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