It was recalled that, in addition to controlling the dislocation sub-structure in coarse-grained materials, the stacking-fault energy also affected the propensity to form deformation twins. However, the influence of stacking-fault energy had not been fully explored in nanocrystalline materials. Here the role of stacking-fault energy in deformation-twinning and work-hardening was systematically studied in bulk artefact-free, nanocrystalline Cu (stacking-fault energy = 55mJ/m2), and a nanocrystalline Cu–12.1Al–4.1at%Zn alloy (stacking-fault energy = 7mJ/m2). The nanocrystalline Cu (23nm) and nanocrystalline Cu alloy (22nm) were synthesized using in situ consolidation during cryo and room-temperature milling. Both materials showed ultra-high tensile strength, significant strain hardening, and good ductility. The nanocrystalline Cu alloy exhibited a higher yield strength and lower uniform elongation (1067MPa, 6.5%) than that of nanocrystalline Cu (790MPa, 14%). The stacking-fault energy variation played a significant role in strengthening the nanocrystalline Cu alloy. High-resolution transmission electron microscopy analyses revealed that the low stacking-fault energy of the nanocrystalline Cu alloy alters the deformation mechanism from a dislocation-controlled deformation, which allows for the higher strain hardening observed in the nanocrystalline Cu, to a twin-controlled deformation.

Effect of Stacking Fault Energy on Mechanical Behavior of Bulk Nanocrystalline Cu and Cu Alloys. K.Youssef, M.Sakaliyska, H.Bahmanpour, R.Scattergood, C.Koch: Acta Materialia, 2011, 59[14], 5758-64