Fretting corrosion examples

Fretting corrosion is a combined wear and corrosion process in which material is removed from contacting surfaces when motion between the surfaces is restricted to very small amplitude oscillations (often, the relative movement is barely discernible ranging from a few tens of nanometers to a few tens of micrometers). Fretting occurs where low-amplitude oscillatory motion in the tangential direction takes place between contacting surfaces, which are nominally at rest. (Waterhouse) It is necessary that the load be sufficient to produce a distortion of surfaces. This is a common occurrence, since most machinery is subjected to vibration, both in transit and in operation. Figure 6.41 shows a typical example. Pressed-on wheels can often fret at the shaft/wheel hole interface.31... 

Figure 6.41 Example of typical fretting corrosion location16...

Mechanism. Basically, fretting is a form of adhesive or abrasive wear, where the normal load causes adhesion between asperities and oscillatory movement causes ruptures, resulting in wear debris. Most commonly, fretting is combined with corrosion, in which case the wear mode is known as fretting corrosion. For example, in the case of steel particles, the freshly worn nascent surfaces oxidize (corrode) to FejO, and the... 

There are some corrosion cases where other factors, i.e. stress, or other mechanical factors are involved. For example, stress corrosion cracking, corrosion fatigue, hydrogen embrittlement, erosion corrosion, cavitation corrosion, fretting corrosion, etc. can be mentioned. 

Being less plentiful and more expensive than nickel, cobalt is usually alloyed with chromium for applications where the alloys have practical advantages over similar nickel- or iron-base alloys. The cobalt-base alloys, for example, are better resistant to fretting corrosion, to erosion by high-velocity hquids, and to cavitation damage. 

Implant design can alter the corrosion performance of alloys in vivo. A case in point of a device whose complex design has spurred much interest in its corrosion behavior is that of the cardiovascular stent [75,76]. To consider another example, many prosthetic devices and fracture fixation implants are by nature multicomponent or modular. This means they have various pieces that mate together, e.g., screws and screw holes in plates. These locations may be foci of localized corrosion processes such as crevice corrosion or (in the case of relative motion) fretting corrosion or both. Careful design of such components can minimize in vivo corrosion problems. 

Fretting corrosion refers to corrosion damage at the asperities of contact surfaces (Fig. 6.50). This damage is induced under load and in the presence of repeated relative surface motion, as induced, for example, by vibration. Pits or grooves and oxide debris characterize... 

What is the essential difference between fretting wear, firetting fatigue and fretting corrosion State two examples of each. 

Prevention. Fretting, because of the significant role of oxidation, is best combatted by oxidation-resistant coatings, for example, electroless nickel or softer self-lubricating coatings like silver or indium. Solid-film lubricants are also successfully employed. Additional information on prevention of fretting corrosion can be found in Chapter 2, Principles of Corrosion. ... 

Mechanical effects Corrosion can often be initiated or intensified by the conjoint action of mechanical factors. Typical examples include the presence of inherent or applied stresses, fatigue, fretting or cavitation effects. Inhibitors that are effective in the absence of some or all of these phenomena may not be so in their presence. In fact it may not always be possible to use inhibitors successfully in these situations and other methods of corrosion prevention will be required. 

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