitationids=\"CR43\" citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eIn order to reveal the influence of temperature on cracks formation. The temperature under different laser powers and the corresponding temperature gradient were calculated, respectively. Figure\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e illustrates the temperature variation and distribution of temperature gradient along the \u003cem\u003eZ\u003c/em\u003e-axis at different laser powers. It was observed that the temperature increased at first and decreased subsequently along the \u003cem\u003eZ\u003c/em\u003e-axis direction (Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(a)). Meanwhile, the temperature was enhanced with the elevated laser power. The calculated temperature gradient was depicted in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e(b). When the laser power increased from 200 W to 350 W, the calculated maximum temperature gradient was 336.8 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e6\u003c/sup\u003e K/m, 290.1 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e6\u003c/sup\u003e K/m, 285.1 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e6\u003c/sup\u003e K/m and 234.8 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e6\u003c/sup\u003e K/m, respectively. It was demonstrated that thermal shrinkage caused by the change in temperature would generate during laser processing [\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e]. In this situation, the larger the temperature gradient was, the more the thermal shrinkage would generate. Furthermore, due to the low coefficient of thermal expansion of tungsten, the shrinkage was prone to result in cracks. When the laser power was low, the cracks were not obvious in comparison of the high laser power. This was because the pores could serve as the source of stress relief in some degree [\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e]. Thus, the cracks were more obvious at an even higher laser power.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eBased on the simulation results, it was concluded that decreasing the temperature gradient was able to reduce the cracks during SLM-processed tungsten parts. Thus, a higher laser power was favorable. Furthermore, the alloying elements with low melting could result in the reduction of the temperature gradient. As a result, alloying design was another effective way to reduce the cracks.\u003c/p\u003e \u003c/div\u003e"},{"header":"Conclusions","content":"\u003cp\u003eIn the present study, a random stacking model of powder particles was established to study the influence of laser power on SLM-processed pure tungsten parts. The temperature evolution, thermodynamic behavior of molten pool, surface morphology and defects evolution during SLM of pure tungsten were analyzed in detail. Meanwhile, the corresponding experiments were conducted. The main conclusions were drawn as follows:\u003c/p\u003e \u003cp\u003e(1) The laser power had a huge influence on the temperature during SLM-processed tungsten parts. The peak temperature and relevant cooling rate were increased with the elevated laser power. Meanwhile, the lifetime of molten pool was prolonged as the laser power increased.\u003c/p\u003e \u003cp\u003e(2) At a high laser power, the resultant velocity of vector was intensified, indicating a strong mass transfer in the molten pool. Simultaneously, the high laser power resulted in an increased width of pool, which was favorable to the metallurgical bonding with adjacent scanning tracks.\u003c/p\u003e \u003cp\u003e(3) Laser power played a crucial role in influencing the surface morphologies of scanning tracks. As the laser power increased, the powder particles were melted completely and resultant good wetting and spreading of molten liquid, promoting a continuous scanning track. Meanwhile, the pores were obviously reduced with enhancing the laser power, which was beneficial to the densification behavior. However, the cracks induced by the high DBTT and large temperature gradient were inevitable in SLM-processed tungsten parts.\u003c/p\u003e \u003cp\u003e(4) The top surface morphologies of scanning tracks and cross section morphologies of tungsten parts by SLM were obtained, respectively. According to the simulation and experimental results, it was proposed that enhancing the laser power and alloying design were feasible methods to reduce the cracks.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003eThe authors gratefully acknowledge the financial support from the Basic Research Program of Jiangsu (No. BK20250521) and Jiangsu Funding Program for Excellent Postdoctoral Talent.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompliance with ethical standards\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflict of interest\u003c/strong\u003e\u0026nbsp; The authors declare that they have no conflict of interest.