Microstructure evolution and lath martensite precipitation behavior of Co@GNPs/CoCrMo composites fabricated by selective laser melting

Abstract

Spherical cobalt nanoparticles were reduced and deposited in situ on the graphene (GNP) surface using a novel hydrothermal method, and the prepared Co@GNPs reinforced powder were uniformly dispersed in the alloy matrix. The Co@GNPs/CoCrMo composite fabricated using selective laser melting (SLM) was densely organized with reduced hole defects, and fine equiaxed grains, elongated columnar grains, and duplex ε + γ were observed in the composite organization. Meanwhile, a high density of dislocations and nanoscale stacked layer dislocations were observed at the equiaxed grain boundaries. Further, the GNPs acted as heterogeneous nucleation sites, which promoted the transformation of the γ-Co (FCC) austenite phase to the ε-Co (HCP) martensite phase by means of slip. A unique characteristic structure of nanoscale parallel-arranged lath martensite is formed on the surface of GNPs. Therefore, a co-lattice structure between ε-co and γ-co shows the specific orientation relationship between the crystallographic plane (1 1 1)γ-co//(0 0 0 2)ε-co and the crystallographic zone axis [1 1 0]γ-co//[1 1 2‾ 0]ε-co.