Cu-25Cr composites processed by in situ alloying in electron beam powder bed fusion

Due to their high thermal and electrical conductivity and high resistance to arc erosion, Cu-Cr alloys (Cr >10 wt%) are used as electrical contacts in medium voltage vacuum circuit breakers. Such electrical contacts are industrially processed using solid-state sintering (SSS) from pure Cu and Cr powders or vacuum arc remelting (VAR). In this work, we confirm the possibility of fabricating dense Cu-25Cr samples with a refined and relatively homogeneous microstructure by electron beam powder bed fusion (EB-PBF) using elemental powder blending. The as-printed microstructure is characterized using SEM imaging and EBSD analysis while the mechanical, electrical, and thermal are probed to establish the microstructure-property relationships of the EB-PBF Cu-25Cr composite. The properties of the EB-PBF composite are systematically compared to their VAR counterparts. The as-printed microstructure results from the presence of a metastable miscibility gap that refines the microstructure (micron-sized Cr particles) by an order of magnitude compared to the VAR. The fine EB-PBF microstructure shows superior mechanical properties (hardness, yield strength and ultimate tensile strength), enhanced electrical conductivity, and equivalent thermal conductivity with respect to its VAR counterpart. The microstructure-property relationships are discussed in light of the mechanisms affecting the mechanical, electrical, and thermal properties of metal matrix composites. This work demonstrates the interest in producing Cu-Cr electrical contacts by additive manufacturing.