Abstract
The changes in the absolute values as well as in the temperature dependences of the elastic constants C11, C44, C′, and CL as a function of dissolved hydrogen up to 1.7 at. %, in palladium single crystals have been determined. The measurements were performed in the temperature range between 140 and 310 K, using both longitudinal and shear 10-MHz ultrasonic waves. In the α phase, the changes in the absolute values of the elastic constants C11, C44, and CL were very small, while a larger effect of −1.2%/ at. % H was obtained in the case of the shear constant C′. The relative changes in the computed bulk modulus and Voight-Reuss average Young’s modulus in that phase are, respectively, +0.2% and −0.5%/ at. % H. The effects of hydrogen in the α phase on the temperature dependences of the elastic constants, however, are found to be significantly large in the case of C11 and CL and small in the case of the shear constants C′ and C44. These effects are discussed in terms of the volume expansion due to H in Pd, the possible electronic effect due to the addition of H to Pd, and finally the hydrogen contributions to the higher-order elastic constants. From this analysis, it is concluded that hydrogen in the α phase contributes primarily to the short-range ion core repulsive interactions in palladium.