Frictional properties of titanium carbide, titanium nitride, and vanadium carbide: Measurement of a compositional dependence with atomic force microscopy

The frictional properties of TiC(100), TiN(100), and VC(100) surfaces have been investigated on the microscopic scale by atomic force microscopy. In t his work, friction measurements were performed under controlled ambient con ditions to emulate the use of these materials as hard coatings. A variety o f tip materials, silicon nitride, titanium carbide, titanium nitride, and t ungsten carbide, were used to investigate the correlation between surface c omposition and frictional properties of the carbide and nitride substrates. The surface compositions of both clean and air-exposed samples were charac terized by x-ray photoelectron spectroscopy to complete the composition/fri ction correlation. In these studies, the TiC(100) substrate exhibited the l owest frictional response of the substrate samples, regardless of tip compo sition. The friction measurements on TiN(100) and VC(100) exhibited a stron g dependence on counterface composition and were consistently higher than t hose of TiC. In addition to the compositional dependence, the influence of humid conditions on the frictional properties of these carbide and nitride substrates has been investigated. The measured friction of each of these sa mples increased monotonically as a function of relative humidity. The magni tude of these increases has been correlated with the substrate surface free energies as probed by water contact angle measurements. (C) 2000 American Vacuum Society.