Hypercooling limit and physical properties of liquid MoNbReTaW refractory high-entropy alloy

ABSTRACT The thermophysical properties of refractory MoNbReTaW high-entropy alloy in both supercooled liquid and high-temperature solid states were explored by an electrostatic levitation technique. The maximum supercooling attains 504 K, and the hypercooling limit is derived as 571 K. The liquid density at liquidus temperature is measured to be 13.3 g cm−3, which increases linearly with decreasing temperature at a slope of 6.83 × 10−4 g cm−3 K−1. The liquid alloy exhibits 5.3% relative volume shrinkage during crystallization. The thermal expansion coefficient of liquid and solid alloy at liquidus temperature are determined as 5.0 × 10−5 K−1 and 3.6 ×10−5 K−1, respectively. The liquid specific heat at liquidus temperature is found to be 38.2 J mol−1 K−1, and basically displays a linear decreasing tendency with temperature. According to the calculated enthalpy of fusion 24.7 kJ mol−1 and measured specific heats, the temperature-dependent entropy and Gibbs free energy difference between supercooled liquid and crystalline solid are obtained.