Transfer films on corundum balls from sulfur deficient molybdenum disulfide (MoSx) coatings with different crystallographic orientations were investigated after fretting tests performed in ambient air of different humidity levels. The morphology of wear tracks on MoSx coatings and of transfer films on corundum balls were investigated by light optical microscopy with Normarski contrast. The thickness of transfer films was measured by scanning white light and optical phase-shifting interferometry, and their composition was analyzed by X-ray photoelectron spectroscopy. The effect of relative humidity in fretting tests on the composition of the transfer films as well as the effect of the transfer film on the tribological performance of MoSx coatings in fretting wear tests is discussed.

A systematic study was carried out by means of paramagnetic susceptibility measurements, X-ray diffractometrv, and X-ray photoelectron spectroscopy (XPS) in order to determine crystal and electronic structure changes along with alloying additions. The experimental NIT temperatures were compared with those calculated for ZrCu-based alloys with the help of Shabalovskaya semi-empirical approach [1]. The results of such a comparison will be discussed.

Fretting tests under dry unlubricated conditions (22 °C to 25 °C, 50 to 55 pct RH) were performed on monolithic TiB 2 , TiB 2 -based cermet with a Ni 3 (Al,Ti) binder, sialon-TiB 2 , and ZrO 2 -TiB 2 composites to assess their relative wear performance against bearing-grade steel. Based on the measured friction and wear data, the relative ranking of the investigated fretting couples is established. The fretting wear of all investigated tribocouples was found to fall in the tribochemical wear regime. The extent of the tribochemical reaction was observed to be strongly dependent on the chemical solubility of TiB 2 and the binder phases in steel at the tribocontacts and was accompanied by tribo-oxidation. For the monolithic TiB 2 and TiB 2 -based cermet materials, however, abrasion and adhesive wear, in addition to the tribochemical reactions, are found to be the cause for the high volumetric wear loss of these tribosystems. On the other hand, mild abrasion coupled with reduced tribochemical reactions is observed to play a major role in the low wear loss of the ZrO 2 -TiB 2 /steel fretting couple. Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analysis of the tribochemical layer formed in the monolithic TiB 2 /steel tribocouple revealed the formation of mixed oxides containing predominantly TiO 2 (anatase), B 2 O 3 , and Fe 2 O 3 . Based on the thermodynamic calculations and the experimental observations, a tribochemical wear model is proposed to explain the observed tribological behavior of the investigated tribosystems.

Mechanically polished NiTi alloy (50at% Ni) was subjected to heat treatment in air in the temperature range 300–800°C and characterised by scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy and Raman spectroscopy. Thermogravimetry measurements were carried out to investigate the kinetics of oxidation. The results of thermodynamic calculations were compared to the experimental observations. It was found that NiTi alloy exhibits different oxidation behaviour at temperatures below and above 500°C. A Ni-free zone was found in the oxide layer for oxidation temperatures of 500°C and 600°C. The oxidation at 500°C produces a smooth protective nickel-free oxide layer with a relatively small amount of Ni species at the air/oxide interface, which is in favour of good biocompatibility of NiTi implants. The oxidation mechanism for the NiTi shape memory alloy is discussed.

Humidity is reported to have a considerable influence on the tribological behaviour of engineering ceramics. This paper reports on fretting wear experiments (mode I, reciprocating sliding) with self-mated polycrystalline tetragonal zirconia (Y-TZP) ceramics under dry, ambient and humid conditions. Based on the friction and wear data as well as the morphological investigation of the worn surfaces, the wear mechanisms under different humidity conditions are elucidated. It is unequivocally demonstrated that high humidity (85-90 % RH) significantly reduces friction and wear of self-mated Y-TZP ceramics. The morphology of the wear pits indicates that tribomechanical wear via cracking induced spalling is the major wear mechanism in dry and ambient humidity conditions. XPS analysis of worn surfaces revealed that the cause for the lower friction and wear under high humidity conditions is the formation of a lubricious hydroxide layer.

The tribological behaviour of MoS2 coatings in air of high humidity is critical for their application in air. An improved friction and wear resistance of sulfur-deficient MoSx coatings in humid air is reported based on fretting wear tests. For random-oriented MoSx coatings, the coefficient of friction and the wear volume are still significantly dependent on the relative humidity. On the contrary, basal-oriented MoSx coatings show an interesting low sensitivity to humidity. MoO3 and SO42− have been detected in the wear track and the debris. The amount of MoO3 and SO42− is related to the crystallographic orientation of the coatings and the relative humidity in the fretting wear tests. However, the structure and grain size of the MoO3 debris are not dependent on the relative humidity and the crystal orientation of the coatings. The effect of humidity on the friction and wear of these sulfur-deficient MoSx coatings with different crystallographic orientations is discussed.

Non-reactive d.c. magnetron sputtering by two magnetron sources with inclined geometry was used for deposition of Cr-C thin films with C:Cr ratio in the range 0.08-2.40. The phase composition of the films was investigated by x-ray diffraction, XPS, SEM and resistivity measurements. Four phase compositional regions were distinguished in the investigated large compositional range: films containing mainly microcrystalline Cr or Cr-C solid solution; films containing both the microcrystalline Cr phase and the stoichiometric Cr23C6 carbide phase (beta-phase); amorphous-like films composed of the ultradisperse Cr crystalline phase and different metastable carbides; and amorphous films consisting of a carbon matrix with a limited amount of a high-carbon carbide phase dispersed in it, The films from the first two regions exhibit very high microhardness and good wear resistivity, and at the same time a relatively low electrical resistivity, which make them promising coating materials for electronic applications. Copyright (C) 2000 John Wiley & Sons, Ltd.

A TiN coating, deposited by PVD, was rubbed against corundum balls in a laboratory fretting experiment for different number of cycles. The surface composition and chemical state of the wear tracks, debris found on the TiN coating and the transfer layer on the corundum counterbody were determined with X-ray photoelectron spectroscopy and Auger electron spectroscopy. The worn surfaces in all the wear tracks are depleted in oxygen when compared to a native surface, but are similar for the different fretting cycles. The transfer layer seems to be composed mainly of TiO2. The debris is also enriched in TiO2. The results indicate that the friction peak in TiN–corundum fretting experiments is not due to chemical differences in the wear tracks or at the surface of the transfer layer.