Effect of Heat Treatment Schedules on Creep Performance of Ni-Based Superalloy Mar-M247 at 871 C and 250 Mpa

The effects of heat treatment (H1 and H2) on the creep behavior and microstructures of Mar-M247 at 871 & DEG;C/250 MPa are studied. The results show that the as-cast microstructure is composed of eutectics, & gamma; phase, & gamma;' phase, MC and M23C6 carbides, while new M6C appears in heat-treated microstructures, indicating the transformation of carbides after heat treatments. The Mar-M247 is excellent, with over 1500 h of creep life, and H1 is 48% higher than H2. The addition of post-brazing and diffusion heat treatment in H2 is detrimental to creep resistance; the two steps promoted the transformation of MC into M23C6 in advance. The increase and coarsening of M23C6 would consume more & gamma;-phase-forming elements, weakening the solution strengthening at grain boundaries. As a result, the resistance of the grain boundary and & gamma;/& gamma;' interface to dislocation motion is significantly reduced, leading to the cracks' initiation and propagation along the grain boundaries.