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eGu DD, Meiners W, Wissenbach K, Poprawe R (2012) Laser additive manufacturing of metallic components: materials, processes and mechanisms. Int Mater Rev 57:133\u0026ndash;164. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1179/1743280411Y.0000000014\u003c/span\u003e\u003cspan address=\"10.1179/1743280411Y.0000000014\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYap CY, Chua CK, Dong ZL et al (2015) Review of selective laser melting: Materials and applications. Appl Phys Rev 2. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1063/1.4935926\u003c/span\u003e\u003cspan address=\"10.1063/1.4935926\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAboulkhair NT, Simonelli M, Parry L et al (2019) 3D printing of Aluminium alloys: Additive Manufacturing of Aluminium alloys using selective laser melting. Prog Mater Sci 106:100578. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.pmatsci.2019.100578\u003c/span\u003e\u003cspan address=\"10.1016/j.pmatsci.2019.100578\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDogu MN, McCarthy E, McCann R et al (2022) Digitisation of metal AM for part microstructure and property control. IntJ Mater Form 15:30. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12289-022-01686-4\u003c/span\u003e\u003cspan address=\"10.1007/s12289-022-01686-4\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMartin JH, Yahata BD, Hundley JM et al (2017) 3D printing of high-strength aluminium alloys. Nature 549:365\u0026ndash;369. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1038/nature23894\u003c/span\u003e\u003cspan address=\"10.1038/nature23894\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eMeng L, Zhao J, Lan X et al (2019) Multi-objective optimisation of bio-inspired lightweight sandwich structures based on selective laser melting. Virtual Phys Prototyp 2759:1\u0026ndash;14. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/17452759.2019.1692673\u003c/span\u003e\u003cspan address=\"10.1080/17452759.2019.1692673\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eOlakanmi EO, Cochrane RF, Dalgarno KW (2015) A review on selective laser sintering/melting (SLS/SLM) of aluminium alloy powders: Processing, microstructure, and properties. Prog Mater Sci 74:401\u0026ndash;477. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.pmatsci.2015.03.002\u003c/span\u003e\u003cspan address=\"10.1016/j.pmatsci.2015.03.002\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eHerzog D, Seyda V, Wycisk E, Emmelmann C (2016) Additive manufacturing of metals. Acta Mater 117:371\u0026ndash;392. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.actamat.2016.07.019\u003c/span\u003e\u003cspan address=\"10.1016/j.actamat.2016.07.019\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang D, Wu S, Fu F et al (2017) Mechanisms and characteristics of spatter generation in SLM processing and its effect on the properties. Mater Des 117:121\u0026ndash;130. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matdes.2016.12.060\u003c/span\u003e\u003cspan address=\"10.1016/j.matdes.2016.12.060\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi R, Wang M, Yuan T et al (2017) Selective laser melting of a novel Sc and Zr modified Al-6.2 Mg alloy: Processing, microstructure, and properties. Powder Technol 319:117\u0026ndash;128. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.powtec.2017.06.050\u003c/span\u003e\u003cspan address=\"10.1016/j.powtec.2017.06.050\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang L, Song B, Liu R et al (2020) Effects of Structural Parameters on the Poisson\u0026rsquo;s Ratio and Compressive Modulus of 2D Pentamode Structures Fabricated by Selective Laser Melting. Engineering 6:56\u0026ndash;67. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.eng.2019.06.009\u003c/span\u003e\u003cspan address=\"10.1016/j.eng.2019.06.009\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eSghaier TAM, Sahlaoui H, Mabrouki T et al (2023) Selective Laser Melting of Stainless-Steel: A Review of Process, Microstructure, Mechanical Properties and Post-Processing treatments. IntJ Mater Form 16:41\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBraun J, Kaserer L, Stajkovic J et al (2019) Molybdenum and tungsten manufactured by selective laser melting: Analysis of defect structure and solidification mechanisms. Int J Refract Met Hard Mater 84:104999. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2019.104999\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2019.104999\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKaserer L, Braun J, Stajkovic J et al (2019) Fully dense and crack free molybdenum manufactured by Selective Laser Melting through alloying with carbon. Int J Refract Met Hard Mater 84:105000. