MD Studies of Phase transformations on Cu and Cu-Ag, Cu-Ni alloys

Y. Qi, T. Cagin, K. A. Mansour, Y. Kimura, W. A. Goddard

Abstract

The development of new metallic alloys which form bulk glasses at low cooling rates has led to significant advances in the study of under-cooled liquid metals and the glass transition in metallic systems. These new materials exhibit a rich variety of phenomena, such as liquid crystal phase separation and nanocrystalline phase formation, and have interesting potential as engineering materials.

We reparametrized the empirical many body potentials of Sutton-Chen type for various FCC metals, based on it we used MD simulation to study the behavior during heating the crystal and cooling the liquid for Cu, and Cu-Ag, Cu-Ni alloys. We used Ag-Cu alloy as a model system for glass former due to the fact that atomic radii of Ag and Cu have disparate values, but Ni and Cu have the similar atomic size. We studied the melting and glass transition of Ag-Cu eutectic alloy, the crystallization of Cu, the results are in good agreement with the experiments.

Liquid Ag6Cu4 forms glass phase when it is cooled down and the glass phase can keep to room temperature. The glass transition temperature Tg gets lower when the cooling rate is slower. But when the liquid Cu is quenched to room temperature at the same cooling rate, it crystallizes to FCC crystal. The lower the temperature it is cooled down, the faster the crystal process.