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 1nm to 100nm. The hardness increases with decreasing h and reaches a maximum at 10nm. A sharp softening has been observed when h is below 10nm. Furthermore, the results show that the phases of Ta layers vary from the coexistence of alpha -Ta and beta -Ta to single alpha -Ta as h decreases from 10nm to 5nm. 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.