Friction and Thermal Effects of Engineering Plastics Sliding Against Steel and DLN-Coated Counterfaces

Polymers are increasingly used in tribological applications, because of their self-lubricating ability, corrosion resistance and chemical compatibility. However, their performance depends strongly on the parameters of the total tribological system. Not only polymer characteristics, but also counterface properties become important because of their influence on friction and wear, on surface energy and on the thermal conductivity of the total system. Applying a Diamond-Like Nanocomposite (DLN) coating on a steel counterface can improve the tribological behaviour of the sliding couple under certain conditions. In the case of metal sliding against DLN, the high hardness and the wear resistance of the coating is advantageous for better tribological properties. However, for polymers sliding against DLN, the lower thermal conductivity of the DLN coating compared with a steel mating surface dominates friction and wear. In case of polyamides this results in worse tribological performance in contact with the DLN coating, because of polymer melting. In the case of more rigid polymers, such as, e.g., POM-H and PETP, lower coefficients of friction lead to lower frictional heat generation. In these cases, the thermal characteristics of the counterface are less important and the lower surface energy of the DLN coating is favourable for decreased adhesion between the polymer and the coating and consequently better tribological properties.     

Global Approach of Tribomechanical Development of Hybrid Aluminium Matrix Syntactic Foams

Hybrid syntactic foams with AlSi12 aluminium matrix were produced by pressure infiltration. The volume ratio of iron to ceramic hollow sphere reinforcement (in the same size range) was varied, and hybrid syntactic foams were also produced with bimodal size ceramic reinforcement. Previously, a very detailed analysis of the mechanical properties of the composites was made with quasi-static compression tests, and their tribological properties were investigated by pin-on-disc method in dry and lubricated conditions. The present article establishes and clarifies the correlations between mechanical and tribological properties. The coefficient of friction, height loss of the specimens and specific wear showed good correlation with different mechanical parameters, e.g. density, structural stiffness and yield strength. The established trends and correlations between mechanical and tribological behaviour enable a better understanding of materials design and selection for further applications of mechanically loaded sliding machine parts.     

Temperature Effects on Friction and Wear of Thermoset Polyester Fabric Composites

The tribological properties of unsaturated polyester with a plain weave polyester fabric and poly(tetrafluoro-ethylene) fillers are evaluated in reciprocating sliding at 23 to 220°C. Thermogravimetric analysis and differential scanning calorimetry show that poly(tetrafluoro-ethylene) restricts the thermostability, while the curing reaction becomes more pronounced in the presence of poly(tetrafluoro-ethylene). The pure polyester composites show continuously increasing friction and overload above 120°C, while the poly(tetrafluoro-ethylene)-filled composites indicate a regime of increasing friction up to 100°C, decreasing friction at 100–160°C, and increasing friction above 160°C. The infrared spectra of worn composites have absorption bands representing poly(tetrafluoro-ethylene), curing, and degradation of the matrix.     

Influence of cylinder‐on‐plate or block‐on‐ring sliding configurations on friction and wear of pure and filled engineering polymers

Polyamides, polyesters and polyacetals are often used in line contacts under reciprocating or continuous sliding. These contacts are simulated on cylinder‐on‐plate (COP) or block‐on‐ring (BOR) tribotests. Comparative tests for pure, oil‐filled and solid lubricated polymers at 100N and 0.3m/s are presented for relative material classification. Differences are discussed according to the sliding geometries. Thermal effects dominate friction and wear behaviour: the polymer glass transition temperature is exceeded in COP tests while the temperature is lower in BOR tests. Thick and brittle films are observed for pure polymers in BOR tests, promoting higher friction. The test configuration is mainly important for evaluation of internal lubricants. The efficiency of oil‐lubricated polymers is not demonstrated in COP tests, while solid lubricants are not efficient in BOR tests. Deformation restricts the diffusion of oil lubricants in COP tests while solid lubricants are deposited on the polymer surface rather than being incorporated in the transfer film in BOR tests. Copyright © 2007 John Wiley & Sons, Ltd.