The asymmetric temperature dependence of yield stress in tantalum single crystals at low temperatures

Abstract

Single crystals of tantalum with a specific orientation for tensile axis were subjected to tests over the temperature range of 77°K to 483°K at two strain rates. The yield behavior at cryogenic temperatures was deduced to be asymmetric, i.e., Schmid's law did not apply for the orientation investigated. The observed flow stress behavior is suggested to be controlled by a Peierls mechanism as verified by activation energy and activation volume calculations. The modified Peierls model of Dorn and Mukherjee, which suggests that low-temperature deformation of body-centered cubic metals is controlled by the rate of thermally assisted nucleation of kink pairs on asymmetric a/2[111] screw dislocations, is used and it is demonstrated that the theory account satisfactori for the temperature and strain-rate dependence of the yield stress.