WELDING
A pickling operation should be conducted before and after welding as well as before and after heat treating. If pickling is performed, welding of niobium alloys can be readily accomplished by both the TIG and electron beam processes. It is recommended that all copper tooling should have a hard chrome plating approximately 0.002" thick without a nickel strike. This prevents copper contamination which causes brittle welds. For TIG, properly designed trailer shields and backup grooves with adequate gas flow can give weldments a quality equal to welds made with electron beam equipment. Where possible, the argon and helium should be passed through hot zirconium chips, maintained at 800° F to gather minute impurities in the gas. Stake welds of any length can be made without mismatch or burn-out. Girth welds by the TIG process have been made up to 54", matching .010" to .020" material. Welding of C-103 sheet is often accomplished without weld wire. Material over 0.100" thick should be welded by electron beam process.

Generally, weld wire is not used because of the high cleanliness requirements for welding. The weld wire often has slight serrations and laps that are difficult to clean. Sheet is welded within two hours after pickling, and it is not possible to pickle a roll of welding wire each time it is used.

In addition, the high melting point of niobium causes the wire to deflect and give an uneven weld bead and incomplete penetration. To eliminate these problems and still get a weld with an adequate crown and root, the mating edges to be welded are rolled up to form a "burned-down flange". The material is then welded with back-up gas and a trailer shield at a very high welding speed. The gases are a combination of helium and argon. TIG welding of second generation niobium alloy, C-129Y to C-103 has been very successful.

TABLE 6 - MECHANICAL PROPERTIES OF BARE METAL TIG WELDMENTS (C-103 TO C-103)

Note: All above anneals one hour at 2200°F

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INDEX  •  CORROSION RESISTANCE PROPERTIES  •  FABRICATION   
NIOBIUM PRODUCTS   •  SPECIFICATIONS of NIOBIUM   
NIOBIUM ELECTRONICS APPLICATIONS