Types of Titanium Alloys

As an allotrope, Titanium with a close-packed hexagonal lattice structure below 882 ℃ is called α titanium and titanium with a body-centered cubic lattice structure between 882.5 ℃ and its melting point 1668 ℃ is called β titanium. For the occurrence of α + β transition at 882.5 ℃, 882.5 ℃ is therefore the α + β transition temperature, briefly known as the phase transition point.

Titanium alloy is divided into α-phase, β-phase, α + β phase by metal structures, respectively using TA, TB and TC to represent its grade and type. Generally speaking, casting and forging use TA series, bars use TC series.

They are classified as follows:

(1) α titanium alloy

α titanium alloy is a single-phase solid solution alloy when its annealed structure takes titanium α as a matrix, with its main alloying element α, stabilizing element Al, neutral elements Sn and zr. Solid solution strengthening can be used. Either at normal temperatures or relatively high practical temperature in its application, its phase is always α and its organization remains stable.With a wear resistance higher than pure titanium and a strong antioxidant capacity, it maintains its strength and creep resistance at 500 ℃ ~ 600 ℃. But it can not be strengthened by heat treatment, its strength at room temperature is not strong.

(2) β titanium alloy

β titanium alloy refers to a kind of single-phase alloy comprising of β-phase solid solution. The main feature of this alloy is adding a lot of β stabilizing elements (> 17%), such as Mo, cr, V and the like. It has a high strength before being heat-treated. After the process of quenching and aging, this alloy will be further strengthened. Its room-temperature strength can be up to 1372 ~ 1666MPa. But with a poor thermal stability, it should not be used at high temperatures.

(3) α+ β titanium alloy

α+ β titanium alloy is composed of α phase and β phase, taking α as the major one and β phase less than 30%. This alloy, with good overall performance, organizational stability, great toughness, ductility and high temperature deformation, can be hot pressure processed well and can be strengthened by way of quenching and aging. Its strength after receiving heat treatment is about 50%~ 100% higher than that in the annealed condition. With good high-temperature strength, it can achieve long-term work at 400 ℃ ~ 500 ℃. The thermal stability of this alloy is only secondary to α titanium alloy.

(4) Near-α titanium alloy

The so-called near-α titanium alloy means (α + β) titanium alloy adds less than 2% of β as its stabilizing element, making αphase and a small amount of β phase its annealed structure. These alloys boasts the best heat resistance.

Except by annealed structure, titanium alloy can be classified according to its performance characteristics as: high plasticity&low intensity titanium alloy, medium intensity titanium alloy, high strength titanium alloy and heat-resistant titanium alloy.

According to methods of production, they can also be divided into deformed titanium, cast titanium and powder metallurgy titanium alloy, the most commonly used one is deformed titanium alloy.