What are the main problems in brazing of titanium and titanium alloys?

The alloy made of titanium and iron, aluminum, vanadium, molybdenum and other metal elements has excellent physical and mechanical properties such as high strength, high heat resistance, and good corrosion resistance. It is widely used in chemical engineering, marine engineering, transportation, medical treatment, and construction. As well as high-tech fields such as aerospace and military industry, they are extremely important lightweight structural materials. Among them, aerospace is an important downstream application field.

Titanium and titanium alloys are active metals and are widely used in aerospace, petrochemical and atomic energy industries. The main problems in brazing of titanium and titanium alloys are shown in the following aspects:

①The oxide film on the surface is stable, titanium and its alloys have a high affinity for oxygen, and a very stable oxide film is easily formed on the surface, which prevents the wetting and spread of the solder. Therefore, it must be removed during brazing.
②It has a strong tendency to get gas. Titanium and its alloys have a tendency to absorb hydrogen, oxygen and nitrogen during the heating process, and the higher the temperature, the more serious the absorption, so that the plasticity and toughness of titanium metal are sharply reduced, so brazing should be Carry out in vacuum or inert atmosphere.
③It is easy to form intermetallic compounds. Titanium and its alloys can chemically react with most needle materials to form brittle compounds, which makes the joints brittle. Therefore, the brazing filler metal used for brazing other materials is basically not suitable for brazing active metals.
④The organization and performance are easy to change. Titanium and its alloys will undergo phase transformation and grain coarsening when heated. The higher the temperature, the more serious the coarsening, so the high-temperature brazing temperature should not be too high.

In short, when brazing titanium and its alloys, attention must be paid to the brazing heating temperature. Generally speaking, the brazing temperature should not exceed 950～1000℃. The lower the brazing temperature, the smaller the impact on the properties of the base metal. For quenched aging alloys, brazing can also be performed under the condition of not exceeding the aging temperature.
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