Pengcheng Xia

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

Abstract 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.

Influence of Aging Temperature on the Microstructure and Stress Rupture Property of DZ951 Alloy

Effect of different aging temperatures on microstructure and stress rupture properties of DZ951 alloy were investigated in this paper. The results show that the shape of carbide changed from script-like in as-cast alloy to block during different aging treatments. MC carbide degrades into M23C6 at the aging temperature of 970°C, which made alloy have a better combination of strength and ductility than that at other aging temperatures. The size of γ′ phase increases and the shape of γ′ phase changed from sphere (870°C) to quasi-cuboid (920°C) and cuboid (970°C) with the increasing aging temperature. The stress rupture life of DZ951 alloy at 1100°C/60MPa improves with the increased of aging temperature. The fractographs at different conditions showed a ductile fracture mode.