MICROSTRUCTURE AND TEXTURE GRADIENT IN TITANIUM SEVERELY STRAINED BY FRICTION ROLL PROCESSING AND SUBSEQUENT ANNEALING

摘要

The microstructure and texture evolution in titanium after severe plastic deformation using friction roll processing (FRP) followed by annealing has been investigated. FRP, which is a promising method to give severe strain in surface layers, was expected to obtain the grain refinement with preferred orientation. Significant changes of strain were imposed into from the surface toward the interior of samples, and then the mechanism of deformation was suggested. A few rotation speeds of roll were used as a parameter for finding the optimum operating conditions. Samples were annealed for various times at 823 K and then examined by scanning electron microscopy/ electron back scatter diffraction pattern (SEM/EBSD). In as processed sample, material flow was observed at the surface layer, while both tensile and compression twins were mainly found between the subsurface and center layers. After annealing for a short time, fine grains with transverse texture were observed only at the surfaces of the samples. With the increase of annealing time both microstructure and texture gradient can be formed on the sample through the thickness. Different deformation modes accompanied to strain gradients were discussed as the reason for formation of these microstructure and texture gradient.