Effects of cold expansion and aging on high-temperature low-cycle fatigue of GH4169 alloy with hole structure

The GH4169 alloy center hole plate samples were cold-expanded, and the effects of cold expansion and (600℃, 500 h) thermal aging on the low-cycle fatigue performance under the conditions of 600℃, 820 MPa, R=0.1, and triangular wave were studied. The results show that the median fatigue life estimation increases from 7278 cycles in the original state to 19536 cycles after cold expansion, representing an increase of about 2.5 times and indicating that the cold expansion process significantly improves the high-temperature fatigue life. While the thermal aging process is subjected, the fatigue life decreases from 7278 cycles to 4, 717 cycles. The 35.8% reduction indicates that fatigue weakening has occurred after thermal aging. The reason for fatigue weakening is that thermal aging transforms the γ" strengthening phase to δ phase, therefore the content of strengthening phase decreases while the number of δ phases increases and the morphology changes. Additionally after thermal aging, the original cold expansion surface residual compressive stress is reduced from -708 MPa to -483 MPa. The stable part of compressive residual stress profiles that still plays a role of strengthening, and the weakening effect of the reduction of the strengthening phase after thermal aging has a comprehensive effect, making the fatigue life of cold expansion and thermal aging (8188 cycles) increases by 12.5% compared to the original life (7278 cycles). © 2021, Science Press. All right reserved.