DISLOCATION CORE DIFFUSION AND UNPINNING IN α-Zr

Abstract
The high temperature, low frequency, internal friction spectrum of deformed and annealed α-Zr is dominated at low strain amplitudes by a peak (P₂) at ≈ 600°C (4 Hz). At higher strain amplitudes, two new peaks P₀ (≈ 480°C) and P₁ (≈ 530°C) appear. It is shown that P₀ is due to the thermally assisted unpinning of dislocations from oxygen interstitials while P₁ and P₂ are due to the longitudinal and transverse movements of the same defects in the dislocation core. P₂, previously attributed to grain-boundary relaxation, is a Snoek-Köster peak. A behavioural map of the temperature-strain amplitude plane can be constructed to facilitate the interpretation of amplitude-dependent results. It is shown that unpinning can be distinguished from longitudinal core diffusion, even when both are observed at the same temperature, provided the modulus defect is measured together with the internal friction.