Nanoindentation investigation on creep behavior of amorphous CuZrAl/nanocrystalline Cu nanolaminates

Berkovich nanoindentation experiments have been performed on amorphous /nanocrystalline nanolaminates with individual CuZrAl layers (45 nm, 90 nm, 225 nm) and Cu layers (7.5 nm & 15 nm). Elastic modulus, hardness and indentation morphology were detected and compared to those of single CuZrAl thin film. Creep deformation was systematically investigated at various holding depths and loading rates. For the sample with thinner amorphous layer, a more pronounced creep deformation was observed and it was confirmed to be due to the size effect of CuZrAl layers and the addition of Cu layers. The creep deformation was identified to be history-independent through applying various loading rates. The strain rate sensitivities were calculated from the steady-state creep and a sharp enlargement appeared as the amorphous layer reduced down to 90 nm, implying a transition of creep mechanism in nanolaminates.