Development of joining technologies for lightweight construction applications with forgeable gamma titanium aluminides with improved ductilities

Brittle TiAl alloys (e.g. Ti‑48Al) exhibit high dangers of cracks and fractures during welding - when subjected not only to mechanical loads during pressure welding but also to thermal shock stresses during fusion welding. Therefore, it was investigated whether improved fabrication weldability could also be proven for newly developed ß‑g‑TiAl alloys because of the improved ductility. For this purpose, friction welding and laser beam welding were refined at SLV München for their application for the joining of the new titanium aluminides. With regard to the plastification and the welding behaviour, the investigated TNM alloy (Ti‑43,5Al‑4Nb‑1Mo‑0.1B) was comparable with a titanium material such as Ti-6-4 with regard to friction welding. Friction welding could be applied in a reliable process without any additional measures such as preheating, postheating or shielding gas (Figs. 1a and 1b). Post-weld heat treatment served to regenerate the material with the healing of the welding region (Fig. 1c). In the case of laser beam welding, the preheating/postheating times could be reduced substantially with the local preheating/postheating of the welding region (< 4 min) in order to guarantee crack-free square-butt-welded joints. The joining technology prerequisites for the fabrication of innovative lightweight components were created with the investigations.