Effects of Process Strategies on the Processability of CM247LC in Powder Bed Fusion of Metals using a Laser Beam

Effects of Process Strategies on the Processability of CM247LC in Powder Bed Fusion of Metals using a Laser Beam | 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 Effects of Process Strategies on the Processability of CM247LC in Powder Bed Fusion of Metals using a Laser Beam Nele Kretzer, Niklas Ostermann, Tobias Grimm, Jan T. Sehrt This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7999951/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 In this work, the processability of the nickel-based superalloy CM247LC in powder bed fusion of metals using a laser beam (PBF-LB/M) is systematically investigated. The focus is on the influence of inter-hatch waiting times and hatch permutation patterns. A baseline parameter set was established in preliminary studies to ensure a stable melt pool formation and defect-free consolidation. Based on these findings, the effects of controlled temporal delays between adjacent vectors and variations in hatch sequence are studied. The samples are analyzed in terms of relative density and the mean peak temperature of each layer, recorded using an in-situ thermographic camera system. PBF-LB/M CM247LC in-situ thermography scan strategies additive manufacturing powder bed fusion of metals using a laser beam Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 1 Introduction The nickel-based superalloy CM247LC, a further development of the original MAR-M247 alloy, offers outstanding mechanical properties such as high-temperature strength, creep resistance, and oxidation stability [1]. Therefore, it is suitable for ap-plications at elevated temperatures, such as turbines and burner components [2]. Since it was originally designed for casting and belongs to the "hard-to-weld" alloys, processing by powder bed fusion of metals using a laser beam (PBF-LB/M) remains a challenge due to a high crack susceptibility [3]. PBF-LB/M is an additive manufactur-ing (AM) process, where three-dimensional parts are built layer upon layer [4]. The geometry is digitally sliced and sent to the PBF-LB/M system, where a recoater ap-plies a new and fresh layer of powder. The cross-section is then exposed with a laser beam using a certain and defined scan strategy [5]. One reason for the cracking be-havior of CM247LC during the PBF-LB/M process is that Aluminum (Al) and Titani-um (Ti) exceed 4 wt.%, which results in γ' precipitates during the PBF-LB/M process [6]. The combination of process-induced high cooling rates and small melt pools re-sults in solidification cracking and liquation cracking [7]. In combination with Al and Ti, the Hafnium (Hf) content is significant, too, as does the content of Zirconium (Zr) and Boron (B), when it comes to the formation of cracks. Ductility dip cracking as well as strain age cracking, are mechanisms also known from welding and have al-ready been reported in studies on CM247LC [8,9]. A common method of counter-acting crack formation is to process the material at high preheating temperatures of up to 1,200°C [10]. There are also approaches to post-processing methods, such as hot isostatic pressing (HIP), in which the components are treated at high temperatures around 1,200°C and pressures around 150 MPa to subsequently close any cracks that have formed. [6]. Further studies have dealt with the application of downstream heat treatments [11–13]. Another way to reduce crack formation is to adjust the chemical composition. In this context, studies have already been conducted on different Hf contents to prevent precipitation and thus brittle phases [14].note that the first paragraph of a section or subsection is not indented. The first paragraphs that follows a table, figure, equation etc. does not have an indent, either. If the original, proven alloy formula is to be retained without post-treatment and complex preheating processes, the only option is to optimize the laser parameters. In the PBF-LB/M process, the interaction between the laser beam with its laser parameters and the powder material is mandatory for determining the resulting microstructure and defect formation. The main laser parameters – laser power, scan speed, hatch distance, and layer thickness – govern the thermal input into the material and thereby influence the solidification dynamics during layer-wise melting [15,16]. Fardan et al. [17] have already shown in a study at 80°C build platform heating that optimizing the laser parameters is not sufficient. In addition to the laser parameters, the scanning strategy has a major influence on the formation of the microstructure [18–20]. Studies have already been conducted that focus in particular on investigations into stripe exposure and the influence of stripe width on crack formation [9], [21]. The results show that the vector length has an influence and that short vectors have a positive effect on the microstructure and fewer hot cracks were detected. In their study, Fardan et al. chose a minimum strip width of 0.2 mm, for example, to approximate a point exposure strategy. They were able to reduce internal stress and, according to the available results, also reduce the proportion of hot cracks. Unfortunately, the height of the samples remains unclear, and it is also unclear whether the effect can be reproduced with increasing build height. The following study also applies the concept of small melt pools, combining the use of different vector lengths with defined inter-hatch times and hatch permutation. According to the state of the art on the topic, this is the first attempt to apply such a strategy in PBF-LB/M. The results of the study are intended to provide an initial indication of whether an influence can be detected. For this purpose, the relative density and average peak temperature of the sample surface are evaluated during the process. 2 Material and Methods Gas-atomized, spherical CM247LC powder (Höganäs AB, Höganäs, Sweden) is used in this study (Fig. 1 A). The particle morphology is predominantly spherical with only a few satellites and particle adhesions. No significant defects are visible. The surface of the particles can be described as smooth. Table 1 Chemical composition of the CM247LC compared to literature values. Element S Cr Ni Si Mo Ti Al Zr W Co B Hf Ta [22] / wt.-% 0.001 8.0 Rest 0.03 0.5 0.7 5.6 0.010 10.0 9.0 0.015 1.4 3.2 Study / wt.