High-temperature lean Cu alloys with Cr-to-Nb atomic ratio of 2

Abstract

Two Cu-Cr-Nb alloys, denoted as alloy 1 (comprising Cu-0.89 at% Cr-0.42 at% Nb) and alloy 2 (comprising Cu-1.84 at% Cr-0.99 at% Nb), were produced through a series of manufacturing processes including vacuum induction melting, melt spinning, consolidation, brazing, and baking, with both alloys aimed at achieving a nominal Cr-to-Nb atomic ratio of 2. Microstructural characterization using transmission electron microscopy and X-ray diffraction identified the cubic C15 Laves-phase Cr2Nb as the dominant precipitate in both alloys, cross-validated by thermodynamic calculations and atomistic simulation-based density functional theory (DFT). Besides cubic C15 Cr2Nb, hexagonal C14-phase Cr2Nb and α-BiF3 cubic structured Cr3Nb were also observed in the alloys, including a coherent interface formed between the Cr3Nb precipitate and the Cu matrix. The hardness of the alloys increases, and the electrical conductivity decreases with increasing alloying addition content; two practical equations described the trends. Further DFT simulations revealed that the electrical conductivity (conductance) of the Cu/Cr2Nb interface is an order of magnitude higher than the intrinsic Cu high-angle grain boundaries.