Effect of counterface on the tribology of UHMWPE in the presence of proteins

Artificial joints in orthopedics occupy a principal position owing to the increase in number of cases suffering from arthritis and associated diseases in addition to impairment caused by accidents. In this work, one of the most commonly used joint material, i.e. ultrahigh molecular weight polyethylene (UHMWPE), was tested against the duplex stainless steels instead of the conventional 316 L stainless steel. The UHMWPE was found to exhibit the lowest friction coefficient and wear rates when lubricated with water followed by globulin and glucose. The friction coefficient in the presence of egg albumen was higher along with high wear rates recorded. Post-test evaluation of surface roughness and wear scar/track analysis was performed to identify the wear mechanisms. Worn surfaces were analyzed using a differential scanning calorimeter for changes in crystallinity with sliding. The specimens tested under lubricated conditions with glucose, egg albumen and globulin indicated the presence of reaction products on the worn surface. Adhesive and corrosive wear mechanisms were the predominant modes of wear identified on the polymer samples. The wear tracks indicated that the proteins did react with the counterface material forming a thin deposit on them. Low temperature nitriding of the duplex stainless steel counterfaces were performed and the UHMWPE specimens were tested under similar conditions against the nitrided surfaces. Low temperature nitriding of the counterface did result in improved tribological behavior of UHMWPE and the corrosive effects were minimal.     

An Analysis and Comparison of the Tribological Behavior of Two Polymers Sliding Against a Polymeric Composite

Two polymers, ultrahigh-molecular-weight polyethylene (UHMWPE) and polycarbonate, were slid dry against continuous fiber graphite/epoxy composites in multiple-pass friction and wear tests. High and low valves of load, speed, fiber orientation, and virgin surface roughness were used to find their effect on the coefficient of friction and wear rate. Regression equations were developed from the data to help describe the effects of various independent variables. For the total distance slid of 176 m, there was no significant effect of sliding speed on coefficient of friction. The coefficient of friction for UHMWPE was found to depend on surface roughness and fiber orientation. For polycarbonate, the coefficient of friction was very complex, containing a three-factor interaction between normal load, surface roughness, and fiber orientation. The wear rate for UHMWPE was a function of normal load, surface roughness, and a nonlinear term in normal load and surface roughness. The wear rate for polycarbonate was significantly affected by all variables except fiber orientation.     

聚丙烯、炭黑和碳纤维共混填充超高分子量聚乙烯复合材料的力学和摩擦磨损性能

采用模压成型的方式制备超高分子量聚乙烯(UHMWPE)复合材料,通过AG-1型电子万能实验机和MM-200型摩擦磨损试验机分别研究填料对复合材料力学性能和摩擦磨损性能的影响,采用光学显微镜分析复合材料磨损表面的形貌。结果表明:聚丙烯(PP)和无机填料炭黑(CB)或CB与碳纤维(CF)混杂填料的加入使UHMWPE复合材料的拉伸强度降低,弯曲模量和硬度增加,其中UHMWPE/PP/CB/CF复合材料的弯曲模量和硬度增幅大于UHM-WPE/PP/CB复合材料。填料的加入可改善UHMWPE复合材料的摩擦磨损性能,当填料的质量分数为5%时,UHMWPE复合材料的摩擦磨损性能最好,且UHMWPE/PP/CB/CF复合材料的耐磨性能优于UHMWPE/PP/CB复合材料。与UHM-WPE相比,UHMWPE/PP/CB/CF复合材料的摩擦因数和磨痕宽度分别下降了10%和44%,UHMWPE/PP/CB复合材料则分别下降了12%和42%。光学显微镜观察表明填料的加入大大改善了UHMWPE的磨粒磨损,复合材料表面以较浅的犁沟磨损为主要特征。     

试验参数对人工滑液边界润滑条件下超高分子量聚乙烯/Ti6Al4V往复摩擦磨损行为的影响

采用自行研制的往复摩擦磨损试验机,在法向载荷50 N、往复频率1 Hz、摩擦副接触形式为圆环外圆周/平面、初始线接触长度为6 mm、相对湿度为80%的试验条件下,研究了钛合金表面粗糙度、试验环境温度、试验延续时间、滑液成分等试验参数对UHMWPE/Ti6A14V摩擦副的往复摩擦磨损行为的影响.结果表明,这些试验参数均显著影响UHMWPE/Ti6A14V摩擦副的往复摩擦磨损行为;在环境温度20℃、25%小牛血清去离子水溶液边界润滑、180 min往复摩擦磨损试验条件下,当钛合金表面粗糙度由Ra0.04 μm增加至Ra0.06μm时,摩擦副的平均摩擦因数由0.033增加至0.096,UHMWPE试样磨损量由0.131 mm3,增加至0.149 mm3;在钛合金表面粗糙度为Ra0.06μm、25%小牛血清去离子水溶液边界润滑、180 min往复摩擦磨损试验条件下,当试验环境温度由10℃上升至37℃时,摩擦副的平均摩擦因数由0.135减少至0.077,UHMWPE试样磨损量由0.188 mm3减少至0.134 mm3.     

