Mapping microscopic residual strain heterogeneity in additively manufactured 316L stainless steel by micro-Laue diffraction

Residual stress and strain are inevitable and often detrimental in additively manufactured metals. To date, microscopic residual stress and strain at the grain scale have been less reported despite their significance to the mechanical performance of final components. Here we employ synchrotron X-ray Laue diffraction to map the micro-strain of an as-built 316L stainless steel fabricated by laser powder bed fusion. The strain level does not vary notably with grain orientation or grain size. Rather, strain concentrations are found at grain boundaries and melt pool boundaries. In the sample reference frame, the tensorial off-diagonal shear terms show the strongest spatial heterogeneity and contribute substantially to the equivalent strain. We reveal high geometrically necessary dislocation densities near these high-strain regions, with lopsided contributions from different slip systems. The observed localization is proposed to arise from shrinkage mismatches between melt tracks and grains, highlighting the presence of heterogeneity in additively manufactured metals.