Fatigue property and fracture analysis on cold-expanded hole structure of GH4169 alloy

Abstract

Cold expansion (CE) was applied on the centre-hole plate of GH4169 alloy. The fatigue lives, as received and after CE, were investigated at 825 MPa/600 ℃/R=0.1. Surface roughness before and after CE, residual stress profiles during fatigue cycles were studied. And the influence of surface integrity on fatigue process was analyzed by the careful fracture observation with two CE samples of different lives (25105 cycles and 10719 cycles). The results show that the median fatigue life estimation of specimens after CE doubles compared with as-received. The lower surface average roughness after CE and the stable residual stress profile during fatigue process are the main reasons for fatigue life promotion. However, the standard deviation of fatigue lives increases after CE. The fractographic quantitative analysis shows the propagation lives of two specimens beyond 0.1 mm from fatigue source are considered, but initiation lives (18786 cycles and 5915 cycles, respectively) are of great difference. As a contrast, the reason of the big dispersion about CE fatigue lives is the different initiation life within 0.1 mm from the source. Therefore, the attention should be paid to the surface integrity control of near surface during cold expansion to improve the stability of hole structure fatigue property.

Keywords

• cold expansion
• hole structure
• fatigue
• fractographic quantitative analysis