Scanning strategy induced cracking and anisotropic weakening in grain texture of additively manufactured superalloys

Abstract

In this work, a multiphysics process model is utilized to explain an observed correlation between cracking and anisotropic texture weakening of a Ni-based superalloy additively produced by laser powder bed fusion (LPBF). Six LPBF scanning strategies were implemented on the IN738LC superalloy, revealing significant variations in crack densities and grain textures. The microstructural analysis confirmed solidification cracks by dendritic surfaces and preferential locations in carbide-deficient regions. The cracking susceptibility was found relating to a specific kind of texture weakening, in which columnar grains revolve around the building direction to reduce grain texture and generate crack susceptible high-angle grain boundaries (HAGB). The melt pools and solidification conditions simulated by a computational fluid dynamic (CFD) based process model indicate texture weakening originating from the non-epitaxial solidification region (NSR) with excessively scattered thermal gradient vectors. The simulated melt pool shapes and the estimated propensity of NSR agree with the cracking and texture tendencies observed. In general, for columnar grain structure, scanning strategies such as rotation on (RO) and alternating (ALT) generate stronger grain texture and less HAGB beneficial for crack suppression. The findings also promote the considerations of scanning vector arrangements in LPBF process for crack susceptible superalloys.