Additive manufacturing of high strength copper alloy with heterogeneous grain structure through laser powder bed fusion

Laser powder bed fusion (L-PBF) additive manufacturing was utilized to fabricate high-strength copper (Cu) alloys through inoculation of pure Cu powder with cobalt (Co) submicron particles. It was found that when the addition level of Co is lower than its maximum solid solubility in Cu (4.75 wt.%), the microstructure of Cu-Co alloys is characterized by coarse columnar grains. Further addition of Co over 4.75 wt.% led to a heterogeneous grain structure, with large equiaxed grains or columnar grains near the centers of melt pools whereas ultrafine equiaxed grains sitting on the melt pool boundaries. Microstructure characterization showed that the in-situ formed dual phase nanoparticles with Co shell and cobalt oxide (CoO) core acted as heterogeneous nucleation sites of Cu, which allowed ultrafine, equiaxed grains to form. The heterogeneously structured as-built Cu-Co alloy achieved a tensile strength of 381.4 ± 2.9 MPa and an elongation of 31.6 ± 1.3%. Co nanoprecipitation driven by post L-PBF heat treatment further increased the tensile strength of the Cu-Co alloy up to 491.1 ± 12.6 MPa without notably sacrificing the ductility. The combination of high strength and high ductility distinguishes Cu-Co alloys from most conventionally and additively manufactured Cu alloys. This study shows a strategy to produce Cu alloys with high performance through remarkable grain refinement by heterogeneous nucleation.