Tribological performances of UHMWPE and PEEK under dry sliding conditions against steel and various polyetherimide polymer counterfaces

Dry sliding wear characteristics of commercially available poly-ether-imide (PEI)+20% ( glass fiber reinforced)GFR and polysulfone (PSU)+20% GFR polymer composite in use in electrical engineering applications were investigated using a pin―on―disc rig. Pin materials are (PEI)+20% GFR and PSU+20% GFR polymer composite. Disc materials are AISI 4140 steel and PA 46+30%GFR polymer composite. Wear tests were carried out at 0.5 and 1.0 m/sec sliding speeds and 20, 40 and 60N load values and under atmospheric conditions of temperature and humidity. Different combinations of rubbing surfaces were examined and the dynamic friction coefficient and specific wear rate values were obtained and compared. For all material combinations, the coefficient of friction shows little sensitivity to sliding speed and applied load values and large sensitivity to material combinations. For specific wear rate, PEI composite has shown little sensitivity to change in load, speed and materials combination while PSU composite shown large sensitivity to the change in load and material combinations. The friction coefficient of PEI+20%GFR and PSU+20GFR rubbing against AISI 4140 steel disc is a round 0.3 and is about 0.12 as rubbing against PA 46+30%GFR. The specific wear rate for PEI and PSU composites are in the order.of 10 -15 to 10 -14mm3 /N.m. The wear mechanisms are a combination of adhesive and abrasive wear.

In this study, the tribological performance of poly-ether-ketone (PEEK), ultrahigh molecular weight polyethylene (UHMWPE), glass fiber reinforced poly-tetra-fluoro-ethylene (PTFE) and PTFE reinforced poly-ether-imide (PEI) composite materials, under dry and lubricated conditions, were compared and evaluated. Wear tests were carried out on a pin-disc arrangement and under 50, 100 and 150 N applied loads and 0.5 m/s sliding speed conditions. The results show that the coefficient of friction and specific wear rates for these materials decreases with the increase in applied load values. Finally, the wear rates for PEEK, UHMWPE polymers, PTFE+20% glass fiber reinforced (GFR) and PEI+10% PTFE composites under dry and lubricated conditions are in the order of 10-14 and 10-15, respectively. The results suggested that it is convenient to use PTFE+20% GFR composites for machine components with low processing and product costs.

Ultra-high molecular weight polyethylene (UHMWPE) and its derivatives have been clinically used as an acetabular liner material in total hip joint replacement (THR) over last six decades. Despite significant efforts, the longevity of UHMWPE implants is still impaired due to their compromised tribological performance, leading to osteolysis and aseptic loosening. The present study aims to critically evaluate and analyze the tribological performance, of the next generation acetabular liner material, that is, a chemically modified graphene oxide (GO) reinforced HDPE/UHMWPE (HU) bionanocomposite (HUmGO), against stainless steel (SS 316L) counterface in lubricated conditions. This work also provides a performance comparative assessment of HUmGO with respect to medical grades, UHMWPE (UC) and crosslinked UHMWPE (XL-UC). Significant attempts have been made to correlate the tribological properties (frictional behavior, wear rate, wear debris shape and size, wear mechanism) with the physicomechanical conditions (contact stresses) at sliding contact and the variation in molecular architecture of different UHMWPE materials. Additionally, an emphasis is put forward to critically anlyze the nature of lubrication regime based on the bearing characterstic parameters. HUmGO exhibited a lower COF (0.07) and specific wear rate (2.86 × 10-8mm3/Nm) than UC and XL-UC under identical sliding conditions. The worn surfaces on HUmGO revealed the signatures of less abrasive wear and limited deformation. Based on the estimated lambda (λ) ratio and Sommerfield number, all the investigated sliding contacts exhibited boundary lubrication. Taken together, the modified GO reinforced HDPE/UHMWPE bionanocomposite can be considered as a new generation biomaterial for the fabrication of acetabular liner for hip-joint prosthesis.

