Precipitate Size in GRCop-42 and GRCop-84 Cu-Cr-Nb Alloy Gas Atomized Powder and L-PBF Additive Manufactured Material

Abstract

Laser powder bed fusion (L-PBF) of Glenn Research Copper 42 or 84 (GRCop-42 or GRCop-84) produces a Cr2Nb precipitation-hardened high-conductivity copper alloy with tensile strength superior to other competing copper alloys. Precipitate diameters within GRCop-42 gas-atomized powder increase with powder diameter due to slower cooling rates, however, unlike GRCop-84, no threshold diameter above which extensive precipitate agglomerations form was observed in GRCop-42. Large Cr2Nb crystals were observed in GRCop-42 powder particles, implying formation within the crucible melt. A consistent precipitate volume of ~7% over a range of powder particle diameters indicated a consistent atomization process. Occasional voids were observed in GRCop-42 powder. Precipitate size was refined in L-PBF GRCop-42 to a greater extent than in GRCop-84, improving Orowan strengthening, however, this benefit was lost after heat treatment due to greater coarsening of precipitates. Precipitates in GRCop-42 accumulated on grain boundaries during heat treatment to a greater extent than in GRCop-84.