New insights into microstructure evolution and deformation mechanisms in additively manufactured 316L stainless steel

Abstract

The evolution of the deformation micro-mechanisms and the dislocation structures in additively manufactured (AM) 316L steel was investigated via in-situ SEM/EBSD tensile tests coupled with fine TEM investigations at different strain levels. We show that the deformation mechanisms are strongly influenced by the initial dual-scale cellular structure, composed of large dislocation cells with chemically segregated cell walls, encapsulating smaller, chemically homogeneous internal regions. At low and medium strain levels, the primary deformation mode is dislocation slip across the dislocation cells interiors and formation of micro-bands while plastic deformation at higher strain is primarily controlled by mechanical nano-twins nucleated through the overlapping of stacking faults ribbons. Unlike conventional 316L, the AM 316L shows a nearly linear increase in dislocation density with increasing applied strain throughout the full range of plastic deformation. The initial cellular structure is preserved under plastic deformation, continuing to act as a barrier to dislocation glide and contributing to the high ductility of the AM 316L steel. A correlation between the work hardening rate and the observed deformation modes is evidenced, strengthening the conclusion that the plasticity of AM 316L is atypical. These findings enhance the understanding of the dislocation structures and the microstructure evolution during plastic deformation in AM 316L steel, providing valuable insights for the development of predictive large-scale plasticity models for these materials.