The structure and properties of titanium alloys

According to the microstructure classification of titanium alloys after annealing treatment, titanium alloys can be divided into three categories: α, (α + β), and β titanium alloys (Experimental Study on PCBN High-speed Cutting of Titanium Alloys).

(1) α titanium alloy
Titanium alloys with a single α phase solid solution in the annealed structure are called α titanium alloys. α titanium alloys are mainly composed of elements such as Al, which stabilizes the α phase, and neutral elements, and generally do not contain or only contain a small amount of β-stabilizing elements. Broadly speaking, α titanium alloys include near-α titanium alloys with a very small amount of β phase in the equilibrium state. The characteristics of α titanium alloys are stable structure, good high-temperature performance, good thermal stability, and they are the basis of heat-resistant titanium alloys. However, due to their inability to withstand heat treatment strengthening, their strength at room temperature is not very high.

(2) β titanium alloy
After quenching from the β zone, the high-temperature β-Ti can be stabilized to room temperature, resulting in β titanium alloy or intermediate β titanium alloy. Broadly speaking, β titanium alloys include fully β titanium alloys without α phase in the equilibrium state, intermediate-stable β titanium alloys with a small amount of α phase, and near-β titanium alloys with a large amount of α phase. Due to the face-centered cubic crystal structure of the β titanium alloy body, there are many slip systems, which are prone to plastic deformation, and the thermal stability of the high-temperature structure is poor.

(3) α + β titanium alloy
α + β titanium alloys are titanium alloys with α phase as the matrix, adding appropriate β-stabilizing elements, and are generally called duplex titanium alloys. Two-phase titanium alloys have better comprehensive mechanical properties, with higher strength than α titanium alloys, while still retaining the heat resistance of α titanium alloys, and can be strengthened by heat treatment, and have good hot workability. However, the stability of the structure of this type of titanium alloy is relatively poorer than that of α titanium alloy. The welding performance of α + β titanium alloys with low β phase content is good, and the more β phase content, the worse the welding performance.

Titanium alloys are classified according to their performance characteristics into heat-resistant titanium alloys, high-strength titanium alloys, medium-strength titanium alloys, low-strength high plasticity titanium alloys, etc.