Abstract
In most cases, machine components, which come in contact with each other, are made of steel. Common steel types include 100Cr6 and X105CrMo17 are widely used in rolling bearings, which are subjected to high static loads. However, more and more sophisticated structural applications require increasingly better performance from steel. The most popular methods for improving the properties of steel is carburisation or nitriding. Unfortunately, when very high surface properties of steel are required, this treatment may be insufficient. Improvement of tribological properties can be achieved by increasing the hardness of the surface, reducing roughness or reducing the coefficient of friction. The formation of composite layers on steel, consisting of a hard nitride diffusion layer and an external carbon coating with a low coefficient of friction, seems to be a prospect with significant potential. The article describes composite layers produced on X105CrMo17 steel and defines their morphology, surface roughness and their functional properties such as: resistance to friction-induced wear, coefficient of friction and corrosion resistance. The layers have been formed at a temperature of 370°C in successive processes of: nitriding in low-temperature plasma followed by deposition of a carbon coating under DC glow-discharge conditions. An evaluation was also made of the impact of the nitrided layers on the properties and morphology of the carbon coatings formed by comparing them to coatings formed on non-nitrided X105CrMo17 steel substrates. A study of the surface topography, adhesion, resistance to friction-induced wear and corrosion shows the significant importance of the substrate type the carbon coatings are formed on. DOI: http://dx.doi.org/10.5755/j01.ms.22.3.7532
Highlights
IntroductionDLC (diamond-like carbon) or NCD (nanocrystalline diamond) carbon coatings have been extensively tested for over 30 years [1], but it is only recently that they have found application in industry
DLC or NCD carbon coatings have been extensively tested for over 30 years [1], but it is only recently that they have found application in industry
A three times higher critical load for the carbon coating formed on steel in initial state is indicative of much better adhesion of the carbon coating to X105CrMo17 steel than to the nitrided layer formed on the same substrate
Summary
DLC (diamond-like carbon) or NCD (nanocrystalline diamond) carbon coatings have been extensively tested for over 30 years [1], but it is only recently that they have found application in industry. The wide interest in these coatings derives from their high resistance to wear by friction and corrosion, good hardness, as well as chemical inertness and the biocompatibility of these materials [3 – 5]. This outstanding combination of different properties gives this material very high potential in tribological applications. Carbon coating deposition in conditions of glow-discharge nitriding takes place in an atmosphere of methane and nitrogen at a temperature, which does not exceed 400 °C This means that the tested coatings can be produced on steel elements without a significant drop in the hardness of their core. An additional advantage of this method is the possibility to carry out (in one technological process) nitriding or carbonitriding, and by changing the composition of the mixture of gas and pressure in the working chamber, a carbon coating can be deposited on the nitrided or carbonitrided substrate
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