Evolution of Structure of Cu–Nb Composite under High-Pressure Torsion and Subsequent Annealing

— The evolution of structure of a multicore in situ Cu-18Nb composite under high-pressure torsion (HPT) by one, three, and five anvil revolutions was investigated by scanning and transmission electron microscopy, and microhardness measurements. Thermal stability of the HPT deformed structure was studied after annealings in the 300–800°C temperature range. The combined use of repeated cold drawing and HPT made it possible to refine the structure and thereby to obtain equiaxed grains with a size of 10–30 nm, which sharply increased the microhardness (to 4800 MPa). Under the subsequent annealing the nanocrystalline structure is retained and; the microhardness remains considerably higher than that of the composite not subjected to HPT. Thus, the combination of repeated cold drawing with further high-pressure torsion provided substantial strengthening and higher thermal stability of the composite in comparison with niobium and copper nanostructured by severe plastic deformation.