Comparison of Friction Performance of Polyether ether ketone Fabricated Using Different Methods Under Dry Sliding Conditions

Comparison of Friction Performance of Polyether ether ketone Fabricated Using Different Methods Under Dry Sliding Conditions | 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 Comparison of Friction Performance of Polyether ether ketone Fabricated Using Different Methods Under Dry Sliding Conditions Sunil Kumar Prajapati, R Gnanamoorthy This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4011448/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 High-temperature additive manufacturing permits printing advanced polyether ether ketone (PEEK) sliding bearings with different surface features needed for better heat dissipation or lubrication of bearings. The as-printed surfaces of fused filament fabrication (FFF) parts are different compared to the molded or extruded surfaces and will influence the performance. The layer orientation with respect to the sliding direction is a key parameter that decides be bearing performance and is investigated using representative pin samples. The accommodation of debris on soft polymer sliding against hard steel during the initial period of sliding influences the friction and wear characteristics and contact temperature rise. The heat buildup in polymers that limits the operating load and speed in the initial period is influenced by the airflow between the layers which depends on the sliding direction. The current observations will assist in choosing the 3D printing over moulded sample for sliding contact conditions. Contact Temperature Friction PEEK Surface properties Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction Advanced polymers like PEEK have good mechanical and tribological properties and are preferred for the replacement of metallic parts due to their lightweight [ 1 ][ 2 ]. The formative and additive methods of fabricating any part show different surface features and properties. Additive manufacturing technology provides the flexibility to achieve custom parts on demand and the end product that can be used directly with the assembly. The print parameters employed control the surface features and influence the tribological properties [ 3 ]. The number of parameters that control the additive manufacturing process is many, and appropriate control of individual parameters is necessary to fabricate the part with the required features. The 3D printed samples with different infill percentages or build orientations like horizontal, vertical, on-edge, and at certain angles have different strengths and resistance against the applied force. The tensile, compression, impact, and flexural strength are found to be higher for horizontally oriented PEEK and PEI samples printed using the Fused Filament Fabrication (FFF) process [ 4 ][ 5 ]. The extrusion temperature, layer thickness, infill pattern, percentage, build orientation, and print speed affect the mechanical and structural properties of the sample [ 5 ][ 6 ][ 7 ]. The infill percentage and build orientation are two important parameters that influence the strength and deformation characteristics of the 3D-printed parts. Parts with different porosity levels are easily fabricable using 3D printing and assist product designers in achieving required features in specific areas. The mechanical and surface properties change by changing the print parameters, and the overlap between two parallel rasters leads to a rougher surface. The orientation of layers against sliding direction can significantly affect the friction and wear characteristics of 3D printed samples. Dangnan et al. [ 8 ] conducted sliding wear tests using a ball-on-flat test to understand the effect of orientation of two 3D-printed ABS sliding against a steel ball. The perpendicular orientation was reported to have a higher friction coefficient and lower specific wear rate compared to the parallel orientation at all loads. Authors have also reported that the raster angle of 90 \(^\circ\) parallel to the sliding direction results in a lower friction coefficient and wear rate due to a less rough surface than the sample with a 0 \(^\circ\) raster angle [ 9 ]. PLA samples printed with horizontal and vertical build orientations and with variable layer thicknesses were investigated when slid against steel [ 10 ]. At low load and speed, the vertically oriented sample showed less hardness and a high friction coefficient compared with the horizontally oriented samples. The 3D-printed sheets of PLA and ABS were investigated using a pin-on-plate tribometer slid in longitudinal and transverse directions. The study for two-layer orientations showed higher friction coefficients when sliding in the transverse direction at different loads [ 11 ]. When PEEK interacts with steel, the tribological behaviour is notably complex, exhibiting different characteristics under different operational conditions and surface and contact characteristics. Advanced polymers like PEEK and PEI, which require processing temperatures exceeding 350°C, have become feasible due to the progress in Fused Filament Fabrication (FFF) technology. This has led to the development of PEEK bearings in short duration with enhanced load-bearing capabilities and the ability to function under elevated temperatures. Additive manufacturing has emerged as a solution, offering the possibility of creating selectively porous materials tailored to the functional requirements of the component without compromising the mechanical and tribological properties. This approach, guided by efficient design principles, saves on materials, and provides flexibility in tailoring components for specific applications. The characteristics of PEEK, including its crystallinity and hardness, are influenced by the processing temperature and the subsequent cooling process [ 12 ]. These factors, in turn, dictate the material's mechanical performance and its friction behaviour. The frictional behaviour of PEEK is not only temperature-dependent but also relies on factors such as the applied load, sliding speed, and test duration [ 13 ]. The configuration of the test setup, encompassing the sample's shape and the nature of the counter body, plays a pivotal role in determining PEEK's frictional performance and wear characteristics [ 14 ]. Numerous researchers have conducted tribological tests on PEEK and its composites under various conditions [ 15 ][ 16 ]. The wear rate and rise in the contact temperature are important in the case of polymers and decide the permissible load and life, in sliding bearing applications. This paper discusses the effect of one of important printing parameters, top layer orientation, on the friction coefficient, wear behaviour, and rise in the temperature at contact and compares it with the commercially extruded PEEK sample. 2 Materials and method 2.1 Sample fabrication The Fused Filament Fabrication (FFF) type 3D printing permits fabrication of polymer parts economically and is used in making the test samples. Before printing, the PEEK filament of diameter 1.7mm, was subjected to a seven-hour drying to remove the moisture content. The cylindrical samples had dimensions of 8 mm in diameter and 13 mm in length. The primary focus of this research was to investigate the impact of infill orientation of the top surface of the printed samples. The tribological test results for these 3D-printed PEEK samples were then compared to commercially available extruded PEEK rods. The printing parameters employed for sample fabrication are given in Table 1 . A consistent 15% overlap between the parallel scanning paths was followed in all types of samples printed. All the samples were printed using a nozzle having a diameter of 0.5 mm. A visual representation of the sample specifications and the printing process is provided in Fig. 1 , where the cylindrical samples were printed vertically and have two outer perimeters. Table 1 The print parameter employed to print the test samples. Parameter Value Nozzle temperature 400 \(^\circ\) C Bed temperature 100 \(^\circ\) C Print speed 15 mmps Layer height 0.2 mm Infill density 90% Raster angle \(0^\circ /90^\circ\) Raster width 0.55 mm 2.2 Adhesive wear test details An in-house developed tribotest device is used in the current study, where the friction force, online wear, and temperature are measured precisely during the test without disturbing the test samples. Figure 2 shows the schematic of the pin-on-disc test configuration used. Bearing steel (SUJ2 steel) disc of 70mm diameter was used as the counterbody. The steel counterface is preferred as in most of the sliding bearing applications the polymer bush slides against the steel shaft. Before each test, the discs were ground and subsequently polished using abrasive paper to ensure an average surface roughness of about 5 µm. All the tests were conducted at a constant load, 20N and fixed sliding velocity, 0.2 m/s, for one hour at a room temperature of ~ 27 \(\pm\) 2 \(℃\) and 75 \(\pm\) 5 RH. This corresponds to 600 m of sliding distance. All tests were conducted in the laboratory atmosphere and under dry sliding conditions. The discs and pin samples were well-cleaned before every test. At least four samples were tested in each type and average values are reported. The friction force is measured using a high precision load cell and friction coefficient is estimated. The volumetric specific wear rate, W, is estimated using the formula W = Δm/ρFL, where Δm represents the weight loss, ρ is the density of the sample, F is the applied load, and L denotes the total sliding distance. A weighing machine with an accuracy of 0.01 mg determined the weight of the sample. The weight and dimension are measured after the test to quantify the wear loss due to adhesion. An infrared thermal camera is used to measure temperature on the pin surface close to the contact. The indentation hardness of all the samples is measured using the dynamic microhardness tester using the Vicker indentor. The indentation was made on the test surface of the sample that slide against the bearing steel counterbody. An indentation load of 500 mN is applied for 20 s and with a dwell of 10 s, followed by the unloading in 20 s. The hardness was measured from at least ten indentations at different locations on the sample. The indentation hardness (MPa) and the indentation modulus (GPa) are estimated. A water droplet is used on the test surface to measure the contact angles and the corresponding surface energy. All test samples' X-ray diffraction (XRD) pattern is obtained using Cu Kα radiation. The pattern was plotted between 10° and 90° and was used to calculate the crystalline and amorphous content of the samples. A digital microscope is used to observe the surface morphology before and after the tests. The adhesion of the wear debris and the wear damage was analyzed using the field-emission scanning electron microscope. The attached EDX platform was used for the element mapping of the test surface. 