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2019.105000\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2019.105000\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang S, Cheng X, Yao Y et al (2015) Porous niobium coatings fabricated with selective laser melting on titanium substrates: Preparation, characterization, and cell behavior. Mater Sci Eng C 53:50\u0026ndash;59. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.msec.2015.04.005\u003c/span\u003e\u003cspan address=\"10.1016/j.msec.2015.04.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou L, Yuan T, Li R et al (2017) Selective laser melting of pure tantalum: Densification, microstructure and mechanical behaviors. Mater Sci Eng A 707:443\u0026ndash;451. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.msea.2017.09.083\u003c/span\u003e\u003cspan address=\"10.1016/j.msea.2017.09.083\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang J, Gu D, Yang Y et al (2019) Influence of Particle Size on Laser Absorption and Scanning Track Formation Mechanisms of Pure Tungsten Powder During Selective Laser Melting. Engineering 5:736\u0026ndash;745. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.eng.2019.07.003\u003c/span\u003e\u003cspan address=\"10.1016/j.eng.2019.07.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eButler BG, Paramore JD, Ligda JP et al (2018) Mechanisms of deformation and ductility in tungsten \u0026ndash; A review. Int J Refract Met Hard Mater 75:248\u0026ndash;261\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eNeu R, Riesch J, Coenen JW et al (2016) Advanced tungsten materials for plasma-facing components of DEMO and fusion power plants. Fusion Eng Des 109\u0026ndash;111:1046\u0026ndash;1052. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.fusengdes.2016.01.027\u003c/span\u003e\u003cspan address=\"10.1016/j.fusengdes.2016.01.027\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhang D, Cai Q, Liu J (2012) Formation of nanocrystalline tungsten by selective laser melting of tungsten powder. Mater Manuf Processes 27:1267\u0026ndash;1270. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1080/10426914.2012.663119\u003c/span\u003e\u003cspan address=\"10.1080/10426914.2012.663119\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eEnneti RK, Morgan R, Atre SV (2018) Effect of process parameters on the Selective Laser Melting (SLM) of tungsten. Int J Refract Met Hard Mater 71:315\u0026ndash;319. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2017.11.035\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2017.11.035\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZhou X, Liu X, Zhang D et al (2015) Balling phenomena in selective laser melted tungsten. J Mater Process Technol 222:33\u0026ndash;42. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmatprotec.2015.02.032\u003c/span\u003e\u003cspan address=\"10.1016/j.jmatprotec.2015.02.032\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWen S, Wang C, Zhou Y et al (2019) High-density tungsten fabricated by selective laser melting: Densification, microstructure, mechanical and thermal performance. Opt Laser Technol 116:128\u0026ndash;138. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optlastec.2019.03.018\u003c/span\u003e\u003cspan address=\"10.1016/j.optlastec.2019.03.018\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo M, Gu D, Xi L et al (2019) Selective laser melting additive manufacturing of pure tungsten: Role of volumetric energy density on densification, microstructure and mechanical properties. Int J Refract Met Hard Mater 84:105025. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2019.105025\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2019.105025\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWu YC, Hwang WS, San CH et al (2018) Parametric study of surface morphology for selective laser melting on Ti6Al4V powder bed with numerical and experimental methods. IntJ Mater Form 11:807\u0026ndash;813. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s12289-017-1391-2\u003c/span\u003e\u003cspan address=\"10.1007/s12289-017-1391-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXia M, Gu D, Yu G et al (2017) Porosity evolution and its thermodynamic mechanism of randomly packed powder-bed during selective laser melting of Inconel 718 alloy. Int J Mach Tools Manuf 116:96\u0026ndash;106. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijmachtools.2017.01.005\u003c/span\u003e\u003cspan address=\"10.1016/j.ijmachtools.2017.01.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhairallah SA, Anderson AT, Rubenchik A, King WE (2016) Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones. Acta Mater 108:36\u0026ndash;45. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.actamat.2016.02.014\u003c/span\u003e\u003cspan address=\"10.1016/j.actamat.2016.02.014\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eQiu C, Panwisawas C, Ward M et al (2015) On the role of melt flow into the surface structure and porosity development during selective laser melting. Acta Mater 96:72\u0026ndash;79. