Stress relaxation behavior comparison of typical nickel-base superalloys for fasteners

Abstract

In the present work, stress relaxation behavior of three typical nickel-base Superalloys: Alloy 718, Waspaloy and AEREX 350, were investigated in a temperature range of 600-800 °C for up to 10 h. The effects of stress relaxation parameters on behavior were analyzed and stress relaxation characteristics of the three superalloys are compared and mechanisms revealed by FESEM and TEM observation. The study results show that the stress relaxation property of Alloy 718 is very sensitive to temperature. It is very stable at 650 °C, but decreases extremely with temperature increasing to 750 °C as a result of serious microstructure degeneration. Moreover, stress relaxation stability is related with initial stress, and appropriate increase of initial stress under normal service temperature can increase the stress relaxation limit of Alloy 718. The stress relaxation resistance of Waspaloy decreases with increasing temperature. The increase of initial stress and initial strain is beneficial for stress relaxation resistance of Waspaloy, but the influencing degree is related with temperature. Furthermore, Waspaloy with heat treatment A (1020 °C × 4 h/AC + 845 °C x 4 h/AC + 760 °C × 16 h/AC) shows better stress relaxation resistance than that with heat treatment B (1080 °C × 4 h/AC + 845 °C × 24 h/AC + 760 °C × 16 h/AC). In addition, stress relaxation stability of AEREX 350 is the best among the three superalloys in the temperature range of 600-800 °C on the whole. The combined effect of γʹ phase and η phase guarantee the stress relaxation property of AEREX 350.