Several methods of heat treatment commonly used for titanium alloys

The commonly used heat treatment methods for titanium alloys are annealing, solid solution and aging treatment. Annealing is applicable to all types of titanium alloys, mainly to obtain the best mechanical properties, eliminate stress, improve plasticity and stabilize the organization. Solid solution and aging treatment is the main means of titanium alloy strengthening.
1. Stress relief annealing:
The annealing temperature is 100-250°C lower than the recrystallization temperature;
The purpose is to eliminate or reduce the internal stresses that occur during processing, and to prevent and reduce deformation. The time required depends on the cross-section size of the workpiece, the processing history and the degree of stress relief required.
2. Complete annealing:
Also known as: recrystallization annealing
The annealing temperature is close to between the recrystallization temperature and the β-transition point, and the annealing process occurs mainly during recrystallization, at a temperature higher than the recrystallization temperature of the alloy.

The purpose is to reduce hardness, improve plasticity, stabilize the organization, and improve machinability. For different kinds of titanium alloys, the type, temperature and cooling method of annealing are different.
3. Double annealing
Including high-temperature and low-temperature annealing, air-cooled after annealing; high-temperature for the β-transition point below 20-160 ℃, low-temperature for the phase transition point below 300-500 ℃.
The purpose is to improve the plasticity of the alloy, fracture toughness and stabilize the organization.
4. Isothermal annealing
A special form of double annealing, first heated to 20-160 ℃ below the β-transition point, insulation, transferred to a low-temperature furnace (600-650 ℃) insulation, and then out of the air-cooled to room temperature.
It is suitable for titanium alloys with high content of β-stabilizing elements, and adopts slow cooling to fully decompose the β phase.
The purpose is to get stable organization.
5.Solid solution treatment
Above the transformation temperature of α+β two-phase region, below the β transformation point 28-83 ℃ heating, special circumstances can also be heated above the β transformation point, followed by quenching.
The purpose is to obtain a high proportion of aging-strengthened substable β-phase.
6. Ageing treatment
Generally heated between 425-650°C, the aging temperature and aging time can be determined according to the aging hardening curve;
The purpose is to promote the decomposition or precipitation of the substable β-phase, thereby increasing the strength of the alloy.