3 Results and Discussion 3.1 Characterization of the as-printed PEEK surfaces Surface Morphology The as-printed parts are preferred for sliding bearing applications and the FFF printing parameters influence the surface morphology. Figure 3 shows the 3D profile of an as-printed sample printed with 90% infill density. The surface of the sample displays hills and valleys, which are formed because of the 10% overlap between the parallel infill rasters. This texture arises from the FFF process, contributing to a rougher surface in samples with a 90% infill density and influence the real contact area. The roughness of the surface directly impacts the interaction between the sample and the counter body during tribology testing. The filament orientation with respect to the sliding direction will influence the tribo behaviour. The contact surface's surface roughness (Sa) of the extruded PEEK rod samples used in the present study had a lower roughness of 5.3 µm compared to the 3D-printed samples of 19.6 µm. The overlapping of filament width affects the surface morphology of the as-printed sample and contributes to the higher roughness of the additive manufactured part. The difference in the cooling rate between the layers also causes a significant high roughness in FFF process. Crystallinity The printing temperature is one of the important parameters that affect the crystallinity, and thereby the mechanical properties of printed parts [ 12 ]. In addition, the printing pattern employed for a particular part geometry also results in a different cooling rate in different regions and crystallinity. The as-printed PEEK is semicrystalline and XRD patterns showed the presence of peaks in the 18–30 degree range (Fig. 4 (a)). The 3D printed sample shows a lower crystallinity of 36.6%, and the extruded rod has a maximum crystallinity of 38%. Crystallinity is directly related to the hardness of the polymer [ 17 ]. The fabrication process affects the solidification and cooling rate of the stacked surfaces depending on the printing parameters. Surface strength Figure 4 (b) shows the load vs indentation depth behaviour. The indentation hardness and modulus of all the tested pin samples are shown in Fig. 4(c). The measured hardness and modulus of the extruded PEEK rod sample are 324 MPa and 4.4 GPa, respectively, which is higher than the additive-manufactured sample, with a hardness and modulus of 278 MPa and 3.7 GPa, respectively. The marginal lower crystallinity of the as-printed surface compared to the extruded PEEK surface contributes to the reduced hardness and modulus in as-printed samples. The manufacturing processes, like additive manufacturing and others, affect the crystallinity of the fabricated sample, which affects the hardness and other mechanical properties. A maximum hardness of 346 MPa was reported for commercial PEEK by Ahmad et al. [ 17 ]. The extruded rod is a single body and homogeneous fabricated in a controlled environment, which makes the polymer achieve high hardness and greater resistance to indentation. Surface energy The surface energy of polymeric surfaces depends upon the molecular architecture and roughness. The water droplet determines the wettability of the PEEK surfaces. The contact angle made by the water and its corresponding surface energy for all PEEK samples is shown in Fig. 4 (d). The water's maximum contact angle is on the 3D printed sample surface, indicating the low surface energy. The contact angle on the extruded pin is 68 ± 1°, while on the 3D printed sample is 73 ± 0.7°. The surface energy of the extruded PEEK pin is 27.3 ± 0.8 mJ/m, which is nearly equal to the value reported by Mei et al. [ 19 ]. The surface energy observed for the 3D printed sample is 21.3 ± 0.6 mJ/m. The contact angle and surface energy are important and affect the wear response of the PEEK samples. Figure 4. (a) XRD pattern, (b) Load vs depth loops from Indentation hardness, (c) Indentation hardness and modulus, and (d) Surface energy and water contact angle of extruded and 3D printed samples. 3.2 Friction behaviour The FFF process permits printing parts in different orientations and the friction and wear response of layer orientation with respect the sliding direction will assist the designers to choose appropriate orientation. Depending on the orientation of the layer to the sliding direction, the friction characteristics differ as the deformation of surfaces and particle entrapment differ. The variation of friction coefficient in as-printed samples in parallel and perpendicular layer orientations to the sliding direction and extruded sample when slid against the polished steel surface for 600 m is shown in Fig. 5 (a). All the samples exhibited a rising friction coefficient during the initial few hundred meters of sliding and reached a steady state (Fig. 5 (a)). The time taken to reach a steady state in 3D printed samples is marginally higher than in the smooth extruded PEEK sample. The material transfer to the pin surface in the 3D printed surface and its influence on the formation of the transfer layer on the disc contribute to the delay in achieving a steady state. As the infill angle chosen was 0/90°, the top surface (test surface) infill is aligned at 0°. The top infill layer of the 3D-printed PEEK surface is subjected to the tangential friction force parallel to the infill (hereafter, 3DP-||el) and perpendicular to the infill (hereafter, 3DP-Ʇar) in two different tests to assess the effect of infill orientation. When the sliding direction is parallel to the layer orientation, there is a reduced contact area than the perpendicular direction, resulting in low resistance to sliding (Fig. 5 (a)) during the initial period. The 3DP-||el sample stabilises after the transition phase and maintains a steady-state friction coefficient after sliding for about 300 m. The layers on the sample gradually deform and wear, leading to the proper contact with the steel surface. As the surface becomes flatter, the resistance to friction increases, and after sliding for 300 me, all samples with parallel orientation reach a steady state. In contrast, the 3DP-Ʇar sample, where the surface infill is oriented perpendicular to the sliding direction, makes high initial contact and exhibits high resistance during the initial friction stage. These samples reach a steady-state condition sooner than other samples. The transition stage causes the surface to experience more resistance, which causes a sudden increase in friction coefficient which stabilises subsequently. Figure 5 (b) shows the steady-state coefficient of friction of the extruded and 3D printed samples in both orientations. The extruded sample's steady-state friction coefficient is less than the 3D printed samples, and the effect of layer orientation is observed clearly. The steady-state friction coefficient of the 3DP-Ʇar sample is the high (0.54), and the extruded sample had a low friction coefficient, 0.47. The steady-state friction coefficient indicates that the surfaces in contact have nearly conformal contact. Therefore, the variation between the as-printed surfaces with parallel and perpendicular orientations made using identical process conditions and raw material is attributed to the material transfer between the surfaces. In the case of samples with perpendicular orientation to the sliding direction, more wear debris comprising of PEEK and iron oxide gets accumulated and adhered to the relatively soft polymer pin compared to the other samples tested. This increases the polymer surface's hardness, which in turn, influences the transfer layer formation on the disc surface and affects the friction coefficient. In addition, the deformation of both the printed samples is also different which influences the local area of contact and the friction coefficient. This difference in the deformed surfaces in both the orientations and associated variations in the contact area contribute to variations in the friction coefficient in these samples. The difference in the accumulated debris in these samples influences the steady-state friction. Figure 5. (a) The variation of friction coefficient for extruded, 3DP-||el, and 3DP-Ʇar samples and (b) steady-state friction coefficient of test samples. 