Thermophysical properties of undercooled liquid Ni-Zr alloys: Melting temperature, density, excess volume and thermal expansion

The thermophysical properties of undercooled liquid Ni-Zr binary alloys were investigated by molecular dynamics simulation combined with a Finnis-Sinclair (F-S) potential, including melting temperature, density, excess volume and thermal expansion. The melting temperatures were obtained by the evolution of crystal-liquid-crystal sandwich model, where there exist rather low differences of 4.14% for Ni_77.8Zr_22.2 alloy and 3.98% for Ni₅₀Zr₅₀ alloy when they were compared with the reported values. The calculated densities of liquid Ni-Zr alloys increase with the decrease of temperature, which agree well with the reported experimental values except for the Ni-rich composition alloys. Thus, the reported experimental density of liquid Ni_77.8Zr_22.2 alloy was employed to re-gauge the current F-S potential and the densities of the Ni-rich composition alloys were recalculated by the re-gauged potential. This binary liquid alloy system shows a negative excess volume, which could be attributed to the strong attractive interactions between Ni and Zr atoms. It is indicated that the Ni-Zr alloy system seriously deviates from the ideal solution, and the accuracy would be very low if the thermophysical properties are estimated by Neumann-Kopp rule. Meanwhile, the thermal expansion coefficients were also derived on the basis of the density data, which increase with the enhancement of temperature except for liquid Ni_77.8Zr_22.2 alloy.