E de Wit

The tribochemical behaviour of TiN-coatings during fretting wear

Abstract To reveal the tribochemical reactions during fretting wear of TiN-coatings sliding against corundum, the microstructure and the chemical composition of debris have been investigated by analytical TEM. Novel observations on fretting wear debris are presented. These observations were possible thanks to a TEM-sample preparation procedure by ultramicrotomy. Based on friction force measurements, the tribological life of the TiN-corundum tribo-pair, was divided in five periods, namely: a running-period, a first transition, an intermediate steady state, a second transition, and a final steady state. Fretting experiments were stopped at different periods after which the debris were collected and characterised. The structure of fretting wear debris appeared to be dependent upon the moment of formation. The collected debris consisted of either amorphous or nanocrystalline rutile-like material. For comparison, fretting tests were also performed on pure titanium sliding against corundum. The debris originating from titanium consisted of nanocrystalline rutile. The observed difference in microstructure between the debris from TiN and pure titanium is mainly due to differences in the tribochemical reactions occurring during fretting wear. The evolution from amorphous to nanocrystalline debris on TiN, is proposed to be due to the combined effect of relative humidity, energy input, and continuous oxidation.

The crystallization of amorphous debris on titanium nitride coatings influenced by sliding wear conditions

The microstructure and the chemical composition of wear debris generated on TiN coatings have been investigated by analytical TEM in order to reveal the influence of the relative humidity on the tribochemical behaviour of these TiN coatings. Novel observations on wear debris generated at different sets of fretting test conditions are presented. The structure of such wear debris appears to be dependent on the relative humidity. Fully amorphous debris are generated at 10% RH, while at 85% RH the debris are nanocrystalline. At 50% RH the debris structure is dependent on the moment of formation. For comparison pin-on-disk tests were performed and the crystallization temperature of amorphous debris in dry air was determined by differential scanning calorimetry. The effect of water vapour on the crystallization temperature was investigated by series of heat treatments. Water vapour decreases the crystallization temperature significantly.

The oxidation reaction during sliding wear influencing the formation of either amorphous or nanocrystalline debris

The microstructure of wear debris originating in sliding tests from pure metals which form stable metal oxides with the rutile structure (like: manganese, tin and titanium) has been investigated by analytical TEM. The influence of the oxidation reaction on the formation of either amorphous or nanocrystalline debris was studied. Data on wear debris generated on manganese and tin are presented and compared with observations on debris from pure titanium. These observations support the thesis that the debris structure is depending on the oxidation kinetics. Evidence is given for the crystallization of amorphous debris due to continuous oxidation during wear.

ULTRAMICROTOMY ON FRETTING WEAR DEBRIS

A TEM‐sample preparation method for small amounts of fretting wear debris is presented. After embedding in a resin, the debris are ultramicrotomed to ultra‐thin sections. In this way, valuable observation of nanocrystalline fretting wear debris originating from TiN‐coatings could be rapidly obtained. Microsc. Res. Tech. 40:492–494, 1998.

Lubricating reaction products on TiN coatings during sliding wear in phosphoric acid

Abstract The debris structure influences the tribological behaviour of TiN coatings sliding against corundum. During sliding wear in environmental air, self-lubricating debris can be generated depending on the conditions. The (micro)structure of the debris varies with the relative humidity, temperature, mechanical attrition and temperature. In this paper, the wear rate and the friction of TiN coatings are compared with uncoated tool steel substrates sliding against corundum in: humid air, demineralised water, and phosphoric acid (0.02 M H 3 PO 4 ). Differences in the tribological behaviour are explained in terms of the interaction with the environment. In phosphoric acid, TiN coatings sliding against corundum show very low friction forces and wear rates due to the formation of a lubricating gel.