Effect of heat treatment on microstructural evolution and creep behaviors of a conventionally cast nickel-based superalloy

The evolution of microstructures caused by heat treatment on Ni-based superalloy CM 247 LC was examined, and the creep behaviors were analyzed at various temperature and stress conditions. Secondary gamma' hardly precipitated in aged specimens subjected to solution treatment, but secondary gamma' precipitated in specimen subjected to two-step aging at 1080 degrees C and 871 degrees C without solution treatment, because the size and volume fraction of precipitated gamma' particles and the width of the gamma' channel depend on the heat-treatment path. The creep properties of the specimen subjected to two-step aging without solution heat treatment under low temperature and high stress was the best, owing to the uniform deformation and damage-relieving effect of the fine secondary gamma' particles in the. channel and the eutectic gamma/gamma' phase. At and above 871 degrees C, the effect of gamma' rafting on the creep properties was very important, and the creep lifetimes of the solution-treated specimens with better rafting were longer than those of the aged specimens.