This article aims to investigate the influence of reinforcing graphene oxide (GO) and graphite flakes (GF) fillers into ultrahigh molecular weight polyethylene (UHMWPE) for orthopedic application. These fillers were expected to physically bond to UHMWPE, thus can enhance the subsurface strength, improving the wear behavior of the composites. UHMWPE/GO and UHMWPE/GF composites were prepared at 0.1 and 1.0 wt% by melt‐blending, followed by a compression molding technique. A multidirectional pin‐on‐disc wear test was performed to simulate the kinematic of hip application. Whilst getting exposed in the artificial in‐vivo lubricant bath (30 v/v% diluted bovine serum). Following this, the wear mechanism fostered by each filler (GO and GF) was determined by wear features obtained from the optical microscope and scanning electron microscope (SEM). The crystallinity degree and crystal defect were assessed using x‐ray diffraction (XRD). The mechanical properties of fabricated composites were evaluated by using a universal testing machine and Vickers microhardness. We found that UHMWPE/GO has the lowest specific wear rate due to the improved subsurface strength, as the reduction of a weak adhesive point was observed on the worn surface. Meanwhile, higher GF content (1 wt%) in UHMWPE displayed a lower specific wear rate than neat UHMWPE after completing the 10 km sliding distance attributed to the filler resurfaced, responsible for providing a strong resistance of the shear stress applied upon sliding with the metal counterface. Interestingly, the hardness and tensile strength for both UHMWPE/GO and UHMWPE/GF increased, although the crystallinity percentage was declining compared to neat UHMWPE.

The authors have clarified that trace impurities such as water and oxygen inevitably contained in a hydrogen environment influence friction and wear of metallic materials substantially and even often govern them. In this study, an experimental technique was devised to enable sliding tests in a hydrogen environment which contains controlled concentration of water and virtually no oxygen as impurities. By comparing data of Fe sliding tests between this study and our previous studies, the influences of water and oxygen were understood separately. Water without oxygen as impurity in a hydrogen environment decreased wear of pure Fe while oxygen in additional to water increased the wear. Sliding of pure Fe consumed water when a hydrogen environment contained only water while it produced water and consumed oxygen when the environment contained both water and oxygen. The number of water molecules consumed by sliding in a hydrogen environment with water more than 5,000 ppb and without oxygen was larger than the estimated number of nascent Fe atoms by sliding. This suggests that multi-layer adsorption of water molecules decreased the wear of pure Fe.

The influence of trace water and oxygen in a hydrogen environment on the sliding behavior of pure iron was studied using a newly developed pin-on-disk apparatus in a vacuum chamber equipped with an advanced gas replacement system. The hydrogen environment in the siding tests contained 0.5 to 95 ppm water and 0.07 to 2 ppm oxygen; a turbo-molecular pump was used for evacuation and a chemical filter for reducing water and oxygen in the hydrogen gas supplied to the chamber. The concentrations of water and oxygen in the hydrogen overflow from the chamber were determined using moisture and oxygen sensors, respectively. Other potential contaminant gases were analyzed using a quadrupole mass spectrometer during evacuation and were found to be insignificant. The amount of wear and the appearance of wear debris as well as the sliding surfaces were significantly different for the different concentrations of water and oxygen. The roles of these gasses are discussed.

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