High-Temperature Wear Resistant CoCrMo Matrix Composites Reinforced by Nano-SiC and Tribological Properties

The high-temperature wear resistant CoCrMo matrix composites reinforced by nano-SiC particle (0.0%, 1.0%, 2.2% and 3.4%, mass fraction) were prepared by using powder metallurgy technology. The phase compositions and high-temperature tribological properties of composites were systematically studied. The tribological properties were determined by using a ball-on-disk high-temperature tribo-tester from room temperature to 1 000 ℃. The results showed that there was no crack in composites, and the microstructure was compacted. The nano-SiC black phase uniformly distributed in matrix. The Cr, Mo and Fe elements diffused into the Co crystal cell because of the solid solution reaction during the sintering process at elevated temperature. The matrix of composites mainly consisted of γ (fcc) and ε (hcp) phases. The MoCr was formed in matrix after adding nano-SiC and some weak SiC peaks were detected according to the XRD, indicating that the nano-SiC did not react with other metal elements. The grain of composites was refined. The nano-SiC dispersively distributed in the matrix and improved the microhardness of composites. Because the density of nano-SiC was lower than that of metal, the density of composites was reduced. The friction coefficient depended on the nano-SiC content and temperature. With the increasing nano-SiC content, more and more hard particles were exposed on the sliding surfaces in order to increase the sliding resistance, resulting in an increase in friction coefficient. The metal elements and wear debris were oxidized during sliding as the testing temperature increased. The formation of the oxide lubricating film played an important part in tribological properties. As a result, the friction coefficient showed an overall downward trend from room temperature to 800 ℃. At 1 000 ℃, the composites containing 2.2 % and 3.4% nano-SiC had low friction coefficients because of their high load bearing capacity. In high-temperature environment, the oxide lubricating film inhibited the further oxidation of composites and segregated the counterpart in order to reduce the wear rate and friction coefficient of composites. The wear resistance of composites at high temperature increased significantly with the increase of nano-SiC content. The composites showed the different wear mechanisms at elevated temperatures. The nano-SiC improved the plastic deformation resistance of reinforced composites, which was ascribed to the high hardness of reinforced composites. Thus, it was concluded that the wear mechanism of composites was abrasive wear and plastic deformation at room temperature. At 600 ℃, the oxide lubricating film, grooves and plastic deformation were observed on the contacting surfaces of composites. The wear mechanism of composites at 600 ℃ were the abrasive wear, mild oxidation wear and plastic deformation. At 1 000 ℃, the oxide 2lubricating film was more intact on the worn surfaces than that at RT and 600 ℃. The oxide lubricating film was composed of FeCr₂O₄, Co₂CrO₄, FeMoO₄, MoO₃ and Co₃O₄, which effectively improved the wear resistance of composites. The oxide lubricating film of composites with 0% and 1% nano-SiC was obviously incomplete. However, the composites containing 2.2% and 3.4% nano-SiC had the high load-bearing capacity for the lubricating film due to the high content of nano-SiC. The wear mechanism of composites was characterized by the oxidation wear at 1 000 ℃. Generally speaking, the CoCrMo-2.2% nano-SiC had an excellent high-temperature wear resistance from room temperature to 1 000 ℃, which was attributed to the high hardness and the intact oxide lubricating film on the worn surfaces.