3.3 Wear mechanism When the pin surface slides against the bearing steel disc, the wear in the initial run-in phase is less. However, under constant load, the surfaces in contact deform due to high local stresses and subsequently wear. The wear volume and specific wear rate measured in the as-printed sample with two different orientations and the extruded sample are shown in Fig. 6 . The extruded sample exhibited a higher wear volume and a specific wear rate of 8.43 \(\times\) 10 − 5 mm 3 /Nm compared with the as-printed samples. At the same time, the sample with the perpendicular orientation showed the lowest wear volume and a specific wear rate of 6.7 × 10 − 5 mm 3 /Nm. The rough surface in perpendicular orientation accommodates more wear particles and this influences the wear characteristics. Dhakal et al. [ 20 ] also reported similar results in the study of ABS, where 3D printed sample with \(0^\circ\) /90 \(^\circ\) showed higher wear resistance than injection-moulded sample. While the sample printed at higher speed exhibited higher wear rate. The load variation under dry conditions also affects the moulded sample's wear rate more than the 3D printed sample [ 21 ]. The material removal in the case of polymer-metal sliding contacts depends on the transfer layer formation and its periodic removal when the materials and test conditions are similar. The smooth polymer samples tend to adhere more and form a transfer layer, which tends to get removed frequently, resulting in an increased wear rate in extruded samples. The amount of debris accumulated in the 3D samples differs due to the difference in the sliding direction, which subsequently affects the wear rate. Increased surface hardness in the sample due to adherence of debris generated results in reduced wear loss. Despite having similar contact areas in both orientations, the specific wear rate is lower for the 3DP-Ʇar sample. The extruded rod exhibits a higher contact area among all the tested samples, resulting in a higher wear volume. The transfer layer formed causes more wear that is abrasive in nature, which can be seen on the sliding surface. The pin surfaces observed after the tests using a digital microscope are shown in Fig. 7 . The dark region on the polymer pin surfaces indicates the debris adhered to the soft polymer; otherwise, the material is transferred to the pin. The amount of material transferred in all three samples is quite different and is clearly seen in the Fig.. The transfer layer formed in the case of the sample with parallel orientation is thinner than the sample sliding perpendicular to the layer orientation. The abrasion marks can be seen at many locations, along with some deep grooves and pits on the surface. The sample's surface does not show any sign of debris adhesion to its surface after the test. The surface roughness is reduced due to wear of surface. The repeated dry sliding also causes friction heating, which results in smearing and pit formation, as indicated in Fig. 7 (a1 and a2). The additively manufactured samples show severe adhesion of wear debris on the surfaces. For the 3DP-||el, the material adhesion is less than the 3DP-Ʇar sample. As the surface infill is aligned with the sliding direction for the 3DP-||el sample, the debris can only adhere to locations that act as a barrier in that direction (Fig. 7 (b)). The continuous sliding causes the deformation on the surface, and some micro-cracks are formed on the surface along with pits (Fig. 7 (b1 and b2)). Fine debris particles seem to adhere and accumulate on the surface at some locations. The debris is trapped at the contact surface and accumulates at the edges due to material transfer. The debris generated during the adhesive wear is a mixture of PEEK and metal oxide. The dark region representing debris adhered to the 3DP-||el sample surface is around 3% of the total surface area. While in the case of the 3DP-Ʇar sample, the debris adhered covered about 13% of the surface area, as shown in Fig. 7 (c). The layers deformed during the sliding, which caused crack formation and delamination (Fig. 7 (c1)). The material transfer is higher as the surface infill is aligned perpendicular, providing more resistance to wear. The schematics of the wear process and debris accumulation that occurred in the 3D printed sample with two orientations are depicted in Fig. 7 (d). The long-deposited filament oriented parallel to the sliding surface could only cover some parts of the surface, while in the perpendicular orientation, it struck with a small alignment. This repeated sliding causes the deformation of the raster filled with debris. Analysing the composition of the worn-out material and the adhered debris is crucial in understanding the wear process and is carried out using Energy-Dispersive X-ray Spectroscopy (EDS) (Fig. 8 (a-f)). Figure 8 (a) shows the wear surface of the 3DP-Ʇar sample. A smaller location marked as (b) is analysed at a higher magnification. Figure 8 (b) shows that over 60% of the frame area is covered with mixed debris. Figure 8 (d-f) shows the EDS material mapping of a concentrated area in the sample, corresponding to Fig. 8 (a-c). Figure 8 (g) presents the spectrum for the complete surface, while Fig. 8 (h) shows the spectrum for a specific location labelled as 'c' in the 3D printed sample. A gold coating was applied on the surface, which resulted in the reflection of specific peaks at a particular energy level in the spectrum. However, the gold and other element's content are excluded from the composition analysis. The inset table shows three major elements, excluding others like Cr, Mn, and Si. The spectrum indicates that the mixed debris deposited to the surface contains iron. The surface of the sample exhibits more hardness and high wear resistance. As mentioned earlier in the section, the wear volume and specific wear rate for the 3DP-Ʇar sample are lower than the extruded sample due to the presence of mixed debris on the surface. The dependency on the orientation of infill on the wear mechanism and failure mode leads to the composite formation on the PEEK’s surface. The debris adherence on the surface, which is a mixture of PEEK and iron oxide, becomes strong due to repeated sliding and compaction. EDX spectrum confirms the formation of the compound on the surface. The strain and plastic deformation are initially higher in the 3D printed sample case, allowing structure damage and debris accumulation [ 22 ]. 3.4 Transfer layer on the disc Figure 9 (a) shows a section of the track formed on the steel disc. A uniform transfer layer with accumulated debris on the track is observed for extruded samples and is evident under dry sliding conditions [ 23 ]. However, in 3D printed samples, the transfer layer formed is not as uniform and smooth compared with extruded samples. Patchy regions were noted in the as-printed samples and are lower in the 3DP-Ʇar sample. The 3DP-||el sample also results in higher wear loss than the 3DP-Ʇar sample, which can be seen through the adhesion of PEEK on the track (Fig. 9 (b-c)). It is observed that the track is covered with PEEK and PEEK with iron oxide debris. It is observed that approximately 80% of the track is covered with the transfer layer for all the samples other than the 3DP-Ʇar sample, which showed ~ 55% covered with the transfer layer. The material transferred and adhered to the polymer pin influences the transfer layer formation on the disc. The samples with increasing porosity also show similar tracks as the 3DP-||el sample, where more than 80% of the steel disc is covered with a transfer layer. Figure 10 (a-d) shows the detailed analysis of the wear track. The track is covered with the PEEK transfer layer for the 3DP-Ʇar sample. The SEM image indicates small patches present on the disc surface containing the debris adhesion in some locations (Fig. 10 (a)). At location b, PEEK material is deposited on the track (Fig. 10 (b)). On the other hand, at location ‘c’, the debris that is deposited constitutes the PEEK and iron element, which is confirmed using EDX spectra (Fig. 10 (c) and (d)). As shown in Fig. 10 , the wear process indicates that the material from the bearing steel disc is also worn out during the sliding process. The debris formed is the mixture of the top oxide layer of the steel disc and the PEEK surface, which forms the transfer layer and is also reported [ 24 ][ 25 ]. 3.5 Temperature rise The friction between the disc and pin leads to heat generation. The friction heat generated can be calculated by the µPV formula, where \(\mu\) is the friction coefficient, P is the pressure, and V is the sliding velocity. The total heat generated by the friction is distributed between the PEEK pin and the steel disc. It is assumed that the thermal contact resistance is constant, and the heat transferred to the disc is given as \(\gamma \mu\) PV and for the pin as \((1-\gamma )\mu\) PV, where \(\gamma\) is heat partition. This generates heat at the contact of the surface and more at the centre. It is obtained that the maximum temperature at the surface is approx. 35°C for the extruded pin, which is 7°C rise from the room temperature. To measure the rise in the temperature close to the sliding surface, a thermal camera is employed to capture the temperature at various time intervals on the outer surface of the pin. Figure 11 shows the rise in temperature for three samples. Notably, the extruded sample exhibits the highest temperature increase, while the 3DP-Ʇar sample demonstrates the lowest. The temperature has increased since the measured surface is constantly exposed to the open atmosphere. Initially, the temperature rise exhibits a linear pattern during the initial running stage, and the temperature rise is higher. However, the temperature gradually increases due to heat dissipation. The difference in cooling due to the presence of the grooves in as-printed samples in the initial stages influences the net heat buildup. 4 Conclusion The effect of surface infill orientation with respect to sliding direction on the dry sliding friction coefficient, wear and contact temperature of PEEK polymer against steel is reported. The following conclusions are drawn based on the current investigation: Considering the requirement of uniform wear theory for smooth operation in practical applications, the 3DP-Ʇar sample achieves a steady state within 300 m of sliding, well before achieved by the extruded sample. The surface roughness influences the contact area, subsequently affecting the friction performance of the 3D printed samples compared to extruded samples. When slid in the perpendicular direction, debris appears to be accommodated between the rasters higher than parallel, increasing the friction coefficient but reducing wear loss. The smearing and delamination dominated the wear of 3D printed samples and formed a relatively thin film of transfer layer than the extruded sample, which is more driven by abrasion wear. The surface experiences plastic deformation and higher strain that causes the surface to accommodate the debris on it. The debris formed due to sliding on the disc has a mixture of PEEK and iron-oxide, which restrict the more wear in perpendicular orientation. This causes the least wear volume generation after the test for the 3DP-Ʇar sample. The wear track on the disc also shows that the track is not fully covered with debris. The surface roughness impacts the samples' contact area and friction performance compared to extruded samples. The effect of trapped debris between the rasters increases the friction coefficient when sliding perpendicularly. The presence of roughness on the surface allows the material to undergo plastic deformation in the sliding direction, thereby accommodating debris and deformed material. This affects the transfer layer formation on the counter body and the interaction of the pin undergoing deformation and adhesion, which concludes the friction coefficient. The rise in contact temperature is less in the 3D printed samples than the extruded sample. Considering the maximum operating temperature of PEEK of 260°C, the 3D printed samples will take a longer duration to reach this temperature than the extruded sample with lesser wear loss. Declarations Fundings: “The authors would like to acknowledge the support from the Department of Science and Technology (DST- SERB) (Grant number – CRG/2018/002549), India.” Competing Interests: “The authors have no conflicts of interest to declare that are relevant to the content of this article.” Author Contributions: “Methodology, Material preparation, Data collection, Formal analysis and investigation, Draft Writing: [Sunil Kumar Prajapati]; Conceptulisation, Resources, Supervision, Review and Editing: [R. Gnanamoorthy].” Data availability statement: “ Data supporting the results and analysis in this article will be available on request to the corresponding author.” References T. J. Hoskins, K. D. Dearn, Y. K. Chen, and S. N. Kukureka, “The wear of PEEK in rolling-sliding contact - Simulation of polymer gear applications,” Wear , vol. 309, no. 1–2, pp. 35–42, 2014, doi: 10.1016/j.wear.2013.09.014. H. Koike, K. Kida, E. C. Santos, J. Rozwadowska, Y. Kashima, and K. 