Influence of stacking fault energy and alloying on stage V hardening of HPT-deformed materials

The grain refinement after high pressure torsion of pure metals and alloys exhibiting fcc crystal structure was examined. The aim was to characterise the influence of the stacking fault energy and the alloying on the grain size in the saturation regime. In this regime no further hardening of the material is observed and a constant mean grain size is obtained. Pure metals such as silver, copper and nickel and different brass alloys were severely deformed using high pressure torsion. During the severe deformation the torque curves were recorded for the different metals at different hydrostatic pressures. Due to the different deformation conditions, the influence of friction on the torque in the saturation regime can be estimated. In addition tensile tests were performed and the results were compared with flow stresses determined in the high pressure torsion experiments. A clear influence of the alloying on the flow stresses and the grain sizes of the materials was found, the stacking fault energy has a significant effect on the refinement, but only a minor effect on the saturation grain size.