The SPD processing resulted in reduction of the grain size. The
original titanium rods presented a 25 μm equiaxed grain structure.
It was reduced to 150 nm after combined SPD and TMT processing,
as shown in Fig. 3. At selected area of the nanostructured Ti microstructure
(Fig. 3c), the electron diffraction pattern further suggests
that the ultra fine grains contained predominantly high-angle grain
boundaries with non-equilibrium distorted structure leading to
their excess energy [28].