Low-temperature acoustic properties of nanostructured zirconium obtained by intensive plastic deformation

The temperature dependences of the logarithmic decrement and dynamic Young's modulus of polycrystalline coarse-grained and nanostructured Zr are studied at temperatures of 2.5-340 K. A nanostructured state of samples with grain sizes on the order of 100 nm was produced by intensive plastic deformation (IPD). The measurements were made using a two-component vibrator technique at frequencies of 73-350 kHz. A relaxation peak in the internal friction near 250 K was discovered in the coarse-grained, annealed Zr which is retained after IPD, but its height increases by roughly a factor of 10 and the localization temperature shifts to lower values. In addition, after IPD a new internal friction peak shows up at moderately low temperatures near 80 K. The activation parameters for the observed peaks are estimated and it is shown that they arise from different thermally activated dislocation processes: interactions of dislocations with impurities and kink pair formation in dislocations. It was found that IPD is accompanied by a significant (1-8%) reduction in the Young's modulus because of quasistatic and dynamic dislocation effects. A glass-like anomaly appears in the temperature dependence of the Young's modulus of nanostructured Zr at T < 20 K which may be determined by tunnelling and thermally activated relaxation of quasilocal excitations. (c) 2011 American Institute of Physics. [doi:10.1063/1.3556667]