Titanium is a lustrous transition metal with a silver color, low density, and high strength. Titanium is resistant to corrosion in sea water, aqua regia, and chlorine. In power plants, titanium can be used in surface condensers. Pure titanium is stronger than common, low-carbon steels, but 45% lighter. It is also twice as strong as weak aluminium alloys but only 60% heavier. The two most useful properties of the metal are corrosion resistance and strength-to-density ratio, the highest of any metallic element. The corrosion resistance of titanium alloys at normal temperatures is unusually high. Titanium’s corrosion resistance is based on the formation of a stable, protective oxide layer. Although “commercially pure” titanium has acceptable mechanical properties and has been used for orthopedic and dental implants, for most applications titanium is alloyed with small amounts of aluminium and vanadium, typically 6% and 4% respectively, by weight. This mixture has a solid solubility which varies dramatically with temperature, allowing it to undergo precipitation strengthening.
Titanium alloys are metals that contain a mixture of titanium and other chemical elements. Such alloys have very high tensile strength and toughness (even at extreme temperatures). They are light in weight, have extraordinary corrosion resistance and the ability to withstand extreme temperatures.
Titanium Alpha + Beta Alloy
Titanium exists in two crystallographic forms. At room temperature, unalloyed (commercially pure) titanium has a hexagonal close-packed (hcp) crystal structure referred to as alpha (α) phase. When the temperature of pure titanium reaches 885 °C (called the β transus temperature of titanium), the crystal structure changes to a bcc structure known as beta (β) phase. Alloying elements either raise or lower the temperature for the α-to- β transformation, so alloying elements in titanium are classified as either α stabilizers or β stabilizers. For example, vanadium, niobium, and molybdenum decrease the α-to-β transformation temperature and promote the formation of the β phase.
- Alpha + Beta Alloy. Alpha + beta alloys have compositions that support a mixture of α and β phases and may contain between 10 and 50% β phase at room temperature. The most common α + β alloy is Ti-6Al-4V. The strength of these alloys may be improved and controlled by heat treatment. Examples include: Ti-6Al-4V, Ti-6Al-4V-ELI, Ti-6Al-6V-2Sn, Ti-6Al-7Nb.
Grade 23 Titanium Alloy – Ti-6Al-4V-ELI
Ti-6Al-4V-ELI or TAV-ELI is the higher purity version of Ti-6Al-4V. ELI stands for Extra Low Interstitial. The essential difference between Ti6Al4V ELI (grade 23) and Ti6Al4V (grade 5) is the reduction of oxygen content to 0.13% (maximum) in grade 23. Reduced interstitial elements oxygen and iron improve ductility and fracture toughness with some reduction in strength. It’s the top choice for any sort of situation where a combination of high strength, light weight, good corrosion resistance and high toughness are required. This grade of titanium, medical grade of titanium, is used in biomedical applications such as implantable components due to its biocompatibility, good fatigue strength and low modulus.
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