Effects of microporosity and precipitates on the cracking behavior in polycrystalline superalloy Inconel 718

Abstract

Cast microporosity in superalloy is one of the most common concerns since it significantly reduces the mechanical properties of components. Effects of microporosity and precipitates on crack behavior in polycrystalline superalloy were investigated with experimental and numerical methods. Characterizations of microporosity were conducted with metallographic, electron microscopy, and synchrotron radiation micro X-ray micro computerized tomography (CT). Digital models of superalloy were obtained with three dimension (3D) reconstruction and utilized in finite element simulation. The experimental results suggest that porosity in metallography and 3D reconstructive model is 0.98% and 0.799%, respectively. Parameters of micropore influencing crack behavior include of magnitude, distribution, spacing length, surficial precipitates, and orientation angle. Numerous original cracks were observed in Laves band at the interdendritic regions of micropore, indicating the cooperation of micropore and Laves in cracking. Lamellar fracture of scripted carbide in dendrite arm provides crack sites. Numerical simulation results reveal that stress concentration on the interdendritic surface of micropore induces microcracks in Laves bands.