Effect of microstructure on low cycle fatigue behavior of Inconel 706 at 650 o C

Four different types of specimens were prepared from the center and the periphery of two large IN706 forged discs of commercial scale, and low cycle fatigue (LCF) tests were conducted at 650 o C. The IN706 specimens with lower LCF lives showed relatively large fraction of cleavage-like fracture along linearly aligned η (Ni 3 Ti) precipitates in the area of crack propagation. The amount of η precipitates for those specimens with greater LCF lives was negligible, and the fracture mode of crack propagation was dominantly intergranular. Crack initiation was mainly by persistent slip band (PSB) cracking at the surface, and no notable difference was found for each specimen. The correlation between tensile properties, grain size and LCF lives of IN706 at 650 o C appeared to be not as significant as expected.