Tribological characterisation of a-C:H coatings at room temperature - effect of counterbody material

Metal free amorphous carbon (a-C:H) coatings with 15 % hydrogen were deposited on bearing steel surfaces. The friction and wear performance of these specimens was characterised in oscillating sliding tests with a ball on flat geometry. Balls of four different ceramic and four metallic materials were investigated in tests at room temperature. Special attention was paid to the effect of moisture by testing in dry, normal and moist air, respectively. The effect of water vapour on friction and wear of the a-C:H coating was quite different for the different counter body materials. The wear is in all cases very low with a coefficient of wear below 10(exp -7) mm(exp 3)/Nm for the most cases. The coefficient of friction is also very low between 0.04 and 0.12 in most of the tests. The smalles wear and friction coefficient were found for oxide ceramics while during tests against SiC and Si3N4 the coating has been worn through during the test. Effects of counter body material and humidity of surrounding air are discussed in terms of friction and wear mechanisms.