Anisotropic damage evolution and modeling for a nickel-based superalloy built by additive manufacturing

Abstract

The objective of the present work is to characterize the effects of microstructural features, including porosity, precipitates, and to quantify their contributions to the damage evolution in the Inconel 718 alloy built by selective laser melting (SLM). 3D morphology of porous defects in the SLM alloy obtained from X-ray micro-computed tomography before and after hot isostatic pressing (HIP) were analyzed and classified based on the pore size, shape, and distribution. The unmelt region pores with the large size and irregular shape are found serving as crack sources and responsible for the anisotropic damage evolution. The inter-dendritic precipitated phases and twin boundaries were observed and preferred to be crack initiation sites and propagation paths, which further promote microstructural damage evolution. The macroscopic anisotropic damage of Inconel 718 alloy was evaluated through the variations of the material stiffness measurement from tensile tests with multiple unloading steps. A microstructure-dependent damage model was introduced to quantitatively describe the contributions of the microstructures o the evolution of macroscopic material degradation. The total damage was decomposed into three components based on the microstructural mechanisms and gives meaningful evolution laws of the microstructural characteristics. The material stiffness degradation processes of SLM can be predicted by the present model with good agreement.