Optimisation of the mechanical properties of a new PM superalloy for disk applications

The roles of the subsolvus solutioning temperature and of the ageing temperature on the microstructure and on tensile and creep properties were evaluated on a new PM superalloy, designated NR3. A single-stage ageing treatment was applied instead of the usual double-stage ageing treatment. The principal objective was to improve the creep resistance of this superalloy while keeping a high tensile strength by using a simplified heat treatment. The solution treatment essentially affected the respective proportions of primary and secondary gamma' precipitates and the grain size. On the other hand, the major influence of the increase of the ageing temperature was to coarsen the tertiary gamma' particles. These microstructural effects were successfully combined to obtained a significant increase of the creep strength associated with a slight rise of the tensile properties.