It was noted that nanolayered materials consisting of alternating layers of two different metals offered enhanced mechanical properties such as hardness. However, the strengthening mechanism was not well understood when the bilayer thickness approached a few nm. The uniaxial compression of aluminum/palladium pillars (900nm diameter) with bilayer thicknesses of 2, 20 or 80nm was reported here. It was observed that the deformation behavior of these pillars depended upon the bilayer thickness: changing from dislocation-driven plasticity at large bilayer thicknesses to shear due to grain rotation via grain boundary sliding at small bilayer thicknesses. The transition occurred at a bilayer thickness of about 20nm, where the operation of a mixture of the two mechanisms was apparent.

Transition from Dislocation Controlled Plasticity to Grain Boundary Mediated Shear in Nanolayered Aluminum/Palladium Thin Films. P.Dayal, M.Z.Quadir, C.Kong, N.Savvides, M.Hoffman: Thin Solid Films, 2011, 519[10], 3213-20