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Bennewitz, “Correlation of friction and wear across length scales for PEEK sliding against steel,” Tribol. Int. , vol. 136, no. March, pp. 462–468, 2019, doi: 10.1016/j.triboint.2019.04.001. M. Padhan, U. Marathe, and J. Bijwe, “Tribology of Poly(etherketone) composites based on nano-particles of solid lubricants,” Compos. Part B Eng. , vol. 201, no. June, 2020, doi: 10.1016/j.compositesb.2020.108323. Z. Yang, H. Peng, W. Wang, and T. Liu, “Crystallisation behavior of poly(ε-caprolactone)/layered double hydroxide nanocomposites,” J. Appl. Polym. Sci. , vol. 116, no. 5, pp. 2658–2667, 2010, doi: 10.1002/app. A. Al Khatib, R. Le-Franc, J. P. Guin, and J. F. Coulon, “Investigating the thermal effects of plasma surface treatment on crystallinity and mechanical behavior of PEEK,” Polym. Degrad. Stab. , vol. 216, no. April, pp. 1–14, 2023, doi: 10.1016/j.polymdegradstab.2023.110500. N. Limaye, L. Veschini, and T. Coward, “Assessing biocompatibility & mechanical testing of 3D-printed PEEK versus milled PEEK,” Heliyon , vol. 8, no. 12, p. e12314, 2022, doi: 10.1016/j.heliyon.2022.e12314. S. Mei et al. , “Influences of tantalum pentoxide and surface coarsening on surface roughness, hydrophilicity, surface energy, protein adsorption and cell responses to PEEK based biocomposite,” Colloids Surfaces B Biointerfaces , vol. 174, no. August 2018, pp. 207–215, 2019, doi: 10.1016/j.colsurfb.2018.10.081. N. Dhakal, X. Wang, C. Espejo, A. Morina, and N. Emami, “Impact of processing defects on microstructure, surface quality, and tribological performance in 3D printed polymers,” J. Mater. Res. Technol. , vol. 23, pp. 1252–1272, 2023, doi: 10.1016/j.jmrt.2023.01.086. H. Amiruddin, M. F. Bin Abdollah, and N. A. Norashid, “Comparative study of the tribological behaviour of 3D-printed and moulded ABS under lubricated condition,” Mater. Res. Express , vol. 6, no. 8, 2019, doi: 10.1088/2053-1591/ab2152. J. A. Williams and Y. Xie, “The generation of wear surfaces by the interaction of parallel grooves,” Wear , vol. 155, no. 2, pp. 363–379, 1992, doi: 10.1016/0043-1648(92)90095-P. M. Rodiouchkina, J. Lind, L. Pelcastre, K. Berglund, Å. K. Rudolphi, and J. Hardell, “Tribological behaviour and transfer layer development of self-lubricating polymer composite bearing materials under long duration dry sliding against stainless steel,” Wear , vol. 484–485, no. July, p. 204027, 2021, doi: 10.1016/j.wear.2021.204027. L. Guo, X. Pei, F. Zhao, L. Zhang, G. Li, and G. Zhang, “Tribofilm growth at sliding interfaces of PEEK composites and steel at low velocities,” Tribol. Int. , vol. 151, no. June, p. 106456, 2020, doi: 10.1016/j.triboint.2020.106456. L. Zhang, G. Li, Y. Guo, H. Qi, Q. Che, and G. Zhang, “PEEK reinforced with low-loading 2D graphitic carbon nitride nanosheets: High wear resistance under harsh lubrication conditions,” Compos. Part A Appl. Sci. Manuf. , vol. 109, no. December 2017, pp. 507–516, 2018, doi: 10.1016/j.compositesa.2018.04.002. 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-4011448","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":276402523,"identity":"64a42201-f8a4-4ab8-9164-4e8598813d29","order_by":0,"name":"Sunil Kumar Prajapati","email":"data:image/png;base64,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","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":true,"prefix":"","firstName":"Sunil","middleName":"Kumar","lastName":"Prajapati","suffix":""},{"id":276402524,"identity":"87ed551e-0781-45cb-b599-21d26b9b67f6","order_by":1,"name":"R Gnanamoorthy","email":"","orcid":"","institution":"Indian Institute of Technology Madras","correspondingAuthor":false,"prefix":"","firstName":"R","middleName":"","lastName":"Gnanamoorthy","suffix":""}],"badges":[],"createdAt":"2024-03-04 10:36:51","currentVersionCode":1,"declarations":{"humanSubjects":false,"vertebrateSubjects":false,"conflictsOfInterestStatement":false,"humanSubjectEthicalGuidelines":false,"humanSubjectConsent":false,"humanSubjectClinicalTrial":false,"humanSubjectCaseReport":false,"vertebrateSubjectEthicalGuidelines":false},"doi":"10.21203/rs.3.rs-4011448/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4011448/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52140800,"identity":"e25293c0-95ec-4aba-84ca-a9852bb9a414","added_by":"auto","created_at":"2024-03-07 10:55:34","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":204981,"visible":true,"origin":"","legend":"\u003cp\u003eDetails of the Fused Filament Fabrication process employed for sample preparation.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/981e7c338e135699ed18b645.png"},{"id":52139520,"identity":"dbec43eb-463a-4ef6-bfcf-25c9f76bae2e","added_by":"auto","created_at":"2024-03-07 10:47:34","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":89484,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic of the pin-on-disc setup used to test adhesive wear\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/d41a76416600e3a8c3548215.png"},{"id":52139523,"identity":"c09d6722-613a-48eb-9fa3-f3a7145931b7","added_by":"auto","created_at":"2024-03-07 10:47:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":2000127,"visible":true,"origin":"","legend":"\u003cp\u003eThe surface texture of the as-printed sample with 90% infill surface shows the layer filament orientation.\u0026nbsp;\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/a20ceca0f2362ce7f110cb0b.png"},{"id":52139522,"identity":"d7895396-cea7-4c54-9b27-77fd2b0f72ac","added_by":"auto","created_at":"2024-03-07 10:47:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":1138648,"visible":true,"origin":"","legend":"\u003cp\u003e(a) XRD pattern, (b) Load vs depth loops from Indentation hardness, (c)Indentation hardness and modulus, and (d) Surface energy and water contact angle of extruded and 3D printed samples.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/43698f7c8c21f76267b2f57c.png"},{"id":52139524,"identity":"e8c7a130-dd36-40de-abaf-9d9c7a32c7ac","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":322799,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The variation of friction coefficient for extruded, 3DP-||el, and 3DP-Ʇar samples and (b) steady-state friction coefficient of test samples.\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/e1cd65c5ae6b6803981bfab4.png"},{"id":52139530,"identity":"4af20602-93c8-4369-a7c5-1cf438ee8b23","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":230728,"visible":true,"origin":"","legend":"\u003cp\u003eWear volume and specific wear rate with different orientations of as-printed compared with the extruded sample.\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/be7d7bc46f200c4376d8d368.png"},{"id":52139525,"identity":"7512ad21-a678-4a85-a78b-84a416717b8d","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":2704590,"visible":true,"origin":"","legend":"\u003cp\u003eWorn surfaces of the test pin samples (a) extruded PEEK, (b) 3DP-||el sample, (c) 3DP-Ʇar sample, and (d) schematic of wear process in two different orientations\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/8b66da2289bd2cdb7c6f0842.png"},{"id":52139526,"identity":"cb9ca27b-f309-4fce-987e-b3294eb531f3","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":3265331,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003e(a-c) SEM images of the as printed (3DP-Ʇar) sample at different magnifications, (d-f) EDS material mapping corresponding to SEM images, and (g-h) EDX spectra for the area covered in (a) and (c) images\u003c/em\u003e\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/bf7734beeb3e9040e473d82f.png"},{"id":52139529,"identity":"cee579b6-7558-486a-94a0-040233b27247","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2166469,"visible":true,"origin":"","legend":"\u003cp\u003eWear tracks on the bearing steel disc for (a) Extruded sample, (b) 3DP-||el sample, and (c) 3DP-Ʇar sample.\u003c/p\u003e","description":"","filename":"Fig9.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/ec5eb0cc241b2866a7180c7b.png"},{"id":52140801,"identity":"0950ac3c-73b5-4356-910d-4d18fb3bf2f4","added_by":"auto","created_at":"2024-03-07 10:55:36","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1250647,"visible":true,"origin":"","legend":"\u003cp\u003eSEM image of the disc (a) Track at a lower magnification, (b) PEEK material transferred at location ‘b’, (c) PEEK with iron oxide debris at ‘c’ location at higher magnifications, and (d) EDX spectra at location ‘c’.\u003c/p\u003e","description":"","filename":"Fig10.