Plastic deformation mechanisms in face-centered cubic materials with low stacking fault energy

The microstructural evolution process of face-centered cubic Cu-30 wt%Zn, which has very low stacking fault (SF) energy of only 14 mJ/m², processed by high-pressure torsion, was investigated using transmission electron microscopy. Results reveal that deformation SFs/twin boundaries and cell blocks play the key role in the grain refinement process from ultrafine grains to nano grains. Equiaxed coarse grains with grain sizes of several microns were refined to ultrafine grains through the formation of high density of SFs, twins and cell blocks. With the accumulation of high density of dislocations at SF/twin boundaries, the emission of secondary SFs/twins further refined grains and transformed ultrafine grains into equiaxed grains with grain size of several tens nanometers. The observed grain refinement mechanism is significantly different from those of materials with medium to high SF energies in which full dislocation activities play a key role for grain refinement.