Delineating dislocation structures and residual stresses in additively manufactured alloys

Abstract

Dislocation structures and residual stresses have tremendous impact over the properties of alloys produced by fusion-based additive manufacturing (AM) processes. Yet, their origin is still unclear. We quantify and map, for the first time, the spatial distribution of dislocations, including those classified as geometrically necessary dislocations (GND), lattice strains, and type-III residual stresses in body-centered cubic (BCC) Ti-42Nb alloy and face-centered cubic (FCC) stainless steel (SS) 316L using a combination of electron channeling contrast imaging and cross correlation-based electron backscatter diffraction. Our findings reveal distinct residual stresses, lattice strains, and dislocation arrangement along cell walls in both alloys. In particular, Ti-42Nb demonstrates no GND network in cell walls, while SS316L exhibits a high GND density. We show that the Ti-42Nb alloy primarily accommodates solidification strains and cooling stresses elastically while SS316L accommodates them by elasto-plastic deformation and builds GNDs. Our work establishes relationships between dislocations and residual stresses in BCC and FCC LPBF alloys and highlights that not all LPBF-manufactured materials contain a dense dislocation network in their microstructures. These findings can also be extended to other AM alloys, therefore enabling a better control over their properties and performance.