Effect of Crack Orientation on Fracture Behaviour of Wire + Arc Additively Manufactured (WAAM) Nickel-Base Superalloy

Abstract

In this study, the effect of crack orientation on the fracture behaviour of two compact tension C(T) specimens extracted from a Wire + Arc Additively Manufactured (WAAM) wall made from Inconel (IN) 625 nickel-base superalloy was investigated. Both specimens had different levels of ductile tearing but their load vs. crack mouth opening displacement (CMOD) behaviour was relatively similar. The total-and-elastic strain distribution around a crack tip was measured in both specimens using Digital Image Correlation (DIC) and neutron diffraction respectively. The results show that the strain distribution and deformation around the crack tip are different in the two directions. In the specimen with crack orientation parallel to the build direction, banding was observed in both the total strain maps and the deformation pattern. Neutron diffraction measurements on this specimen also showed non-monotonic elastic strain evolution, suggesting the occurrence of intergranular load shedding mechanisms. These were not observed in the specimen with crack orientation perpendicular to the build direction. Electron Backscatter Diffraction (EBSD) maps show that the WAAM IN625 material is strongly textured with coarse columnar grains elongated in the build direction. The effect of microstructure has been correlated with the differences in strain distribution in the two specimens.