Reinforced PTFE materials can be designed to show high mechanical stability against harder materials under sliding wear conditions. Especially bearing metal-reinforced PTFE is of high practical interest. In this class of materials, bronze-filled PTFE was reported to obtain high wear resistance, a low coefficient of friction (COF), and excellent self-lubrication properties in sliding conditions. In the statistical approach of this work, PTFE composites reinforced with 25 vol%, 40 vol%, and 60 vol% bronze particles were evaluated against pure PTFE regarding wear behavior under varied wear test parameters, i.e., material, normal load, and sliding speed. Wear tests were planned to use a standard orthogonal array based on the Taguchi design method. An analysis of variance test was utilized to quantify the effects of test parameters on the wear behavior of the bronze/PTFE composites and pure PTFE. According to the variance analysis, the material type has the largest influence on the COF and the specific wear rate (SWR) under test conditions of this work. Both COF and SWR were found to be influenced by the material type (29.83% and 96.16%), the normal load (33.34% and 0.95%), and sliding speed (9.14% and 1.28%). The lowest SWR and COF values were achieved at the optimum wear test conditions where the wear test parameters were 1 m/s sliding speed (A4B2C2) at PTFE + 60 vol.% bronze reinforced composite 50 N application load and 0.32 m/s sliding speed (A4B3C1) at PTFE + 60 vol.% bronze reinforced composite 100 N application load, respectively.

Purpose Mechanical components often operate under water-lubricated conditions, where metals are prone to corrosive wear. Polyether ether ketone (PEEK), a high-performance plastic, is widely used in bearings but exhibits suboptimal tribological performance in such environments. This study aims to enhance PEEK’s performance by incorporating a low content of ultra-high molecular weight polyethylene (UHMWPE) and analyzing its wear mechanisms. Design/methodology/approach A series of PEEK composites with UHMWPE contents ranging from 1.0 to 10.0 wt% were fabricated via hot pressing. The tribological performance of the samples under water-lubricated conditions was evaluated with a reciprocating wear tester. The wear surfaces were characterized in terms of both three-dimensional topography and micro-morphology. In addition, the effect of varying loads on the tribological behavior of the composites was investigated. Findings The friction coefficient and wear rate of PEEK composites initially decrease and then increase with increasing UHMWPE content. At a UHMWPE content of 3.0 wt%, the composites exhibit the lowest friction coefficient and wear rate, with reductions of 42% and 71%, respectively, compared to pure PEEK, along with a 44% reduction in worn surface roughness. Scanning electron microscope (SEM) analysis reveals that the wear surface of the 3.0 wt% UHMWPE-reinforced PEEK composite is smooth, whereas the surface of pure PEEK predominantly shows plastic deformation and adhesive wear. Originality/value This study reveals that incorporating low-content UHMWPE significantly enhances the tribological performance of PEEK in water-lubricated environments. These findings provide valuable insights for optimizing PEEK bearing performance and broadening its engineering applications under water-lubricated conditions.

Epoxy with ultra-high molecular weight polyethylene (UHMWPE) and MoS2 fillers was coated on a bearing steel (SAE 52100). Frictional and wear properties of the coated samples in sliding contact were investigated on a pin-on-disc tribometer under a normal load of 10 N and a linear sliding speed of 1 m/s against a bearing steel ball. The optimized coating composition (72 wt% Epoxy + 7 wt% hardener + 18 wt% UHMWPE + 3 wt% MoS2) showed highly improved tribological properties compared to pure epoxy and other epoxy-based composites. There was 75% reduction in the coefficient of friction (COF) in the dry interfacial condition (COF reduced from 0.2 to 0.05) over pure epoxy and 80% reduction with grease as the lubricant. The specific wear-rate of the composite was lower by five orders of magnitude over that of pure epoxy. Other mechanical properties such as hardness, tensile strength, and Young's modulus of the composite showed increments of 86%, 121%, and 43%, respectively, with respect to those of pure epoxy. 2–3 wt% of MoS2 had drastic effects on improving strength and reducing friction and wear of the composites. For dry sliding, initial abrasive and adhesive wear mechanisms led to transfer film formation on the steel counterface, and the shearing was mainly within the transfer film. For the grease-lubricated case, a thin layer of grease helped in easy shearing, and the transfer film formation was avoided. This epoxy-based composite will have applications as tribological coatings for journal bearings.

