Effects of Zr addition on the microstructures, mechanical properties and thermal stability of Cu-Ta alloys

In this work, Cu-1.4 wt%Ta-Zr alloys with different Zr content (0, 0.1, 0.2 and 0.5 wt%) were fabricated by mechanical alloying combined with spark plasm sintering. The effect of Zr addition on the microstructures, mechanical properties and thermal stability of Cu-Ta alloy were characterized. Cu-Ta alloys composes of ultrafine equiaxed grains along with the uniformly dispersion of semi-coherent Ta nanoclusters and incoherent Ta coarse particles. As Zr is introduced into Cu-Ta alloy, the Ta precipitates were effectively refined, especially for the reduction of Ta coarse particles. The significant refinement effect of the grains is realized when Zr content reaches 0.2 wt%, and high-proportioned nano-sized grains are facilitated to form, along with the activation of a lot of twins and the formation of intermetallic composed of Cu and Zr. The dislocation density and strength increase remarkably with the increase of Zr content, and the highest strength (499 MPa for yield strength and 600 MPa for ultimate tensile strength) is achieved as the Zr content is up to 0.2 wt%. Compared with Cu-Ta alloy (382 MPa for yield strength and 560 MPa for ultimate tensile strength), the significant increment of 31% for the yield strength is successfully realized by Cu-Ta-0.2 wt%Zr alloy. Cu-Ta-0.2 wt%Zr alloys exhibit the excellent thermal stability, and the hardness keeps stable even the sample was annealed at 700 °C for 300 h, showing superior microstructural stability in comparison with Cu-Ta alloy (∼4.5% reduction of the hardness after 300 h at 700 °C). The softening temperature of Cu-Ta-0.2 wt%Zr alloy is up to 1028 °C (1022 °C for Cu-Ta alloy) along with higher hardness than that of Cu-Ta alloy at the same annealing temperature. This study provides a new way to fabricate dispersion strengthened Cu alloys with high strength, exceptional thermal stability and softening resistance, which have great potential application value in the field of future fusion reactor.