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

The effect of various alloy preheatings followed by full solid solution tre atments on the resultant strength and ductility of as-cast Co-Cr-Mo-C alloy s was investigated. Three preheating temperatures were evaluated: 815 degre es C, 950 degrees C, and 1100 degrees C for 4 hours and then solid solution treated at 1225 degrees 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 ove r the as-cast condition. In particular, optimum ductility of the heat-treat ed alloys and alloy strength were promoted by preheating at 815 degrees 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 ass ociated with the development of numerous plastic bands combined with band i nterlockings. Alloy preheats at 950 degrees C and 1100 degrees C prior to s olutionizing lead to inferior strength and ductility. Although preheating a t 1100 degrees C led to slight improvements, in both cases, the fracture pa th was dominated by the presence of continuous carbide films surrounding th e dendritic grains. Hence, less than optimum combinations of strength and d uctility were achieved by the heat treatments at the higher temperatures.