Damage Evaluation of Inconel 738LC Nickel-Base Superalloy in Creep-Fatigue

This paper studies creep-fatigue damage evaluation of a nickel-base superalloy Inconel 738LC by X-ray diffraction, hardness and ultrasonic wave methods as well as replication method. Since its deformation behavior is almost elastic at 1123K, the nondestructive measures, which detect the plastic deformation, such as hardness and ultrasonic wave are not effective to evaluate the creep-fatigue damages. X-ray diffraction is occasionally effective for the creep-fatigue damage evaluation. On the other hand, the replication method is available for creep-fatigue damage evaluation. Cracks were mostly initiated and propagated along the grain boundaries of the [001] oriented crystal. Simulation of the 3-dimensional FEM analysis, taking account of the elastic anisotropy of the grains, revealed that the crack nucleation along such crystals is mainly attributed to the large stressing due to the elasticity anisotropy. Therefore, as a damage evaluation method, it is effective to detect the cracks by replication method on the [001] grains and to measure the misorientation of the most [001] oriented crystals.