On the machining of selective laser melting CoCrFeMnNi high-entropy alloy

Highlights: • Studied the machinability of selective laser melt CoCrFeMnNi high-entropy alloy. • Evaluated the effects of different machining processes on surface and subsurface quality were quantitatively. • Identified the correlation between microhardness, residual stress and subsurface deformation. High-entropy alloys (HEAs) have attracted significant attention due to its superior low temperature mechanical properties. Recently, with the success of 3D additive manufacturing (AM) of CoCrFeMnNi HEA by selective laser melting (SLM), the fabrication of complex components in one step became possible. However, due to the low surface quality, post-machining is necessary. Up to date, there is no study that comprehensively reported the machinability of SLM CoCrFeMnNi HEA. Hence, this research presents a pioneer work on the machinability study of SLM CoCrFeMnNi HEA by commonly used mechanical, thermal and electro chemical machining processes. The surface and subsurface quality generated by different machining processes were quantitatively evaluated from the aspects of surface morphology and roughness, microhardness, residual stress and subsurface quality. The results show that milling and grinding smoothed the surface, enhanced surface microhardness but induced tool marks and compressed residual stresses. Wire EDM flattened the surface but caused a heat melt layer resulting in the increase of the tensile residual stress and surface microhardness. EP released the residual stress and with the combination of mechanical and electrical processes, smoother surfaces were obtained and subsurface damages were removed. A super smooth surface without subsurface damages was achieved by mechanical polishing.