Effect of UHMWPE Microparticles on the Tribological Performances of High-Strength Glass Fabric/Phenolic Laminate Composites Under Water Lubrication

The tribological behaviors of ultra-high molecular weight polyethylene (UHMWPE) microparticle-modified high-strength glass fabric/phenolic laminate composites sliding against stainless steel under water lubrication have been investigated. Results showed that the incorporation of UHMWPE microparticles, especially at the mass fraction of 5.0 %, improved the wear resistance of the laminate composite to a significant extent, because UHMWPE microparticle can effectively absorb and dissipate the friction energy through a plastic deformation during the formation of the regular ripple-like abrasion patterns on its worn surface. During the sliding process, after the phenolic resin was firstly worn off, UHMWPE microparticles with much better wear resistance were protruded from the worn surface of the laminate composite, leading to a fundamental change in the contact status of the matched surfaces from rigid resin and fibers/steel to flexible UHMWPE/steel. As a result, low and steady friction coefficient was obtained due to good adaptability of UHMWPE to water lubrication.     

Effect of Blowing Air and Floating Sand-dust Particles on the Friction and Wear Behavior of PTFE, UHMWPE and PI

The friction and wear behaviors of polytetrafluoroethylene (PTFE), ultra-high molecular weight polyethylene (UHMWPE), and polyimide (PI) have been comparatively evaluated under dry sliding, blowing air, and simulated sand-dust conditions. The tribological tests were conducted on an improved block-on-ring test rig equipped with an attachment for simulating the sand-dust environment. The reason for the difference in the tribological behavior of these polymers under the three test conditions was also comparatively discussed, based on scanning electron microscopic examination of the worn polymer specimens and counterfaces. Under blowing air conditions, the decrease of the contact temperature produced by blowing air led to the increase in the shearing strength of the sliding surface when compared with dry sliding conditions and hence to cause an increase in the friction coefficient and a remarkable decrease in the wear rate of PTFE and UHMWPE. On the contrary, blowing air produced a decrease in the friction coefficient of PI because of the formation of transfer film on the counterfaces, and an increase in the wear rate, because the blowing air considerably promoted the transfer of PI onto the counterfaces when compared with dry sliding conditions. Both PTFE and UHMWPE registered the lowest wear rate under sand-dust conditions, owing to the tribolayer formation on the worn surfaces, while PI exhibited the highest wear rate because no tribolayer was formed during the abrasive wear process.     

UHMWPE与橡胶共混水润滑轴承摩擦磨损性能试验研究

为改善丁腈橡胶水润滑轴承的摩擦学性能，以丁腈橡胶为基体，通过添加不同量的超高分子量聚乙烯（UHMWPE）粉末（分别为丁腈橡胶量的12%、50%、100%）制得3种复合材料；分析不同复合材料的结构，研究其在水润滑条件下的摩擦磨损特性，并与纯丁腈橡胶和纯UHMWPE材料进行对比。结果表明：制备的UHMWPE与丁腈橡胶复合材料中，UHMWPE以分散相的形式分布在丁腈橡胶基体中，分布较为均匀；UHMWPE的加入提高了丁腈橡胶材料的自润滑性能，其中UHMWPE的添加量为丁腈橡胶的50%和100%时复合材料在低速时的摩擦因数明显减小；UHMWPE的加入提高了丁腈橡胶基体的硬度，改善了复合材料摩擦表面的挤压变形，使得复合材料的磨损量有所降低。研究表明，一定添加量的UHMWPE添加量可明显改善丁腈橡胶水润滑轴承的摩擦学性能，其最佳添加量为丁腈橡胶的50%。     

Comparison of the effects of surface texture on the surfaces of steel and UHMWPE

Surface texture has been well studied for metals and ceramics. For the tribo-pair consisted of soft and stiff materials, in order to find out which side is better for texturing, friction tests between steel and UHMWPE were performed to evaluate the effect of dimple patterns at different load–speed conditions.At a light load of 100 N, surface texture on either steel or UHMWPE can reduce friction, but their optimum area densities are different. However, at a heavy load of 700 N, only the pattern textured on UHMWPE can effectively reduce friction. Test results are further analyzed in terms of contact stress.     

