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| Overview of Titanium Alloys |
Titanium and its characteristicsTitanium was discovered in 1910 and got its name from the enormously strong giant from Greek mythology; "Titan". Titanium is a light metal highly resistant to corrosion. Titanium is highly resistant to heat with a melting temperature as high as 1668 . Its melting point is higher than that of steel. Although heat conductivity of titanium is almost the same as that of stainless steel, its weight is almost half of stainless steel. Titanium is also non-toxic and non-allergenic, often used in piercing jewelry. Due to its unprecedented strength, lightness, stable market and non-corrosive characteristics, titanium has emerged as the metal of choice for aerospace, industry and medical, leisure and consumer products, notably golf clubs and bicycle frames. Furthermore, due to its strength and lightness, titanium is currently being tested in the automobile industry which has found that the use of titanium for connecting rods and moving parts has resulted in significant fuel efficiency. Aerospace: Chemical plants: Seawater usage: In the oil platform industry, titanium was previously employed "topside" for seawater management systems, however, due to its low modulus, high fracture toughness and fatigue resistance, titanium is now being used for stress joints and complete riser systems. Titanium in daily life: Ti and its Alloys There are three structural types of titanium alloys:
Outstanding Corrosion resistance Titanium is immune to corrosive attack by saltwater or marine atmospheres. It also exhibits exceptional resistance to a broad range of:
Superior strength-to-weight ratios The combination of high strength and low density results in exceptionally favorable strength-to-weight ratios for titanium-based alloys. The densities of titanium-based alloys range between 4.43 gm/cm3 (0.160lb/in3) and 4.85 gm/cm3 (0.175lb/in3). Yield strengths range from 172 MPa (25,000 psi) for commercially pure Grade 1, to above 1380 MPa (200,000 psi) for heat treated beta alloys. These ratios for titanium- based alloys are superior to almost all other metals and are important in such diverse applications as deep well tubestrings in the petroleum industry and surgical implants in the medical field.
High heat transfer efficiency Under 'in service' conditions, the heat transfer properties of titanium are similar to those of admiralty brass and copper-nickel. There are several reasons for this; the higher strength of titanium permits the use of thinner walled equipment, the oxide film confers unusual characteristics which are beneficial to heat transfer, the absence of corrosion leaves the surface bright and smooth for improved lamellar flow, and titanium's erosion-corrosion resistance allows significantly higher operating velocities. Titanium's oxide film Titanium develops a thin, tenacious and highly protective surface oxide film. The surface oxide of titanium will, if scratched or damaged, immediately reheal and restore itself in the presence of air or even very small amounts of water. The corrosion resistance of titanium depends on this protective TiO2 surface oxide film. Titanium and methanol Anhydros methanol is unique in its ability to cause stress corrosion cracking of titanium and titanium alloys. Industrial methanol normally contains sufficient water to provide immunity to titanium and for there to be no problem in practical applications. Work is in hand to confirm the actual level of water required to provide immunity to stress corrosion cracking in all conditions. Testing conducted to date confirm levels above 2%, but safely below 5% are required. Halogen compounds Titanium alloys are highly resistant to wet (aqueous) chlorine, bromine, iodine and other chlorine chemicals because of their strongly oxidizing natures. Titanium's outstanding resistance to aqueous chlorides has been the primary historical incentive for utilizing titanium in industrial service. In many chloride and bromide-containing environments, titanium has cost-effectively replaced stainless steels, copper alloys and other metals which have experienced severe localized corrosion and stress corrosion cracking. Chlorine chemicals, gas and chlorine solutions Titanium is fully resistant to solutions of chlorites, hypochlorites, chlorates, perchlorates and chlorine dioxide. It has been used to handle these chemicals in the pulp and paper industry for many years with no evidence of corrosion. Titanium is widely used to handle moist or wet chlorine gas, and has earned a reputation for outstanding performance in this service. The strongly oxidizing nature of moist chlorine passivates titanium resulting in low corrosion rates. Titanium is used in chloride salt solutions and other brines over the full concentration range, especially as temperatures increase. Near nil corrosion rates can be expected in brine media over the pH range of 3 to 11. Oxidizing metallic chlorides, such as FeCl3, NiCl2 or CuCl2, extend titanium's passivity to much lower pH levels. Titanium alloys are also used because of their:
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