Effect of cyclic rapid thermal loadings on the microstructural evolution of a CrMnFeCoNi high-entropy alloy manufactured by selective laser melting

Metallic materials produced by additive manufacturing experience complex stress and thermal gyrations along the build direction. This has the potential to produce complicated heterogeneous microstructures that may exhibit a wide variety of mechanical properties. There remains a paucity of studies on the nature and the formation mechanisms of the microstructural heterogeneity and this limits our capability for microstructural design in additively manufactured metallic materials. Here, we present an electron microscopy-based investigation of a CrMnFeCoNi high-entropy alloy produced by selective laser melting. We have focussed on a systematic investigation of the microstructural evolution along the build direction. Our results reveal a remarkable hierarchy of microstructures, including the formation of nanocrystalline grains, elemental segregation and precipitation, cellular dislocation structures, deformation twinning, and deformation-induced phase transformation. Our research clarifies the relationships amongst different features, and provides guidance for future structural manipulation of materials produced by additive manufacturing.