Comparative study of micro- and nano-ZnO reinforced UHMWPE composites under dry sliding wear

This is a comparative study between ultra-high molecular weight polyethylene (UHMWPE) reinforced with micro-zinc oxide (ZnO) and nano-ZnO under different filler loads. These composites were subjected to dry sliding wear test under abrasive conditions. The micro- and nano-ZnO/UHMWPE composites were prepared by using a hot compression mould. The wear and friction behaviours were monitored using a pin-on-disc (POD) test rig. The pin-shaped samples were slid against 400 grit SiC abrasive papers, which were pasted, on the stainless steel disc under dry sliding conditions. The worn surfaces and transfer film formed were observed under the scanning electron microscope (SEM). Experimental results showed that UHMWPE reinforced with micro- and nano-ZnO would improve the wear behaviour. The average coefficient of friction (COF) for both micro- and nano-ZnO/UHMWPE composites were comparable to pure UHMWPE. The weight loss due to wear for nano-ZnO/UHMWPE composites are lower compared to micro-ZnO/UHMWPE and pure UHMWPE. The optimum filler loading of nano-ZnO/UHMWPE composites is found to be at 10 wt%. The worn surface of ZnO/UHMWPE composites shows the wear mechanisms of abrasive and adhesive wear. Upon reinforcement with micro- and nano-ZnO, the abrasive and adhesive wear of worn surfaces transited from rough to smooth.     

Tribological Behavior of UHMWPE Reinforced with Graphene Oxide Nanosheets

In this article, a series of graphene oxide (GO)/ultrahigh molecular weight polyethylene (UHMWPE) composites are successfully fabricated through an optimized toluene-assisted mixing followed by hot-pressing. The mechanical and tribological properties of pure UHMWPE and the GO/UHMWPE composites are investigated using a micro-hardness tester and a high speed reciprocating friction testing machine. Also, the wear surfaces of GO/UHMWPE composites are observed by a scanning electron microscope (SEM), to analyze the tribological behavior of the GO/UHMWPE composites. The results show that, when the content of GO nanosheets is up to 1.0 wt%, both the hardness and wear resistance of the composites are improved significantly, while the friction coefficient increases lightly. After adding GO, the tribological behavior of the GO/UHMWPE composites transforms from fatigue wear to abrasive wear associated with the generation of a transfer layer on the contact surface, which efficiently reduced the wear rate of the GO/UHMWPE composites.     

Tribological Performance of UHMWPE and PFPE Coated Films on Aluminium Surface

A thin layer of Ultra High Molecular Weight Polyethylene (UHMWPE) or UHMWPE + PFPE is coated onto cylindrical aluminium (Al) pin (4.6 mm diametre) surface with the aim of providing wear resistant coating on this soft and tribologically poor metal. The coefficient of friction and wear life of the coated samples are investigated on a pin-on-disk tribometre under different normal loads (394–622 g) and two sliding speeds (0.1 and 0.31 m/s) against uncoated Al disk as the counterface. Both coatings provide coefficient of friction values in the range of 0.02–0.2 as compared to 0.4–1.0 for uncoated Al. There is tremendous improvement in the wear life of the pin, with UHMWPE + PFPE film giving wear life approximately twice to thrice higher than that with only UHMWPE film. A thin polymer film is transferred to the disk surface during sliding providing very long-term wear life (continuous low coefficient of friction) despite visual removal of the film from the pin surface. The present films will have applications in gears and bearings as solid or boundary lubricants for automotive and aerospace component.     

Pattern abrasion of ultra-high molecular weight polyethylene: Microstructure reconstruction of worn surface

The friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against bearing steel (AISI 52100) in a ring-on-block contact mode under the lubrication of aqueous solution of 3.5% NaCl was evaluated. The worn polymer surfaces were analyzed by means of three dimensional profiling, atomic force microscopy, Polarized Raman microanalysis, field emission scanning electron microscopy, and nanoindentation testing. It was found that unusual wavelike abrasion patterns were formed on the worn surface of UHMWPE under properly selected sliding conditions. In the presence of plowing effect, the molecular chains of UHMWPE and short-rod like microcrystalline grains of abrasion pattern were both further oriented along the plowing direction and became tiny and dense owing to microstructure reconstruction. Resultant microstructurally reconstructed worn surface of UHMWPE had a higher nanoindentation hardness and modulus as well as increased wear resistance.     

