Investigation into high-temperature deformation of beryllium

The realization conditions, characteristics and the mechanism of the superplastic flow in the polycristalline beryllium were studied. The investigations were performed in the temperature range of 600-800 deg C and the stress range of 0.25-5 kg/mm2. The results of determining the creep activation energy and the dependence of the creep velocity upon the grain size and the stress applied, confirmed the assumption, that the most probable mechanism of beryllium creep is the Herring-Nabaro creep. The estimate of the contribution of the creep over the grain boundaries into the general deformation of a polycrystalline metal at high temperatures showed that with the temperature increase from 400 to 500 deg C the contribution increases, attains the maximum and decreases with further temperature increase. The temperature and rate dependences of the plastic flow stress, as well as the deformation curves are presented. Changes in the material structure and texture in the course of the flow are considered. Some characteristics of the flow process are theoretically estimated