Fretting corrosion prevention

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. 

Herbeck and Strohecker used machines designed particularly for comparing the merits of lubricants in preventing fretting corrosion of antifriction bearings. One provided for both oscillating conditions and combination radial and thrust loads to simulate service. Another was concerned primarily with thrust bearings and correlated satisfactorily with the radial load tester. 

The notion of a gas-tight seal as the product of a proper press-fit is crucial to connection reliability. If an electrical contact is to be rehable, the interface between the two mating surfaces must remain chemically and mechanically stable. The gas-tight, smeared, metal-to-metal contact attained during the press-fit operation mitigates oxidation of either contact (FTH barrel or press-fit pin) and prevents fretting corrosion, which is a common failure mechanism for mechanically mated contacts, especially those subjected to vibration. Press-fit interconnection is considered at least as rehable as a soldered connection and there is no solder joint to degrade or crack with time. 

The effect of humidity on fretting is opposite to the effect of general corrosion where an increase in humidity causes an increase in the rate of corrosion, and an increase in dryness causes a decrease in corrosion. Fretting corrosion is increased in dry air rather than decreased for metals which form rust in air. In case of fretting, in dry air, the debris which is formed as a consequence of wear on the metal surface is not removed from the surface and, therefore, prevents direct contact between two metallic surfaces. If the air is humid, debris becomes more mobile and it may escape from the metal surface, providing sites for metal-to-metal contact. 

State four methods of prevention of fretting corrosion. 

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. ... 

Processes that induce compressive stresses into the surface of the metal such as shot-peening, carburizing, and nitriding are frequently beneficial in preventing corrosion fatigue and fretting corrosion. 

For prevention of fretting corrosion observe precautions and preventing measures as follows ... 

The tube-sheet joints are sufficiently smooth to prevent fretting corrosion by the slurry. 

Even though copper is soft, it has many engineering applications in addition to its decorative function. One such application is the corrosion protection of steel. It can be used as an alternative to nickel to prevent fretting and scaling corrosion. Copper can be deposited electrochemically from various aqueous solutions. The properties of the deposit will depend on the chosen bath and the applied procedures. The hardness of the layers varies from 40 to 160 HV. 

Erosion-corrosion (as impingement or water drop corrosion) is a serious problem since it keeps the active state of magnesium at low pH values or prevents the formation and stability of the passive layer in alkaline solutions. Preventive measurements of erosion-corrosion and fretting fatigue corrosion include better passive surfaces that can be achieved by inhibitors, surface treatments and selected coating to improve wear resistance and wear corrosion of Mg alloys. 

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