纳米SiC增强CoCrMo高温抗磨复合材料及摩擦学性能

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

采用粉末冶金技术制备了纳米SiC陶瓷颗粒(0.0%、1.0%、2.2%和3.4%,质量分数,后面未作特殊说明,均为质量分数)强化的CoCrMo基高温抗磨复合材料,对复合材料的相组成及高温摩擦学性能进行了系统性研究.在室温至1000℃范围内利用球-盘式高温摩擦试验机测试了材料的高温摩擦学性能.结果表明:复合材料的基体主要由γ(fcc)和ε(hcp)合金相构成,加入纳米SiC后复合材料出现了MoCr相,这有利于复合材料硬度的提高;纳米SiC提高了复合材料的硬度,同时降低了复合材料的密度;摩擦系数与纳米SiC的含量和温度相关,摩擦系数随纳米SiC含量的增加而增大,室温至800℃的摩擦系数整体呈下降趋势,1000℃时含2.2%和3.4%SiC的复合材料具有较低的摩擦系数;高温环境下复合材料的抗磨损性能随纳米SiC含量的增加而显著提高;复合材料的磨损机理在不同温度下存在差异,随着温度升高,磨损机理逐渐由磨粒磨损和塑性变形转变为氧化磨损.室温至1000℃范围内CoCrMo-2.2%SiC具有较优异的高温抗磨损性能,这主要归因于复合材料的高硬度和磨损表面完整的氧化物润滑层.

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 1000℃.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)andε(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 1000℃,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 1000℃,the oxide 2lubricating film was more intact on the worn surfaces than that at RT and 600℃.The oxide lubricating film was composed of FeCr_(2)O_(4),Co_(2)CrO_(4),FeMoO_(4),MoO_(3) and Co_(3)O_(4),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 1000℃.Generally speaking,the CoCrMo-2.2% nano-SiC had an excellent high-temperature wear resistance from room temperature to 1000℃,which was attributed to the high hardness and the intact oxide lubricating film on the worn surfaces.