MoSi_(2)对CoCrNiW合金干摩擦磨损性能的影响研究

Effects of MoSi_(2)on Friction and Wear Properties of CoCrNiW Alloy under Dry-sliding Condition

目的系统研究MoSi_(2)含量对Co基合金干摩擦磨损性能的影响,以开发摩擦学性能优异的CoCrNiW基复合材料。方法利用热压烧结技术,设计制备CoCrNiW-MoSi_(2)(质量分数分别为0%、3%、7%、11%)抗磨复合材料。采用往复式球–盘摩擦磨损试验机,研究不同载荷和滑动速度对复合材料干摩擦磨损性能的影响,进一步优化MoSi_(2)的含量。采用XRD、SEM、EDS等技术分析材料的物相组成、微观结构及磨损形貌。结果MoSi_(2)的添加有效提高了材料的硬度及致密度,MoSi_(2)质量分数为7%的试样,硬度为386HV。复合材料的物相包括γ–fcc、ε-hcp、MoSi_(2)、CrSi_(2)、Mo_(1.24)Ni_(0.76)、MoSi_(2.43)W_(0.211)相。摩擦系数随载荷和滑动速度的增加而减小,磨损率随载荷的增加而增大,随滑动速度的增加而减小。硅化物硬质颗粒起到了弥散强化作用,提高了磨损表面的承载能力。其中,添加7%和11%MoSi_(2)的试样,磨损率较低且接近,高载和高速下,磨损率较未添加试样分别下降约31.3%和25.5%。适当含量的MoSi_(2)具有一定的减摩性,添加7%MoSi_(2)的试样,摩擦系数始终最低,变化范围为0.24~0.53。结论CoCrNiW-7wt.%MoSi_(2)表现出了最佳的摩擦学性能,其磨损机理在高载条件下主要为磨粒磨损,在高速条件下主要为磨粒磨损和轻微氧化磨损。

The work aims to design the wear resistant CoCrNiW matrix composites,and the effect of MoSi_(2)on the friction and wear properties of CoCrNiW alloys under dry-sliding condition,to develop CoCrNiW-based composites of excellent tribology performance.The wear resistant CoCrNiW-MoSi_(2)(0 wt.%,3 wt.%,7 wt.%,11 wt.%)composites were fabricated with the powder metallurgy technology.The effects of load and sliding speed on the tribological properties of composites were studied under dry-sliding condition with a reciprocating ball-on-disk tribo-tester,and the MoSi_(2)content was further optimized.The phase composition,microstructure and wear morphology of materials were analyzed by XRD,SEM and EDS.During the sintering process,the high-temperature solid solution reaction occurred at the interface of MoSi_(2)and metal matrix.The composites consisted ofγ-fcc,ε-hcp,MoSi_(2),CrSi_(2),Mo_(1.24)Ni_(0.76)and MoSi_(2.43)W_(0.211)phases.The microstructure of composite was dense,and no hole was noted on the surfaces.The addition of MoSi_(2)effectively improved the hardness and compactness of materials as well as the stability ofγ-fcc phase.The friction coefficients decreased with the increase of load.This was caused by the fact that the increasing rate of load was faster than that of the actual contacting area of the tribo-pairs.The friction coefficients of composites with sliding speed showed the similar trend,resulting from the decrease in hardness of worn surfaces due to the friction heat.The reasonable MoSi_(2)content played an important part in decreasing the friction coefficient of composites.The sample with 7wt.%MoSi_(2)had the lowest friction coefficients as compared with other samples.The friction coefficients of CoCrNiW-7wt.%MoSi_(2)were in the range of 0.24-0.53,which were significantly lower than those of unreinforced sample.The effect of sliding speed and load on the wear rates of composites was different.The wear rates increased with the increase of load,and decreased with the increase of sliding speed.The hard silicide particles had the dispersion strengthening effect and improved the loading capacity of the worn surface.The samples with 7 wt.%and 11 wt.%MoSi_(2)had the low wear rates,and the wear rate was 31.3%lower than that of unreinforced composites at 20 N and 0.15 m/s.Meanwhile,the wear rate was 25.5%lower than that of the sample without MoSi_(2)at 40 N and 0.083 m/s.CoCrNiW-7 wt.%MoSi_(2)showed the best tribological properties,and the wear rates were in the range of 4.98×10–6-9.41×10–6mm^(3).N–1.m–1.It was attributed to the high loading capacity and the tribo-layer containing oxides on the worn surface.For the sample containing 7 wt.%MoSi_(2),the oxides content on the worn surface was high at high sliding speed.The tribo-layers formed by the oxides prevented the contacting surface from wear.In addition,it was observed that the size of wear debris decreased when the load increased from 20 N to 40 N.At 20 N and 0.15 m/s,an incomplete transferred layer was noted on the worn surface of steel ball which could reduce the direct contacting area of tribo-pairs during the friction process.CoCrNiW-7 wt.%MoSi_(2)show the best tribological properties.The main wear mechanism is abrasive wear at high load.The abrasive wear and slight oxidative wear are the main wear mechanism at high sliding speed.