Balancing the mechanical properties and electrical conductivity of Cu–3Zr alloy by in-situ synthesized ZrC and thermomechanical processing

In this study, flake graphite (C) was incorporated into the Cu-3Zr alloy, and Cu-3Zr alloys with x C ( x =0.2, 0.4, 0.6 wt.%) were obtained by powder metallurgy together with two-stage thermomechanical processing. The phase structure and constituents were characterized by XRD, SEM and TEM, and the electrical conductivity and mechanical properties were tested. The strengthening and conductive mechanisms were discussed as well. Compared with the as-sintered Cu-3Zr alloy, the elongation increases and then decreases with increase of C content for the as-sintered Cu-3Zr- x C composites whereas the ultimate tensile strength progressively decreases. The electrical conductivity is increased by 9.84%, 13.11% and 16.39%, respectively. Compared with the as-drawn Cu-3Zr alloy, the ultimate tensile strength of as-drawn Cu-3Zr-0.2C is decreased by 4.3% while the elongation is increased by 44.4%, and the electrical conductivity is increased by 5.4%. It demonstrates that graphite addition and thermomechanical processing facilitates the enhancement on the comprehensive properties. At a C content of 0.2wt.%, an optimal balance between mechanical properties and electrical conductivity is achieved, with an ultimate tensile strength of 658 MPa, yield strength of 573 MPa, elongation of 6.5%, and electrical conductivity of 78%IACS. The microstructural analysis reveals that the secondary particles present different distribution for the Cu-3Zr alloy and Cu-3Zr-0.2C composite. For the Cu-3Zr alloy, the coarse Cu x Zr y intermetallic compounds are distributed randomly at the grain boundaries and within the Cu grains, whereas fine ZrC particles are primarily distributed along grain boundaries for the Cu-3Zr-0.2C composite. In addition, ZrC particles in the Cu-3Zr-0.2C has the lower volume fraction than Cu x Zr y in the Cu-3Zr, and the addition of C can purify the Cu matrix by virtue of the strong reaction tendency between C and Zr. Moreover, the directed Cu grains can provide fast channel for electrons transport and special loading transferring effect. As a result, although the strength decreases, the electrical conductivity and elongation increase by introducing C into ZrC, and the extrusion and drawing are also benefit for both mechanical and electrical properties.