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.actamat.2015.06.004\u003c/span\u003e\u003cspan address=\"10.1016/j.actamat.2015.06.004\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eKhairallah SA, Anderson A (2014) Mesoscopic simulation model of selective laser melting of stainless steel powder. J Mater Process Technol 214:2627\u0026ndash;2636. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jmatprotec.2014.06.001\u003c/span\u003e\u003cspan address=\"10.1016/j.jmatprotec.2014.06.001\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eGuo M, Gu D, Xi L et al (2019) Formation of scanning tracks during Selective Laser Melting (SLM) of pure tungsten powder: Morphology, geometric features and forming mechanisms. Int J Refract Met Hard Mater 79:37\u0026ndash;46. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2018.11.003\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2018.11.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYuan P, Gu D (2015) Molten pool behaviour and its physical mechanism during selective laser melting of TiC/AlSi10Mg nanocomposites: Simulation and experiments. J Phys D Appl Phys 48:35303. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1088/0022-3727/48/3/035303\u003c/span\u003e\u003cspan address=\"10.1088/0022-3727/48/3/035303\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXia M, Gu D, Yu G et al (2016) Selective laser melting 3D printing of Ni-based superalloy: understanding thermodynamic mechanisms. Sci Bull (Beijing) 61:1013\u0026ndash;1022. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11434-016-1098-7\u003c/span\u003e\u003cspan address=\"10.1007/s11434-016-1098-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang D, Yu C, Zhou X et al (2017) Dense Pure Tungsten Fabricated by Selective Laser Melting. Appl Sci 7:430. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.3390/app7040430\u003c/span\u003e\u003cspan address=\"10.3390/app7040430\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eDas M, Balla VK, Basu D et al (2010) Laser processing of SiC-particle-reinforced coating on titanium. Scr Mater 63:438\u0026ndash;441. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.scriptamat.2010.04.044\u003c/span\u003e\u003cspan address=\"10.1016/j.scriptamat.2010.04.044\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eParadis PF, Ishikawa T, Yoda S (2005) Viscosity of liquid undercooled tungsten. J Appl Phys 97. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1063/1.1896432\u003c/span\u003e\u003cspan address=\"10.1063/1.1896432\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eRomano J, Ladani L, Razmi J, Sadowski M (2015) Temperature distribution and melt geometry in laser and electron-beam melting processes - A comparison among common materials. Addit Manuf 8:1\u0026ndash;11. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.addma.2015.07.003\u003c/span\u003e\u003cspan address=\"10.1016/j.addma.2015.07.003\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLe KQ, Tang C, Wong CH (2019) On the study of keyhole-mode melting in selective laser melting process. Int J Therm Sci 145. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijthermalsci.2019.105992\u003c/span\u003e\u003cspan address=\"10.1016/j.ijthermalsci.2019.105992\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eYu G, Gu D, Dai D et al (2016) Influence of processing parameters on laser penetration depth and melting/re-melting densification during selective laser melting of aluminum alloy. Appl Phys Mater Sci Process 122:1\u0026ndash;12. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00339-016-0428-6\u003c/span\u003e\u003cspan address=\"10.1007/s00339-016-0428-6\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang DZ, Li KL, Yu CF et al (2019) Cracking Behavior in Additively Manufactured Pure Tungsten. Acta Metall Sinica (English Letters) 32:127\u0026ndash;135. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s40195-018-0752-2\u003c/span\u003e\u003cspan address=\"10.1007/s40195-018-0752-2\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eWang D, Wang Z, Li K et al (2019) Cracking in laser additively manufactured W: Initiation mechanism and a suppression approach by alloying. Mater Des 162:384\u0026ndash;393. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.matdes.2018.12.010\u003c/span\u003e\u003cspan address=\"10.1016/j.matdes.2018.12.010\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eN\u0026eacute;meth AAN, Reiser J, Armstrong DEJ, Rieth M (2015) The nature of the brittle-to-ductile transition of ultra fine grained tungsten (W) foil. Int J Refract Met Hard Mater 50:9\u0026ndash;15. