Titanium erosion resistance

Uses. In spite of unique properties, there are few commercial appUcations for monolithic shapes of borides. They are used for resistance-heated boats (with boron nitride), for aluminum evaporation, and for sliding electrical contacts. There are a number of potential uses ia the control and handling of molten metals and slags where corrosion and erosion resistance are important. Titanium diboride and zirconium diboride are potential cathodes for the aluminum Hall cells (see Aluminum and aluminum alloys). Lanthanum hexaboride and cerium hexaboride are particularly useful as cathodes ia electronic devices because of their high thermal emissivities, low work functions, and resistance to poisoning. 

For many years, CVD TiN has been used for wear-and erosion-resistant applications. TiN has a low coefficient of friction and is relatively chemically inert, which makes it attractive for this purpose. In addition, the coating of stainless steel with TiN is of interest for increased biocompatibility of surgical tools and human implants. The reactions used to deposit TiN are very similar to those used for the deposition of Ti02. TiCU is the most common titanium precursor. Nitrogen or ammonia can be used as the nitrogen source. 

Cutting tools made from nanomaterials such as tungsten carbide, tantalum carbide, and titanium carbide suffer less wear, display more erosion resistance, and last longer than their conventional (large-grained) counterparts. They are used to drill holes in... 

All refractory nitrides can be produced as coatings by CVD and, for most of them, CVD remains a major production process. CVD titanium nitride (TiN) is the most important nitride coating from an application standpoint. It is used extensively mainly for wear- and erosion-resistant applications and as a difrusion barrier and antireflection coating in semiconductor devices.l l... 

Flinn, D.R. Electrodeposition of erosion resistant titanium diboride coatings. Rep. Of invest. 8332, Bureau of Mines, U.S.Dep.of Interior,l-29 (1979)... 

Gaseous hydrogen has had no embrittlement effects on titanium. The presence of as little as 2% moisture effectively prevents the absorption of molecular hydrogen up to a temperature as high as 600°F (315°C). This may reduce the ability of the titanium to resist erosion, resulting in a higher corrosion rate. 

Ti-15Mo-5Zr has high corrosion resistance to reducing atmospheres. It has better corrosion resistance in boiling hydrochloric acid or sulfuric add solutions than commerdally piu e titanium. Additionally, Ti-15Mo-5Zr has higher erosion resistance compared to Ti-6A1-4V or other P titanium alloys. 

J.P. Massoud and G. CoquereUe, Hi Power Laser Surface TVeatments on Ti-6A1-4V in Order to Improve Its Erosion Resistance, Sixth World Conference on Titanium (Prance), 1988, p 1847-1852... 

The heat-transfer quaUties of titanium are characterized by the coefficient of thermal conductivity. Even though the coefficient is low, heat transfer in service approaches that of admiralty brass (thermal conductivity seven times greater) because titanium s greater strength permits thinner-walled equipment, relative absence of corrosion scale, erosion—corrosion resistance that allows higher operating velocities, and the inherently passive film. 

Titanium resists erosion—corrosion by fast-moving sand-laden water. In a high velocity, sand-laden seawater test (8.2 m/s) for a 60-d period, titanium performed more than 100 times better than 18 Cr—8 Ni stainless steel. Monel, or 70 Cu—30 Ni. Resistance to cavitation, ie, corrosion on surfaces exposed to high velocity Hquids, is better than by most other stmctural metals (34,35). 

Metals that depend on a relatively thick protective coating of corrosion product for corrosion resistance are frequently subject to erosion-corrosion. This is due to the poor adherence of these coatings relative to the thin films formed by the classical passive metals, such as stainless steel and titanium. Both stainless steel and titanium are relatively immune to erosion-corrosion in most cooling water environments. 

Because alterations to equipment design can be cumbersome and expensive, a more economical approach may be to change the metallurgy of affected components. Metals used in typical cooling water environments vary in their resistance to erosion-corrosion. Listed in approximate order of increasing resistance to erosion-corrosion, these are copper, brass, aluminum brass, cupronickel, steel, low-chromium steel, stainless steel, and titanium. 

This example of aluminium illustrates the importance of the protective him, and hlms that are hard, dense and adherent will provide better protection than those that are loosely adherent or that are brittle and therefore crack and spall when the metal is subjected to stress. The ability of the metal to reform a protective him is highly important and metals like titanium and tantalum that are readily passivated are more resistant to erosion-corrosion than copper, brass, lead and some of the stainless steels. There is some evidence that the hardness of a metal is a signihcant factor in resistance to erosion-corrosion, but since alloying to increase hardness will also affect the chemical properties of the alloy it is difficult to separate these two factors. Thus althou copper is highly susceptible to impingement attack its resistance increases with increase in zinc content, with a corresponding increase in hardness. However, the increase in resistance to attack is due to the formation of a more protective him rather than to an increase in hardness. 

The original saltwater condenser tube made of admiralty brass was found to be susceptible to erosion-corrosion at tube ends. Aluminum brass containing 2% aluminum was more resistant to erosion in saltwater. Inhibition with arsenic is necessary to prevent dezincification as in the case of admiralty brass. The stronger naval brass is selected as the tube material when admiralty brass mbes are used in condensers. Cast brass or bronze alloys for valves and fittings are usually Cu-Sn-Zn compositions, plus lead for machinability. Aluminum bronzes are often used as tube sheet and channel material for exchangers with admiralty brass or titanium tubes exposed to cooling water. 

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