Fatigue crack propagation induced by SiO2 inclusions in P/M superalloys studied by in situ SEM

Abstract

High-temperature in situ fatigue experiments were carried out on the P/M superalloy FGH96 containing SiO2 inclusions. The experimental results indicated that cracking occurred first on an inclusion itself, and then local misorientation and dislocations aggregated at the crack tips to prompt crack propagation into inner alloy. The annealing twins’ Schmidt factor was lower than its surrounding alloys and this structure hinder crack propagation by changing the crack direction. Aggregation of plastic strain and orientation variation were found in the crack tip to prompt cracking. Microtwins induced by single-layer and multilayer atomic derangement along the <112> twin direction on the (11−1) plane were observed at the crack tip, and an atomic-scale microtwins mechanism of inclusion-induced microcrack propagation was proposed. In conclusion, in situ crack experiments provided intrinsic clues for understanding inclusion-induced cracking and its propagation.