-% < 0.001 8.2 Rest 0.02 0.5 0.8 5.6 0.007 9.5 9.2 0.01 1.6 3.2 Table 1 shows the chemical composition of the powder feedstock, which was determined by energy dispersive X-Ray fluorescence spectrometry (EDXRF) (Vanta C-Series, Olympus Corporation, Shinjuku, Japan). Dynamic image analysis (Camsizer X2, Microtrac, Haan, Germany) was used to measure particle size distribution (Fig. 1 B). The particle size distribution shows an unimodal curve with a main peak between approximately 20 µm and 35 µm, indicating that most particles fall within this range. The distribution is slightly skewed towards finer particles, with a noticeable but smaller fraction below 20 µm and only a few particles above 45 µm. Table 2 Process Laser Parameter. Condition Laser power Scanning speed Hatch distance Layer thickness Unheated 300 W 1000 mm∙s -1 0.078 mm 0.05 mm The cumulative distribution (Q3 curve) reaches 50% at around 28–30 µm, suggesting this as the median particle diameter (D50). The D10 and D90 values can be estimated at roughly 15 µm and 45 µm, respectively. An AconityMIDI PBF-LB/M system (Aconity3D, Herzogenrath, Germany) was used to manufacture the samples for this study. The system is equipped with an IPG YLR-400-AC (IPG Photonics Corporation, Marlborough, MA, USA) fiber laser with a wavelength of 1070 nm, a maximum laser power of 400 W, and a 3D-scanning optic to allow the use of variable focus diameters. For this study, the machine operated with a beam diameter of 80 µm. 40 cubic samples were manufactured with dimensions of 10 × 10 × 10 mm³. The manufacturing process is performed under an argon-inert gas atmosphere, and the parameters used are taken from a previous study (Table 2 ). The manufacturing process was monitored using thermographic imaging of an Optris PI 640i (Optris GmbH & Co. KG, Berlin, Germany) through a Germanium infrared window (Edmund Optics Inc., Tucson, USA). The optical axis of the thermographic camera is oriented at 45° relative to the build platform, in the opposite direction to the recoating process. The temperature range for the measurements was set to 150°C – 900°C with a framerate of 32 Hz. Therefore, the temperatures measured are expected to be lower than the actual melt pool temperature. It was shown that the surface condition during the PBF-LB/M process influences the emissivity of the surface and, therefore, the measured temperature [23]. An emissivity value of 0.36 was chosen based on preliminary studies with another nickel-based alloy [23]. The calibration procedure is also described in the aforementioned study. Table 3 . Assignment and information on the scanning strategies used. Since the emissivity is highly sensitive, the measured temperatures can only be used for comparisons between process strategies. The peak temperatures of each sample over time are determined using the software PIX connect (Optris GmbH & Co. KG, Berlin Germany). Comparing the thermal conditions, the mean peak temperature of each sample during its exposure is averaged over the last 20 layers of the manufacturing process. Three cross-sections of the PBF-LB/M samples are prepared for density measurements by grinding and polishing (Saphir 250 A2-ECO, ATM Qness GmbH). The density is determined by the binarization of microscopic images (VHX-6000, Keyence). The design of the experiment involves the variation of two factors: the vector length, which varied in four steps from 0.625 mm to 5 mm, and the scanning strategy (Table 3 ). The scanning strategy varies in terms of waiting times. Five different additional waiting times (25%, 50%, 100%, 200%, 400%) are chosen relative to the individual vector exposure time calculated by vector length and scan speed. Figure 2 A shows an example of inter-hatch waiting times of 5 ms for scan strategy A with a vector length of 2.5 mm. The reference sample was manufactured without a set waiting time. Besides the waiting time, hatch permutation is used to create waiting times through successive skipping of vectors in a controlled manner. For a hatch permutation of n, the exposure is divided into n sequences. In the first sequence, every nth vector is exposed, while in the second sequence, every (n + 1)th vector is exposed, and so on. Four settings were used, from 2 over 4 and 8 to 16. Figure 2 B shows an example of a sequence of eight vectors exposed using a hatch permutation of Type 2. The use of hatch permutation simulates local waiting times without a significant increase of laser-off times. All samples are being processed with a 90° hatch rotation without stripe shift. The full factorial experimental design results in a total sample size of 40. 3 Results and Discussion 3.1 Density Figure 3 A shows the main effect diagram between the factors vector length, scan strategy and the relative density. It is noticeable that the use of scan strategies utilizing inter-hatch waiting times (A-E) achieves a higher density than the use of hatch permutation (F-I). Hatch permutation type 4 (G) achieves a particularly low average relative density of less than 85%. Type 2 (F) and Type 8 (H) achieve an average of over 90%. Type 16 (I) achieves the highest densities with an average of almost 94%, but the value is still well below the minimum density of 99% specified by VDI 3405. The cross-section of the hatch permutation samples show clear lack-of-fusion defects (Fig. 5 A), that might be caused by denudation effects described by Manyalibo et al [24]. A look at the evaluation, depending on the vector length, shows that this factor has no significant influence across all scanning strategies. The density fluctuates between 95% and 96% for all vector lengths. Due to the low relative densities of the hatch permutation strategies, the effects of the inter-hatch waiting time strategies are not clearly apparent. For this reason, the inter-hatch waiting time strategies are shown separately in Fig. 3 B in order to be able to draw conclusions about their effects. When looking at the inter-hatch waiting times without the hatch permutation strategies, the measured densities rise depending on the vector lengths. The densities initially decrease with increasing vector lengths, from 99% to 98.8%, but then rises steadily to an average density value of 99.45% at a vector length of 5 mm. The self-imposed goal of a minimum density of 99% is only achieved by the reference sample and the samples manufactured with inter-hatch waiting times in this experiment. This is possibly due to low process temperatures resulting from relatively long laser-off times during the hatch permutation startegies as well as denudation effects that can occur. Looking at the density values in relation to the inter-hatch waiting times, the data does not show a clear trend. A downward outlier to 98.9% can be observed in the data set without waiting time. The results of the density evaluation show severe lack-of-fusion defects (Fig. 5 A), particularly in the hatch permutation experiments. As described above, individual vectors are exposed in a predefined line order. As the laser scans over the powder bed, the melt pool does not only melt the material directly below the laser beam but also partially incorporates adjacent powder particles. This occurs due to capillary forces at the melt pool boundary and thermocapillary convection within the liquid metal, which draw the surrounding powder into the melt [24,25]. Since the individual vectors are exposed with an offset and there is no continuous “melt wave” (melt front) as with conventional scanning strategies, convection can cause melt traces that are exposed at a later point in time to no longer contain any powder material to melt. If there is not enough material available for melting, the defects mentioned above occur. This effect appears to have been particularly noticeable in Type 4 (G). Figure 4 A) shows the heat map of density values plotted against the scanning strategy and vector length. The highest density achieved for samples processed by hatch permutation Type 4 is only 87.32%. This effect appears to have been particularly pronounced in Type 4 (G). A higher distance between the scan tracks seems to counteract the effect somewhat, as the highest densities were achieved with type 16 (I). With a vector length of 1.25 