Titanium corrosion behaviour

The basic corrosion behaviour of stainless steels is dependent upon the type and quantity of alloying. Chromium is the universally present element but nickel, molybdenum, copper, nitrogen, vanadium, tungsten, titanium and niobium are also used for a variety of reasons. However, all elements can affect metallurgy, and thus mechanical and physical properties, so sometimes desirable corrosion resisting aspects may involve acceptance of less than ideal mechanical properties and vice versa. 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

In its general corrosion behaviour, beryllium exhibits characteristics very similar to those of aluminium. Like aluminium, the film-free metal is highly active and readily attacked in many environments. Beryllium oxide, however, like alumina, is, a very stable compound (standard free energy of formation = —579kJ/mol), with a bulk density of 3-025g/cm as compared with 1 -85 g/cm for the pure metal, and with a high electronic resistivity of about 10 flcm at 0°C. In fact, when formed, the oxide confers the same type of spurious nobility on beryllium as is found, for example, with aluminium, titanium and zirconium. 

Mechanical properties of various titanium alloys are given in Table 5.16. In general the corrosion behaviour of those titanium alloys developed for the aircraft industry is very similar to that of unalloyed titanium . The addition of some alloying elements may increase resistance to one medium, but decrease it to others . 

It should be noted that swarf from a zirconium-titanium alloy containing approximately 50% by weight of each element is prone to pyrophoricity in air. It has also been reported that when zirconium is welded to titanium, the welded zone is much more sensitive to corrosion than either of the parent metals. If, therefore, it is proposed to use my construction in which zirconium is welded to titanium, caution should be observed in the machining of welds, and the corrosion behaviour of the weld should be checked by prior testing in the environment with which the construction will be employed. 

Zhou, X. and Mohanty, P. (2012b) Corrosion behaviour of cold sprayed titanium coatings in simulated body fluid. Corros. Eng., Sci. Technol., 47 (2), 145-154. 

S. Ban, 1. Hasegawa and S. Maruno, Electrochemical Corrosion Behaviour of Hydroxyapatite-Glass-Titanium Composite, Biomaterials 12, 205—209 (1991). 

After insertion of wires of different metals into the epiphyseal region of rabbits and an exposure time of fifteen months, the histology showed different results. With materials of inert or biocompatible behaviour the cells in the vicinity of the implant were still supplied with blood, while the cells in the neighbourhood of toxic materials underwent an inflammatory reaction and died. A few elements (Cr, Co, Ni and V) have toxic effects and also have a relatively low polarization resistance. Ti and its alloys, Nb and Ta, which have a high polarization resistance, exhibit an inert behaviour. In between the materials were found which are capsu-lated. The results also show that not only the corrosion behaviour provided by the polarization resistance is responsible for the biocompatibility of the material exposed to the tissue. The steel 316L and the CoCr alloy, which have a polarization resistance similar to that of titanium, are encapsulated by a tissue membrane and their behaviour is not inert [13]. 

Fraker, A.C., Ruff, A.W., Sung, P. von Orden, A.C. and Speck, K.M. (1983) Surface Preparation and Corrosion Behaviour of Titanium Alloys for Surgical Implants, in Titanium Alloys in Surgical Implants, (eds H.A. Cuckey and F. Kubli), ASTM STP 796, pp. 206-219. 

Low additions of titanium (about 0.6%) improve the corrosion behaviour of ferritic steels with 13 or 18% chromium, in particular after a short pre-oxidation. The influence of pre-oxidation on the corrosion behaviour of Ti-stabUised ferritic steels in high purity water with < 20 pS/cm, 5-10 pg/1 oxygen at 215 °C (488 K) up to 2000 h was investigated [70]. The steel SUS XM8 with 17% chromium and SUS 410Ti with 13% chromium and carbon contents of0.008 and 0.006 C, respectively, as well as Ti-stabilised, each with about 0.6% titanium (see also Table 5) were examined. Preoxidation took place at 850 C (1123 K) in an oxygen poor atmosphere (Ar). It was... 

The corrosion behaviour of nickel and 14 nickel alloys was tested in comparison to titanium and stainless austenitic steel (Table 66) by means of exposure in stagnant and flowing natural seawater (flow rate 0.23 m/s) over a period of 1.6 years [205]. 

There are no comprehensive standards or literature available on the corrosion behaviour of such nanostmctured implants. Figure 15.4 schematically represents a few likely outcomes. The following sections discuss the effeets of these modifications on the corrosion resistance of orthopaedic and dental implants More specifically, Section 15.4 discusses the effect of nanoscale surface modifications on the corrosion behaviour of titanium based alloys. Section 15.5 discusses nanoceramic coatings with emphasis on HA coatings. Current approaches in making nanostmctured coatings and nanocomposites for Mg based resorbable implants are presented in Section 15.6. 

On the other hand, metals such as Ta, Nb, Ti, Zr, Al, etc. (the valve metals ) do not exhibit transpassive behaviour, and in appropriate electrolyte solutions film growth at high fields rather than corrosion and/or oxygen evolution is the predominant reaction thus aluminium can be anodised to 500 V or more in an ammonium borate buffer titanium can be anodised to about 400 V in formic acid and tantalum can be anodised to high voltages in most acids, including hydrochloric acid. 

Buchanan, R. A. and Lemons, J. E., In-vivo corrosion —Polarization Behaviour of Titanium-Base and Cobalt-Base Surgical Alloys , Transactions of the 8th Annual Meeting of the Society of Biomaterials, 5, 110 (1982)... 

Zirconium, like titanium, depends upon the integrity of a surface film, usually of oxide, for its corrosion resistance, but there are differences in behaviour between the two metals when they are exposed to aggressive aqueous environments. 

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