Effect of hydrogen on the temperature dependence of the elastic constants of tantalum single crystals

Abstract

An investigation was undertaken to determine whether or not a significant Snoek relaxation mechanism exists when hydrogen is dissolved in tantalum. The experimental approach involved the determination of the changes in the absolute values and the temperature (in the range 136–298 °K) dependence of the elastic constants of single crystals charged with varying amounts of hydrogen up to 10.3 at %. Changes in the absolute values of the elastic constants, as a function of hydrogen concentration, were found to be linear, with positive slopes for C11, CL, and C44, and a negative slope for C′. The small negative slope of C′ yields the distortion parameter (λ1−λ2) value of 0.0274. The bulk modulus and the Voight average Young’s modulus were found to increase when hydrogen was introduced into the crystal lattice. The elastic constants exhibit no change in their temperature dependence when either the temperature (in the range 245–298 °K) or the hydrogen concentration (in the range 0–10.3 at.%) was varied. It is concluded that a Snoek relaxation attributed to tetrahedral symmetry of the locally distorted tantalum cubic lattice by hydrogen is insignificant.