mm, the density was 96.14%. Nevertheless, this value is not even close to the required 99%. The inter-hatch waiting times have already been described above. Although higher densities were achieved in principle, not all samples' densities exceeded 99% (Fig. 4 B). The highest density of 99.77% was achieved with a vector length of 0.625 mm and an inter-hatch waiting time of 0.078 ms (Fig. 5 C). When examining the results of the waiting times, it is noticeable that systematic errors occur, particularly in the stripe overlap (Fig. 5 B). In these areas, there are more pore seams, which are due to insufficient strip overlap. It must also be considered that there was no strip shift in addition to the 90° hatch rotation, which can also impair the wetting of the melt traces. If the strips are not offset, gaps can form which cannot be sufficiently melted by the laser beam. 3.2 Peak Temperature Figure 6 shows the measured peak temperatures of the individual samples averaged over the time of exposure in the last 20 layers of the manufacturing process. It is noticeable that the shortest used vector length of 0.625 mm resulted in the lowest mean peak temperature across most strategies. Increasing the vector length mostly led to higher measured mean peak temperatures. This may be due to a change in the ratio of laser-on to laser-off time. The shorter the vectors, the shorter their exposure time. Since the inter-hatch waiting times are chosen relative to the exposure times of the vectors, these do not influence the ratio of laser-on to laser-off times. However, the time required to perform skywriting – acceleration of the scanner mirrors between two vectors without laser exposure – remains constant. Therefore, the ratio of laser-on to laser-off time shifts towards more laser-off time for shorter vectors, resulting in lower mean energy input during the exposure of a single layer of a whole sample. The lower mean energy input leads to lower part and consequently peak temperatures. In contrast, a short vector exposure time could result in less cooling of the previously exposed vector and, consequently, a higher peak temperature during exposure. Figure 6 also shows lower measured mean peak temperatures for samples manufactured with a scan strategy utilizing hatch permutation (scan strategies F to I). This may have multiple reasons. On the one hand, a permutation of even numbers requires the scanner to jump back to the opposite side of a stripe, as shown in Fig. 2 B. Thus, increasing the laser-off time and reducing the average energy input, leading to lower peak temperatures. On the other hand, a vector is not exposed next to the previously exposed vector. Thus, the effect of higher temperatures of the surrounding material is reduced, also resulting in lower peak temperatures. When analyzing samples manufactured using inter-hatch waiting times (scan strategies A to E), a reduction in mean peak temperatures is observed as the inter-hatch waiting time increases. This is likely due to the ratios of laser-on and laser-off times and their effect on the mean energy input. This trend can be observed in some samples (e.g., for a vector length of 0.625 mm) but not in all (e.g., for a vector length of 1.25 mm). It is expected that using neither hatch permutation nor inter-hatch waiting times (scan strategy J) results in the highest peak temperatures for all vector lengths. However, the measured peak temperatures do not show this behavior. It should be noted that many deviations in the measured mean peak temperature cannot be explained by the vector length and/or the scan strategy used. At this stage, in addition to the scan strategies and vector length, other factors influencing the measured mean peak temperature must also be considered. The samples are arranged in a randomized pattern on the build platform. However, the process was not repeated with different randomized arrangements. Thus, the influence of the samples' positions on the build platform must be explained. On the one hand, the inert gas flows from one side of the build platform to the other. On its way, the gas might heat up or change its flow conditions, resulting in different temperatures of the surface of the sample due to convection. The positions of the sample relative to the gas flow might also influence their surface condition and, therefore, their emissivity values and measured temperatures. Additionally, the thermographic camera is oriented at 45° towards the build platform. Consequently, the distance between the samples and the thermographic camera is not constant, which may affect the amount of thermal radiation reaching it. Besides the possible influence of the position on the build platform, the condition of the top surface generated by using different vector lengths and scan strategies may differ. This would influence the emissivity values of the generated top surfaces and, consequently, the emitted radiation, leading to deviations when calculating temperatures from recorded thermal radiation using a constant emissivity setting. These potential effects highlight the difficulty of thermal monitoring of the PBF-LB/M process when using different vector lengths and scan strategies. 3.3 Crack formation At this point, the fracture behavior of the samples examined should be discussed and evaluated. However, at this stage, no final conclusion can be drawn yet regarding the formation of cracks in connection with the examined scanning strategies. It can be observed that cracks occur more severely on some samples (Fig. 7 A) and less severely on others (Fig. 7 B). No final trend, depending on the high number of influencing factors, can be identified. Identifying these connections is part of ongoing research, which is still in progress and has not yet been finalized. Due to the high porosity of the samples, it is difficult to establish a correlation, as dense samples have a different structure and thermal influences also affect the result and thus the formation of cracks. 4 Conclusion and Summary The aim of the study is to analyze the effect of different waiting time strategies for crack reduction in CM247LC with no preheating. The results show that the chosen approach must further be refined, with a broader parameter window and adjusted stripe overlap. It appears that the density achieved with the laser parameters used is not yet enough to produce a sufficiently dense sample. For highly porous samples, no reliable conclusion can be drawn regarding the influence of the applied scan strategy on crack formation, since porosity itself strongly affects the built of residual stresses and cracking behavior. High porosity indicates unstable processing conditions – such as insufficient melting, lack of fusion, or irregular energy input – which significantly alter the microstructure, heat flow, and residual stress distribution compared to dense samples. As a result, the effects of porosity overlap with those of the scan strategy, making it impossible to isolate the specific influence of the scan strategy on crack formation. Thermal monitoring of the PBF-LB/M process revealed that shorter vector lengths generally resulted in lower mean peak temperatures, likely due to a reduced ratio of laser-on to laser-off times and, consequently, a lower mean energy input per layer. Scan strategies utilizing hatch permutation