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Categories of Titanium Alloys
- Alpha alloys contain neutral alloying elements like tin or alpha stabilizers like aluminum or oxygen. Examples include Ti-5Al-2Sn-ELI and Ti-8Al-1Mo-1V.
- Near-alpha alloys contain a small amount of ductile beta-phase and are alloyed with beta phase stabilizers like molybdenum, silicon, or vanadium. Examples include Ti-6Al-2Sn-4Zr-2Mo and Ti-5Al-5Sn-2Zr-2Mo.
- Alpha and beta alloys are metastable and include a combination of alpha and beta stabilizers. They can be heat treated. Examples include Ti-6Al-4V and Ti-6Al-6V-2Sn.
- Beta and near beta alloys are metastable and contain sufficient beta stabilizers to maintain the beta phase. They can be solution treated and aged to improve strength. Examples include Ti-10V-2Fe-3Al and Ti-13V-11Cr-3Al.
Beta-Titanium
- Beta titanium alloys exhibit the BCC allotropic form of titanium (beta phase) and contain elements like molybdenum, vanadium, niobium, tantalum, zirconium, manganese, iron, chromium, cobalt, nickel, and copper.
- Beta titanium alloys have excellent formability and can be easily welded.
- Beta titanium alloys replaced stainless steel for certain uses in orthodontics due to their strength/modulus of elasticity ratios and reduced force per unit displacement.
- Some beta titanium alloys can convert to hard and brittle hexagonal omega-titanium at cryogenic temperatures or under the influence of ionizing radiation.
Transition Temperature
- Titanium has a hexagonal alpha phase at ambient temperature and pressure, which transforms to a body-centered cubic beta phase at about 890°C.
- Alpha stabilizers raise the alpha-to-beta transition temperature, while beta stabilizers lower it.
- Alpha stabilizers include aluminum, gallium, germanium, carbon, oxygen, and nitrogen. Beta stabilizers include molybdenum, vanadium, tantalum, niobium, manganese, iron, chromium, cobalt, nickel, copper, and silicon.
Properties of Titanium Alloys
- Beta-phase titanium is more ductile, while alpha-phase is stronger yet less ductile.
- Alpha-beta-phase titanium has mechanical properties in between both phases.
- Titanium alloys may contain oxide precipitates, which offer some strength but decrease toughness and are not very responsive to heat treatment.
- Titanium and its alloys have outstanding corrosion resistance to seawater and are used in boats, airplanes, missiles, rockets, and biological implants.
- Titanium is stronger than low-carbon steels but 45% lighter, and twice as strong as weak aluminum alloys but only 60% heavier.
Applications
- Titanium is commonly used in aerospace structures for its resistance to corrosion and heat.
- Titanium alloys are stronger than aluminum alloys and lighter than steel.
- Titanium alloys are extensively used in biomedical applications, such as orthopedic joint replacements.
- Titanium alloys can be produced through various techniques, including CNC machining and powder metallurgy.
- Solid freeform fabrication (3D printing) is emerging as a method for producing titanium alloy products.
- Aerospace Structures
- Titanium is chosen for aviation due to its corrosion resistance, heat resistance, and high strength-to-weight ratio.
- Titanium alloys are used in aircraft structures, such as blades, discs, rings, airframes, and fasteners.
- The aerospace industry accounts for a significant portion of titanium alloy usage.
- Titanium alloys offer superior performance in aerospace applications compared to aluminum and steel.
- Titanium alloys are able to withstand high temperatures and harsh environments in aviation.
- Biomedical
- Titanium alloys are extensively used in orthopedic joint replacements and bone plate surgeries.
- Different production methods, such as CNC machining and powder metallurgy, are used to manufacture biomedical titanium products.
- Wrought products have material loss during machining, while cast samples have limitations in further processing.
- Traditional powder metallurgy methods are material efficient but may face challenges in achieving fully dense products.
- Solid freeform fabrication (3D printing) is a promising technique for biomedical titanium products.
Titanium alloys are alloys 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. However, the high cost of both raw materials and processing limit their use to military applications, aircraft, spacecraft, bicycles, medical devices, jewelry, highly stressed components such as connecting rods on expensive sports cars and some premium sports equipment and consumer electronics.
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. This heat treatment process is carried out after the alloy has been worked into its final shape but before it is put to use, allowing much easier fabrication of a high-strength product.
