Effect of thermal exposure on stress rupture properties of a Re bearing Ni base single crystal superalloy

The effect of thermal exposure on microstructure and creep properties of a Re bearing single crystal superalloy is investigated. The alloy is exposed at 950 °C for 100–2000 h. The coarsening behavior of γ′ varies with local position. The γ′ particles in dendrite core and interior secondary arm form raft when aged longer than 100 h. The γ′ in periphery of secondary arm can retain cuboidal morphology aged to 2000 h in addition to normal growth. The γ′ in interdendrite region develops into irregular raft. The various behavior of γ′ is attributed to the segregation of refractory elements. The MC carbide demonstrates high stability even though it begins to decompose to M6C after 500 h exposure. This is explained from its high contents of Ta and Nb. μ phase precipitates in both dendrite core and interdendrite region when aged more than 100 h, but the μ phase in these two areas have different morphologies, which is attributed to their unique nucleation site and orientation relationship with matrix. The creep lives of exposed samples at 1000 °C/280 MPa decrease with increasing of aging time generally, especially, the life of 500 h aged sample drops lower than that of 1000 h aged sample. The degradation of creep life is accounted for based on coarsening of γ′ and deposition of dislocation during thermal exposure.