Thermal and mechanical characterization of under-2-µm-thick AlCrNbSiTi high-entropy thin film

Abstract

High-entropy alloys (HEAs) exhibit extraordinary physical properties such as superior strength-to-weight ratios and enhanced corrosion and oxidation resistance, making them potentially useful in energy storage and generation industries. However, thermal and mechanical properties of HEAs with various compositions vary significantly. Furthermore, these properties have rarely been investigated simultaneously owing to material or instrumentation limitations. Herein, we synthesize an HEA (AlCrNbSiTi) coating with a thickness of less than 2 $\mu$m. We customize a frequency-domain photothermal testing system to characterize the thermal and mechanical properties of the proposed coating with high accuracy. Owing to the large mixing enthalpy of the Al-Ti, Nb-Si, and Ti-Si pairs in the coating, its hardness and elastic modulus are 15.2 and 254.7 GPa, respectively which are higher than those of previously reported HEAs. The thermal conductivity of the AlCrNbSiTi coating is characterized to be 2.90 W·m⁻¹·K⁻¹, within the expected range and well explained by the free-electron consistency diversity and phonon scattering from the amorphous structure. Additionally, the coating exhibits adequate wear performance, with a wear rate of 5.4 × 10⁻⁸ mm³·N⁻¹·m⁻¹. This relatively low thermal conductivity, combined with extraordinary mechanical properties, makes the proposed material an excellent candidate as a protective coating material for nuclear reactor components which require high strength, irradiation resistance, and thermal protection.