Fretting attack

Figure 22. Fretting attack inside engine jacket at contact points with ribbed...

Figure 23. Cylinder-liner ribs show metal loss by fretting attack and crevice corrosion plus worm holing attack on liner at base of ribs...

Fretting Corrosion This attack occurs when metals shde over each other and cause mechanical damage to one or both. In such a case, frictional heat oxidizes the metal and this oxide then wears away or the mechanical removal of protective oxides results in exposure of fresh surface for corrosive attack. Fretting corrosion is minimized by using harder materials, minimiziug friction (via lubrication), or designing equipment so that no relative movement of parts takes place. 

Erosion —corrosion, fretting corrosion, impingement attack, cavitation damage stress corrosion cracking, hydrogen cracking, corrosion fatigue... 

Erosion-corrosion in the widest sense of the term will include impingement attack, cavitation damage and fretting corrosion, but since the latter two are dealt with in separate sections (see Sections 8.7 and 8.8) they will not be considered here. 

When two metals in intimate contact are subjected to vibration, a dark powder forms at the areas of contact. The effect is referred to as fretting corrosion though it is due to wear rather than true corrosive attack. The galling effect between nickel and steel ensures good resistance to fretting corrosion and lubricated nickel against steel is a very satisfactory combination used widely in industry for components assembled by press-fitting. 

Coordination of an alkene to platinum(O) differs from complexation to platmum(Il) Zerovalent platinum is an electron-rich metal center, whereas platinum(II) is electron poor. A a consequence alkenes coordinated to platinum(0) became more electron rich than in their fret state, and therefore susceptible to electrophilic attack. For alkenes complexed to platinum(II) their primary mode of reactivity is by attack from an external nucleophile. 

Corrosion is the destructive attack of a metal by chemical or electrochemical reaction with its environment. Deterioration by physical causes is not called corrosion, but is described as erosion, galling, or wear. In some instances, chemical attack accompanies physical deterioration, as described by the following terms corrosion-erosion, corrosive wear, or fretting corrosion. Nonmetals are not included in this definition of corrosion. Plastics may swell or crack, wood may split or decay, granite may erode, and Portland cement may leach away, but the term corrosion, in this book, is restricted to chemical attack of metals. 

As a final note it must be stressed that laboratory static tests should only be used to eliminate dangerous metal-metal combinations, and not as an acceptance criterion. Fretting may substantially alter the properties of the interface, by continuously removing the passive oxide film, thereby inducing severe attack of a metal which, otherwise, would remain unaffected. 

Connectors are a critical part of an electronic S5rstem. Corrosion mechanisms at connector interfaces include pore corrosion, corrosion product creep, fretting, and SCC and general attack. Pore corrosion in connectors is associated with surfaces plated with gold or other precious metals. Corrosion product creep in connectors usually involves copper corrosion products originating from exposed base... 

Chain joints with brown or rusty color indicate fretting or corrosive attack. 

The main degradation mechanisms identified are stress corrosion cracking (SCC) at different locations of tubes, intergranular attack (IGA), "denting" and "fretting. ... 

The applications for hard particle composites He, for example, in internal combustion engines, textile machinery and gas turbine compressors, where combined properties can include resistance to wear, fretting, scuffing and heat and chemical attack. The softer particles display an advantageously low coefficient of friction and effective self-lubricating properties. 

The movement of solutions above a certain threshold velocity level can result in another form of attack that is the result of the interaction of fluid-induced mechanical wear or abrasion plus corrosion. The general term erosion corrosion (E/C) includes all forms of accelerated attack in which protective surface films and/or the metal surface itself are removed by this combination of solution velocity and corrosion such as impingement attack, cavitation damage and fretting corrosion. 

The term "erosion" applies to deterioration due to mechanical force. When the factors contributing to erosion accelerate the rate of corrosion of a metal, the attack is called "erosion corrosion." Erosion corrosion is usually caused by an aqueous or gaseous corrodent flowing over the metal surface or impinging on it. The mechanical deterioration may be aggravated by the presence of a corrodent, as in the case of fretting or corrosive wear. 

When two metal surfaces are in contact and experience a very slight relative motion that results in damage to one or both siufaces, fretting corrosion, a special form of erosion corrosion, takes place. The movement causes mechanical damage to the protective film this can lead to erosion corrosion when a corrodent is present. This corrosion usually takes the form of a pitting attack. 

Velocity effects include erosion-corrosion, a form of attack caused by high velocity flow cavitation caused at even higher flow by the collapse of bubbles formed at areas of low pressure in a flowing stream and fretting that is caused by vibratory relative motion of two surfaces in close contact under load erosion-corrosion, cavitation, fretting). 

Fig. 10.16 Types of localized corrosion initially associated with the environment, (a) Crevice corrosion, (b) Deposit corrosion, (c) Waterline attack, (d) Filiform corrosion (e) Erosion corrosion, (f) Drop corrosion, (g) Turbulent-flow corrosion, (h) Fretting.

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