Anomalous plastic deformation in nanoscale Cu/Ta multilayers

This work presents a length-scale induced anomalous plastic deformation of Cu/Ta multilayers with individual layer thickness (h) varying from 1 nm to 100 nm. The hardness increases with decreasing h and reaches a maximum at 10 nm. A sharp softening has been observed when h is below 10 nm. Furthermore, the results show that the phases of Ta layers vary from the coexistence of α-Ta and β-Ta to single α-Ta as h decreases from 10 nm to 5 nm. The phase transition causes the variation of interface structures as well as the hardness of Ta layers and results in the anomalous decrease in hardness. The strengthening mechanisms at different length scales are discussed separately.