or inter-hatch waiting times also tended to reduce peak temperatures by increasing laser-off times or minimizing thermal accumulation between adjacent vectors. However, deviations in the measured temperatures indicate that additional factors – such as sample position on the build platform, gas flow direction, the thermographic camera's viewing angle, and variations in surface emissivity – significantly affect the recorded thermal data. These influences limit the direct interpretation of thermal monitoring results based solely on vector length and scan strategy. Future studies should therefore incorporate complementary, high-precision thermal measurement techniques to better isolate and understand these effects. Due to numerous factors influencing thermal monitoring results, further statistical analysis of the measured mean peak temperature was not conducted. Future experiments should be performed using additional thermal monitoring, such as on-axis high-speed pyrometry, to better understand the effects of vector length and scan strategies on peak temperatures. Important information about the process behavior can already be obtained by using waiting times. The approach remains promising, as temperature peaks in the process can be prevented, which has a positive effect on the microstructure development of CM247LC. Melting tracks for example do not penetrate as deeply into already melted material, thus counteracting the formation of liquation cracks. Declarations Contributions X.X.: Experimental design, methodology, data curation, formal analysis, writing, original draft X.X.: Experimental design, methodology, data curation, formal analysis, writing, original draft X.X.: Writing-review and editing X.X.: Resources, writing-review and editing, supervision, project administration, funding acquisition All authors: Project Management, technical consultant Author Contribution N.K.:Experimental design, methodology, data curation, formal analysis, writing, original draftN.O.: Experimental design, methodology, data curation, formal analysis, writing, original draftT.G.: Writing-review and editingJ.T.S.:Resources, writing-review and editing, supervision, project administration, funding acquisitionAll authors: Project Management, technical consultant Acknowledgement The authors thank the German Research Foundation (DFG) for funding this project through SPP 2419 (523837500). 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King, "Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones," Acta Materialia, Jg. 108, S. 36–45, 2016, doi: 10.1016/j.actamat.2016.02.014. 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. 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17:29:10","extension":"html","order_by":20,"title":"","display":"","copyAsset":false,"role":"acdc-reference","size":59584,"visible":true,"origin":"","legend":"","description":"","filename":"earlyproof.html","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/900ee70d9d053406c1390a2e.html"},{"id":96206942,"identity":"d4943739-ea91-48f4-8352-f4143201d967","added_by":"auto","created_at":"2025-11-18 17:29:10","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":343726,"visible":true,"origin":"","legend":"\u003cp\u003eA) Particle morphology of the CM247LC powder (450x magnification), B) Particle size distribution.\u003c/p\u003e","description":"","filename":"Picture1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/0fd609b6b96c6091f4fc1504.jpg"},{"id":96252415,"identity":"152a31a1-ebba-4672-996a-cd012d94a874","added_by":"auto","created_at":"2025-11-19 07:40:55","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":70410,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic representation of A) inter-hatch waiting times of 5 ms for scan strategy A with a vector length of 2.5 mm and, B) the principle of hatch permutation – here Type 2 for a sequence of eight vectors.\u003c/p\u003e","description":"","filename":"Picture2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/4694b48deced5cef842a793b.jpg"},{"id":96250589,"identity":"3df92987-8c1f-4719-8667-77f4a587a423","added_by":"auto","created_at":"2025-11-19 07:38:44","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":193725,"visible":true,"origin":"","legend":"\u003cp\u003eMain effect plots for the mean relative density of A) the scan strategy combinations examined and B) without hatch permutation (F-I).\u003c/p\u003e","description":"","filename":"Picture3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/c076e2b152b92127c25edd05.jpg"},{"id":96252984,"identity":"29115ef8-16ba-4090-8960-28bf450b9121","added_by":"auto","created_at":"2025-11-19 07:41:46","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":52179,"visible":true,"origin":"","legend":"\u003cp\u003eA) Relative density of the scan strategy combinations examined and B) without hatch permutation (F-I).\u003c/p\u003e","description":"","filename":"Picture4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/ab2f4add9b837b86621aa7ab.jpg"},{"id":96206951,"identity":"0263afe3-2ea7-44b0-b3c5-7532b9635f7e","added_by":"auto","created_at":"2025-11-18 17:29:10","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":56477,"visible":true,"origin":"","legend":"\u003cp\u003eCross-section of samples manufactured with A) scan strategy G (Hatch permutation Type 4) and a vector length of 0.625 mm, B) scan strategy B (inter-hatch waiting time of 5 ms) and a vector length of 5 mm, C) scan strategy E (inter-hatch waiting time of 0.078 ms) and a vector length of 0.625 mm.\u003c/p\u003e","description":"","filename":"Picture5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/9e30465f81211fa6f077e7ae.jpg"},{"id":96206948,"identity":"180ab422-d776-486b-a0d4-29aa20b7098c","added_by":"auto","created_at":"2025-11-18 17:29:10","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":25575,"visible":true,"origin":"","legend":"\u003cp\u003eHeatmap of the measured mean peak temperatures during the exposure of the last 20 layers of samples manufactured out of CM247LC with different vector lengths and scan strategies.\u003c/p\u003e","description":"","filename":"Picture6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/84ca82552ab652c392dc9f0c.jpg"},{"id":96251536,"identity":"4a005d4c-ac01-47c3-9354-33a5ecd32855","added_by":"auto","created_at":"2025-11-19 07:39:47","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":41234,"visible":true,"origin":"","legend":"\u003cp\u003eCross-section of samples manufactured with A) scan strategy C (inter-hatch waiting time of 1.25 ms) and a vector length of 2.5 mm, B) scan strategy B (inter-hatch waiting time of 0.625 ms) and a vector length of 1.25 mm.\u003c/p\u003e","description":"","filename":"Picture7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/8695820d138d12c0732656d7.jpg"},{"id":96368680,"identity":"bd262a34-f052-4f5e-b7ca-d65f308971aa","added_by":"auto","created_at":"2025-11-20 10:19:08","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1280142,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7999951/v1/f878170c-088f-486c-ad68-74b424715a25.