Effect of Aging Time on Phase Transformation, Microstructure And Hardness of Co-Cr-Mo Alloys

Abstract

The effect of heat-treatment on phase relationships, microstructures and hardness of CoCr-Mo alloys were investigated in detail. The samples were produced by investment casting techniqueand subsequently solutionized (1240 °C for 4 h) and aged (720 °C for 2, 4, 8 and 16 h). Phase analysis ofthe samples were performed via X-ray diffraction analysis, microstructural examination were done bylight optical and scanning electron microscopy. The microstructures of as-cast and short-time (2 and 4 h)aged samples were composed of FCC ?-Co matrix phase and fine M23C6 (where M= Co, Cr and Mo)precipitates. Increasing the aging time to 8 and 16 h led to partial transformation of FCC ?-Co matrixphase into HCP ?-Co phase. The volume fraction of ?-Co phase increased with increasing aging time.Moreover, hardness of the Co-Cr-Mo samples were significantly enhanced with formation of ?-Co phase.