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/6f2db2188974fec5ed7bb71b.png"},{"id":52139527,"identity":"c3b408f6-f9ff-44cd-855a-2c22de4ee4ea","added_by":"auto","created_at":"2024-03-07 10:47:35","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":121160,"visible":true,"origin":"","legend":"\u003cp\u003eTemperature rise near the sliding surface\u003c/p\u003e","description":"","filename":"Fig11.png","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/b458915ae65aa599e1ed0a72.png"},{"id":52417626,"identity":"7507dbc6-1e03-43c2-ab16-cba3c03559b2","added_by":"auto","created_at":"2024-03-11 12:09:02","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":5093884,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4011448/v1/4fae0ef7-2944-48b3-915a-c98739bef445.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Comparison of Friction Performance of Polyether ether ketone Fabricated Using Different Methods Under Dry Sliding Conditions","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eAdvanced polymers like PEEK have good mechanical and tribological properties and are preferred for the replacement of metallic parts due to their lightweight [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e][\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. The formative and additive methods of fabricating any part show different surface features and properties. Additive manufacturing technology provides the flexibility to achieve custom parts on demand and the end product that can be used directly with the assembly. The print parameters employed control the surface features and influence the tribological properties [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. The number of parameters that control the additive manufacturing process is many, and appropriate control of individual parameters is necessary to fabricate the part with the required features. The 3D printed samples with different infill percentages or build orientations like horizontal, vertical, on-edge, and at certain angles have different strengths and resistance against the applied force. The tensile, compression, impact, and flexural strength are found to be higher for horizontally oriented PEEK and PEI samples printed using the Fused Filament Fabrication (FFF) process [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e][\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e]. The extrusion temperature, layer thickness, infill pattern, percentage, build orientation, and print speed affect the mechanical and structural properties of the sample [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e][\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e][\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. The infill percentage and build orientation are two important parameters that influence the strength and deformation characteristics of the 3D-printed parts. Parts with different porosity levels are easily fabricable using 3D printing and assist product designers in achieving required features in specific areas.\u003c/p\u003e \u003cp\u003eThe mechanical and surface properties change by changing the print parameters, and the overlap between two parallel rasters leads to a rougher surface. The orientation of layers against sliding direction can significantly affect the friction and wear characteristics of 3D printed samples. Dangnan et al. [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e] conducted sliding wear tests using a ball-on-flat test to understand the effect of orientation of two 3D-printed ABS sliding against a steel ball. The perpendicular orientation was reported to have a higher friction coefficient and lower specific wear rate compared to the parallel orientation at all loads. Authors have also reported that the raster angle of 90\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(^\\circ\\)\u003c/span\u003e\u003c/span\u003e parallel to the sliding direction results in a lower friction coefficient and wear rate due to a less rough surface than the sample with a 0\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(^\\circ\\)\u003c/span\u003e\u003c/span\u003e raster angle [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. PLA samples printed with horizontal and vertical build orientations and with variable layer thicknesses were investigated when slid against steel [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. At low load and speed, the vertically oriented sample showed less hardness and a high friction coefficient compared with the horizontally oriented samples. The 3D-printed sheets of PLA and ABS were investigated using a pin-on-plate tribometer slid in longitudinal and transverse directions. The study for two-layer orientations showed higher friction coefficients when sliding in the transverse direction at different loads [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eWhen PEEK interacts with steel, the tribological behaviour is notably complex, exhibiting different characteristics under different operational conditions and surface and contact characteristics. Advanced polymers like PEEK and PEI, which require processing temperatures exceeding 350\u0026deg;C, have become feasible due to the progress in Fused Filament Fabrication (FFF) technology. This has led to the development of PEEK bearings in short duration with enhanced load-bearing capabilities and the ability to function under elevated temperatures. Additive manufacturing has emerged as a solution, offering the possibility of creating selectively porous materials tailored to the functional requirements of the component without compromising the mechanical and tribological properties. This approach, guided by efficient design principles, saves on materials, and provides flexibility in tailoring components for specific applications. The characteristics of PEEK, including its crystallinity and hardness, are influenced by the processing temperature and the subsequent cooling process [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e]. These factors, in turn, dictate the material's mechanical performance and its friction behaviour. The frictional behaviour of PEEK is not only temperature-dependent but also relies on factors such as the applied load, sliding speed, and test duration [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. The configuration of the test setup, encompassing the sample's shape and the nature of the counter body, plays a pivotal role in determining PEEK's frictional performance and wear characteristics [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. Numerous researchers have conducted tribological tests on PEEK and its composites under various conditions [\u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e][\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe wear rate and rise in the contact temperature are important in the case of polymers and decide the permissible load and life, in sliding bearing applications. This paper discusses the effect of one of important printing parameters, top layer orientation, on the friction coefficient, wear behaviour, and rise in the temperature at contact and compares it with the commercially extruded PEEK sample.\u003c/p\u003e"},{"header":"2 Materials and method","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Sample fabrication\u003c/h2\u003e \u003cp\u003eThe Fused Filament Fabrication (FFF) type 3D printing permits fabrication of polymer parts economically and is used in making the test samples. Before printing, the PEEK filament of diameter 1.7mm, was subjected to a seven-hour drying to remove the moisture content. The cylindrical samples had dimensions of 8 mm in diameter and 13 mm in length. The primary focus of this research was to investigate the impact of infill orientation of the top surface of the printed samples. The tribological test results for these 3D-printed PEEK samples were then compared to commercially available extruded PEEK rods. The printing parameters employed for sample fabrication are given in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A consistent 15% overlap between the parallel scanning paths was followed in all types of samples printed. All the samples were printed using a nozzle having a diameter of 0.5 mm. A visual representation of the sample specifications and the printing process is provided in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e, where the cylindrical samples were printed vertically and have two outer perimeters.\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 print parameter employed to print the test samples.\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\u003eParameter\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\u003eNozzle temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e400 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(^\\circ\\)\u003c/span\u003e\u003c/span\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBed temperature\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e100 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(^\\circ\\)\u003c/span\u003e\u003c/span\u003eC\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003ePrint speed\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e15 mmps\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eLayer height\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.2 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eInfill density\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e90%\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRaster angle\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e\u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(0^\\circ /90^\\circ\\)\u003c/span\u003e\u003c/span\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eRaster width\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e0.55 mm\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Adhesive wear test details\u003c/h2\u003e \u003cp\u003eAn in-house developed tribotest device is used in the current study, where the friction force, online wear, and temperature are measured precisely during the test without disturbing the test samples. Figure\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the schematic of the pin-on-disc test configuration used. Bearing steel (SUJ2 steel) disc of 70mm diameter was used as the counterbody. The steel counterface is preferred as in most of the sliding bearing applications the polymer bush slides against the steel shaft. Before each test, the discs were ground and subsequently polished using abrasive paper to ensure an average surface roughness of about 5 \u0026micro;m. All the tests were conducted at a constant load, 20N and fixed sliding velocity, 0.2 m/s, for one hour at a room temperature of ~\u0026thinsp;27 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\pm\\)\u003c/span\u003e\u003c/span\u003e 2 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(℃\\)\u003c/span\u003e\u003c/span\u003e and 75 \u003cspan class=\"InlineEquation\"\u003e\u003cspan class=\"mathinline\"\u003e\\(\\pm\\)\u003c/span\u003e\u003c/span\u003e5 RH. This corresponds to 600 m of sliding distance. All tests were conducted in the laboratory atmosphere and under dry sliding conditions. The discs and pin samples were well-cleaned before every test. At least four samples were tested in each type and average values are reported. The friction force is measured using a high precision load cell and friction coefficient is estimated. The volumetric specific wear rate, W, is estimated using the formula W\u0026thinsp;=\u0026thinsp;Δm/ρFL, where Δm represents the weight loss, ρ is the density of the sample, F is the applied load, and L denotes the total sliding distance. A weighing machine with an accuracy of 0.01 mg determined the weight of the sample. The weight and dimension are measured after the test to quantify the wear loss due to adhesion. An infrared thermal camera is used to measure temperature on the pin surface close to the contact.