Dental decay still presents a major health problem among children. Its treatment usually requires the use of stainless steel crowns. This study compares the wear behavior of 316 L stainless steel and polyetheretherketone (PEEK) composite under identical test conditions. The wear tests were conducted in a reciprocating ball-on-plate tribometer (Plint TE67/R) using alumina balls as a counterface and artificial saliva as a lubricant at 37 °C to faithfully mimic oral conditions. The coefficient of friction (COF) and specific wear rate (k) values were determined and SEM/EDS examinations were performed to identify the predominant wear mechanisms. Results showed that PEEK exhibited a significantly lower coefficient of friction (COF = 0.094 ± 0.004) and thus lower wear volume (ΔV = 0.0078 ± 0.0125 mm3) and higher wear resistance, with an average value of specific wear rate of k = 9.07 × 10−6 mm3N−1m−1 when compared to stainless steel (COF = 0.32 ± 0.03, ΔV = 0.0125 ± 0.0029 mm3, k = 1.45 × 10−5 mm3N−1m−1). PEEK was revealed to be a potential material for use in pediatric crowns due to its high wear resistance while overcoming the disadvantages associated with steel at both an aesthetic and biological level.

In this investigation the friction and wear performance of GUR 1020 medical grade ultra-high molecular weight polyethylene (UHMWPE) polymer under dry sliding, distilled water and egg albumen lubrication conditions were evaluated. The sliding experiments were carried out on a pin-on-disc tribometer. The contact configuration used was a polymer pin on a rotating AISI 304L stainless steel disc. Wear tests were carried out for 30 min duration at room temperature with 50, 100 and 150 N applied load values and at 0.50, 1.0 and 2.0 m/s sliding speeds condition. The results show that the coefficient of friction for GUR 1020 medical grade UHMWPE polymer is more significantly influenced by applied load and sliding speed values under dry sliding condition rather than lubricant media condition. Furthermore, the coefficient of friction and specific wear rate increases with the increase in applied load and speed values. This increase is much pronounced under dry sliding condition. Moreover, for the range of load and speed values of this study the specific wear rate using egg albumen lubricant registered lower values than that of the distilled water lubricant and the dry conditions. Finally, the specific wear rate values for GUR 1020 medical grade UHMWPE polymer under dry, water lubricant and egg albumen lubricant conditions are at the levels of 8x10-14, 1.4x10-14 and 0.5x10-14m2/N respectively. Key words: Medical Grade UHMWPE, tribology, distilled water, wear.

The wear and friction performance of GUR 1020 grade ultrahigh molecular weight polyethylene (UHMWPE) polymer was studied in distilled water, HASS (Hank’s balanced salt solution) and several protein lubrication environments. Wear tests were carried out using polymer pin -on AISI 304L stainless steel disc apparatus. Tests conditions were room temperature, 40N, 80N and 120N applied loads and 0.5 m/s sliding speed. For the range of load and speed value of this work, the coefficient of friction and wear rate for UHMWPE polymer decreases with the increase in applied load values. The coefficient of friction is highest and the specific wear rate values is lowest under HASS +HA solution lubricant. The average specific wear rate values for UHMWPE polymer under distilled water and HASS+HA (Hank’s balanced salt solution with Hyaluronic acid) lubrication conditions are in the order of 9x10-15 m2/N and 3x10-15 m2/N respectively. The wear mechanism includes abrasion and adhesive processes.

This work targets the production of novel biomaterials and an optimized process to disperse Zirconia (ZrO2) and reduced graphene oxide (rGO) in the ultra‐high molecular weight polyethylene (UHMWPE) matrix. The mechanical and wear performance of the developed samples were evaluated through compression and tribological tests utilizing a bio‐tribometer. The developed samples are tested under simulated body fluid (SBF) lubricating media. In particular, the hybrid material is made of 5 wt% zirconia and 1 wt% rGO have an enhanced compression modulus of 0.29 GPa. This indicates a 26.08% improvement over pristine UHMWPE. Besides this, the compressive strength of this hybrid material is about 46.75% higher than that of pristine UHMWPE. The gray theory provided optimum settings as 1 wt% rGO and 5 wt% ZrO2 fillers are loading with 60 N load and 900 sec cycle time. The long‐range organized lamellar structures and microfibers were formed between the crystals with the help of the graphene layers. The inclusion of rGO nanofillers (1 wt%) and zirconia improve the wear resistance, which signifies the best‐desired values for coefficient of friction (Cf) and Specific wear rate (Wr). Improved loading conditions for prosthetics and implant components are possible with modified UHMWPE.Highlights This work highlights the tribological performances of hybrid nanocomposites. The effect of rGO and ceramic (ZrO2) nanofillers on UHMWPE was examined. Zirconia/rGO enhanced bio‐inert, wear‐resistant and biocompatibility. Compared to pristine, 1 wt% rGO and 5 wt% ZrO2 sample shows better results. Orthopedic and dental prostheses may be made using hybrid nanocomposite.

