Surface Property Enhancement of Gears

The overall performance of a gear system is intimately linked to the surface integrity of the gear surfaces. This usually implies that smooth and fully functional performance for an extended service life at high loads requires an improved surface durability. Surface durability is affected most notably by wear and fatigue resistance. Improved durability can be accomplished by surface modification techniques such as surface hardening and/or the applications of coatings. Various types of gear coatings such as molybdenum disulfide, tungsten carbide carbon, conversion, and polymer coatings; and advanced coating methods, namely, magnetron sputtering-based physical vapor deposition and plasma-enhanced chemical vapor deposition are detailed in this chapter. Modern surface hardening techniques such as laser treatment, ultrasonic peening, and water jet peening are also discussed. This is followed by the introduction of advanced methods of case-hardening including plasma nitriding, and induction and flame hardening. The working principle, process mechanism, and tangible benefits are presented, along with the latest trends and research aspects for each of the processes.