The Formation Of Friction-Induced Nanocrystalline Structure In Submicrocrystalline Cu-Cr-Zr Alloy Processed By Dcap

The paper studies the effect of high strain rate (10(5) s(-1)) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) under sliding friction on the evolution of the structure and properties of low-alloyed dispersion-hardened Cu-Cr-Zr alloys. It is shown that alloying of copper with chromium (0.09 - 0.14 %) and zirconium (0.04 - 0.08 %) microadditives changes mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: the cyclic character of structure formation associated with alternating of high-rate processes of fragmentation and dynamic recrystallization is changed to processes of fragmentation and partial strain aging resulting in precipitation of nanosized particles of the second-phase. The temperature-time regime of annealing (aging) of Cu-Cr-Zr SMC alloys processed by DCAP was established to improve the mechanical properties and electrical conductivity. In particular, for Cu-0.14 Cr-0.04 Zr SMC alloy it was shown that the optimal combination of microhardness (HV = 1880 MPa), electrical conductivity (80 % IACS), strength (sigma(0.2) = 464 MPa, sigma(u) = 542 MPa) and ductility (delta = 11 %) can be obtained by DCAP and aging at 400 degrees C for 1 h. The improved mechanical properties of the alloys as compared to copper are associated with extra hardening caused by precipitation of Cu5Zr and Cr nanoparticles (5 - 10 nm) in the process of DCAP and aging. It was shown that low-alloyed Cu-Cr-Zr alloys possessed a high work-hardenability due to the methods of DCAP and SPD under sliding friction. By the example of Cu-0.09 Cr-0.08 Zr alloy it was established that the wear rate of samples with SMC structure obtained by the DCAP method decreased by a factor of 1.4 as compared to the coarse-grained state. It was also established that the combination of the treatment by DCAP, aging at 400 degrees C, and SPD under friction of the alloy resulted in the formation of the friction-induced nanocrystalline structure with the grain size of 15 - 60 nm in the surface-layer material, which provided a high level of microhardness (3350 MPa) and low values of the friction coefficient (0.35).