Elastic-Constant Anomalies in Metallic Superlattices: A Molecular-Dynamics Study

The elastic constants of Ni are calculated with use of molecular dynamics; at ∼ 5% [111] axial strain there is a large (∼ 35%) softening of the $C_{44}$ shear modulus and a stiffening of the in-plane Young's (∼9.5%) and biaxial (∼8%) moduli. These calculations are in remarkable agreement with experimental $C_{44}$ for Mo/Ni superlattices. The experimentally observed transition to a highly disordered state occurs at the same strain value at which in the calculation the crystal becomes unstable.