The ultra-high enhancement of hardness and elastic modulus in Ag/Nb multilayers

In this work, the hardness and elastic modulus were investigated in Ag/Nb multilayers with the individual layer thickness (h) ranging from 1 to 50 nm. The hardness increases with decreasing h, and the magnitudes of hardness of multilayers with h≤5 nm are higher than that of either constituent. This ultra-high strengthening results from the coherency stresses and high density stacking faults in Ag layers. Meanwhile, the enhancement of elastic modulus is achieved due to the lattice contraction when h≤20 nm, where the modulus values are higher than that of either constituent, showing a supermodulus effect.