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eThe indentation hardness of all the samples is measured using the dynamic microhardness tester using the Vicker indentor. The indentation was made on the test surface of the sample that slide against the bearing steel counterbody. An indentation load of 500 mN is applied for 20 s and with a dwell of 10 s, followed by the unloading in 20 s. The hardness was measured from at least ten indentations at different locations on the sample. The indentation hardness (MPa) and the indentation modulus (GPa) are estimated. A water droplet is used on the test surface to measure the contact angles and the corresponding surface energy.\u003c/p\u003e \u003cp\u003eAll test samples' X-ray diffraction (XRD) pattern is obtained using Cu Kα radiation. The pattern was plotted between 10\u0026deg; and 90\u0026deg; and was used to calculate the crystalline and amorphous content of the samples. A digital microscope is used to observe the surface morphology before and after the tests. The adhesion of the wear debris and the wear damage was analyzed using the field-emission scanning electron microscope. The attached EDX platform was used for the element mapping of the test surface.\u003c/p\u003e \u003c/div\u003e"},{"header":"3 Results and Discussion","content":"\u003cdiv id=\"Sec6\"\u003e\n \u003ch2\u003e3.1 Characterization of the as-printed PEEK surfaces\u003c/h2\u003e\n \u003cp\u003e\u003cem\u003eSurface Morphology\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe as-printed parts are preferred for sliding bearing applications and the FFF printing parameters influence the surface morphology. Figure\u0026nbsp;\u003cspan\u003e3\u003c/span\u003e shows the 3D profile of an as-printed sample printed with 90% infill density. The surface of the sample displays hills and valleys, which are formed because of the 10% overlap between the parallel infill rasters. This texture arises from the FFF process, contributing to a rougher surface in samples with a 90% infill density and influence the real contact area. The roughness of the surface directly impacts the interaction between the sample and the counter body during tribology testing. The filament orientation with respect to the sliding direction will influence the tribo behaviour. The contact surface\u0026apos;s surface roughness (Sa) of the extruded PEEK rod samples used in the present study had a lower roughness of 5.3 \u0026micro;m compared to the 3D-printed samples of 19.6 \u0026micro;m. The overlapping of filament width affects the surface morphology of the as-printed sample and contributes to the higher roughness of the additive manufactured part. The difference in the cooling rate between the layers also causes a significant high roughness in FFF process.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eCrystallinity\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe printing temperature is one of the important parameters that affect the crystallinity, and thereby the mechanical properties of printed parts [\u003cspan\u003e12\u003c/span\u003e]. In addition, the printing pattern employed for a particular part geometry also results in a different cooling rate in different regions and crystallinity. The as-printed PEEK is semicrystalline and XRD patterns showed the presence of peaks in the 18\u0026ndash;30 degree range (Fig.\u0026nbsp;4 (a)). The 3D printed sample shows a lower crystallinity of 36.6%, and the extruded rod has a maximum crystallinity of 38%. Crystallinity is directly related to the hardness of the polymer [\u003cspan\u003e17\u003c/span\u003e]. The fabrication process affects the solidification and cooling rate of the stacked surfaces depending on the printing parameters.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eSurface strength\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;4 (b) shows the load vs indentation depth behaviour. The indentation hardness and modulus of all the tested pin samples are shown in Fig.\u0026nbsp;4(c). The measured hardness and modulus of the extruded PEEK rod sample are 324 MPa and 4.4 GPa, respectively, which is higher than the additive-manufactured sample, with a hardness and modulus of 278 MPa and 3.7 GPa, respectively. The marginal lower crystallinity of the as-printed surface compared to the extruded PEEK surface contributes to the reduced hardness and modulus in as-printed samples. The manufacturing processes, like additive manufacturing and others, affect the crystallinity of the fabricated sample, which affects the hardness and other mechanical properties. A maximum hardness of 346 MPa was reported for commercial PEEK by Ahmad et al. [\u003cspan\u003e17\u003c/span\u003e]. The extruded rod is a single body and homogeneous fabricated in a controlled environment, which makes the polymer achieve high hardness and greater resistance to indentation.\u003c/p\u003e\n \u003cp\u003e\u003cem\u003eSurface energy\u003c/em\u003e\u003c/p\u003e\n \u003cp\u003eThe surface energy of polymeric surfaces depends upon the molecular architecture and roughness. The water droplet determines the wettability of the PEEK surfaces. The contact angle made by the water and its corresponding surface energy for all PEEK samples is shown in Fig.\u0026nbsp;4 (d). The water\u0026apos;s maximum contact angle is on the 3D printed sample surface, indicating the low surface energy. The contact angle on the extruded pin is 68\u0026thinsp;\u0026plusmn;\u0026thinsp;1\u0026deg;, while on the 3D printed sample is 73\u0026thinsp;\u0026plusmn;\u0026thinsp;0.7\u0026deg;. The surface energy of the extruded PEEK pin is 27.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.8 mJ/m, which is nearly equal to the value reported by Mei et al. [\u003cspan\u003e19\u003c/span\u003e]. The surface energy observed for the 3D printed sample is 21.3\u0026thinsp;\u0026plusmn;\u0026thinsp;0.6 mJ/m. The contact angle and surface energy are important and affect the wear response of the PEEK samples.\u003c/p\u003e\n \u003cdiv\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;4.\u003c/strong\u003e \u003cem\u003e(a) XRD pattern, (b) Load vs depth loops from Indentation hardness, (c) Indentation hardness and modulus, and (d) Surface energy and water contact angle of extruded and 3D printed samples.\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\"\u003e\n \u003ch2\u003e3.2 Friction behaviour\u003c/h2\u003e\n \u003cp\u003eThe FFF process permits printing parts in different orientations and the friction and wear response of layer orientation with respect the sliding direction will assist the designers to choose appropriate orientation. Depending on the orientation of the layer to the sliding direction, the friction characteristics differ as the deformation of surfaces and particle entrapment differ. The variation of friction coefficient in as-printed samples in parallel and perpendicular layer orientations to the sliding direction and extruded sample when slid against the polished steel surface for 600 m is shown in Fig.\u0026nbsp;5 (a). All the samples exhibited a rising friction coefficient during the initial few hundred meters of sliding and reached a steady state (Fig.\u0026nbsp;5 (a)). The time taken to reach a steady state in 3D printed samples is marginally higher than in the smooth extruded PEEK sample. The material transfer to the pin surface in the 3D printed surface and its influence on the formation of the transfer layer on the disc contribute to the delay in achieving a steady state.\u003c/p\u003e\n \u003cp\u003eAs the infill angle chosen was 0/90\u0026deg;, the top surface (test surface) infill is aligned at 0\u0026deg;. The top infill layer of the 3D-printed PEEK surface is subjected to the tangential friction force parallel to the infill (hereafter, 3DP-||el) and perpendicular to the infill (hereafter, 3DP-Ʇar) in two different tests to assess the effect of infill orientation. When the sliding direction is parallel to the layer orientation, there is a reduced contact area than the perpendicular direction, resulting in low resistance to sliding (Fig.\u0026nbsp;5 (a)) during the initial period. The 3DP-||el sample stabilises after the transition phase and maintains a steady-state friction coefficient after sliding for about 300 m. The layers on the sample gradually deform and wear, leading to the proper contact with the steel surface. As the surface becomes flatter, the resistance to friction increases, and after sliding for 300 me, all samples with parallel orientation reach a steady state. In contrast, the 3DP-Ʇar sample, where the surface infill is oriented perpendicular to the sliding direction, makes high initial contact and exhibits high resistance during the initial friction stage. These samples reach a steady-state condition sooner than other samples. The transition stage causes the surface to experience more resistance, which causes a sudden increase in friction coefficient which stabilises subsequently.