The fundamentals of coating tribology are presented in a generalised holistic approach to friction and wear mechanisms of coated surfaces in dry sliding contacts. This is based on a classification of the tribological contact process into macromechanical, micromechanical, tribochemical contact mechanisms and material transfer. The tribological contact process is dominated by the macromechanical mechanisms, which have been systematically analysed by using four main parameters: the coating-to-substrate hardness relationship, the film thickness, the surface roughnesses and the debris in the contact. The description covers both soft and hard coatings with thicknesses typically in the range 0.1–50 μm, where the interaction between the coating and the substrate is essential to the tribological behaviour. The concept is supported by experimental observations. The important influence of thin tribo- and transfer layers formed during the sliding action is shown. Optimal surface design both regarding friction and wear can be achieved by new multilayer techniques giving reduced stresses, improved adhesion to substrate, more flexible coatings and harder and smoother surfaces. The differences in contact mechanisms in dry, water- and oil lubricated contacts with coated surfaces is illustrated by experimental results from diamond-like coatings sliding against a steel ball. The mechanisms of the formation of dry transfer- and tribolayers and lubricated boundary and reaction films are discussed.

Tribology of thin coatings

The tribological properties of hybrid polytetrafluoroethylene (PTFE)/aramid fibers 1414 (Kevlar) fabric self-lubricating composite under different conditions was studied. To improve tribological properties and the bonding performance of PTFE, the hybrid Kevlar/PTFE fabrics were treated by sodium-naphthalene complex liquid. PTFE/Kevlar fabric composite was prepared by phenolic-epoxy (6:4) resin. Tribological properties of the composite, friction coefficient and wear amount, were analyzed using varying loads and speeds on a friction and wear testing machine. Worn surface morphology and transfer film were observed by Scanning electron microscopy (SEM). The results showed that the coefficient of friction decreased with the decrease of load and the increase of rotating speed. In addition, the composites with higher PTFE content showed better lubricating behavior. The friction coefficient of the composites reinforced by modified fabrics were more stable and the PTFE transfer film remains more complete.

Preparation and tribological properties of hybrid PTFE/Kevlar fabric self-lubricating composites

Nano Ag@AgBr surface-sensitized Bi2WO6 photocatalyst: oil-in-water synthesis and enhanced photocatalytic degradation

This work concerns rheological and frictional behaviour of lubricating oils containing platelet molybdenum disulfide (MoS2) nanoparticles (average diameter similar to 50 nm; single layer thickness similar to 3 nm). Stable nano-MoS2 lubricants were formulated and measured for their rheological behaviour and tribological performance. Rheological experiments showed that the nano-MoS2 oils were non-Newtonian following the Bingham plastic fluid model. The viscosity data fitted the classic Hinch-Leal (H-L) model if an agglomeration factor of 1.72 was introduced. Tribological experiments indicated that the use of MoS2 nanoparticles could enhance significantly the tribological performance of the base lubricating oil (reduced frictional coefficient, reduced surface wear and increased stability). Scanning electron microscopy, laser confocal microscope and x-ray energy dispersive spectroscopy analyses suggested that the reduced frictional coefficient and surface wear be associated with surface patching effects. Such patching effects were shown to depend on the concentration of MoS2 nanoparticles, and an effective patching required a concentration over approximately 1 wt%. The increased stability could be attributed to the enhanced heat transfer and lubricating oil film strength due to the presence of nanoparticles.

Rheological and tribological behaviour of lubricating oils containing platelet MoS2 nanoparticles

The tribological performances of modified magnesium silicate hydroxide as lubricant additive

Comparative tribological properties of magnesium hexasilicate and serpentine powder as lubricating oil additives under High temperature

Tribological Behaviors of Hybrid PTFE/Kevlar Fabric Composite with Fine Serpentine Particle Under Dry Sliding Condition

Tribological behaviors and wear process of the unﬁlled and 2% nano-serpentine ﬁlled polymer-based hybrid PTFE/Kevlar fabric composites were evaluated on a MMU-5G friction and wear tester. The variation of the morphologies of the worn surface and the morphologies of transfer film during the wear processes of the two composites were observed and analyzed by means of the confocal laser scanning microscope (CLSM). The results show that the addition of nano-serpentine can effectively slow down the wear process and obviously improve the wear resistance of the hybrid PTFE/Kevlar fabric composite, meanwhile the friction property was ameliorative. That probably because the nano-serpentine does not only have the admirable tribological performance, but also have excellent surface activity, which improved the formation of the self-lubricating transfer film.

Influence of Nano-Serpentine on Tribological Behaviors and Wear Process of Hybrid PTFE/Kevlar Fabric Composites

Some terrible disasters of aircrafts were caused by inadequate lubrication or interruption of lubricant delivery of the gas turbine engine mainshaft bearings. This paper introduces the design of the test equipment, performs the experiments of failure performance for 51306 coated bearings to respond to oil interruption under the actual situation. The main failure performance of test coated bearings has been demonstrated to be the cage damage of the test coated bearing. The failure mechanism model of the damaged cage of test coated bearings under oil interruption condition is established for the failure analysis of damage cages. The failure mechanism of the damaged cages is revealed. The main reason for the damages of test coated bearing cages under lubricant interruption condition is that the perpendicular component force acted on the cage increases continually to go with the increase of the friction force between the balls and the cage due to inadequate lubrication until the cage is broken.

Experimental Study of Failure Performances of 51306-Coated Bearings under Lubricant Interruption Condition

The hybrid Kevlar/PTFE(polytetrafluroethylene) fabric composites filled with nano-additives at the content of 1wt% of the matrix resin were fabricated. To determine the influence of the load on the tribological properties, the filled and unfilled composites sliding against AISI-1045 steel were performed on the block-on-ring wear tester under varied load condition. Scanning electron microscopy(SEM) was utilized to examine the morphology of worn surfaces of the composites and the counterparts. The results show that: the addition of nano-titania and nano-alumina can enhance the wear resistance of the composite; at the low load, the influence of load on the friction coefficient of the composite is obvious, the main wear mechanism of the composite is microcutting; with the increase of the load, the influence of the load on the wear resistance of the fabric composite becomes significant, the main wear mechanisms of the composite are plastic deformation and matrix-fiber debonding.

Tribological Performance of Fabric Composites Filled with Nano-Additive under Varied Load Conditions

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