LOW-TEMPERATURE PHYSICS OF PLASTICITY AND STRENGTH

Multipass rolling of VT1-0 titanium at a temperature near that of liquid nitrogen to a strain e = -2 resulted in grain refinement from similar to 10 mu m to similar to 35 nm and a nearly twofold increase in microhardness. The microindentation measurements showed that the cryorolled samples had a rather homogeneous structure. An increase in the microhardness with increasing the strain can be described by the modified empirical Voce equation. The grain size dependence of the microhardness in the Hall-Petch coordinates consists of two parts with the slopes k(HP1) and k(HP2) < k(HP1) for the grain size smaller than similar to 250 nm. The strong temperature dependence of the microhardness for the investigated samples suggests that their plastic deformation has a thermally activated character. Close values of the thermoactivation parameters presumably indicate a common deformation mechanism in this material placed under an indenter over the entire grain size range. (C) 2015 AIP Publishing LLC.