Low cycle fatigue behavior of Inconel 706 at 650 °C

Low cycle fatigue (LCF) behavior of 2- and 3-step-aged Inconel 706 (IN706) specimens that were prepared from the center and the periphery of forged disc was examined at 650 °C and an R ratio of −1. The resistance to LCF of IN706 alloy was greater in approximately half order at 650 °C than that of IN718 alloy for the same aging condition. Elevated temperature Coffin–Manson relationship between 2- and 3-step-aged IN706 specimens was similar with each other, despite a considerable difference in microstructure. The fractographic analysis suggested that cluster of carbides provided the sites for crack initiation for both 2- and 3-step-aged specimens. The mode of fatigue crack growth for each specimen was intergranular and transgranular, but with different magnitude for each mode. Depending on the location of specimen preparation form the forged block of IN706 alloy, no notable difference in LCF resistance was found. The role of grain boundaries, clusters of carbides and bands of acicular η platelets on the initiation and propagation mechanism of IN706 alloy was discussed based on detailed fractographic and micrographic analyses.