Zhihao Yao

A Study on the Recrystallization Behavior of Ni-Based Alloy G3 During Hot Deformation

An integrated microstructure evolution model of thermomechanical processing was developed in terms of dynamic recrystallization (DRX), post-dynamic recrystallization (PDRX) and grain growth. Hot compression tests were carried out on a Gleeble-1500 thermal simulator under different conditions to model DRX, PDRX and short-time grain growth during the post-deformation and cooling process. Furthermore, in combination with the established microstructure evolution models, an elastic–plastic finite element model was built using DEFORM-2D software to simulate the microstructure evolution during the hot extrusion process. The simulation result was compared with the microstructure of a hot-extruded pipe of alloy G3 manufactured in a factory. The simulation results agree well with the experimental ones, validating the accuracy of the established microstructure evolution model. Furthermore, the finite element simulation is an effective method for hot deformation analysis, which can provide theoretical guidance for the optimization manufacturing parameters.

Stress Relaxation Behavior Comparison of Typical Nickel-Base Superalloys for Fasteners

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 × 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 γ′ phase and η phase guarantee the stress relaxation property of AEREX 350.