Effects of Heat Treatment Process on Microstructure and Properties of Vacuum Melting CoCrMoW Alloy

The alloy bar with a mass ratio of w（Co）∶w（Cr）∶w（Mo）∶w（W）∶w（Si）=63.9∶24.7∶5.0∶5.4∶1 was prepared by vacuum melting. The microstructure and mechanical properties of the alloy samples after different solid solution/aging heat treatment were observed and analyzed, and the mechanism of strengthening cobalt-chromium alloy by Mo,W element was analyzed. The results show that, the main phase of vacuum melting CoCrMoW alloy is γ-Co and a small amount of ε-Co. The σ（CrCo）phase, Co₇Mo₆ phase and Co₃W phase rich in Cr are identified between crystals. With the increase of solid solution temperature, the Cr atom in the intergranular phase is dissolved into the γ-Co matrix, and the grain changes from columnar crystal to coarse dendrite. The strengthening of the aging treatment on the alloy depends on the rate of phase formation and the density of lamellar structure, and accelerates the formation of ε phase at high temperature. The formation rate is the fastest under the condition of 850 ℃ for 2 h, and the mechanical properties reach the hardness of 802 HV, the strength is 839.46MPa, and the fracture is the cleavage fracture. Before and after heat treatment, the phase of Co₇Mo₆ and Co₃W changes little,which limit the grain boundary shift and the slip between ε photo layers, so that the strength of CoCrMoW alloy is much higher than those of the same kinds of CoCr alloy.