Influence of heat treatment on the microstructure and mechanical properties of DZ951 alloy

DZ951 directionally solidified nickel-base superalloy is mainly strengthened by γ′ phase. Regularly aligned cuboidal and bimodal γ′ precipitates were attained by two heat treatments. The effect of microstructure on the mechanical properties of DZ951 alloy has been investigated. The results indicate that MC carbide changes to little blocks during aging treatment at 1050°C (HT1). MC carbide partly degrades into M23C6 and there is a layer of γ′ around the carbide during aging treatment at 1150°C (HT2), which is beneficial to the elongation of DZ951 alloy. Small γ′ volume fraction and the uneven deformation structure are contributed to low mechanical properties of the as-cast alloy. HT1 alloy has a better stress rupture life at 1100°C/50 MPa and yield stress at 20°C, 800°C and 1100°C, which is attributed to regularly aligned cuboidal γ′ phase and even deformation structure. HT2 alloy has a good combination of strength and ductility. This arises from the bimodal γ′ precipitates and the degeneration of MC carbide.