The influence of interstitial impurities on true grain-boundary sliding of titanium in coarse-grained and submicrocrystalline states

The structure and temperature dependence of low-frequency internal friction of Grade-2 and Grade-4 titanium specimens following equal-channel angular pressing is investigated. It is established that specimens of both grades in submicrocrystalline states possess a high fraction of high-angle boundaries (η ~ 70%) for the average grain size d ~ 0.8 μm. Formation of this structure results in a much lower temperature of initiation and development of true grain-boundary sliding compared to the coarse-grained titanium. It is noted that the grain-boundary sliding activation energy in submicrocrystalline titanium increases with the impurity concentration from 74 ± 4 (Grade-2) to 88 ± 4 (Grade-4) kJ/mol, but is found to be much lower for the coarse-grained recrystallized titanium (140 ± 4 kJ/mol).