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.
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