Effect of heat treatment on microstructure and stress rupture life of Ni-base single crystal superalloy

A Ni-base single crystal superalloy was prepared by screw selecting method. The homogenizing heat treatment carried out in an antivacuum chamber oven, and the effect of heat treatment on the microstructure and stress rupture life at 1100°C was studied. The results show that the as-cast structure of the alloy is composed of γ-Ni solid solution phase, primary and secondary γ-Ni₃Al phase, and γ/γ′ phases. After solid solution treatment under the condition of 1305-1310°C for 16 h, secondary γ′ is solved completely but a small amount of γ/γ′ eutectic remains. While after the solid solution treatment at 1315°C for 16 h, γ/γ′ eutectic is solved completely. A small amount of primary melting appears after the solid solution treatment at 1320°C for 2 h. It is found that the sizes, morphologies and distributions of Y phase change greatly by double aging treatment. After full heat treatment of 1180°C, 2 h + 1290°C, 2 h + 1315°C, 16 h AC + 1140deg;C, 4 h AC + 870deg;C, 24 h AC, the stress rupture life of alloy is 100 h under the condition of 1100°C and 137 MPa. The study of the microstructure for cracked specimens shows that the cracks propagate mainly along the interdentritic area perpendicular to the tensile stress. It is also found that the remained γ/γ′ eutectic is the weak and crack initiation points during the creep tests of the alloy.