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.

KEYWORDS:

• Thermal properties
• refractory alloys
• undercooled melts
• specific heat
• thermodynamics

Acknowledgements

We are grateful to Mr Y. J. Jin and Mr Z. X. Wan for their help with ESL experiments.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Data availability statement

The data that support the findings of this study are available within this article.

Additional information

Funding

This work was financially supported by the National Natural Science Foundation of China [grant numbers 51874244, 52088101 and 51401169] and NPU Excellent Personnel Supporting Project of Ao Xiang New Star.

Notes on contributors

L. Hu

L. Hu is an associated professor of NPU, main research interest is rapid solidification of high entropy alloys.