1. Determination of welding temperature: The pure niobium recrystallization temperature is between 980~1090℃, and the recrystallization temperature is about 1200℃. The welding temperature of niobium, tantalum and stainless steel should be controlled under the corresponding recrystallization temperature; The recrystallization temperature of niobium and tantalum alloys increases with the addition of other elements and the welding temperature can be increased when brazing niobium and tantalum alloys respectively.
2. Selection of welding atmosphere: Niobium and tantalum are sensitive to nitrogen, oxygen, hydrogen and other impurity gases at welding temperature. More than 200 ℃ will combine with oxygen strong oxidation; Higher than this temperature, niobium and tantalum will also strongly absorb hydrogen and nitrogen, making the metal brittle and hard, and the mechanical properties of welded joints deteriorated.
Third, brazing technology
1. Surface treatment before welding: remove the thick oxide layer on the surface by mechanical method; Dilute hydrochloric acid and hot chromic acid shall be cleaned successively, copper or nickel plating shall be carried out on the premise of keeping the surface wet film of the metal parts, and the diffusion treatment shall be carried out above 1000℃;
2. Solder selection: Because silver or silver alloy is easily dissolved in niobium or tantalum, making the base material near niobium or tantalum weld brittle, avoid using silver-based solder; Palladium - based, gold - based, nickel - based solder can be used, cost - sensitive workpiece can be used nickel - based solder joints, compared to gold - based solder brittle and hardness is higher;
3, the choice of welding anger
The welding of niobium and tantalum is carried out in a high-purity atmosphere or in a high-vacuum environment. When selecting high-purity gas, argon gas with a purity of no less than 99.996% and a dew point no higher than -60℃ is generally selected. The vacuum degree should not be lower than 8.8*10-3Pa when selecting the vacuum atmosphere.
