Effect of ball-milling process in combination with the addition of carbide microparticles on the microstructure and wear resistance of a Co–Cr–W alloy prepared by powder metallurgy method

Abstract

Co–Cr–W alloys were widely used in the inlet exhaust valve of aeroengine. However, the traditional manufacturing process of Co–Cr–W alloys can not meet the demand for higher comprehensive performance, and an optimum method needs to be developed. Herein, a Co–Cr–W alloy reinforced by exogenous carbides was prepared by the powder metallurgy method. Effect of ball-milling time on the microstructure and wear resistance of the alloy was investigated, and the formation mechanisms of the reinforcing phases were discussed. Results showed that with prolonging the ball-milling time, the uniformity of the reinforcing phases was improved, grain refinement was achieved, the hardness increased, a suitable bonding interface was formed between the matrix and reinforcing phases, and better wear resistance was thus achieved. However, when the ball-milling time increased from 60 h to 70 h, local segregation of the reinforcing phases occurred, the hardness decreased from 64 HRC to 60 HRC, and the friction coefficient increased from 0.53 to 0.58. Based on our experimental results, we proposed two formation mechanisms of the reinforcing phases (carbides): In-situ precipitation from the matrix and in situ autogenic reaction between the elements of the matrix and the added carbides (WC and Cr _3 C _2 particles). Both mechanisms contributed to the formation of M _23 C _6 and M _6 C carbides. Our results underscore the importance of added reinforcing phases and help to optimize the ball-milling process in preparing the Co–Cr–W alloys.

Keywords

• Co–Cr–W alloy
• carbides
• powder metallurgy
• microstructure
• wear resistance