Composite Layers with Ceramic Matrix Modified with Glassy Carbon Destined for Oil-Less Sliding Pairings

Abstract

The paper presents basic knowledge about producing and some results of tribological and metallographical research on composite layers with porous, anodic hard coating matrix which were modified with glassy carbon nanotubes. These composite layers were formed as surface layers of machine parts operating under conditions of sparse lubrication (limited lubrication) and friction in air. The layers were tested at sliding mating with EN-GJL-350 cast iron used for piston rings in combustion engines and air compressors. On the basis of the metallographical tests was the structure of the composite layer described. It was fount that on the surface of the oxide is a glassy carbon layer and in the pores of oxide are regullary carbon nanotubes. On the basis of the obtained results of tribological tests it was found that glassy carbon layer on the oxide surface shorts the wering-in time, and the glassy carbon nanotubes formed inside the pores of anodic hard coating upon EN-AW-6061 aluminum alloy prove to be effective solid lubricants and complement lubrication function of the graphite in cast iron. Consequently the coefficient of friction was lower than in case of nanotubes-free oxide layers.Keywords: composite layer, carbon nanotubes, sliding, lubrication, anodic hard coating W pracy przedstawiono podstawy wytwarzania oraz wyniki badań metalograficznych i tribologicznych warstw kompozytowych na osnowie porowatej, anodowej warstwy tlenkowej modyfikowanej węglem szklistym. Warstwy te zostały wytworzone jako warstwy powierzchniowe części maszyn współpracujących ślizgowo w warunkach ograniczonego smarowania (oszczęd-nego) oraz w warunkach tarcia technicznie suchego. Warstwy te zostały przebadane we współpracy ślizgowej z żeliwem EN GJL 350 używanym na pierścienie tłokowe silników spalinowych i tłokowych sprężarek powietrza. Na podstawie przeprowadzonych badań metalograficznych określono budowę i strukturę warstw kompozytowych, stwierdzając że na powierzchni tlenku wytwarza się warstewka węgla szklistego, a wewnątrz porów są regularne nanorurki węglowe. Na podstawie badań tribologicznych stwierdzono, że znajdująca się na powierzchni warstewka węgla szklistego skraca czas docierania skojarzenia a nanorurki węglowe wytworzone w porach anodowej warstwy tlenkowej na stopie aluminium EN-AW-6061 są skutecznym środkiem smarowym i wspomagają funkcje smarne grafitu znajdującego się w żeliwie. Współczynnik tarcia w skojarzeniu z warstwą kompozytową był mniejszy niż w skojarzeniu z warstwą tlenkową.

Glassy Carbon Coating Deposited on Hybrid Structure of Composite Materials

“…Secondly, glassy carbon distribution within the entire volume of the composite is uniform, with sedimentation or agglomeration and particles clustering being no matter of concern. Similar effect might be achieved in composites with porous ceramic matrix saturated with glassy carbon precursor subjected to pyrolysis in the presence of argon [9].…”

Composite Coatings with Ceramic Matrix Including Nanomaterials as Solid Lubricants for Oil-Less Automotive Applications

“…The synthesis of carbon nanotubes has been conducted due to bringing of liquid substance (polymer of polyfurfuryl alcohol in the presence of a catalyst, e.g., hydrochloric acid) including carbon into the pores and its carbonization in argon atmosphere at temperature of 1000°C [4]. The result of this is a composite coating with very hard, wear resistant oxide coating with regularly distributed glassy carbon nanotubes (9-16 CNTs per μm 2 )…”

“…The properties of carbon nanotubes can be shaped by the selected conditions of the pyrolysis of a precursor introduced into the pores of the oxide coating. Pyrolysis temperature and time help regulate the shear strength of the glassy carbon used as the material for nanotubes [4,6,7].…”

“…It is possible due to a formation of a permanent boundary lubricant layer, provided the pairing is lubricated with oil or greases. In vehicles, including engines and air compressors, the aim is to replace the oils and greases with solid lubricants [1][2][3][4]. To maintain the lubricating properties of oils (viscosity) it is necessary to ensure a proper cooling of compressors and engines which would result in their lower performance.…”

Effect of SiC and GR Reinforcement Particles on the Structure and Functional Properties of Composite Casting E43 MMC Reinforced with SiC Particles

“…The lubricant used most commonly is graphite. In places hard to access where the lubricant can not be applied, the composite structure is enriched with particles of graphite (GR) [11][12][13][14] or glassy carbon (Cg) [15][16][17][18]. As a result of this addition, when the composite is rubbing against a metal part, the effect of self-lubrication is triggered, reducing thereby the wear due to friction.…”