Tribological Property of FG/UHMWPE Composites

Fluorinated graphene/ultra high molecular weight polyethylene (FG/UHMWPE) composites were prepared by ultrasonic dispersion and hot pressing. The mechanical propertys and tribological property of pure UHMWPE and FG/UHMWPE composites were investigated by micro hardness tester and high-speed reciprocating friction tester. The wear volume of the sample was measured by the scanning electron microscope, and Micro-XAM noncontact 3D surface profiler, and the corresponding volume wear rate was also calculated. The results showed adding FG could obviously improve the microhardness of UHMWPE. Adding FG not only reduced the friction coefficient of UHMWPE, but also significantly reduced the volume wear rate of UHMWPE, and the higher the FG content, the smaller the volume wear rate of FG/UHMWPE composites. The addition of FG can improve the tribological property of UHMWPE. Introduction Ultrahigh molecular weight polyethylene (UHMWPE) has been widely used in artificial joint for its excellent advantages, such as low friction coefficient and good biocompatibility [1-4]. But UHMWPE has the obvious disadvantages of low Young's modulus and poor wear resistance, which limit its wide application. Therefore, many research works have been done to improve the performance of UHMWPE. One method to improve the wear resistance and mechanical property of the UHMWPE is filling inorganic materials. Carbon nanotubes (CNT), hydroxyapatite, zirconia and alumina served as reinforced filler can improve the wear resistance of UHMWPE to some extent. However, CNT and other reinforcing fillers can reduce the mechanical property, such as tensile strength and impact strength[5-6]. In 2004, by using the method of micro mechanical stripping, Geim Andre prepared graphene. Graphene and its derivatives have attracted much attention because of there unique crystal structure, excellent physical and chemical property, and wide application prospect. Fluorinated graphene (FG) not only has the specific characteristics of graphene, such as the physical and chemical properties[7], but also has good dispersion, high mechanical strength and excellent lubrication performance. Therefore, in order to improve the tribological properties of UHMWPE, composite was prepared by ultrasonic dispersion and hot pressing. The results show the FG/UHMWPE composites have better wear resistance compared with FG/UHMWPE. Experiment Materials. M-II type UHMWPE powder (molecular weight, 200 million) was purchased from Shanghai Chemical Research Institute Tiandi Technology Development Co., Ltd.. Graphene oxide was purchased from Nanjing Xian Feng nano material technology Co., Ltd.. Zirconia ball (diameter, 5 mm; rough degree, 0.04 μm) was purchased from Shanghai Xinmao precision ceramic technology Co., Ltd.. Hydrofluoric acid (w=40%), anhydrous ethanol, nitrate, sodium chloride were purchased 5th International Conference on Information Engineering for Mechanics and Materials (ICIMM 2015) © 2015. The authors Published by Atlantis Press 407 from the Sinopharm Chemical Reagent Co., Ltd.. Preparation of FG/UHMWPE Composites. FG with high fluorine content was synthesized according to the literature 1. 50 mg graphene oxide sample was dispersed into 50 ml ultrapure water by ultrasonic for 30 min, then 5 ml hydrofluoric acid (w=40%) and nitrate were added in the former dispersion. Then the mixture was shifted into a 100 ml thermal water kettle with Teflon liner, and the The hydrothermal reaction ws carried out at 180 for 12 h. After the reaction, the reaction liquid under 50 °C to obtain FG sample. A certain amount of FG powder was dispersed into 40 ml ethanol with the aid of ultrasonic for 30 min. 2 g UHMWPE powder was added into the former suspension to get mixed liquid, and the mixed liquid was stirred for 60 min. Then, ethanol in the mixed liquid evaporated to get mixed powder. The mixed powder was treated by thermal forming at 195°C and 10 Mpa to obtian FG/UNMWPE composite sample. By using the method, FG/UNMWPE composite samples with the FG content of 0%, 0.1%, 0.3%, 0.5% and 1% were prepared respectively. Characterization of FG/UHMWPE Composites. Microhardness testing was carried out on a microhardness tester (Shanghai Hengyi Precision Instrument Co., China), with a load of 10 N for 5 s. In order to ensure the accuracy of the experimental results, each FG/UHMWPE composite sample were test averaged ten points. After completion of the experiment using software Origin8.0, calculated on the basis of the test sample μ=F/N and plotted the coefficient of friction (coefficient of friction, COF) and its stable phase COF average. At the same time according to the equation K= V/LS alculate the wear rate (Wear rate, WR). Where μ is the coefficient of friction; F is the frictional force in N; N is the normal load force in N; K is the wear rate in mm3/(Nm); V is the volume of the amount of wear in mm3 / (N•m) : mm3; L is sliding distance in mm; S is the surface of the test the wear scar cross-sectional area in mm2.. Worn surface of FG/UHMWPE Composites is observed by SEM morphology. Results and discussion Fig.1 Variations of friction coefficient of the FG/UHMWPE composites with time Figure 1 shows that the friction coefficient of the friction pair which is composed of the FG/UHMWPE composite material and zirconia is changed over time. It can be seen that the friction coefficient of FG/UHMWPE composites is lower, and the friction coefficient is decreased with the increase of FG content. This is due to the good self lubrication performance of FG.