Nanoscale gradient grain structure formation on selective laser melted (SLM) FeCoCrNiMn alloy surface by single point diamond cutting

In this study, single-point diamond cutting was employed to successfully generate a nanoscale gradient grain structure on the surface of a selective laser-melted FeCoCrNiMn high-entropy alloy, leading to significant enhancement of its mechanical properties. Cutting depth critically influences gradient-structure evolution, with 4 μm yielding finer layering and better surface quality than 16 μm. The evolution mechanism of the nanoscale gradient structure is revealed to be governed by the coupled effects of geometrically necessary dislocation accumulation, grain refinement, grain boundary evolution, deformation twinning, and face-centred cubic to hexagonally closed packed phase transformation. Smaller cutting depths promote localized shear deformation, increasing the fractions of high-angle grain boundaries and the hexagonally closed packed phase, whereas larger cutting depths favor the formation of twin-related low-angle grain boundaries through expansion of the shear-affected layer. These structural changes enhance resistance to plastic deformation and improve the strain accommodation capability of the machined surface. These findings demonstrate that single-point diamond cutting is an effective post-processing strategy for generating nanoscale gradient grain structures and enhancing the mechanical performance of additively manufactured high-entropy alloys.