Small reductions in friction can result in large savings in power requirements, particularly at high speed. Lowering the viscosity of lubricating oils helps, but there is a lower limit on lubricant viscosity where functionality in the application is retained. Nanocomposite thin-film coatings have been employed in various applications to reduce sliding friction and surface wear and are proposed for use in gear applications. This work aims to demonstrate the potential benefit of applying nanocomposite coatings to gear teeth to reduce operating friction and wear by presenting tribological test data. A brief history of thin film coating technology development history is given in the following paragraphs (Refs. 1, 2). World War II Era Optical Coatings: During World War II, the demand for improved optics led to advancements in optical coatings. Antireflective coatings, composed of thin films, were developed to enhance the performance of lenses and other optical devices. Post-World War II Thin-Film Deposition Techniques: In the post-war period, there was significant progress made in thin-film deposition techniques. Vacuum deposition methods emerged, such as Physical Vapor Deposition (PVD) and Chemical Vapor Deposition (CVD). These techniques enabled precise control over coating thickness, microstructure, and composition, laying the foundation for developing nanocomposite coatings. 

 1950s–1960s Semiconductor Industry: The semiconductor industry’s growth in the 1950s and 1960s drove advancements in thin-film technology. Thin films became integral to the manufacturing of semiconductors, with techniques like sputtering and evaporation becoming widely adopted. 

 1970s–1980s

Plasma-Assisted Techniques: The use of plasmas to assist in thin-film deposition gained prominence in the 1970s and 1980s. Plasma-Assisted Chemical Vapor Deposition (PACVD) and Plasma Enhanced Chemical Vapor Deposition (PECVD) techniques were developed, improving thin film coatings’ mechanical and chemical properties and lowering processing temperatures. Late 20th Century Advancements in Coating Materials: Continued research led to the development of a wide range of coating materials. Thin films were now being applied not only for functional purposes like corrosion resistance and optical enhancement but also for novel applications in electronics, sensors, and medical devices.