tailieunhanh - Handbook Corrosion (1992) WW Part 4

Tham khảo tài liệu 'handbook corrosion (1992) ww part 4', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Source Ref 107 a maximum present but not determined analytically. Fig. 11 Internal surface of carbon steel pipe section damaged by cavitation Fretting is erosion-corrosion that occurs at the contact area between two metals under load and subject to slight relative movement by vibration or some other force Ref 108 109 110 . Damage begins with local adhesion between mating surfaces and progresses when adhered particles are ripped from a surface and react with air or other corrosive environment. Affected surfaces show pits or grooves with surrounding corrosion products. On ferrous metals corrosion product is usually a very fine reddish iron oxide on aluminum it is usually black. Fretting is detrimental not only because of the destruction of metallic surfaces but also because of a severe effect on the fatigue life. It has been shown that fretting can reduce the endurance limit of a metal by 50 to 70 Ref 109 . The relative motion necessary to produce fretting is very small. Displacements as small as 10-8 cm have produced fretting. Fretting generally does not occur on contacting surfaces in continuous motion such as ball or sleeve bearings. Fretting can be minimized or eliminated in many cases by one or more of the following Increasing the hardness of contacting surfaces. This may mean increasing the hardness of bother just one of the components. Surface-hardening treatments such as shot peening nitriding chrome plating and carburizing are beneficial Increasing the friction between the mating members by roughening or by plating lead copper nickel silver gold Applying phosphate coatings to exclude air or applying anaerobic sealants or adhesives to increase the tightness of the fit Increasing the fit interference which reduces slippage by increasing the force on mating components Switching to materials with more fretting resistance as shown in Table 6 Table 6 Relative fretting resistance of various material combinations Combination Fretting resistance Aluminum on cast