Corrosion fretting

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 

Cracks originate on ID surface. Note wedge- or needle-shaped, nonbranching cracks typical of corrosion fatigue. Faint black line near bottom of photo is an inclusion not related to the failure. (125x original magnification) 

Damage can occur at the interface of two highly loaded surfaces which are not designed to move against each other. The most common type of fretting is caused by vibration. The protective film on the metal surfaces is removed by the rubbing action and exposes fresh. 

Fontana MG, Greene ND. Corrosion Engineering. New York, N.Y. McGraw Hill, 1967. 

Mlon GP. Forms of Corrosion Recognition and Prevention. Houston, Tex NACE International, 198Z 

Fretting corrosion occurs at the interface between two closely fitting components when they are subjected to repeated slight relative motion. The relative motion may vary from less than a nanometer to several micrometers in amplitude. Vulnerable objects are fits, bolted joints and other assemblies where the interface is under load.  

General Description. 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). Usually, the condition exists in machine components that are considered fixed and not expected to wear. Pressed-on wheels can often fret at the shaft/wheel hole interface. 

Fretting corrosion takes the form of local surface dislocations and deep pits. These occur in regions where slight relative movements have occurred between mating, highly loaded surfaces. 

Prevention. Susceptibility to intergranular corrosion in austenitic stainless steels can be avoided by controlling their carbon contents or by 

This phenomenon is a combination of wear and corrosion in which the material is removed from the contacting surfaces when the motion of the surfaces consists of small amplitude oscillations with the relative movement ranging from fractional nanometers to fractional micrometers. Fretting occurs when low-amplitude oscillatory motion in the tangential direction takes place between two contacting surfaces, which are nominally at rest (67, 68). It is necessary that the load be sufficient to produce distortion of the surfaces. Fretting corrosion occurs in most machinery subject to vibration both in transit and in operation. 

The most common factor in fretting is oxidation. In oxidizing systems, fine metal particles removed by adhesive wear are oxidized and trapped between the fretting surfaces. The oxides act like abrasives and increase the rate of material removal. The red 

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Fretting corrosion (36,37) can lead to high contact resistance of base metal contacts, such as tin plate in electronic connectors. Small cycHcal displacements of the connector halves occur because of external vibration or differential thermal expansion and contraction of the mating contacts. The wear debris that is formed remains in the contact zone. The accumulation of oxide debris in the contact region leads to increased contact resistance. Solutions to this problem are stmctures that do not permit movement of contact surfaces with respect to one another, the use of gold as a contact finish, and the appHcation of thick coatings of contact lubricants and greases, which reduce the rate of wear and restrict access of air to the contact surfaces. 

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. 

In-vitro fretting corrosion experiments have been performed using weight loss , polarisation and corrosion potential measurements. Thull and Schaldach have performed corrosion potential versus time measurements in-vitro in a joint simulator with different values of applied load. Brown and Simpson have performed similar studies with screw/plate fretting. Both studies found larger shifts towards active potentials with larger loads . 

Brown, S. A. and Merritt, K., Fretting Corrosion in Saline and Serum , Journal of Biomedical Materials Research, 15, 479-488 (1981)... 

Syrett, B. C. and Wing, S S., An Electrochemical Investigation of Fretting Corrosion of Surgical Implant Materials , Corrosion, 34, 379-386 (1978)... 

Fretting or fretting corrosion may be defined as that form of damage which occurs at the interface of two closely fitting surfaces when they are subject to slight relative oscillatory slip. The surfaces are often badly pitted and finely divided oxide detritus is formed. 

Although the term fretting corrosion implies chemical reaction, it has often been used even when the latter is absent. Campbell has suggested that to avoid confusion the word fretting be used to describe the wear process, and that the expression fretting corrosion be applied in those cases where one or both of the surfaces, or the wear particles from them, react with their environment. 

Campbell, W. E., Symposium on Fretting Corrosion, Amer. Soc. Test. Mater. Special Technical Publication No. 114, 3 (1953)... 

For protection of engineering parts against fretting corrosion, on electrical cables and on printing cylinders. Temporary protection allied with lubrication is provided by immersion deposits of copper on steel wire. 

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. 

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