Observation of the shear failure mode in nanostructured titanium under quasistatic uniaxial compression at 300-4.2 K

Abstract

Nanostructured Ti (100-300 nm average grain size), processed by severe plastic deformation through equal channel angular pressing of commercially pure Ti rods after quasi-static compression (at 0.0004 s -1 strain-rate) of prismatic (2x2x7mm) samples has at low temperatures (77 and 4,2K) yield strsses two times larger than the initial CP-Ti, failure stresses ranging from 1.4 to 2.4 GPa. The shear failure phenomenon has been observed at 77 and 4,2K. Nanostructured Ti is absolutely thermomechanically unstable against catastrophic plastic shear under low temperature straining. The catastrophic plastic shear spreads through the whole section of the sample with a velocity close to the transverse sound velocity and has a dynamical character. It is supposed that the micro mechanism of the shear failure of nanostructured Ti consists in extending of the catastrophic shear by grain boundary dislocations.