Evolution of dislocations during the rapid solidification in additive manufacturing
Lin Gao, Yan Chen, Xuan Zhang, Sean R. Agnew, Andrew Chihpin Chuang, Tao Sun
Abstract
Materials processed by fusion-based additive manufacturing (AM) typically exhibit relatively high dislocation densities, along with cellular structures and elemental segregation. This representative structural feature significantly influences material performance; however, post-mortem microstructure characterizations of AM materials cannot capture the dynamic evolution of dislocations during the manufacturing process, thereby offering limited mechanism-based guidance for further advancing AM techniques and facilitating the qualification and certification of AM products. In this study, we conduct operando high-energy synchrotron X-ray diffraction experiments on wire-laser directed energy deposition of 316 L stainless steel. Through a unique configuration, our operando synchrotron experiments semi-quantitatively probe the dislocation density in solid phases and their dynamic changes during solidification and subsequent cooling. By integrating this advanced synchrotron technique with multi-physics simulation, in-situ neutron diffraction, and multi-scale electron microscopy characterization, our mechanistic study aims to elucidate the effects of rapid cooling and subsequent thermal cycling on the dislocation generation and evolution. This study aims to address a critical knowledge gap concerning the unique microstructure in 3D-printed metals by quantitatively characterizing the phase and dislocation density during the printing process using operando synchrotron X-ray diffraction.