A cluster-induced structural disorder and melting transition in the grain boundary of B2NiAl: a molecular-dynamics simulation on parallel computers

A structural disorder and melting transition of the sigma = 5 bicrystalline interface of B2 NiAl with a large boundary plane is investigated by molecu lar-dynamics simulations. The calculations have been performed at various t emperatures using an embedded-atom-method potential fitted to NiAl. It is o bserved that the atoms in the grain-boundary region tend to form clusters i n a thermal structural disorder transition, which is initiated at a tempera ture well below the thermodynamic melting point T-m (around 0.52T(m)). The number and size of the clusters are monitored over a wide temperature range including T-m. Below T-m, the number and size of the clusters increase con tinuously with increasing temperature. At temperatures up to T-m, the abrup t appearance of the clusters induces melting. At temperatures above T-m the number and size of the clusters decrease significantly upon raising temper ature. The calculations of the potential energy also indicate that the ther mal disorder transition is a continuous process, in contrast to the first-o rder melting transformation.