Study On Wear Resistant System And Tribological Properties Of Cobalt Matrix High-temperature Self-lubricating Composites

The wear and lubrication of bearings,gears,blades and other wearable transmission parts of equipment working under harsh conditions such as high temperature and high load are directly related to the stability and safety during operation.Compared with other superalloys,Co-based superalloys have more favorable high temperature strength,oxidation resistance and corrosion resistance.The design of a self-lubricating composite material based on cobalt alloy with excellent wear resistance within a wide temperature range is of profound significance to solving the problem of the wear of high-temperature components.The choice of lubrication phase and wear resistance phase is an important factor affecting the high temperature wear resistance of composites.In this paper,a series of cobalt-based high temperature self-lubricating composites were prepared by high temperature hot pressing sintering technology.The impact of lubrication components and anti-wear components on the tribological properties of cobalt-based composites at high temperature was studied,and a prediction model of the friction coefficient of cobalt-based composites was established.CoCrNi based high temperature wear resistant composites reinforced by nano-sized and micron-sized Al₂O₃ ceramic particles were prepared respectively.The high temperature wear resistance mechanism of ceramic particles within the range of room temperature to1000℃was systematically studied.It was found that the addition of Al₂O₃ increased the friction coefficient and reduced the wear rate of CoCrTi matrix composites withina wide temperature range.Specially,when the temperature was higher than 600℃,the wear rate decreased significantly.Within a wide temperature range,nano-Al₂O₃composites showed the best wear resistance.The wear rate was in the range of 0.84-4.62×10^-5mm³/N·m,and the wear rate was 0.5-5 times lower than that of the composites without and with micro-Al₂O_3.This was attributed to the high hardness of the composites and the oxide lubrication film generated on the wear surface.CoCrTi-WS₂ high temperature self-lubricating composites were prepared by hot pressing sintering at high temperature.The tribological properties of CoCrTi-WS₂ high temperature self-lubricating composites were investigated under different temperatures,different loads and different sliding speeds.It was found that the addition of WS₂ improved the hardness and tribological properties of the materials.Within a wide temperature range,the friction coefficient of the composites decreased first and then stayed stable,in the range of 0.409-0.559.The wear rate increased first and then decreased,and the lowest wear rate at1000℃was around 0.9×10^-6mm³/N·m.Under different loads and sliding velocities,at the temperature of 400℃,the friction coefficient reached its minimum at the load of 15N and sliding velocity of 0.3m/s,and its value was in the range of 0.418-0.443 and 0.387-0.416respectively.The wear rate increased as the velocity and load increased.At 600℃,the friction coefficient increased first and then decreased.The wear increased first and then tends to be stable,within the range of 0.91-3.148×10^-5mm³/N·m.WS₂ and CuO were selected as the composite lubrication phases of CoCrTi matrix composites.The tribological properties of the composites were studied within a wide temperature range,from room temperature to 1000℃.The results show that the addition of WS₂ and CuO significantly improved the hardness and tribological properties of the materials within a wide temperature range.The friction coefficient first increased and then decreased as the temperature increased.The composites with 9wt%WS₂ and 3wt%CuO have the best tribological properties.Especially at 1000℃,the friction coefficient and wear rate of the material were the lowest,which are 0.38 and 0.119×10^-6 mm³/N·m respectively.WS₂ can be lubricated within a range of temperature,from 20℃to 400℃,and the addition of CuO enabled the material to demonstrate favorable tribological properties at high temperatures,from 600℃to 1000℃.Due to the synergistic lubrication mechanism between WS₂ and CuO,Cobalt-based self-lubricating composites demonstrated excellent tribological properties within a wide temperature range.The friction coefficient prediction model of cobalt matrix composites was established using multiple linear regression equation and least square method.The results show that the model is accurate and the curves are in agreement with each other.