Atomistic modeling of solid-state amorphization in an immiscible Cu-Ta system

An embedded-atom potential for the equilibrium immiscible Cu-Ta system is constructed with an important aid of first principles calculation, which provides some physical properties of two nonequilibrium CuTa and ${\mathrm{Cu}}_3\mathrm{Ta}$ alloy phases for fitting the potential. Applying the constructed potential, molecular dynamics simulations with a Cu-based solid solution model reveal that when the Ta solute atoms exceed a critical value of 30 at. % in Cu, the enthalpy of the model is elevated up to a high level, thus triggering first a fcc-to-orthorhombic martensitic transition and second a diffusion-controlled orthorhombic-to-disordered transition. Surprisingly, an anomalously large volume expansion of the Cu-based solid solution upon amorphization transition is observed and is calculated to be around 10%, which is much greater than the value of <2% usually observed in the binary metal systems characterized by a negative heat of formation. The simulation results are compared with the experimental observations and the agreement between them is fairly good. Besides, the physical meaning as well as the implication of the simulation results are also discussed.