Effect of alloy preheating on the mechanical properties of as-cast Co-Cr-Mo-C alloys

Abstract

The effect of various alloy preheatings followed by full solid solution treatments on the resultant strength and ductility of as-cast Co-Cr-Mo-C alloys was investigated. Three preheating temperatures were evaluated: 815 °C, 950 °C, and 1100 °C for 4 hours and then solid solution treated at 1225 °C for 4 hours. Tensile and compressive tests were carried out on the heat-treated alloys. It was found that the strength and ductility of the heat-treated alloys exhibited significant improvements over the as-cast condition. In particular, optimum ductility of the heat-treated alloys and alloy strength were promoted by preheating at 815 °C. A relatively fine grained structure coupled with a uniform distribution of second-phase particles promoted homogeneous plastic deformation in the bulk. Fractographic observations indicated that the exhibited ductility was associated with the development of numerous plastic bands combined with band interlockings. Alloy preheats at 950 °C and 1100 °C prior to solutionizing lead to inferior strength and ductility. Although preheating at 1100 °C led to slight improvements, in both cases, the fracture path was dominated by the presence of continuous carbide films surrounding the dendritic grains. Hence, less than optimum combinations of strength and ductility were achieved by the heat treatments at the higher temperatures.