Frictional wear occurs primarily on the surface of materials, and the failure of most mechanical components is due to the resulting surface wear, which not only reduces their reliability and safety, but is typically unavoidable in most mechanical systems with moving parts. The durability and reliability of engineering components are closely related to their wear resistance. The development of advanced materials to reduce the energy and material losses in moving mechanical systems remains a significant challenge. Novel high-entropy alloys composed of multiple principal elements offer promising prospects for the development of materials with excellent wear resistance owing to their superior hardness, outstanding wear resistance, and excellent corrosion resistance. However, the preparation cost of block high-entropy alloys is high, and high-entropy alloy films are difficult to apply in practical situations. Therefore, high-entropy alloy coatings have become a popular research topic. By preparing high-entropy alloy coatings on the surface of materials, the surface hardness, mechanical properties, friction, and wear properties can be significantly improved, thus extending the service life. High-entropy alloy coatings have shown enormous potential for applications in areas where the wear resistance of the base material is more demanding; however, there are few relevant review papers. Hence, it is necessary to review current research results on the wear resistance of high-entropy alloy coatings. It is imperative to review the current research results on the wear resistance of high-entropy alloy coatings. Additionally, it is of utmost significance to understand the research progress in improving the wear resistance of high-entropy alloy coatings and to facilitate their applications in industry. According to the materials science and engineering tetrahedron, it can be concluded that the microstructure, heat treatment method, temperature, cooling method, holding time, preparation process, processing process, and whether a protective oxide layer is produced during the friction and wear experiments contribute to a significant impact on the tribological properties of high-entropy alloy coatings. Nevertheless, alloy composition is a fundamental factor affecting the wear resistance of high-entropy alloy coatings. Therefore, this paper reviews existing research and summarizes the effects of metallic elements such as Al, Ti, Cu, Co, Nb, Mo, and W; non-metallic elements such as Si, B, C, and O; composite effects of elements; and ceramic particles such as TiC and WC on the microstructure, hardness, and abrasion resistance of high-entropy alloy coatings. The results showed that the microstructure of high-entropy alloy coatings and their strengthening mechanisms could be changed by a trace or a substantial number of alloying components, which in turn improves their wear resistance. Alloying is an effective way to improve the tribological properties of high-entropy alloy coatings. An appropriate alloying composition will not only lead to lattice distortion and solid solution strengthening of the coatings, but also generate hard phases, thus elevating their hardness and wear resistance. The lubrication mechanism of precipitation hardening and reinforcement doping into high-entropy alloy coatings originates from the formation of hard reinforcement phases during the preparation process. Although the wear resistance of high-entropy alloy coatings is linearly related to their hardness, the hard phase can also function as abrasive particles to accelerate damage to the wear surface and reduce the wear resistance of the base material when the hard phase is exfoliated. Accordingly, it is crucial to rationally adjust the type and content of the reinforcing phase. The challenges faced in the current research work are highlighted, and the application prospects and development directions of high-entropy alloy coatings are envisioned. It has a positive effect on the development of more scientific and reasonable wear-resistant design schemes, enhancement of coating durability, and practical application effects to systematically review the current research related to the influence of alloy composition on the wear resistance of high-entropy alloy coatings. In addition, it contains reference values for scholars and researchers in related fields.
