Abstract
Fatigue life curves and cyclic stress-strain curves of ultrafine-grained (UFG) copper of purity 99.9 pct produced by equal-channel angular pressing (ECAP) were determined under stress control at room temperature (RT) and at a temperature of 173 K. The obtained curves were compared to the corresponding curves obtained on conventional-grain (CG) copper. At both temperatures, the lifetime of UFG copper is longer than that of CG copper. The S-N curve of UFG copper is temperature dependent, while its cyclic stress-strain curve is temperature insensitive. To explain this temperature effect, two mechanisms of cyclic plastic deformation were proposed: the temperature-independent bulk dislocation mechanism taking place in the entire loaded volume and the temperature-dependent localized mechanism consisting of cooperative grain boundary (GB) sliding along the shear plane of the last ECAP pass taking place in the surface layer and leading to formation of surface fatigue markings.
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