Titanium alloys, surface chemistry

Metals such as aluminium, steel, and titanium are the primary adherends used for adhesively bonded structure. They are never bonded directly to a polymeric adhesive, however. A protective oxide, either naturally occurring or created on the metal surface either through a chemical etching or anodization technique is provided for corrosion protection. The resultant oxide has a morphology distinct from the bulk and a surface chemistry dependent on the conditions used to form the oxide 39). Studies on various aluminum alloy compositions show that while the oxide composition is invariant with bulk composition, the oxide surface contains chemical species that are characteristic of the base alloy and the anodization bath40 42). 

The surface chemistry of Titanium alloys varies with each physical or chemical treatment. An example of ISS/SIMS results from a typical chemical pretreatment for T1-6A1-4V Is seen in Figure 1. Here the sample was degreased, etched in HN0-/HF and converted with a mixture of HF, NaF and Na PO In aqueous solution. Spectra from... 

The most well-known SMA, which exhibits superelasticity above its transformation temperature, is NiTi ( 51% Ni by weight), also known by its trade name, nitinol, for nickel-titanium-naval ordnance laboratory. This alloy was developed in 1959 by William J. Buehler (b. 1923) at the United States Naval Ordnance Laboratory, now the Naval Surface Warfare Center, in White Oak, Maryland. Buehler was looking for a new impact-resistant alloy to serve as the nose cone for a new missile. The alloy s superelastic properties were discovered in 1962 by Frederick E. Wang (b. 1932), whom Buehler hired. The very first observation of superelasticity was by the University of Stockholm chemistry professor Arne Olander, who discovered a rubber-hke effect in an Au-Cd alloy (47.5% Au) in 1932 (Olander, 1932). 

More recently, attention has been directed to the "ninth form of corrosion, biologically influenced corrosion, which includes studies on an area referred to as "ennoblement. The presence of biofilms on metals and alloys immersed in natural seawater produces a complex, heterogeneous chemistry along the metallic surface. It has usually been observed that passive alloys such as aluminum, stainless steels, nickel-base alloys, or titanium show an increase to more noble (electropositive) potentials or ennoblement of several hundred millivolts with exposure time in natural seawater, thus magnifying the potential differences that may exist between dissimilar alloys [26,55-64]. Ennoblement is likely caused by the formation of microbiological films, which increase the kinetics of the cathodic reaction [55-63],... 

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