In vitro evaluation of delamination resistance of PEEK and CFR-PEEK.

To elucidate the key material parameters governing the tribological performance of ceramic composites under dry sliding against steel, this study presents a comprehensive comparative assessment of the microstructural characteristics, mechanical performance, and tribological behavior of two alumina–zirconia (Al2O3–ZrO2) ceramic composites, each reinforced with a 42 vol.% carbide phase: zirconium carbide (ZrC) and tungsten carbide (WC). Specifically, tungsten carbide (WC) was selected for its exceptional bulk mechanical properties, while zirconium carbide (ZrC) was chosen to contrast its potentially different interfacial reactivity against a steel counterface. ZrC and WC were selected as reinforcing phases due to their high hardness and distinct chemical and interfacial properties, which were expected to critically affect the wear and friction behavior of the composites under demanding conditions. Specimens were consolidated via spark plasma sintering (SPS). The investigation encompassed macro- and nanoscale hardness measurements (Vickers hardness HV1, HV10; nanoindentation hardness H), elastic modulus (E), fracture toughness (KIC), coefficient of friction (COF), and specific wear rate (Ws) under unlubricated reciprocating sliding against 100Cr6 steel at normal loads of 10 N and 25 N. The Al2O3–ZrO2–WC composite exhibited an ultrafine-grained microstructure and markedly enhanced mechanical properties (HV10 ≈ 20.9 GPa; H ≈ 33.6 GPa; KIC ≈ 4.7 MPa·m½) relative to the coarse-grained Al2O3–ZrO2–ZrC counterpart (HV10 ≈ 16.6 GPa; H ≈ 27.0 GPa; KIC ≈ 3.2 MPa·m½). Paradoxically, the ZrC-reinforced composite demonstrated superior tribological performance, with a low and load-independent specific wear rate (Ws ≈ 1.2 × 10−9 mm3/Nm) and a stable steady-state COF of approximately 0.46. Conversely, the WC-reinforced system exhibited significantly elevated wear volumes—particularly under the 25 N regime—and a higher, more fluctuating COF. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM–EDX) of the wear tracks revealed the formation of a continuous, iron-enriched tribofilm on the ZrC composite, derived from counterface material transfer, whereas the WC composite surface displayed only sparse tribofilm development. These findings underscore that, in steel-paired tribological applications of Al2O3–ZrO2–based composites, the efficacy of interfacial tribolayer generation can supersede intrinsic bulk mechanical attributes as the dominant factor governing wear resistance.

In the present work, polycarbonate-poly­(butylene terephthalate)/multiwalledcarbon nanotubes (PC-PBT/MWCNT) nanocomposites were produced via melt-compounding,extrusion, and molding techniques with nanofiller wt. fractions of0, 1, 3, 5, and 7 wt %. Nanofiller induced microstructural, mechanicaland dry sliding wear property changes were evaluated, and coefficientsof friction (COF) and specific wear rate (SWR) responses were predictedby employing machine learning (ML) models with and without featureengineering (FE) integration. One wt % nanofiller addition resultedin 52%, 41%, and 119% increase in tensile modulus, flexural modulus,and impact strength of neat samples, respectively. Nanofiller additionalso resulted in up to 52% and 41% enhancement in tensile and flexuralmoduli, and up to 91% and 22% reduction in SWR and COF values. Thelowest COF and SWR were recorded as 0.231 for 1 wt % MWCNT under 10N and 4.48 (×10–15) m3/Nm for 0.5wt % MWCNT under 5 N, respectively. Wear data and worn surface analysisresults indicate that COF is directly affected by a transfer-film-formationmechanism at the contact interface, whereas SWR is sensitive to avariety of other factors including contact mechanics features. FE-assistedK-Star model demonstrated the highest prediction accuracy (R2 = 0.96), whereas the highest accuracy withoutFE was achieved by Lasso model (R2 = 0.87).The improved accuracy of FE-assisted models is ascribed to their higherrobustness against inconsistencies in the data sets.

Evaluation of mechanical and tribological characteristics of hot-pressed self-lubricating CuO/MgO/ZTA ceramic composites

Tribological Characterization of Dental Restorative Materials