Back pressure equal channel angular (BP-ECA) processing was utilised to consolidate a
dehydrided (DH) Ti powder of high interstitial content (1.15 wt.% O, 0.09 wt.% N) at 630°C into
fully dense bulk ultrafine-grained (UFG) Ti. The consolidated samples showed an increase in the
contents of oxygen (1.34 wt.%) and nitrogen (0.3 wt.%). The measured densities of 4.53 g/cm3 for
the consolidated samples after 1 and 3 passes were very close to the theoretical value of pure Ti.
TEM revealed the formation of a bimodal microstructure in the one-pass sample, comprising
equiaxed grains of several micrometers in size with ultrafine grains of the order of 100 nm
uniformly distributed at the triple grain junctions. Most grains had high-angle grain boundaries with
some boundaries exhibiting non-equilibrium characteristics. Upon further BP-ECA processing to
three passes, the micrometer-sized grains were refined down to the ultrafine level and copious
nanoscale deformation twins were introduced by severe plastic strain into those ultrafine grains of
the order of 100 nm. As a result of high interstitial contents and refined grains, the sample after
processing for 3 passes exhibited remarkably enhanced true yield and ultimate strengths of 1510
and 2050 MPa, respectively. Significantly, a noticeable compressive ductility was simultaneously
attained despite such a high interstitial content, thanks probably to the non-equilibrium grain
boundaries, bimodal grain structure and the occurrence of deformation twinning.