\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;5 (b) shows the steady-state coefficient of friction of the extruded and 3D printed samples in both orientations. The extruded sample\u0026apos;s steady-state friction coefficient is less than the 3D printed samples, and the effect of layer orientation is observed clearly. The steady-state friction coefficient of the 3DP-Ʇar sample is the high (0.54), and the extruded sample had a low friction coefficient, 0.47. The steady-state friction coefficient indicates that the surfaces in contact have nearly conformal contact. Therefore, the variation between the as-printed surfaces with parallel and perpendicular orientations made using identical process conditions and raw material is attributed to the material transfer between the surfaces. In the case of samples with perpendicular orientation to the sliding direction, more wear debris comprising of PEEK and iron oxide gets accumulated and adhered to the relatively soft polymer pin compared to the other samples tested. This increases the polymer surface\u0026apos;s hardness, which in turn, influences the transfer layer formation on the disc surface and affects the friction coefficient. In addition, the deformation of both the printed samples is also different which influences the local area of contact and the friction coefficient. This difference in the deformed surfaces in both the orientations and associated variations in the contact area contribute to variations in the friction coefficient in these samples. The difference in the accumulated debris in these samples influences the steady-state friction.\u003c/p\u003e\n \u003cdiv\u003e\n \u003c/div\u003e\n \u003cp\u003e\u003cstrong\u003eFigure\u0026nbsp;5.\u003c/strong\u003e \u003cem\u003e(a) The variation of friction coefficient for extruded, 3DP-||el, and 3DP-Ʇar samples and (b) steady-state friction coefficient of test samples.\u003c/em\u003e\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003e3.3 Wear mechanism\u003c/h2\u003e\n \u003cp\u003eWhen the pin surface slides against the bearing steel disc, the wear in the initial run-in phase is less. However, under constant load, the surfaces in contact deform due to high local stresses and subsequently wear. The wear volume and specific wear rate measured in the as-printed sample with two different orientations and the extruded sample are shown in Fig.\u0026nbsp;\u003cspan\u003e6\u003c/span\u003e. The extruded sample exhibited a higher wear volume and a specific wear rate of 8.43 \u003cspan\u003e\u003cspan\u003e\\(\\times\\)\u003c/span\u003e\u003c/span\u003e 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e mm\u003csup\u003e3\u003c/sup\u003e/Nm compared with the as-printed samples. At the same time, the sample with the perpendicular orientation showed the lowest wear volume and a specific wear rate of 6.7 \u0026times; 10\u003csup\u003e\u0026minus;\u0026thinsp;5\u003c/sup\u003e mm\u003csup\u003e3\u003c/sup\u003e/Nm. The rough surface in perpendicular orientation accommodates more wear particles and this influences the wear characteristics. Dhakal et al. [\u003cspan\u003e20\u003c/span\u003e] also reported similar results in the study of ABS, where 3D printed sample with \u003cspan\u003e\u003cspan\u003e\\(0^\\circ\\)\u003c/span\u003e\u003c/span\u003e/90\u003cspan\u003e\u003cspan\u003e\\(^\\circ\\)\u003c/span\u003e\u003c/span\u003e showed higher wear resistance than injection-moulded sample. While the sample printed at higher speed exhibited higher wear rate. The load variation under dry conditions also affects the moulded sample\u0026apos;s wear rate more than the 3D printed sample [\u003cspan\u003e21\u003c/span\u003e]. The material removal in the case of polymer-metal sliding contacts depends on the transfer layer formation and its periodic removal when the materials and test conditions are similar. The smooth polymer samples tend to adhere more and form a transfer layer, which tends to get removed frequently, resulting in an increased wear rate in extruded samples.\u003c/p\u003e\n \u003cp\u003eThe amount of debris accumulated in the 3D samples differs due to the difference in the sliding direction, which subsequently affects the wear rate. Increased surface hardness in the sample due to adherence of debris generated results in reduced wear loss. Despite having similar contact areas in both orientations, the specific wear rate is lower for the 3DP-Ʇar sample. The extruded rod exhibits a higher contact area among all the tested samples, resulting in a higher wear volume. The transfer layer formed causes more wear that is abrasive in nature, which can be seen on the sliding surface.\u003c/p\u003e\n \u003cp\u003eThe pin surfaces observed after the tests using a digital microscope are shown in Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e. The dark region on the polymer pin surfaces indicates the debris adhered to the soft polymer; otherwise, the material is transferred to the pin. The amount of material transferred in all three samples is quite different and is clearly seen in the Fig.. The transfer layer formed in the case of the sample with parallel orientation is thinner than the sample sliding perpendicular to the layer orientation. The abrasion marks can be seen at many locations, along with some deep grooves and pits on the surface. The sample\u0026apos;s surface does not show any sign of debris adhesion to its surface after the test. The surface roughness is reduced due to wear of surface. The repeated dry sliding also causes friction heating, which results in smearing and pit formation, as indicated in Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (a1 and a2).\u003c/p\u003e\n \u003cp\u003eThe additively manufactured samples show severe adhesion of wear debris on the surfaces. For the 3DP-||el, the material adhesion is less than the 3DP-Ʇar sample. As the surface infill is aligned with the sliding direction for the 3DP-||el sample, the debris can only adhere to locations that act as a barrier in that direction (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (b)). The continuous sliding causes the deformation on the surface, and some micro-cracks are formed on the surface along with pits (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (b1 and b2)). Fine debris particles seem to adhere and accumulate on the surface at some locations. The debris is trapped at the contact surface and accumulates at the edges due to material transfer. The debris generated during the adhesive wear is a mixture of PEEK and metal oxide. The dark region representing debris adhered to the 3DP-||el sample surface is around 3% of the total surface area. While in the case of the 3DP-Ʇar sample, the debris adhered covered about 13% of the surface area, as shown in Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (c). The layers deformed during the sliding, which caused crack formation and delamination (Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (c1)). The material transfer is higher as the surface infill is aligned perpendicular, providing more resistance to wear. The schematics of the wear process and debris accumulation that occurred in the 3D printed sample with two orientations are depicted in Fig.\u0026nbsp;\u003cspan\u003e7\u003c/span\u003e (d). The long-deposited filament oriented parallel to the sliding surface could only cover some parts of the surface, while in the perpendicular orientation, it struck with a small alignment. This repeated sliding causes the deformation of the raster filled with debris.\u003c/p\u003e\n \u003cp\u003eAnalysing the composition of the worn-out material and the adhered debris is crucial in understanding the wear process and is carried out using Energy-Dispersive X-ray Spectroscopy (EDS) (Fig.\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (a-f)). Figure\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (a) shows the wear surface of the 3DP-Ʇar sample. A smaller location marked as (b) is analysed at a higher magnification. Figure\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (b) shows that over 60% of the frame area is covered with mixed debris. Figure\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (d-f) shows the EDS material mapping of a concentrated area in the sample, corresponding to Fig.\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (a-c). Figure\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (g) presents the spectrum for the complete surface, while Fig.\u0026nbsp;\u003cspan\u003e8\u003c/span\u003e (h) shows the spectrum for a specific location labelled as \u0026apos;c\u0026apos; in the 3D printed sample. A gold coating was applied on the surface, which resulted in the reflection of specific peaks at a particular energy level in the spectrum. However, the gold and other element\u0026apos;s content are excluded from the composition analysis. The inset table shows three major elements, excluding others like Cr, Mn, and Si. The spectrum indicates that the mixed debris deposited to the surface contains iron. The surface of the sample exhibits more hardness and high wear resistance. As mentioned earlier in the section, the wear volume and specific wear rate for the 3DP-Ʇar sample are lower than the extruded sample due to the presence of mixed debris on the surface. The dependency on the orientation of infill on the wear mechanism and failure mode leads to the composite formation on the PEEK\u0026rsquo;s surface. The debris adherence on the surface, which is a mixture of PEEK and iron oxide, becomes strong due to repeated sliding and compaction. EDX spectrum confirms the formation of the compound on the surface. The strain and plastic deformation are initially higher in the 3D printed sample case, allowing structure damage and debris accumulation [\u003cspan\u003e22\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.4 Transfer layer on the disc\u003c/h2\u003e\n \u003cp\u003eFigure\u0026nbsp;\u003cspan\u003e9\u003c/span\u003e (a) shows a section of the track formed on the steel disc. A uniform transfer layer with accumulated debris on the track is observed for extruded samples and is evident under dry sliding conditions [\u003cspan\u003e23\u003c/span\u003e]. However, in 3D printed samples, the transfer layer formed is not as uniform and smooth compared with extruded samples. Patchy regions were noted in the as-printed samples and are lower in the 3DP-Ʇar sample. The 3DP-||el sample also results in higher wear loss than the 3DP-Ʇar sample, which can be seen through the adhesion of PEEK on the track (Fig.