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

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 e + gamma 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 gamma-Co (FCC) austenite phase to the e-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 e-co and gamma-co shows the specific orientation relationship between the crystallographic plane (1 1 1)gamma-co//(0 0 0 2)e-co and the crystallographic zone axis [1 1 0]gamma co//[1 1 2 0]e-co.