Heat treatment of titanium and titanium alloys

Titanium is an important structural metal developed in the 1950s. Titanium alloys are widely used in various fields because of their high strength, good corrosion resistance, and high heat resistance. Titanium is a commonly used material in many industrial applications due to its excellent strength-to-weight ratio, corrosion resistance, and biocompatibility. Titanium alloy refers to a variety of alloy metals made of titanium and other metals. Titanium is an important structural metal developed in the 1950s. Titanium alloys have high strength, good corrosion resistance, and high heat resistance. In the 1950s and 1960s, the main focus was on the development of high-temperature titanium alloys for aero-engines and structural titanium alloys for airframes.

Titanium is an allotrope with a melting point of 1668°C. It has a close-packed hexagonal lattice structure below 882°C, which is called alpha titanium; it has a body-centered cubic lattice structure above 882°C, which is called beta titanium. By utilizing the different characteristics of the above two structures of titanium, adding appropriate alloying elements to gradually change the phase transformation temperature and phase content, titanium alloys with different structures are obtained. At room temperature, titanium alloys have three matrix structures, and titanium alloys are divided into the following three categories: α alloy, (α+β) alloy and β alloy.

However, in order to optimize their mechanical properties, heat treatment is often required. Heat treatment is a crucial step in the processing of titanium and titanium alloys. It can improve the performance of materials and increase the stability of materials. This article will introduce in detail the solid solution treatment, stabilization treatment, annealing treatment and hydrogen removal treatment in the heat treatment of titanium alloys.

1. Solid solution treatment
Solid solution treatment aims to fully dissolve the alloying elements in titanium and titanium alloys to form a supersaturated solid solution, thereby improving the strength and hardness of the material. The solid solution process mainly includes the following steps:
Heating titanium and titanium alloys to a high temperature (above the phase transformation point) and maintaining it for a certain period of time allows the alloy elements to be fully dissolved. Rapidly cool titanium and titanium alloys to room temperature to obtain a supersaturated solid solution.
2. Stabilization treatment
Stabilization treatment is mainly used to eliminate harmful phases in titanium and titanium alloys and improve the plasticity and toughness of the material. Stabilization treatment mainly includes the following steps: heating titanium and titanium alloys to high temperatures (above the phase transformation point) and maintaining them for a certain period of time to fully dissolve the harmful phases.
Quickly cool titanium and titanium alloys to room temperature to obtain a stable metallographic structure.
3. Annealing treatment
Annealing treatment is mainly used to eliminate internal stress during the processing of titanium and titanium alloys and improve the plasticity and toughness of the material. Annealing treatment mainly includes the following steps: heating titanium and titanium alloys below the critical point and maintaining them for a certain period of time to release the internal stress.
Slowly cool titanium and titanium alloys to room temperature to avoid the generation of new internal stresses.
4. Hydrogen removal treatment
Titanium and titanium alloys easily absorb hydrogen during processing, causing cracks and hydrogen embrittlement in the material. Hydrogen removal treatment aims to remove hydrogen from titanium and titanium alloys and improve the reliability and stability of the material. Hydrogen removal treatment mainly includes the following steps:
Heating titanium and titanium alloys to a high temperature (above the phase transformation point) and maintaining it for a certain period of time allows hydrogen to be released. Quickly cool titanium and titanium alloys to room temperature to prevent newly adsorbed hydrogen from entering the material. 

In short, solid solution treatment, stabilization treatment, annealing treatment and hydrogen removal treatment are all very important links in the heat treatment of titanium and titanium alloys. In order to obtain titanium and titanium alloy products with excellent properties, we must understand and master the principles, methods and application scope of these heat treatment processes, and select the appropriate heat treatment process according to the specific situation to improve the performance, stability and reliability of the material.