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Effects of Process Strategies on the Processability of CM247LC in Powder Bed Fusion of Metals using a Laser Beam ","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eThe nickel-based superalloy CM247LC, a further development of the original MAR-M247 alloy, offers outstanding mechanical properties such as high-temperature strength, creep resistance, and oxidation stability [1]. Therefore, it is suitable for ap-plications at elevated temperatures, such as turbines and burner components [2]. Since it was originally designed for casting and belongs to the \"hard-to-weld\" alloys, processing by powder bed fusion of metals using a laser beam (PBF-LB/M) remains a challenge due to a high crack susceptibility [3]. PBF-LB/M is an additive manufactur-ing (AM) process, where three-dimensional parts are built layer upon layer [4]. The geometry is digitally sliced and sent to the PBF-LB/M system, where a recoater ap-plies a new and fresh layer of powder. The cross-section is then exposed with a laser beam using a certain and defined scan strategy [5]. One reason for the cracking be-havior of CM247LC during the PBF-LB/M process is that Aluminum (Al) and Titani-um (Ti) exceed 4 wt.%, which results in γ' precipitates during the PBF-LB/M process [6]. The combination of process-induced high cooling rates and small melt pools re-sults in solidification cracking and liquation cracking [7]. In combination with Al and Ti, the Hafnium (Hf) content is significant, too, as does the content of Zirconium (Zr) and Boron (B), when it comes to the formation of cracks. Ductility dip cracking as well as strain age cracking, are mechanisms also known from welding and have al-ready been reported in studies on CM247LC [8,9]. A common method of counter-acting crack formation is to process the material at high preheating temperatures of up to 1,200\u0026deg;C [10]. There are also approaches to post-processing methods, such as hot isostatic pressing (HIP), in which the components are treated at high temperatures around 1,200\u0026deg;C and pressures around 150 MPa to subsequently close any cracks that have formed. [6]. Further studies have dealt with the application of downstream heat treatments [11\u0026ndash;13]. Another way to reduce crack formation is to adjust the chemical composition. In this context, studies have already been conducted on different Hf contents to prevent precipitation and thus brittle phases [14].note that the first paragraph of a section or subsection is not indented. The first paragraphs that follows a table, figure, equation etc. does not have an indent, either.\u003c/p\u003e\u003cp\u003eIf the original, proven alloy formula is to be retained without post-treatment and complex preheating processes, the only option is to optimize the laser parameters. In the PBF-LB/M process, the interaction between the laser beam with its laser parameters and the powder material is mandatory for determining the resulting microstructure and defect formation. The main laser parameters \u0026ndash; laser power, scan speed, hatch distance, and layer thickness \u0026ndash; govern the thermal input into the material and thereby influence the solidification dynamics during layer-wise melting [15,16]. Fardan et al. [17] have already shown in a study at 80\u0026deg;C build platform heating that optimizing the laser parameters is not sufficient. In addition to the laser parameters, the scanning strategy has a major influence on the formation of the microstructure [18\u0026ndash;20]. Studies have already been conducted that focus in particular on investigations into stripe exposure and the influence of stripe width on crack formation [9], [21]. The results show that the vector length has an influence and that short vectors have a positive effect on the microstructure and fewer hot cracks were detected. In their study, Fardan et al. chose a minimum strip width of 0.2 mm, for example, to approximate a point exposure strategy. They were able to reduce internal stress and, according to the available results, also reduce the proportion of hot cracks. Unfortunately, the height of the samples remains unclear, and it is also unclear whether the effect can be reproduced with increasing build height. The following study also applies the concept of small melt pools, combining the use of different vector lengths with defined inter-hatch times and hatch permutation. According to the state of the art on the topic, this is the first attempt to apply such a strategy in PBF-LB/M. The results of the study are intended to provide an initial indication of whether an influence can be detected. For this purpose, the relative density and average peak temperature of the sample surface are evaluated during the process.\u003c/p\u003e"},{"header":"2 Material and Methods","content":"\u003cp\u003eGas-atomized, spherical CM247LC powder (H\u0026ouml;gan\u0026auml;s AB, H\u0026ouml;gan\u0026auml;s, Sweden) is used in this study (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA). The particle morphology is predominantly spherical with only a few satellites and particle adhesions. No significant defects are visible. The surface of the particles can be described as smooth.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eChemical composition of the CM247LC compared to literature values.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eElement\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCr\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMo\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eW\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCo\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eB\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHf\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTa\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e[22] /\u003c/p\u003e\n \u003cp\u003ewt.-%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.03\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.010\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStudy /\u003c/p\u003e\n \u003cp\u003ewt.-%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e\u0026lt;\u0026thinsp;0.001\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eRest\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.007\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.01\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eTable \u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e shows the chemical composition of the powder feedstock, which was determined by energy dispersive X-Ray fluorescence spectrometry (EDXRF) (Vanta C-Series, Olympus Corporation, Shinjuku, Japan). Dynamic image analysis (Camsizer X2, Microtrac, Haan, Germany) was used to measure particle size distribution (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). The particle size distribution shows an unimodal curve with a main peak between approximately 20 \u0026micro;m and 35 \u0026micro;m, indicating that most particles fall within this range. The distribution is slightly skewed towards finer particles, with a noticeable but smaller fraction below 20 \u0026micro;m and only a few particles above 45 \u0026micro;m.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eProcess Laser Parameter.