Microstructural evolution and twins formation under tensile test of Ni-free Mn-N austenitic stainless steel using laser powder bed fusion method

Abstract

At the initial uniaxial tensile stage, predominant planar dislocation slip occurs to generate dislocation pile-ups and dipole bundles. Low-energy Taylor lattice structure is then formed by co-planar slip bands along the primary slip system along [001]γ and [111]γ directions to form primary twins. Increasing the straining and generation of numerous micro-bands and crystallographic defects led to the strong restriction for dislocation motion, enhancing the formation of secondary twins with stacking fault near the deformation twin's energy. Decreasing the mean slip band and micoband spacing and configuration of complex dislocation arrangement would cause the dislocation slip, generating an extensive number of dislocation walls and cell blocks, resulting in forming a noncrystalline structure with multi-orientation. Molecular dynamics (MD) analyses revealed that deformation began by nucleation of Shockley partial dislocations with a burger vector of 1/6 〈112〉 from none-periodic boundaries. Afterwards, dislocations junctions created Hirth dislocations with a Burger vector of 1/3 〈100〉, which causes strain hardening in the system. At this point, Shockley dislocations nucleated from Hirth dislocations and strain hardening increases.