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

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 gamma ' (gamma s ') and tensile properties of the experimental alloy at 750 degrees C. Results show that the size of gamma s ' increases sharply with the decreasing cooling rate, and morphologies of gamma s ' 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 degrees C/2 h, air cooling/AC) and two-step aging treatment (i.e., 870 degrees C/8 h, AC + 760 degrees 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 gamma ' and dislocations indicates that the deformation mechanism of the alloy exhibits stacking faults on (111) [121] and microtwins, which depends on the size of gamma s '. The increasing size of gamma s ' precipitates drives a transition in the dominant deformation mechanism from stacking faults shearing to microtwinning.