Elastic modulus and hardness of Cu-Ta amorphous films

Mechanical properties were detected by the nanoindentation method for the Cu-Ta amorphous films with Ta content from 25.6 to 96 at.%. The hardness and elastic modulus are found to vary linearly with the Ta concentration. The incremental change of the elastic modulus is 1.35 GPa per Ta atom and that of the hardness is 0.205 GPa per Ta atom. The samples with Ta content higher than 71 at.% have higher elastic moduli than the crystalline counterparts of the mechanical mixture. This is similar to the supermodulus effect observed in the multilayers in many immiscible binary alloy systems. A model based on the inter-atomic potential is proposed to explain the enhanced modulus and relate it to the additional Gibbs free energy stored in the alloy after amorphization.