High entropy alloy coatings for biomedical applications: A review

Metallic biomaterials are widely used as short and long-term implantable devices by virtue of their outstanding mechanical properties, such as high load-bearing capacity and fatigue resistance. Due to their inherent bioinertness, potential corrosion, and some inferior surface properties, metallic biomaterials generally require coating and surface modification to improve their function and extend their lifespan in the body. High entropy alloys (HEAs) are a novel class of materials that are composed of at least five principal metallic elements with equiatomic or close-to-equiatomic compositions. Some of the unique properties of HEAs for surface modification and coating include excellent corrosion resistance, remarkable wear resistance, high strength/hardness, and strong diffusion resistance. The coating of HEAs on metallic substrates can be achieved through different techniques, including thermal spraying, laser deposition, and vapor deposition. HEAs have become a promising candidate for biomedical applications by combining tailor-made surface topography, excellent biocompatibility, appropriate surface chemistry, and element composition design. The present article is a thorough review of the research on the surface modification and coating of metallic biomaterials using HEAs.