Microyielding in tantalum single crystals-II. High-amplitude damping

Abstract

The damping at high amplitudes and low frequencies in tantalum single crystals of three purity levels has been determined from uniaxial compression tests at temperatures in the range 77-300 K. Specimens were tested in the as-annealed or 77 K-prestained states. The results have an amplitude- and temperature-dependence which can be related to previous studies of internal friction and to the microflow parameters of the same specimens. It is concluded that at total strain amplitudes ≲ 5 × 10-5, non-screw dislocation motion is controlled by double-kink nucleation on 71° segments, which is the α' mechanism, and the motion of dislocations close to the screw orientation is controlled by kink migration, which is the α mechanism. Screw dislocation segments can move by double-kink nucleation at room temperature and this is the γ mechanism. At higher amplitudes, dislocations moving by these mechanisms can overcome the barriers provided by interstitial impurity atoms. © 1977.