Deformation mechanisms of ultra-thin Al layers in Al/SiC nanolaminates as a function of thickness and temperature

The mechanical properties of Al/SiC nanolaminates with layer thicknesses between 10 and 100 nm were studied by nanoindentation in the temperature range 25 to 100 degrees C. The strength of the Al layers as a function of the layer thickness and temperature was obtained from the hardness of the nanolaminates by an inverse methodology based on the numerical simulation of the nanoindentation tests by means of the finite element method. The room temperature yield stress of the Al layers showed a large 'the thinner, the stronger' effect, which depended not only on the layer thickness but also on the microstructure, which changed with the Al layer thickness. The yield stress of the Al layers at ambient temperature was compatible with a deformation mechanism controlled by the interaction of dislocations with grain boundaries for the thicker layers (>50 nm), while confined layer slip appeared to be dominant for layers below 50 nm. There was a dramatic reduction in the Al yield stress with temperature, which increased as the Al layer thickness decreased, and led to an inverse size effect at 100 degrees C. This behavior was compatible with plastic deformation mechanisms controlled by grain boundary and interface diffusion at 100 degrees C, which limit the strength of the ultra-thin Al layers.