Wetting of MoNbTaW HEA coated graphite/diamond by molten copper at 1100 °C

This work investigates the wetting of copper (Cu) on surface-modified graphite/diamond substrates for transpiration cooling in extreme environments. Refractory metal films (W, Nb, Ta, Mo) and a WNbTaMo high-entropy alloy (HEA) coating were deposited via magnetron sputtering for the purpose of surface modification. Results show that carbide formation (e.g., WC, Mo 2 C, (WNbTaMo)C) significantly improves Cu wettability (contact angle as low as 10°), with the sequence W > Mo > WNbTaMo > Nb > Ta. The HEA film contributes approximately 20.3 % of the solid/liquid interfacial energy (∼923 mJ/m 2 ), attributed to its high interfacial entropy (−0.137 mJ/(m 2 ·K)), which significantly exceeds that of conventional metal/metal systems. The Cu/WNbTaMo-graphite composite exhibits self-driven transpiration cooling when oxidized, as the HEA layer decomposes into volatile oxides, releasing liquid Cu. This work provides quantitative insights for designing high-temperature thermal management materials, demonstrating ∼32 % enhanced thermal conductivity (484 W/(m·K) at 1100 °C) through HEA interfacial engineering. • Refractory metals (W, Mo, Nb, Ta) and WNbTaMo HEA form carbides with graphite, achieving 10° copper contact angles (W > Mo > WNbTaMo>Nb > Ta). • WNbTaMo HEA's high entropy (−0.137 mJ/(m 2 ·K)) contributes 20.3 % of 923 mJ/m 2 interfacial energy, outperforming metals. • HEA decomposes at 1100 °C into volatile oxides, switching bonding from chemical to physical and enabling self-regulating copper exudation for cooling.