The internal friction of tantalum and columbium foils at ultrasonic frequencies

Abstract

The internal friction and effective elastic moduli of polycrystalline Ta and Nb foils were measured at vibrational frequencies of about 37 kilocycles and (for Nb) 111 kilocycles. Relaxation effects readily identified with O and N impurities were observed, and correlated with the low frequency data of other investigators. Activation energies for O and N diffusion in both Ta and Nb were observed to decrease with increasing temperature, while the internal friction peaks were shifted upward on the temperature scale when the impurity content was increased. Measurements extended over the temperature interval from about −160°C to about 1000°C. Low temperature anomalies in the internal friction of Ta are believed to be caused by hydrogen. Room temperature plastic deformation of both Ta and Nb produced large but poorly defined decrement increases between 20°C and 200°C, a range which showed no anomalies for annealed specimens.