① The oxide film on the surface is stable. Titanium and its alloys have a strong affinity with oxygen. It is easy to form a very stable oxide film on the surface, which prevents the wetting and spreading of the solder. Therefore, it must be removed during brazing.
② It has a strong tendency to absorb air. Titanium and its alloys have a tendency to absorb hydrogen, oxygen and nitrogen during heating. The higher the temperature, the more severe the absorption, which sharply reduces the plasticity and toughness of titanium metal. Therefore, brazing should be carried out in a vacuum or inert atmosphere.
③ It is easy to form intermetallic compounds. Titanium and its alloys can react chemically with most needle materials to form brittle compounds, causing the joints to become brittle. Therefore, the solder used for brazing other materials is basically not suitable for brazing active metals.
④ The structure and properties are easy to change. Titanium and its alloys will undergo phase change and grain coarsening when heated. The higher the temperature, the more severe the coarsening, so the temperature of high-temperature brazing should not be too high.
