Effect of annealing treatment on microstructure evolution and creep behavior of a multiphase Ni3Al-based superalloy

The microstructure evolution and creep behavior of a novelly designed as-cast Ni3Al-based superalloy with multiphase configuration are investigated by high-temperature annealing treatments. The as-cast microstructure comprises dominant gamma'+gamma dendritic and less (similar to 19.37 vol%) interdendritic beta areas, annealing treatments at 1160-1280 degrees C promoted the growth of gamma(1)(I) phase in the gamma'+gamma dendrite, during which the interdendritic beta phase aggregated and coarsened rapidly in width with keeping its relatively constant volume fraction. Meanwhile, the annealing treatments significantly promoted the precipitation of quasi-spherical alpha-Cr phase particles within the beta phase. The original as-cast microstructure exhibited inferior creep resistance at 800 degrees C/200 MPa with the shortest creep rupture life of 194 h, however, the annealing treatments at 1160-1280 degrees C prolonged the creep rupture life to beyond 611 h. Although the steady-state creep rate was gradually reduced with increasing annealing temperatures, the creep ductility was degraded by higher-temperature annealing at 1240 and 1280 degrees C compared with original as-cast microstructure. The 1160 degrees C annealed microstructure exhibited the longest creep rupture life of 665 h and the maximum creep strain to fracture of 3.21%, while the minimum steady-state creep rate was obtained on account of the largest gamma(1)(I) phase sized 0.91 mu m after annealing at 1280 degrees C. Despite its positive role in the castability, thermoplasticity and weldability of the explored multiphase Ni3Al-based superalloy, interdendritic beta phase has negative effects on the creep properties due to its incoherent existence with the dominant gamma'+gamma dendrite.