I would suggest crimping if it an electrical joint. Even super-conducting materials are crimped. Standard ferrules and tools are available. You can get supplier to do a voltage drop test and pull (mechanical)test, if needed.
Brazing is possible. Tantalum must be brazed in a high purity inert atmosphere or in a vacuum for high corrosion resistance.
For low temperature brazing , the Tantalum can be plated with with another metal such as copper or nickel that is readily wet by the brazing filler metal. The brazing filler should alloy with and dissolve the plating during the brazing cycle.
Note: Alloying with and erosion of the tantalum by the filler metal can cause brittleness and low joint strength. Tantalum forms brittle intermetallic compounds with most commercial brazing filler metals. In general the brazing time always be a minimum. Silver-copper filler metals produce joints with useful strength at room temperature.
THIS DATA FROM AWS WELDING HANDBOOK, 7TH EDITION, VOLUME 4. "METALS AND THEIR WELDABILITY."
