Atmosphere dependence of the frictional wearing properties of partly-polished polycrystalline diamonds

Low friction and low wear states were realized with partly-polished diamond films. Polycrystalline diamond films were deposited onto TiC substrates by microwave chemical vapor deposition using a gas mixture of CH₄ and H₂. The deposited diamond film was polished with each other up to a surface roughness R_a = 0.25 μm. A newly developed pin-on-disk examination method was proposed in order to realize sliding between parallel flat surfaces without misalignment. These pins were fabricated using one of the following metals: hard die steel, D2, and stainless steels, AISI440C, AISI420 and AISI304. Friction and wear tests were carried out in ambient air, dry air and in a nitrogen atmosphere. In the case of D2, we confirmed a very low and stable friction coefficient μ = 0.08 when the test were performed in an ambient atmosphere without the usage of lubrications. Furthermore, we obtained much lower friction coefficients in the nitrogen atmosphere. Among all metals studied, the wear volume was also very minute in the case of the hard metals of D2 and AISI440C.