Plasticity in Nanocrystalline and Amorphous Metals: Similarities at the Atomic Scale

ABSTRACTFor metallic alloys, the amorphous state is often regarded as the limiting structure as grain size is reduced towards zero. One interesting consequence of this limit is that the properties of the finest nanocrystalline metals must begin to resemble those of metallic glasses. In this work we focus upon the nature of the plastic yield mechanisms in these material classes, and seek to identify commonalities and disparities in the nature of plastic yield in glasses and nanocrystals. The discussion is presented with reference to static atomistic simulations of (i) an amorphous binary alloy, and (ii) a nanocrystalline Ni specimen with grain size of 3 nm. We show that both these materials deform by the operation of fine atomic shearing events, and both exhibit asymmetric yielding as a consequence.

Evaluation of Anisotropic Film Structure of Amorphous Alloy by Computer Simulation

ABSTRACTA film growth of a virtual GdCo amorphous binary alloy was studied with a molecular dynamics simulation. A deviation of the atomic environment δ and an atomic pair distribution index η were calculated to evaluate the atomic structure of the prepared film. It was found that an anisotropic atomic distribution is induced in the film. The value of δ for a Gd atom environment is of the order of 10−4 and is almost in quantitatively agreement with the experimental value. The anelastic deformation is affected by the roughness of the substrate and becomes large in the film deposited on a smooth substrate. The value of η shows that the atomic pairs preferentially orient toward a horizontal film plane. The obtained results strongly support a single ion model as a main origin of a perpendicular magnetic anisotropy experimentally observed in amorphous rare earth-transition metal alloy films.