Microstructure, high temperature mechanical properties and sliding wear behavior of (NiCrW)1-x(Bi2O3)x

Abstract

Composite materials of (NiCrW)_1-x(Bi₂O₃)_x (x = 0, 1, 2.5, 5 wt%) were prepared using powder metallurgy techniques. The study investigated the effects of Bi₂O₃ content on the microstructure, phase composition, high-temperature mechanical properties, and tribological performance over a wide temperature range of the composites. The results indicate that during the hot pressing sintering process, Bi₂O₃ in the composites undergoes a decomposition reaction, leading to the formation of new phases such as NiBi, NiBi₃, and Cr₂O₃, which enhance the high-temperature lubrication and wear resistance of the composites. However, this transformation has a detrimental effect on the mechanical properties of the composites, altering the fracture mechanism from microporous aggregation-type fracture to predominantly cleavage and intergranular fractures. Thanks to the formation of lubricating phases like NiBi, the addition of 1 wt% Bi₂O₃ effectively reduces the wear rate of the composites at room temperature. At 800 °C, NiBi is reoxidized during the high-temperature friction process, forming a friction layer composed of Bi₂O₃ and NiO on the wear surface of the composites, effectively lowering the friction coefficient at high temperatures.