High temperature internal friction in α-zirconium

The high temperature internal friction spectrum of α-Zr is resolved into five peaks, P0 to P4, in addition to a background, B, that increases exponentially with the temperature. P0 is attributed to the thermally assisted unpinning of dislocations from oxygen interstitial pinning points. P1 is caused by the longitudinal redistribution of the same pinning points in the dislocation core, while P2 is caused by the transverse core diffusion of these pinning points. Both P0 and P1 give rise to characteristic peaks of internal friction as a function of strain amplitude. The ratio of the modulus defect to the internal friction at the peak position is 0.5 in the case of unpinning, and significantly greater than 0.5 in the case of longitudinal core diffusion. A behavioural phase diagram or map is constructed to interpret the complex non-linear behaviour occurring in the temperature-strain amplitude plane in the regions where P0, P1 and P2 overlap. (author)