Plastic Deformation in Highly-Concentrated KCl-KBr Solid Solution Single Crystals from 1.6 K to 923 K

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Abstract
Compression tests are performed on KCl- 9∼92 mol% KBr crystals with dynamic observation of the group motion of dislocations using a polarizing microscope to examine the stress birefringence pattern. With increasing temperature, the yield stress τy decreases rapidly below 350 K but has a plateau region from 350 K to 750 K and decreases again rapidly above 750 K. The relation τy∝c(1-c), where c is the concentration of KBr, is found above 79 K. The yield stress below 350 K is controlled by the thermally-activated motion of dislocations overcoming concentrated solute atoms. In the plateau region, intermittent progression of edge dislocation walls, which induces serrations in the stress-strain curves, is observed using the birefringence, and the stress change due to the strain-rate change tests almost equals zero. These results are in good agreement with the theory of plateau stress [Jpn. J. Appl. Phys. 17 (1978) 251].