Stress-Induced Variant Selection of γ″ Phase in Inconel 718 During Service: Mechanism and Effects on Mechanical Behavior

The stress-induced variant selectionStress-induced variant selection (SIVS) of γ″ phase caused by thermo-mechanical couplingThermo-mechanical coupling condition is studied systematically. The SIVS index f is devised and utilized to quantify the degree of SIVSStress-induced variant selection via SEM image post-processing within <001> oriented grains. Applied stress condition does not affect the volume fraction, average size, and crystallographic orientation of the γ″ but changes the proportion of the three variants. The SIVSStress-induced variant selection behavior of γ″ phase is dependent upon the applied stress direction and grain orientation. By considering the variation of the SIVSStress-induced variant selection index with thermal aging and creep parameters, a causal relationship between degree of SIVSStress-induced variant selection with temperature, stress, and time is elucidated. The yield strength and tensile strength at 650 °C decrease with the increase of SIVSStress-induced variant selection degree. Contour map for the degree of SIVSStress-induced variant selection is presented to evaluate the service temperature and stress of an Inconel 718Inconel 718 component. The formation mechanism of SIVSStress-induced variant selection of γ” is proposed: the orienting effect of stress condition is appreciable only during Ostwald ripening, due to the change of the γ″/γ lattice mismatch.