Microstructural study of the nano-scale martensitic lamellar α-Co and ε-Co phases of a Co–Cr alloy fabricated by selective laser melting

An interfacial microstructural study was carried out to clarify the hardening mechanism of an as-built Co–Cr alloy fabricated by selective laser melting (SLM). Using transmission electron microscopy, we found a unique martensitic lamellar microstructure with a specific orientation relationship between the α-Co and ε-Co phases; specifically, a nanoscale microstructure consisting of (111)α-Co//(0002¯)ε-Co and [01¯1]α-Co//[1¯21¯0]ε-Co was formed on the Co–Cr alloy. The Co–Cr alloy fabricated by SLM with a martensitic microstructure achieved a Vickers hardness value of approximately 369.36 ± 11.86 HV without any secondary-phase particles such as carbides.