Tribological characterisation of carbon coatings at room temperature: Effect of counter-body material and humidity

Using high-current pulse-arc techniques (Laser-Arc, HCA), ta-C films of about 3 µm thickness and hardness up to 60 GPa have been deposited onto steel substrates. The films are characterized with respect to their density, elastic modulus, ad hesion, and surface roughness. The friction and wear behaviour was studied with oscillating sliding motion (gross slip fretting) with a ball-on-flat configurati on at room temperature. Since the tribological behaviour of carbon coatings can depend sensitively on the counter body material the coatings were tested against balls of different materials (bearing steel 100Cr6, alumina Al2O3, silicon nitr ide Si3N4). The effect of moisture content on friction and wear was investigated in the range of 3 % to 100 % R.H.. In all tests the friction was determined during the test, the wear (loss of material) was determined after the test for the ball and for the coated disk separately. The wear behaviour depends on the counter body material and on relative humidity of surrounding air. Against steel and alumina a high wear resistance is found in all environments the coating tends to fail in dry air against silicon nitride.