Neutron irradiation strengthening in copper single crystals

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Abstract
The temperature and strain rate dependence of the flow stress have been measured from 4·2°K to 373°K in neutron-irradiated copper single crystals as a function of neutron dose and solute additions. Between 77°K and 373°K solutes have very little effect on the flow stress and its temperature dependence. At 4·2°K a large amount of solute, 7–14 at. %, lowers the flow stress of pure copper crystals. From these measurements an activation energy and activation volume have been calculated. Both are solute independent and are analysed on the basis of a stress dependence, rather than a temperature dependence. It is thus shown that the results can be explained by assuming a single-valued energy for the thermally activated deformation process, rather than by assuming an obstacle size spectrum. The experimental results are shown to be in rather good agreement with Fleischer's strengthening theory based upon tetragonal distortions.