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 alpha-Co and epsilon-Co phases; specifically, a nanoscale microstructure consisting of (111)(alpha-Co)//(000 (2) over bar)(epsilon-Co) and [0 (1) over bar1](alpha-Co)//[(1) over bar2 (1) over bar0](epsilon-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. (C) 2021 The Authors. Published by Elsevier B.V.