Interplay of dislocation substructure and elastic strain evolution in additively manufactured Inconel 625

Abstract

The unique thermal history of direct metal laser sintering (DMLS) leads to complex microstructures and local elastic residual strains which accumulate to affect the global residual stress and mechanical properties of components. Characterization of residual stress using neutron and x-ray diffraction result in bulk and grain level residual stress measurements; however, the contribution of the microscale residual strain remains largely unaccounted for. High-resolution electron backscatter diffraction (HR-EBSD) has emerged as a promising tool for the characterization of such micron-level elastic strains. This work presents an early effort in analysis of microscale elastic strain in conjunction with subgrain dislocation structures to further the understanding of microstructural evolution during laser additive manufacturing (AM) techniques. Elastic strain in DMLS fabricated IN625 is analyzed using open source cross-correlation software OpenXY while the geometrically necessary dislocation (GND) density is calculated from EBSD data using the Nye tensor. Dislocation structures previously seen in similar materials are shown here to contain low elastic strain gradients, supporting the assertion that these structures occur as strain minimization mechanisms during solidification.