Correlation between secondary γ′ and high-temperature tensile behavior of a powder metallurgy nickel-based superalloy EP962NP

Abstract

A powder metallurgy nickel-based superalloy EP962NP was subjected to solid solution treated and cooled in four media (water, oil, air and furnace) followed by aging treatment to investigate the correlation between secondary γ′ (γs′) and tensile properties of the experimental alloy at 750 °C. Results show that the size of γs′ increases sharply with the decreasing cooling rate, and morphologies of γs′ depend on the cooling regime and present various characteristics including spherical, rod-shaped, cubic, etc. By implementing the heat treatment process of solid solution treatment (1210 °C/2 h, air cooling/AC) and two-step aging treatment (i.e., 870 °C/8 h, AC + 760 °C/16 h, AC), superior comprehensive mechanical properties can be obtained with ultimate tensile strength, yield strength and elongation of 1251 MPa, 1079 MPa and 13.3%, respectively, due to the high density of stacking faults. Interaction between γ′ and dislocations indicates that the deformation mechanism of the alloy exhibits stacking faults on (1‾11‾) [121] and microtwins, which depends on the size of γs′. The increasing size of γs′ precipitates drives a transition in the dominant deformation mechanism from stacking faults shearing to microtwinning.