\u0026nbsp;\u003cspan\u003e9\u003c/span\u003e (b-c)). It is observed that the track is covered with PEEK and PEEK with iron oxide debris. It is observed that approximately 80% of the track is covered with the transfer layer for all the samples other than the 3DP-Ʇar sample, which showed\u0026thinsp;~\u0026thinsp;55% covered with the transfer layer. The material transferred and adhered to the polymer pin influences the transfer layer formation on the disc. The samples with increasing porosity also show similar tracks as the 3DP-||el sample, where more than 80% of the steel disc is covered with a transfer layer.\u003c/p\u003e\n \u003cp\u003eFigure\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e (a-d) shows the detailed analysis of the wear track. The track is covered with the PEEK transfer layer for the 3DP-Ʇar sample. The SEM image indicates small patches present on the disc surface containing the debris adhesion in some locations (Fig.\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e (a)). At location b, PEEK material is deposited on the track (Fig.\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e (b)). On the other hand, at location \u0026lsquo;c\u0026rsquo;, the debris that is deposited constitutes the PEEK and iron element, which is confirmed using EDX spectra (Fig.\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e (c) and (d)). As shown in Fig.\u0026nbsp;\u003cspan\u003e10\u003c/span\u003e, the wear process indicates that the material from the bearing steel disc is also worn out during the sliding process. The debris formed is the mixture of the top oxide layer of the steel disc and the PEEK surface, which forms the transfer layer and is also reported [\u003cspan\u003e24\u003c/span\u003e][\u003cspan\u003e25\u003c/span\u003e].\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\"\u003e\n \u003ch2\u003e3.5 Temperature rise\u003c/h2\u003e\n \u003cp\u003eThe friction between the disc and pin leads to heat generation. The friction heat generated can be calculated by the \u0026micro;PV formula, where \u003cspan\u003e\u003cspan\u003e\\(\\mu\\)\u003c/span\u003e\u003c/span\u003e is the friction coefficient, P is the pressure, and V is the sliding velocity. The total heat generated by the friction is distributed between the PEEK pin and the steel disc. It is assumed that the thermal contact resistance is constant, and the heat transferred to the disc is given as \u003cspan\u003e\u003cspan\u003e\\(\\gamma \\mu\\)\u003c/span\u003e\u003c/span\u003ePV and for the pin as \u003cspan\u003e\u003cspan\u003e\\((1-\\gamma )\\mu\\)\u003c/span\u003e\u003c/span\u003ePV, where \u003cspan\u003e\u003cspan\u003e\\(\\gamma\\)\u003c/span\u003e\u003c/span\u003e is heat partition. This generates heat at the contact of the surface and more at the centre. It is obtained that the maximum temperature at the surface is approx. 35\u0026deg;C for the extruded pin, which is 7\u0026deg;C rise from the room temperature. To measure the rise in the temperature close to the sliding surface, a thermal camera is employed to capture the temperature at various time intervals on the outer surface of the pin. Figure\u0026nbsp;\u003cspan\u003e11\u003c/span\u003e shows the rise in temperature for three samples. Notably, the extruded sample exhibits the highest temperature increase, while the 3DP-Ʇar sample demonstrates the lowest. The temperature has increased since the measured surface is constantly exposed to the open atmosphere. Initially, the temperature rise exhibits a linear pattern during the initial running stage, and the temperature rise is higher. However, the temperature gradually increases due to heat dissipation. The difference in cooling due to the presence of the grooves in as-printed samples in the initial stages influences the net heat buildup.\u003c/p\u003e\n\u003c/div\u003e"},{"header":"4 Conclusion","content":"\u003cp\u003eThe effect of surface infill orientation with respect to sliding direction on the dry sliding friction coefficient, wear and contact temperature of PEEK polymer against steel is reported. The following conclusions are drawn based on the current investigation:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eConsidering the requirement of uniform wear theory for smooth operation in practical applications, the 3DP-Ʇar sample achieves a steady state within 300 m of sliding, well before achieved by the extruded sample. The surface roughness influences the contact area, subsequently affecting the friction performance of the 3D printed samples compared to extruded samples. When slid in the perpendicular direction, debris appears to be accommodated between the rasters higher than parallel, increasing the friction coefficient but reducing wear loss. The smearing and delamination dominated the wear of 3D printed samples and formed a relatively thin film of transfer layer than the extruded sample, which is more driven by abrasion wear.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe surface experiences plastic deformation and higher strain that causes the surface to accommodate the debris on it. The debris formed due to sliding on the disc has a mixture of PEEK and iron-oxide, which restrict the more wear in perpendicular orientation. This causes the least wear volume generation after the test for the 3DP-Ʇar sample. The wear track on the disc also shows that the track is not fully covered with debris.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe surface roughness impacts the samples' contact area and friction performance compared to extruded samples. The effect of trapped debris between the rasters increases the friction coefficient when sliding perpendicularly. The presence of roughness on the surface allows the material to undergo plastic deformation in the sliding direction, thereby accommodating debris and deformed material. This affects the transfer layer formation on the counter body and the interaction of the pin undergoing deformation and adhesion, which concludes the friction coefficient.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe rise in contact temperature is less in the 3D printed samples than the extruded sample. Considering the maximum operating temperature of PEEK of 260\u0026deg;C, the 3D printed samples will take a longer duration to reach this temperature than the extruded sample with lesser wear loss.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eFundings:\u0026nbsp;\u003c/strong\u003e\u0026ldquo;The authors would like to acknowledge the support from the Department of Science and Technology (DST- SERB) (Grant number \u0026ndash; CRG/2018/002549), India.\u0026rdquo;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCompeting Interests:\u0026nbsp;\u003c/strong\u003e\u0026ldquo;The authors have no conflicts of interest to declare that are relevant to the content of this article.\u0026rdquo;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor Contributions:\u0026nbsp;\u003c/strong\u003e\u0026ldquo;Methodology, Material preparation, Data collection, Formal analysis and investigation, Draft Writing: [Sunil Kumar Prajapati]; Conceptulisation, Resources, Supervision, Review and Editing: [R. Gnanamoorthy].\u0026rdquo;\u003c/p\u003e\n\u003ch4\u003e\u003cstrong\u003eData availability statement: \u0026ldquo;\u003c/strong\u003eData supporting the results and analysis in this article will be available on request to the corresponding author.\u0026rdquo;\u003c/h4\u003e\n\u003cp\u003e\u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eT. J. Hoskins, K. D. Dearn, Y. K. Chen, and S. N. Kukureka, \u0026ldquo;The wear of PEEK in rolling-sliding contact - Simulation of polymer gear applications,\u0026rdquo; \u003cem\u003eWear\u003c/em\u003e, vol. 309, no. 1\u0026ndash;2, pp. 35\u0026ndash;42, 2014, doi: 10.1016/j.wear.2013.09.014.\u003c/li\u003e\n\u003cli\u003eH. Koike, K. Kida, E. C. Santos, J. Rozwadowska, Y. Kashima, and K. Kanemasu, \u0026ldquo;Self-lubrication of PEEK polymer bearings in rolling contact fatigue under radial loads,\u0026rdquo; \u003cem\u003eTribol. 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December 2017, pp. 507\u0026ndash;516, 2018, doi: 10.1016/j.compositesa.2018.04.002.\u003c/li\u003e\n\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":"Contact Temperature, Friction, PEEK, Surface properties","lastPublishedDoi":"10.21203/rs.3.rs-4011448/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4011448/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eHigh-temperature additive manufacturing permits printing advanced polyether ether ketone (PEEK) sliding bearings with different surface features needed for better heat dissipation or lubrication of bearings. The as-printed surfaces of fused filament fabrication (FFF) parts are different compared to the molded or extruded surfaces and will influence the performance. The layer orientation with respect to the sliding direction is a key parameter that decides be bearing performance and is investigated using representative pin samples. The accommodation of debris on soft polymer sliding against hard steel during the initial period of sliding influences the friction and wear characteristics and contact temperature rise. The heat buildup in polymers that limits the operating load and speed in the initial period is influenced by the airflow between the layers which depends on the sliding direction. The current observations will assist in choosing the 3D printing over moulded sample for sliding contact conditions.\u003c/p\u003e","manuscriptTitle":"Comparison of Friction Performance of Polyether ether ketone Fabricated Using Different Methods Under Dry Sliding Conditions","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-07 10:47:30","doi":"10.21203/rs.3.rs-4011448/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":"f3c7a8d6-12a5-4f80-b930-c0c17def8dd8","owner":[],"postedDate":"March 7th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-11T12:06:51+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-07 10:47:30","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4011448","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4011448","identity":"rs-4011448","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}