Research on high entropy alloy thin films and their potential applications

Jyh-Wei Lee

Since the pioneering work of Prof. J.W. Yeh and coworkers in 2004, high entropy alloys (HEAs) have emerged as a new class of materials with exceptional properties, including high strength, good ductility, excellent wear resistance, thermal stability, corrosion resistance, and radiation tolerance. In addition to bulk HEAs, HEA thin films deposited by magnetron sputtering have attracted significant attention because they often exhibit superior corrosion resistance, oxidation resistance, mechanical strength, and tribological performance compared with conventional alloy coatings.

In this lecture, HEA nitride, carbide, oxide, and boride thin films were synthesized using high power impulse magnetron sputtering (HiPIMS). The effects of reactive elements—nitrogen, carbon, oxygen, and boron—on the phase evolution, mechanical properties, corrosion resistance and biocompatibility of TiZrNbTaFe, TiZrNbTaFeN, TiZrNbTaFeC, VNbMoTaWO, and HfVTiZrWB thin films were systematically investigated. Through the in-vitro cell tests and in-vivo animal tests, the TiZrNbTaFe HEA coatings improved both the quality and quantity of regenerated bone, highlighting their strong potential for orthopedic implant applications.

The hardness of TiZrNbTaFeN thin films increased significantly from 9.8 GPa to 36.2 GPa with the incorporation of 32 at.% nitrogen, which is attributed to the formation of metal–nitride phases and enhanced solid-solution strengthening effects. The influence of acetylene flow rate on the phase structure, hardness, and corrosion resistance of TiZrNbTaFeC coatings was also examined. Furthermore, VNbMoTaWO oxide films deposited on graphite felt electrodes were evaluated for their electrocatalytic performance in vanadium redox flow batteries, demonstrating improved energy efficiency of the system. In addition, the effects of deposition temperature on the mechanical properties, corrosion resistance and anti HF plasma etching performance of HfVTiZrWB boride thin films were explored.

These results demonstrate that precise control of reactive element content and sputtering parameters enables the design of multifunctional HEA thin films with tailored mechanical, electrochemical, biomedical, and catalytic properties, highlighting their strong potential for advanced protective coatings and sustainable energy applications.