Microstructure and mechanical properties of additively manufactured stainless steel 316L
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Date
2021
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University of New Brunswick
Abstract
The effects of crystallographic texture and microstructure on the mechanical behavior of a selectively laser melted (SLM) 316L stainless steel subjected to uniaxial tensile loading was discussed. The microstructure of the as-built sample exhibits a hierarchical structure at macro-, micro-, and nano-scales, with good chemical homogeneity and no elemental segregation. The chemical homogeneity was attributed to a very high cooling rate (2.7 × 10[superscript 6]K/s) present in SLM, discrete melt pools, and the formation of nanosized silicon-rich oxides. Due to the formation of a dislocation network during additive manufacturing, 316L showed twinning-induced plasticity (TWIP) behavior with a high strain-hardening rate exhibited in five stages. Pre-existing dislocation networks, where their configuration was maintained during deformation, promoted the formation of nano-twins, resulting in enhanced twin-dislocation and dislocation-dislocation interactions. The formation of deformation-induced nano-twins maintained a constant high-level of strain hardening rate in two stages, enhanced by the development of pronounced <111> texture in the tensile direction and a fiber texture. In addition, the high yield strength of this alloy was attributed to the high density of dislocation cells. The dislocation cellular structure combined with distributed nano-oxide inclusions were responsible for the formation of nanometer ductile dimples (as a nano-scale structure). This microstructure hindered crack propagation and tailored several process-induced defects compared to traditionally manufactured ones. Plastic deformation was governed by dislocation glide and deformation-induced twinning; thus, the final microstructure contained several types of twins and highly misoriented dislocation boundaries. As a final stage, the high temperature behavior of 316L was also studies and some perspectives on its deformation was brought forward.