In-situ grain refinement in wire-arc DED of 316L via hot forging

Abstract This study evaluates how heat input influences an in-situ interlayer hot-forging strategy applied to wire-arc directed energy deposition (DED) of 316L stainless steel. By integrating a compact pneumatic hammer with a controlled short-circuit GMAW-based DED system, the process enables high-temperature deformation capable of refining the solidification microstructure during layer-by-layer fabrication. Using a reciprocating-wire short-circuit GMAW process, changes in wire-feed speed produced distinct heat-input levels that significantly affected the thermal profile, weld bead shape, and the in-situ forging. Electron backscatter diffraction (EBSD) revealed a transformation from coarse columnar grains (158.6 µm) with strong < 100 > {200} texture in the non-forged condition to fine equiaxed grains (~ 45 µm) with reduced texture intensity in the deformed deposits, most pronounced at lower heat input. In the hot-forged samples, the storage strain energy increased, reflected by higher Kernel Average Misorientation (KAM) values and broader distribution compared to the conventional condition. Hot forging also increased microhardness, reaching up to 264 HV compared to 175 HV in conventional wire-arc DED. These findings demonstrate that in-situ forging at high temperatures is a promising method to enhance the microstructure and mechanical performance of wire-arc DED components, although geometric distortion and increased surface roughness remain important considerations for future process optimization.