Evolution of Ni structure at dynamic channel-angular pressing

Evolution of structure of polycrystalline Ni subjected to high-speed severe plastic deformation (SPD) by dynamic channel-angular pressing (DCAP) has been studied by transmission and scanning electron microscopy and electron back-scatter diffraction (EBSD) analysis. Possibility of obtaining ultra-fine grained structure in pure Ni by DCAP is demonstrated, and its specific features are discussed. It is shown that fragmentation of Ni structure by DCAP is accompanied with significant strengthening, the fragmentation mechanism at DCAP being in general the same as at equal-channel angular pressing (ECAP). The refinement of structure and strengthening at DCAP occur faster, by less number of passes than at ECAP. The thermal stability of the structure obtained by DCAP is close to that after ECAP, and is somewhat higher than after high pressure torsion (HPT).