High densities of growth twins and stacking faults were found in polycrystalline-Cu/AISI330 austenitic stainless steel multi-layered films with a <111> texture. In particular, the stainless steel layers exhibited twinning and faults on a scale of 3 to 4nm whereas, in the Cu layers, a large fraction of the grains exhibited twins with spacings of a few tens of nm. A model was developed which accounted for the formation of nanoscale twins, during sputter deposition, in terms of twin boundary or stacking fault energy and deposition rate. An increase in hardness with decreasing layer thickness obeyed the Hall–Petch law for layer thicknesses greater than about 50nm. At lower layer thicknesses, the hardness saturated at a value of about 5GPa. The hardening mechanisms were explained in terms of the layer thickness, and the twin spacing within layers.

Enhanced Hardening in Cu/330 Stainless Steel Multilayers by Nanoscale Twinning. X.Zhang, A.Misra, H.Wang, T.D.Shen, M.Nastasi, T.E.Mitchell, J.P.Hirth, R.G.Hoagland, J.D.Embury: Acta Materialia, 2004, 52[4], 995-1002