Hard and adherent a-C:H gradient coatings by stress engineering

Hydrogenated diamond like carbon (a-C:H) coatings typically have low friction but high residual stress. The hardness which depends on the sp3 proportion increases not only the coating lifetime, but also the residual stress which can lead to easy film delamination especially for thick coatings. In this work, several thick a-C:H coatings (>10 μm) with different stress and hardness are prepared using stress engineering to mitigate stress accumulation while the hardness is retained. A low compressive residual stress of 0.42–0.84 GPa is achieved from the 8 μm thick a-C:H coating in addition to a high critical load of 63–74 N and hardness of over 26 GPa. The other desirable tribological and anticorrosion properties include a small friction coefficient of 0.13, low wear rate of 1.01 × 10−15 m3/N·m, high corrosion potential of - 479.6 mV, as well as small corrosion current density of 1.77 μA/cm2.