Microstructure and mechanical properties of bulk nanostructured Cu-Ta alloys consolidated by equal channel angular extrusion

Nanostructured Cu-Ta alloys have shown promise as high-strength nanocrystalline materials in part due to their limited grain growth at high temperatures. In the present study, Cu-Ta alloy powders, synthesized via high-energy cryogenic mechanical alloying, were consolidated into bulk nanostructured specimens using equal channel angular extrusion (ECAE) at high temperatures. Subsequent microstructure characterization indicated full consolidation, which resulted in an equiaxed grain structure for the Cu matrix along with the formation of fine Ta precipitates, the size distributions of which varied both with composition and processing temperature. Microhardness, compression and shear punch testing indicated, in some cases, an almost threefold increase in mechanical properties above that predicted by Hall-Petch estimates for pure nanocrystalline Cu. Stress relaxation tests substantiated the strain-hardening behavior and grain-size-dependent dislocation activity observed in the nanocrystalline Cu-Ta samples.