Anti-Wear and Anti-Friction High-Entropy Alloy Coatings

High-entropy alloy (HEA) coatings have emerged as a transformative solution for wear-critical applications by leveraging their unique multi-principal-element compositions to deliver exceptional mechanical, thermal, and chemical properties. This chapter explores the fundamental principles underlying the tribological behavior of HEA coatings, emphasizing their capacity to mitigate wear and friction under diverse operating conditions. The chapter details various deposition techniques, such as physical vapor deposition, laser cladding, and thermal spraying, alongside their influence on microstructural evolution and coating performance. Key relationships between composition, microstructure, and tribological properties are analyzed, and their role in oxide scale formation, grain morphology, and lattice distortion is highlighted. The chapter also examines the performance of HEA coatings in environments ranging from room temperature to extreme conditions, including corrosive and abrasive settings. Industrial case studies and emerging applications underscore the potential of HEA coatings in sectors such as the aerospace, energy, and manufacturing industries. The chapter concludes with a discussion of challenges and future directions, including sustainability and large-scale implementation, that provides a comprehensive overview of HEA coatings as a next-generation solution for tribological challenges.