Metals fretting

Kawalec, J. S., Brown, S. A., Payer, J. H., et al., "Mixed-Metal Fretting Corrosion of T16A14V and Wrought Cobalt Alloy, ... 

Another special case of erosion-corrosion, fretting corrosion, occurs when two heavily loaded metals rub rapidly together, causing damage to one or both metals. Vibration is usually responsible for the damage, but corrosion is also a factor because the frictional heat increases oxidation. In addition, mechanical removal of protective corrosion products continually exposes fresh metal. Fretting corrosion occurs more frequently in air than in water. 

R. B. Waterhouse and A. Niku-Lari, Metal Treatments Mgainst Wear, Corrosion, Fretting, andFatigue, Vol. 6, Pergamon Press, New York, 1988. 

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. 

In the presence of an inert atmosphere fretting of surfaces still occurs and is generally accompanied by the formation of finely divided debris. In a high vacuum, seizure of metal surfaces may take place. 

Most of the cases of fretting met with in practice appear to fall into two distinct classes according to whether or not the surfaces involved in the component are intended to undergo some relative motion. If the surfaces are not intended to move, then the first objective should be to prevent slip, either by eliminating the source of vibration, or by increasing the friction between the surfaces. It is believed that the success of certain soft metal electrodeposits in reducing fretting may be due to the improved fit, and hence possibly increased friction, which is obtained from their use. If the displacements cannot be controlled in this way, it may be possible to interpose a thin sheet of an elastic material which can accept the relative movement without slip. 

Much of the early work on fretting was confined to mild steel or carbon steel. Although many of the same principles apply to the fretting of other metals such as gold , titanium and the superalloystheir reaction to the environment may be a more significant factor. In addition, non-metallic materials such as polymers composites and ceramics are becoming widely applied and the principles of contact here are very dififerent from the metallic case. 

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. 

Keywords Amplification Fluorescent reporter Fluorophore FRET In vitro In vivo Labeling Lanthanide chelate Multiplexing Nanoparticle Quantum dot Transition metal complex... 

Besides targeting single metal ions, the development of FRET systems for the highly sensitive and selective detection of more than a single analyte has also been reported. The system shown in Fig. 36 also serves as an example for a second strategy frequently employed for FRET signaling, i.e., the deliberate use of a... 

Since the same dye molecules can serve as both donors and acceptors and the transfer efficiency depends on the spectral overlap between the emission spectrum of the donor and the absorption spectrum of the acceptor, this efficiency also depends on the Stokes shift [53]. Involvement of these effects depends strongly on the properties of the dye. Fluoresceins and rhodamines exhibit high homo-FRET efficiency and self-quenching pyrene and perylene derivatives, high homo-FRET but little self-quenching and luminescent metal complexes may not exhibit homo-FRET at all because of their very strong Stokes shifts. 

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