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.ijrmhm.2014.11.005\u003c/span\u003e\u003cspan address=\"10.1016/j.ijrmhm.2014.11.005\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eArakcheev AS, Huber A, Wirtz M et al (2015) Theoretical investigation of crack formation in tungsten after heat loads. J Nucl Mater 463:246\u0026ndash;249. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jnucmat.2014.10.090\u003c/span\u003e\u003cspan address=\"10.1016/j.jnucmat.2014.10.090\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eLi C, Zhu D, Li X et al (2017) Thermal\u0026ndash;stress analysis on the crack formation of tungsten during fusion relevant transient heat loads. Nuclear Mater Energy 13:68\u0026ndash;73. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.nme.2017.06.008\u003c/span\u003e\u003cspan address=\"10.1016/j.nme.2017.06.008\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eBudaev VP, Martynenko YV, Karpov AV et al (2015) Tungsten recrystallization and cracking under ITER-relevant heat loads. J Nucl Mater 463:237\u0026ndash;240. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.jnucmat.2014.11.129\u003c/span\u003e\u003cspan address=\"10.1016/j.jnucmat.2014.11.129\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eZheng B, Zhou Y, Smugeresky JE et al (2008) Thermal behavior and microstructural evolution during laser deposition with laser-engineered net shaping: Part I. Numerical calculations. Metall Mater Trans Phys Metall Mater Sci 39:2228\u0026ndash;2236. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s11661-008-9557-7\u003c/span\u003e\u003cspan address=\"10.1007/s11661-008-9557-7\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eXia Z, Wang H, Xu Q (2012) The stress relief mechanism in laser irradiating on porous films. Opt Commun 285:70\u0026ndash;76. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.optcom.2011.09.012\u003c/span\u003e\u003cspan address=\"10.1016/j.optcom.2011.09.012\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Selective laser melting, Tungsten, Temperature evolution, Thermodynamic behavior, Defects formation","lastPublishedDoi":"10.21203/rs.3.rs-8814992/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8814992/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSelective laser melting of pure tungsten has always been a challenge due to its intrinsic properties such as high melting point, high surface tension and dynamic viscosity. In order to reveal the physical phenomenon during SLM-processed pure tungsten, a transient mesoscale model was developed by finite volume method (FVM). The temperature evolution and thermodynamic behavior within the molten pool were investigated. The simulation results demonstrated that the peak temperature and cooling rate were enhanced as the laser power increased. The peaking temperature and cooling rate reached 5742 K and 4.66 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\:\\times\\:\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e7\u003c/sup\u003e K/s using a high laser power of 350 W, respectively. Accordingly, the long liquid lifetime of 182 \u0026micro;s was obtained. At a high laser power of 350 W, the velocity vectors within the molten pool were intensified obviously, generating a strong mass transfer. A regular molten pool with a large width of 62 \u0026micro;m was obtained, which was favorable to metallurgical bonding with adjacent scanning tracks. The laser power played an important role in influencing the surface morphologies of SLM-processed tungsten parts. At a relatively low laser power of 200 W, the scanning track was discontinuous with a large number of unmelted particles. Simultaneously, the corresponding SLM-processed tungsten parts were observed with large pores. However, as a high laser power of 350 W was applied, the top surface of scanning track was continuous with regular liquid flow. Under this situation, the corresponding SLM-processed tungsten part was nearly free of pores. Moreover, the cracks were inevitable regardless of the applied laser powers and the formation mechanism of cracks was revealed. Based on the simulation results of SLM-processed tungsten, the available methods used to reduce the cracks were proposed.\u003c/p\u003e","manuscriptTitle":"Multiscale investigation of pore and crack formation during selective laser melting of pure tungsten: Simulation and experimental validation","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-02-21 10:42:28","doi":"10.21203/rs.3.rs-8814992/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"bee8adfe-1fa8-46f1-b7cb-0abaff47153b","owner":[],"postedDate":"February 21st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-20T07:10:34+00:00","versionOfRecord":[],"versionCreatedAt":"2026-02-21 10:42:28","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8814992","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8814992","identity":"rs-8814992","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}