\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCondition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLaser power\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eScanning speed\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eHatch distance\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eLayer thickness\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eUnheated\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e300 W\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1000 mm∙s\u003csup\u003e-1\u003c/sup\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.078 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.05 mm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n\u003c/div\u003e\n\u003cp\u003eThe cumulative distribution (Q3 curve) reaches 50% at around 28\u0026ndash;30 \u0026micro;m, suggesting this as the median particle diameter (D50). The D10 and D90 values can be estimated at roughly 15 \u0026micro;m and 45 \u0026micro;m, respectively. An AconityMIDI PBF-LB/M system (Aconity3D, Herzogenrath, Germany) was used to manufacture the samples for this study. The system is equipped with an IPG YLR-400-AC (IPG Photonics Corporation, Marlborough, MA, USA) fiber laser with a wavelength of 1070 nm, a maximum laser power of 400 W, and a 3D-scanning optic to allow the use of variable focus diameters. For this study, the machine operated with a beam diameter of 80 \u0026micro;m. 40 cubic samples were manufactured with dimensions of 10 \u0026times; 10 \u0026times; 10 mm\u0026sup3;. The manufacturing process is performed under an argon-inert gas atmosphere, and the parameters used are taken from a previous study (Table \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). The manufacturing process was monitored using thermographic imaging of an Optris PI 640i (Optris GmbH \u0026amp; Co. KG, Berlin, Germany) through a Germanium infrared window (Edmund Optics Inc., Tucson, USA).\u003c/p\u003e\n\u003cp\u003eThe optical axis of the thermographic camera is oriented at 45\u0026deg; relative to the build platform, in the opposite direction to the recoating process. The temperature range for the measurements was set to 150\u0026deg;C \u0026ndash; 900\u0026deg;C with a framerate of 32 Hz. Therefore, the temperatures measured are expected to be lower than the actual melt pool temperature. It was shown that the surface condition during the PBF-LB/M process influences the emissivity of the surface and, therefore, the measured temperature [23]. An emissivity value of 0.36 was chosen based on preliminary studies with another nickel-based alloy [23]. The calibration procedure is also described in the aforementioned study.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e3\u003c/strong\u003e\u003cstrong\u003e.\u003c/strong\u003e Assignment and information on the scanning strategies used.\u003c/p\u003e\n\u003cp\u003e\u003cimg src=\"https://myfiles.space/user_files/69519_bce2c0439cd956a6/69519_custom_files/img1763486524.png\"\u003e\u003c/p\u003e\n\u003cp\u003eSince the emissivity is highly sensitive, the measured temperatures can only be used for comparisons between process strategies. The peak temperatures of each sample over time are determined using the software PIX connect (Optris GmbH \u0026amp; Co. KG, Berlin Germany). Comparing the thermal conditions, the mean peak temperature of each sample during its exposure is averaged over the last 20 layers of the manufacturing process. Three cross-sections of the PBF-LB/M samples are prepared for density measurements by grinding and polishing (Saphir 250 A2-ECO, ATM Qness GmbH). The density is determined by the binarization of microscopic images (VHX-6000, Keyence).\u003c/p\u003e\n\u003cp\u003eThe design of the experiment involves the variation of two factors: the vector length, which varied in four steps from 0.625 mm to 5 mm, and the scanning strategy (Table \u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The scanning strategy varies in terms of waiting times. Five different additional waiting times (25%, 50%, 100%, 200%, 400%) are chosen relative to the individual vector exposure time calculated by vector length and scan speed. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA shows an example of inter-hatch waiting times of 5 ms for scan strategy A with a vector length of 2.5 mm. The reference sample was manufactured without a set waiting time. Besides the waiting time, hatch permutation is used to create waiting times through successive skipping of vectors in a controlled manner. For a hatch permutation of n, the exposure is divided into n sequences. In the first sequence, every nth vector is exposed, while in the second sequence, every (n\u0026thinsp;+\u0026thinsp;1)th vector is exposed, and so on. Four settings were used, from 2 over 4 and 8 to 16. Figure \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB shows an example of a sequence of eight vectors exposed using a hatch permutation of Type 2. The use of hatch permutation simulates local waiting times without a significant increase of laser-off times. All samples are being processed with a 90\u0026deg; hatch rotation without stripe shift. The full factorial experimental design results in a total sample size of 40.\u003c/p\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\u003ch2\u003e3.1 Density\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eA shows the main effect diagram between the factors vector length, scan strategy and the relative density. It is noticeable that the use of scan strategies utilizing inter-hatch waiting times (A-E) achieves a higher density than the use of hatch permutation (F-I). Hatch permutation type 4 (G) achieves a particularly low average relative density of less than 85%. Type 2 (F) and Type 8 (H) achieve an average of over 90%. Type 16 (I) achieves the highest densities with an average of almost 94%, but the value is still well below the minimum density of 99% specified by VDI 3405. The cross-section of the hatch permutation samples show clear lack-of-fusion defects (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA), that might be caused by denudation effects described by Manyalibo et al [24]. A look at the evaluation, depending on the vector length, shows that this factor has no significant influence across all scanning strategies. The density fluctuates between 95% and 96% for all vector lengths. Due to the low relative densities of the hatch permutation strategies, the effects of the inter-hatch waiting time strategies are not clearly apparent. For this reason, the inter-hatch waiting time strategies are shown separately in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB in order to be able to draw conclusions about their effects.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eWhen looking at the inter-hatch waiting times without the hatch permutation strategies, the measured densities rise depending on the vector lengths. The densities initially decrease with increasing vector lengths, from 99% to 98.8%, but then rises steadily to an average density value of 99.45% at a vector length of 5 mm.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe self-imposed goal of a minimum density of 99% is only achieved by the reference sample and the samples manufactured with inter-hatch waiting times in this experiment. This is possibly due to low process temperatures resulting from relatively long laser-off times during the hatch permutation startegies as well as denudation effects that can occur. Looking at the density values in relation to the inter-hatch waiting times, the data does not show a clear trend. A downward outlier to 98.9% can be observed in the data set without waiting time.