TWI

The feasibility of friction stir welding TIMETAL 21S beta titanium in the annealed condition was investigated. The composition of the alloy is Ti, 14-16%Mo, 2.4-3.2%Nb, 2.5-3.5%Al, 0.15-0.25%Si, max.0.4%Fe, 0.11-0.17%O, max.0.05%C, max.0.05%N, max.0.015%H. A TIMETAL 21S sheet of 1.6 mm thickness in a butt joint configuration was used for all welding studies. W-Re was the pin tool material and Ar was the shielding gas. The anvil was made of stainless steel. The effects of tool shape and welding conditions on weld quality, control of heat distribution in the weld, and purging conditions to avoid discolouration were investigated. Microstructure, wormhole defects, thickness changes in welded joints, ultimate tensile strength and elongation were determined. It was possible to make defect-free friction stir welds in TIMETAL 21S with little or no pin tool wear. Damage to the stainless steel anvil occurred after each weld. Friction stir welding in the annealed condition increased strength and reduced ductility. Post-weld ageing at 538 deg.C for 8 hours reduced strength and ductility.

5th International Symposium, 14-16 Sep 2004, Session 7B: Metallurgy/Microstructure, Paper 02