High cycle fatigue and wear behavior of ta-C and a-C:H coated PEEK polymer spur gears under dry contact conditions

Diamond-like carbon (DLC) coatings are under investigation as a potential solution for extending the service life of polymer gears. This study examines the fatigue and wear behavior of polyetheretherketone (PEEK) polymer gears coated with tetrahedral amorphous carbon (ta-C) and hydrogenated amorphous carbon (a-C:H) at thicknesses of 2 μm and 5 μm. The gears were subjected to reference gear pair testing at 1.8 Nm torque under dry contact conditions in a climate-controlled environment. The PEEK substrate and the DLC coated gear failure mechanisms include both tooth flank and root fatigue fractures, with minor tooth surface wear observed. Although DLC coatings wore off relatively early when meshing with steel gears, the service life of the ta-C (5 μm) and a-C:H (5 μm) coated gears was approximately twice that of the PEEK substrate gears and ta-C (2 μm) coated gears. In addition, the a-C:H coatings caused minimal wear on the steel counterparts due to their higher sp 2 hybridized graphite structure, whereas the ta-C coatings caused major wear due to their predominantly sp 3 hybridized diamond structure. Overall, the results demonstrate that ta-C (5 μm) and a-C:H (5 μm) coatings significantly improve the durability and performance of PEEK polymer gears, highlighting their potential for demanding applications. • Gear failure mechanisms primarily include tooth flank and tooth root fractures. • The DLC coatings wear off the tooth flanks early in the service lives of the gears. • The 5 μm coatings provide significantly longer gear service lives compared to 2 μm. • The 5 μm DLC coatings approximately double the average service life of PEEK gears.