\u003c/p\u003e\u003cp\u003eThe results of the density evaluation show severe lack-of-fusion defects (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eA), particularly in the hatch permutation experiments. As described above, individual vectors are exposed in a predefined line order. As the laser scans over the powder bed, the melt pool does not only melt the material directly below the laser beam but also partially incorporates adjacent powder particles. This occurs due to capillary forces at the melt pool boundary and thermocapillary convection within the liquid metal, which draw the surrounding powder into the melt [24,25]. Since the individual vectors are exposed with an offset and there is no continuous \u0026ldquo;melt wave\u0026rdquo; (melt front) as with conventional scanning strategies, convection can cause melt traces that are exposed at a later point in time to no longer contain any powder material to melt. If there is not enough material available for melting, the defects mentioned above occur. This effect appears to have been particularly noticeable in Type 4 (G). Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eA) shows the heat map of density values plotted against the scanning strategy and vector length. The highest density achieved for samples processed by hatch permutation Type 4 is only 87.32%. This effect appears to have been particularly pronounced in Type 4 (G). A higher distance between the scan tracks seems to counteract the effect somewhat, as the highest densities were achieved with type 16 (I). With a vector length of 1.25 mm, the density was 96.14%. Nevertheless, this value is not even close to the required 99%.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eThe inter-hatch waiting times have already been described above. Although higher densities were achieved in principle, not all samples' densities exceeded 99% (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eB). The highest density of 99.77% was achieved with a vector length of 0.625 mm and an inter-hatch waiting time of 0.078 ms (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eC). When examining the results of the waiting times, it is noticeable that systematic errors occur, particularly in the stripe overlap (Fig.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003eB). In these areas, there are more pore seams, which are due to insufficient strip overlap. It must also be considered that there was no strip shift in addition to the 90\u0026deg; hatch rotation, which can also impair the wetting of the melt traces. If the strips are not offset, gaps can form which cannot be sufficiently melted by the laser beam.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec5\" class=\"Section2\"\u003e\u003ch2\u003e3.2 Peak Temperature\u003c/h2\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e shows the measured peak temperatures of the individual samples averaged over the time of exposure in the last 20 layers of the manufacturing process. It is noticeable that the shortest used vector length of 0.625 mm resulted in the lowest mean peak temperature across most strategies. Increasing the vector length mostly led to higher measured mean peak temperatures. This may be due to a change in the ratio of laser-on to laser-off time. The shorter the vectors, the shorter their exposure time. Since the inter-hatch waiting times are chosen relative to the exposure times of the vectors, these do not influence the ratio of laser-on to laser-off times. However, the time required to perform skywriting \u0026ndash; acceleration of the scanner mirrors between two vectors without laser exposure \u0026ndash; remains constant. Therefore, the ratio of laser-on to laser-off time shifts towards more laser-off time for shorter vectors, resulting in lower mean energy input during the exposure of a single layer of a whole sample. The lower mean energy input leads to lower part and consequently peak temperatures. In contrast, a short vector exposure time could result in less cooling of the previously exposed vector and, consequently, a higher peak temperature during exposure.\u003c/p\u003e\u003cp\u003eFigure \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e also shows lower measured mean peak temperatures for samples manufactured with a scan strategy utilizing hatch permutation (scan strategies F to I). This may have multiple reasons. On the one hand, a permutation of even numbers requires the scanner to jump back to the opposite side of a stripe, as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003eB. Thus, increasing the laser-off time and reducing the average energy input, leading to lower peak temperatures. On the other hand, a vector is not exposed next to the previously exposed vector. Thus, the effect of higher temperatures of the surrounding material is reduced, also resulting in lower peak temperatures.\u003c/p\u003e\u003cp\u003eWhen analyzing samples manufactured using inter-hatch waiting times (scan strategies A to E), a reduction in mean peak temperatures is observed as the inter-hatch waiting time increases. This is likely due to the ratios of laser-on and laser-off times and their effect on the mean energy input. This trend can be observed in some samples (e.g., for a vector length of 0.625 mm) but not in all (e.g., for a vector length of 1.25 mm). It is expected that using neither hatch permutation nor inter-hatch waiting times (scan strategy J) results in the highest peak temperatures for all vector lengths. However, the measured peak temperatures do not show this behavior. It should be noted that many deviations in the measured mean peak temperature cannot be explained by the vector length and/or the scan strategy used. At this stage, in addition to the scan strategies and vector length, other factors influencing the measured mean peak temperature must also be considered. The samples are arranged in a randomized pattern on the build platform. However, the process was not repeated with different randomized arrangements. Thus, the influence of the samples' positions on the build platform must be explained. On the one hand, the inert gas flows from one side of the build platform to the other. On its way, the gas might heat up or change its flow conditions, resulting in different temperatures of the surface of the sample due to convection. The positions of the sample relative to the gas flow might also influence their surface condition and, therefore, their emissivity values and measured temperatures.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eAdditionally, the thermographic camera is oriented at 45\u0026deg; towards the build platform. Consequently, the distance between the samples and the thermographic camera is not constant, which may affect the amount of thermal radiation reaching it. Besides the possible influence of the position on the build platform, the condition of the top surface generated by using different vector lengths and scan strategies may differ. This would influence the emissivity values of the generated top surfaces and, consequently, the emitted radiation, leading to deviations when calculating temperatures from recorded thermal radiation using a constant emissivity setting. These potential effects highlight the difficulty of thermal monitoring of the PBF-LB/M process when using different vector lengths and scan strategies.