Cryogenic temperature equal channel angular pressing of pure titanium: microstructure and homogeneity

Samples of pure titanium with a purity of 99.99 wt.% were successfully processed by equal channel angular pressing (ECAP) at cryogenic temperature. Deformed microstructures of ECAPed samples were characterized by electron backscattering diffraction (EBSD), and its homogeneity was studied by color-coded contour mapping of microhardness distribution. EBSD results indicate the original coarse grains with an average grain size of 196 μm were significantly refined to 0.56 μm after four passes, and that the prism slip systems were activated in the whole deformation process and with increasing passes number more slip systems were activated. The hardness mapping reveals that the microstructure of samples prior to ECAP is basically homogeneous but becomes inhomogeneous after one pass and then gradually homogeneous with additional passes. In addition, the grain refinement of ECAPed titanium at cryogenic temperature was discussed and confirmed by CDRX. Also, the factors of influence on the homogeneity of microstructure were analyzed.