The surface tension of superheated and undercooled liquid Ni–5 wt % Si alloy was measured by an electromagnetic oscillating drop method over a wide temperature range from 1417 to 1994 K. The maximum undercooling of 206 K (0.13 TL) was achieved. The surface tension of liquid Ni–5 wt % Si alloy is 1.697 N m−1 at the liquidus temperature 1623 K, and its temperature coefficient is −3.97×10−4 N m−1 K−1. On the basis of the experimental data of surface tension, the other thermophysical properties such as the viscosity, the solute diffusion coefficient, and the density of liquid Ni–5 wt % Si alloy were also derived.

The surface tension of superheated and undercooled liquid Co 25wt.% Si alloy was measured by an electromagnetic oscillating drop method. The experimental temperature regime was from 1384 to 2339K and a maximum undercooling of 223K (0.14TL) was achieved. The surface tension of liquid Co 25wt.% Si alloy is 1.604Nm−1 at the liquidus temperature of 1607K, and its temperature coefficient is −4.0×10−4Nm−1K−1. On the basis of previous research results of pure Co and Si, an expression is developed to predict the surface tension of binary Co–Si alloy system. The other thermophysical properties, such as the viscosity, the solute diffusion coefficient, and the density of liquid Co 25wt.% Si alloy are also derived by the relevant theoretical models.