Friction and Wear Behavior of Ultra-High Molecular Weight Polyethylene Sliding Against GCr15 Steel and Electroless Ni–P Alloy Coating Under the Lubrication of Seawater

The friction and wear behavior of ultra-high molecular weight polyethylene (UHMWPE) sliding against GCr15 steel and electroless Ni-P alloy coating under the lubrication of seawater was investigated and compared with that under dry sliding and lubrication of pure water and 3.5 wt.% NaCl solution, respectively. It was found that under the lubrication of aqueous medium, the friction and wear behavior of UHMWPE mainly depended on the corrosion of counterface and the lubricating effect of the medium. Because of serious corrosion of counterface by the medium, the wear rates of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution were much larger than that under other conditions, and such a kind of wear closely related to the corrosion of counterface can be reckoned as indirect corrosive wear. However, when sliding against corrosion-resistant Ni–P alloy under the lubrication of seawater, the lowest coefficient of friction and wear rate of UHMWPE were obtained, owing to superior lubricating effect of seawater. Moreover, periodic ripple patterns were observed on the worn surfaces of UHMWPE sliding against GCr15 under the lubrication of seawater and NaCl solution, which were ascribed to the intelligent reconstruction of surface microstructure of UHMWPE upon large plowing effect of the counterface asperities. Based on scanning electron microscopic (SEM) and three-dimensional (3D) profile analyses of the worn surfaces of UHMWPE, a stick–slip dynamic mechanism was proposed to illustrate the pattern abrasion of UHMWPE. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Effect of aerosil organophilization on tribological properties of low-filled UHMWPE composites

The effect of aerosil on the formation of structure and surface layers of ultrahigh-molecular-weight polyethylene (UHMWPE) and its low-filled composites is studied during friction. Surface modification of aerosil by vinyl triethoxysilane is found to result in elevated crystallinity degree and hardness of the filled polymeric system, and hardening of the composite surface layer under friction. This can be, evidently, attributed to friction-induced grafting of binder macromolecules to the organophilicized aerosil surface. Strengthening of the matrix bonding with the filler is accompanied by worsening of lubricity, growth of wear resistance, and increasing contribution of the adhesive mechanism instead of the abrasive one to the wear of low-filled UHMWPE composites.     

超高分子量聚乙烯/纳米Al2O3复合材料的磨损表面特征分析

用热压成型法制备了纳米氧化铝填充超高分子量聚乙烯(UHMWPE)复合材料,采用销盘式摩擦磨损试验机考察了纳米粒子对复合材料摩擦磨损性能的影响;采用扫描电子显微镜观察了复合材料磨损表面形貌,并借助X射线能谱仪对试样磨损表面进行了微区分析。结果表明:UHMWPE/nano-A l2O3复合材料中的纳米A l2O3粒子含量不同,其磨损表面的碳元素含量也发生不同程度的变化。填充质量分数为15%的纳米A l2O3能较好地改善UHMWPE/nano-A l2O3复合材料的摩擦磨损性能,其磨损表面出现了明显的贫A l区和富A l区,且富A l区以“岛”的形式分布在贫A l区中。     

Fabrication and Wear Test of a Continuous Fiber/Particulate Composite Total Surface Hip Replacement

Continuous fiber woven E-glass/epoxy composite femoral shells having the same elastic properties as bone have been fabricated. These shells were coated with filled epoxy wear-resistant coatings consisting of 1 to 64 micron particles of: Al₂O₃, Al₂O₃ + Cu, and 18–8 stainless steel + Al₂O₃ in an epoxy matrix. The resulting femoral shells were wear tested dry against ultrahigh-molecular-weight polyethylene (UHMWPE) acetabular cups for up to 250 000 cycles on a total hip simulator. The best femoral shell tested was the one containing particles of 18–8 stainless steel + Al₂O₃ in an epoxy base. Articulation of this shell dry against UHMWPE for 250 000 cycles resulted in a friction force that was about 10 percent lower than that of the current total hip prosthesis; that is, a vitallium ball articulating dry with an UHMWPE cup. An UHMWPE acetabular cup when articulating with a vitallium ball showed a weight loss of 0.0004 gram, while an UHMWPE cup when articulating with the 18–8 stainless steel + Al₂O₃ epoxy shell in the 250 000 cycle wear test showed a 0.0058 gram weight loss. Addition of graphite fibers to the UHMWPE acetabular cup and articulation with the 18–8 stainless steel + Al₂O₃ epoxy shell increased the friction force but reduced the surface damage to the UHMWPE. When femoral shells containing Al₂O₃ + Cu particles in an expoxy matrix were run dry against UHMWPE for 42 000 cycles, the friction force was continually increasing and there was evidence of more surface damage to the UHMWPE cup than when the shell contained particles of 18–8 stainless steel + Al₂O₃.     

