Effects of equal channel angular pressing temperature on deformation structures of pure Ti

A single equal channel angular pressing at various temperatures (473 to ∼873 K) was conducted on commercially pure titanium in order to investigate the effects of the pressing temperature on the microstructures. Optical and scanning electron microscopy showed that fine shear traces, elongated along the direction of approximately 25° inclined to the longitudinal axis of a sample, were well developed over the whole temperature range. Transmission electron microscopy revealed that the shear traces were composed of parallel bands having a width of a submicrometer scale. It was also revealed that the bands of a sample pressed at 473 K resulted from slip but those of samples pressed above 523 K resulted from {101̄1} deformation twinning. For the twinned samples, the twin density initially increased with temperature up to 623 K and then decreased at higher temperatures. Contrary to the changes of the twin density, the dislocation density decreased with temperature up to 623 K and then increased. At a pressing temperature of 873 K, fine recrystallized grains were also observed to appear in the vicinity of the shear traces. These anomalous microstructural changes with the pressing temperature were discussed in terms of the characteristics of {101̄1} twinning produced by equal channel angular pressing.