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Tham khảo tài liệu 'engineering tribology 2011 part 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 426 Engineering Tribology reduction of the coefficient of friction from 0.25 to 0.18 and a small reduction in wear 53 . On the other hand it has also been shown that molybdenum disulphide when added to nylon oxidizes during wear and does not develop an effective transfer film 54 . Under these conditions the friction performance of nylon molybdenum disulphide blend was found to be inferior to plain nylon 54 . MoS2 present below desorption temperature Figure 9.16 Conceptual model of the mechanism of lubrication by molybdenum disulphide suspended in oil. MoS2 present above desorption temperature in polyimides the addition of the same amount of graphite reduced the coefficient of friction to less than half of pure polyimide and significantly reduced wear. Although molybdenum disulphide showed the same reduction of coefficient of friction as graphite polyimide blend its reduction in wear rate was inferior to that of graphite polyimide blend 53 . improvements achieved by adding molybdenum disulphide and graphite to polytetrafluoroethylene PTFE are very limited 55 56 . The coefficients of friction for PTFE filled with graphite and molybdenum disulphide are very similar to that of unfilled PTFE and slightly lower than those obtained with most other fillers 55 . interest in graphite has recently been extended by the incorporation of carbon fibres into polymers. Carbon fibres offer a unique combination of mechanical reinforcement and lubricity 57 . It has been shown that a carefully formulated polyimide carbon fibre composite can sustain high contact loads and maintain a friction coefficient close to 0.2 at temperatures reaching 300 C with very low wear rates 58 59 . 9.3 WEAR RESISTANT COATINGS AND SURFACE TREATMENTS Wear resistant coatings consist of carefully applied layers of usually hard materials which are intended to give prolonged protection against wear. Abrasive wear adhesive wear and fretting are often reduced by wear resistant coatings. There are numerous methods