Friction and sliding wear of UHMWPE modified cotton fibre reinforced polyester composites

Ultrahigh molecular weight polyethylene (UHMWPE) modified polyester-cotton composites were developed and studied for friction and sliding wear behaviour at different applied loads and UHMWPE concentrations. Sliding wear tests were conducted by using pin-on-disc apparatus. Composites in the form of the pin were tested against EN-24 steel disc. The specific wear rate of polyester reduced on reinforcement of cotton and on addition of UHMWPE. The coefficient of friction of polyester resin increased on cotton reinforcement and reduced significantly on addition of UHMWPE in cotton polyester composite. The composites exhibited reductions in specific wear rate against the normal load in the specimens those containing 7.41 or higher volume percent of UHMWPE. The significant reduction in wear rate of UHMWPE modified polyester-cotton composite has been discussed with the help of SEM observations of worn surfaces and coefficient of friction. The addition of 14.19 vol.% UHMWPE in polyester resin brought down the value of μ to nearly half to that of polyester resin and 1/3rd of cotton polyester composite.     

A study of the nanotribological fatigue of ultra-high molecular weight polyethylene

Ultra-high molecular weight polyethylene (UHMWPE) provides a low friction, high toughness interface in artificial knees and hips. Micron-sized wear debris forms over time in these transplants leading to osteolysis and poor clinical outcomes. Using the atomic force microscope (AFM) as a model single asperity contact, tribological studies were performed on nanometer smooth samples of UHMWPE under dry conditions to elucidate the mechanisms of debris formation. Low loads produced no changes in friction or topography despite repeated scanning. Above a critical load, polymer accumulated at the perimeter of the scan and led to the formation of a wear debris particle. Plastically deformed material exhibited a surprisingly high friction compared to surrounding pristine areas, and may partially explain macroscale observations of adhesive wear. In contrast, the polymer in the interior of the scanned area exhibited a friction identical to pristine polymer. These data link strain-softening and delamination of the surface to the formation of wear debris.     

Optimization on wear performance of UHMWPE composites using response surface methodology

This study examined the wear characteristics of ultra-high molecular weight polyethylene (UHMWPE) reinforced with talc particles. Analysis of variance (ANOVA) was used to construct empirical models to show the connection between control factors (filler loading, load and sliding speed) and responses (wear rate and average coefficient of friction (COF)) of UHMWPE. Response Surface Methodology (RSM) was employed to project the optimization of the control variables in order to reduce the wear of UHMWPE. It was discovered that the rate of wear and the average COF of UHMWPE could be minimized by the inclusion of talc. The SEM analyses of the worn surfaces and transfer films indicated that the degree of wear on the surface of the UHMWPE was reduced.     

Tribological and nanoscale research on model friction couples intended for hip joint prostheses

Abstract

The paper presents the results of tribological and nanoscale research on model friction couples intended for hip joint prostheses. The tribological tests were performed by means of reciprocating pin on plate testing machine. The investigated friction pairs contained plates rubbing against polymer pins. The test plates were made from seven kinds of ceramics containing different concentrations of ZrO₂ and Al₂O₃, and two kinds of Co–Cr alloy. The test pins were made from UHMWPE. Tribological tests were performed in conditions of Ringer solution circulation. On the basis of friction force measurements, for each investigated friction couple, the average coefficient of friction was calculated. On the basis of total wear measurements, for each investigated couple, the wear intensity was calculated. Before and after every test, the plates and pins were analysed by means of atomic force microscopy. The difference in plate surface roughness was determined by the results of the atomic force microscopy analyses.

It was stated, that in the case of investigated friction joints, working under reciprocating motion, the wear and friction coefficient correlates with the surface roughness of plate specimens. For the plates with higher surface roughness, the lower friction coefficient and also lower UHMWPE pin wear intensity were observed. The friction coefficient and wear intensity were increasing with decreasing surface roughness. The correlation is confirmed by the differences in material transfer process. Considering investigated friction couples, the pin polymer material is smeared on the ceramic plates with the highest surface roughness creating a thin polymer film. In the case of ceramic surfaces with the lowest surface roughness, the strong adhesive bounds are created and some large particles of polymer are transferred to ceramic surface.