Tribofilm formation on cemented carbides in dry sliding conformal contact

The friction properties and the tribofilm formation of a binderless cemented carbide and two conventional cemented carbides have been evaluated in an unlubricated sliding contact in either air or nitrogen surroundings. A continuously varied normal load and two rotational speeds were used. The tribofilms were analysed with SEM, XPS, TEM and EELS. For all cemented carbides, friction was lower at higher sliding speed. The two conventional carbides also tended to give a lower friction in air than in nitrogen, whereas the binderless carbide gave about the same friction in both environments. All materials formed tribofilms during the tests. Mild tests with the conventional cemented carbides resulted in relatively thick tribofilms (a couple of mu m) with low amounts of oxides. At more severe test conditions the tribofilms became thinner (< 1 mu m) and contained large amounts of oxides, together with WC and Co. The mechanisms behind the tribofilm formation are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.