\u003c/p\u003e\u003c/div\u003e\u003cdiv id=\"Sec6\" class=\"Section2\"\u003e\u003ch2\u003e3.3 Crack formation\u003c/h2\u003e\u003cp\u003eAt this point, the fracture behavior of the samples examined should be discussed and evaluated. However, at this stage, no final conclusion can be drawn yet regarding the formation of cracks in connection with the examined scanning strategies. It can be observed that cracks occur more severely on some samples (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eA) and less severely on others (Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003eB). No final trend, depending on the high number of influencing factors, can be identified. Identifying these connections is part of ongoing research, which is still in progress and has not yet been finalized. Due to the high porosity of the samples, it is difficult to establish a correlation, as dense samples have a different structure and thermal influences also affect the result and thus the formation of cracks.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003c/div\u003e"},{"header":"4 Conclusion and Summary","content":"\u003cp\u003eThe aim of the study is to analyze the effect of different waiting time strategies for crack reduction in CM247LC with no preheating. The results show that the chosen approach must further be refined, with a broader parameter window and adjusted stripe overlap. It appears that the density achieved with the laser parameters used is not yet enough to produce a sufficiently dense sample. For highly porous samples, no reliable conclusion can be drawn regarding the influence of the applied scan strategy on crack formation, since porosity itself strongly affects the built of residual stresses and cracking behavior. High porosity indicates unstable processing conditions \u0026ndash; such as insufficient melting, lack of fusion, or irregular energy input \u0026ndash; which significantly alter the microstructure, heat flow, and residual stress distribution compared to dense samples. As a result, the effects of porosity overlap with those of the scan strategy, making it impossible to isolate the specific influence of the scan strategy on crack formation.\u003c/p\u003e\u003cp\u003eThermal monitoring of the PBF-LB/M process revealed that shorter vector lengths generally resulted in lower mean peak temperatures, likely due to a reduced ratio of laser-on to laser-off times and, consequently, a lower mean energy input per layer. Scan strategies utilizing hatch permutation or inter-hatch waiting times also tended to reduce peak temperatures by increasing laser-off times or minimizing thermal accumulation between adjacent vectors. However, deviations in the measured temperatures indicate that additional factors \u0026ndash; such as sample position on the build platform, gas flow direction, the thermographic camera's viewing angle, and variations in surface emissivity \u0026ndash; significantly affect the recorded thermal data. These influences limit the direct interpretation of thermal monitoring results based solely on vector length and scan strategy. Future studies should therefore incorporate complementary, high-precision thermal measurement techniques to better isolate and understand these effects. Due to numerous factors influencing thermal monitoring results, further statistical analysis of the measured mean peak temperature was not conducted. Future experiments should be performed using additional thermal monitoring, such as on-axis high-speed pyrometry, to better understand the effects of vector length and scan strategies on peak temperatures.\u003c/p\u003e\u003cp\u003eImportant information about the process behavior can already be obtained by using waiting times. The approach remains promising, as temperature peaks in the process can be prevented, which has a positive effect on the microstructure development of CM247LC. Melting tracks for example do not penetrate as deeply into already melted material, thus counteracting the formation of liquation cracks.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003ch2\u003eContributions\u003c/h2\u003e\u003cp\u003eX.X.: Experimental design, methodology, data curation, formal analysis, writing, original draft\u003c/p\u003e\u003cp\u003eX.X.: Experimental design, methodology, data curation, formal analysis, writing, original draft\u003c/p\u003e\u003cp\u003eX.X.: Writing-review and editing\u003c/p\u003e\u003cp\u003eX.X.: Resources, writing-review and editing, supervision, project administration, funding acquisition\u003c/p\u003e\u003cp\u003eAll authors: Project Management, technical consultant\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eN.K.:Experimental design, methodology, data curation, formal analysis, writing, original draftN.O.: Experimental design, methodology, data curation, formal analysis, writing, original draftT.G.: Writing-review and editingJ.T.S.:Resources, writing-review and editing, supervision, project administration, funding acquisitionAll authors: Project Management, technical consultant\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors thank the German Research Foundation (DFG) for funding this project through SPP 2419 (523837500). 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King, \"Laser powder-bed fusion additive manufacturing: Physics of complex melt flow and formation mechanisms of pores, spatter, and denudation zones,\" Acta Materialia, Jg. 108, S. 36–45, 2016, doi: 10.1016/j.actamat.2016.02.014.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":true,"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":"PBF-LB/M, CM247LC, in-situ thermography, scan strategies, additive manufacturing, powder bed fusion of metals using a laser beam","lastPublishedDoi":"10.21203/rs.3.rs-7999951/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7999951/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eIn this work, the processability of the nickel-based superalloy CM247LC in powder bed fusion of metals using a laser beam (PBF-LB/M) is systematically investigated. The focus is on the influence of inter-hatch waiting times and hatch permutation patterns. A baseline parameter set was established in preliminary studies to ensure a stable melt pool formation and defect-free consolidation. Based on these findings, the effects of controlled temporal delays between adjacent vectors and variations in hatch sequence are studied. The samples are analyzed in terms of relative density and the mean peak temperature of each layer, recorded using an in-situ thermographic camera system.\u003c/p\u003e","manuscriptTitle":"Effects of Process Strategies on the Processability of CM247LC in Powder Bed Fusion of Metals using a Laser Beam","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-18 17:29:05","doi":"10.21203/rs.3.rs-7999951/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":"53b21392-1c04-4669-98df-02d69033a8a2","owner":[],"postedDate":"November 18th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2026-04-27T13:23:22+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-18 17:29:05","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7999951","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7999951","identity":"rs-7999951","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}