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

摘要

The microstructure and texture evolution in titanium after severe plastic deformationusing friction roll processing (FRP) followed by annealing has been investigated. FRP, whichis a promising method to give severe strain in surface layers, was expected to obtain the grainrefinement with preferred orientation. Significant changes of strain were imposed into fromthe surface toward the interior of samples, and then the mechanism of deformation wassuggested. A few rotation speeds of roll were used as a parameter for finding the optimumoperating conditions. Samples were annealed for various times at 823K and then examined byscanning electron microscopy/ electron back scatter diffraction pattern (SEM/EBSD). In asprocessed sample, material flow was observed at the surface layer, while both tensile andcompression twins were mainly found between the subsurface and center layers. Afterannealing for a short time, fine grains with transverse texture were observed only at thesurfaces of the samples. With the increase of annealing time both microstructure and texturegradient can be formed on the sample through the thickness. Different deformation modesaccompanied to strain gradients were discussed as the reason for formation of thesemicrostructure and texture gradient.