Nitrides ceramic coatings for tribological applications: A journey from binary to high-entropy compositions

Friction and wear are two critical tribological factors that instigate unavoidable failures of moving components in the mechanical system. Additionally, these factors have a huge impact on global energy consumption, economy, and CO2 emissions. Minimization of friction and wear in mechanical systems is rather challenging, however, significant advancement has been achieved in the development of new techniques to mitigate these tribological issues. Surface coating is one of the most commonly used techniques to reduce/eliminate tribological failures. Though a wide range of hard and anti-wear coating materials (metallic alloys, carbon, metallic glasses, polymers, ceramics, and composites) have been developed in the last few decades, however, ceramic coatings have always been a prime interest to researchers owing to their outstanding hardness, wear resistance, corrosion resistance, and damping capacity. Specifically, nitride ceramic coatings have been passed a long journey as hard and wear-resistance protective coatings in multiple industries such as manufacturing, automobile, aerospace, etc. This article reviews the journey of the development of nitride coatings for tribological applications. These developments include first-, second-, and third-generation nitride ceramic coatings, which include binary, ternary, multi-elemental as well as multi-layered coating compositions. This review paper sheds light on the available literature, merits, demerits, and applications of all nitride ceramics coatings for tribological applications. Recently, an innovation in nitride ceramic coatings has been reported, which is the utilization of the high entropy concept in these coatings, which has been reported to improve their tribological properties tremendously. This review paper also delivers a comprehensive review of high-entropy nitride ceramic coatings (both equimolar and non-equimolar compositions) for tribological applications, which is the latest and hot topic for researchers working on ceramics coatings and tribology. At last, this review paper identifies the gaps and provides the future possibilities of research in this area.