The main goal of high-pressure torsion (HPT) process is to reduce the grain size. Experiments have shown that this aim is achievable, but there is a limit in reducing the grain size. The present paper investigates this limit through a thermodynamics-based model. However, this was investigated by other researches through dislocation density-based model. At first, the validity of the model in description of the limiting grain size obtainable by HPT of different materials is examined. Then, the influence of inherent material parameters is investigated. Finally, the present results are compared with those obtained by equal channel angular pressing.
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