Fractographic Analysis on Fatigue Crack Propagation Behavior of Inconel 706 at 25, 450 and 650oc

Abstract

Fatigue crack propagation (FCP) behavior of Inconel 706 (IN706) was examined at two different R ratios of 0.1 and 0.7 and three different testing temperatures of 25, 450 and 650oC. Several points were notable, including the increase in near-threshold ΔK value with increasing temperature, extremely high starting da/dN values for stage II regime at elevated temperature and the change in Paris' slope, m, at certain test conditions. To identify the reasons for these issues, quantitative fractographic analysis was conducted on the FCP-tested IN706 specimens. It was found that intergranular fracture, cleavage fracture competed with one another, determining the shape of da/dN vs ΔK curves of IN706.

Keywords: Inconel 706, fatigue crack propagation, fractograph, R ratio, Temperature