A multiscale investigation of deformation heterogeneity in additively manufactured 316L stainless steel

Highlights: • Deformation heterogeneity in additively manufactured 316L stainless steel is studied. • Effects of process-induced features and inhomogeneous microstructure are examined. • Different levels of strain heterogeneity are revealed and origins are discussed. • Understanding of the process-structure-property relationship in AM 316L is enriched. Additive manufacturing (AM) builds materials layer upon layer with the aid of an energy source. During AM processing, the complex thermal behaviors—directional heat flux, rapid solidification, and repeated thermal cycles—facilitate the formation of heterogeneous microstructures. Consequently, the mechanical behavior of AM parts can intrinsically differ from that of conventionally processed materials. This work focuses on characterizing deformation behavior in relation to AM-pertinent features and attempts to improve quantitative understanding of the process-structure-property relationships of metallic AM parts. A sample of as-deposited 316L stainless steel manufactured by the directed energy deposition technique is examined on different scales via microscope digital image correlation and electron backscatter diffraction. First, anisotropy in tensile properties is examined in the transverse plane perpendicular to the build direction. Then, it is revealed that the characteristic wavelength of strain bands formed due to deformation localization is strongly affected by tracks of deposits. Subsequently, strain localization at the grain scale is analyzed. The origin of plastic strains from the perspective of the activation of slip systems is examined, and the implications of the statistical distribution of local strain are discussed. Lastly, plastic strain accumulation and transmission in the vicinity of grain boundaries and substructure colonies are studied. The current observations and findings enrich the understanding of strain inhomogeneity in metallic AM parts and its relation to features at different length scales.