The effect of ultrasonic vibrations on the mechanical properties of nanocrystalline titanium

Mechanical properties of nanocrystalline titanium were studied under uniform confined compression with ultrasound oscillations of 20 kHz to clarify the way high frequency vibrations affect mechanical properties of nanocrystals. The nanocrystalline VT1-0 titanium of commercial purity used in the experiments was produced employing cryogenic grain fragmentation technique. This material has a broad distribution in grain size (20...80 nm) with the average size amounting to 40 nm. The amplitude of cyclic stress approaches 275 MPa. The high frequency vibrations are found to lower the yield stress and to initiate the formation of shear bands. With the deformation rate of 10^-4 s^-1 the yield stress becomes 2.5 times lower, and the major shear band forms under the deformation of 0.11 which is 5.7 times lower than the true deformation before the major shear band formation without action of the vibrations. On increasing the deformation rate up to 10-3 s-1 the consequences of high frequency vibrations impact weaken substantially.