Laser Welding Parametric Study to Predict Fracture Toughness of Metastable Beta Titanium Alloys

Recent advances in aerospace technology have created the demand for improved structural materials. A metastable beta titanium alloy, TIMETAL Beta-21S, has been identified as a potential alloy for application in hypersonic vehicles such as the National AeroSpace Plane (NASP) because of its high strength-to-weight ration, high temperature service capability, excellent room temperature ductility and resistance to oxidation, corrosion, and hydrogen. High speed welding of this alloy will be necessary to achieve economic production of future aerospace structural members and skins. Previous research has indicated the suitability of CO2 laser welding in the production of large, thin sheets; however, further research is needed to optimize process parameters and develop techniques for predicting ultimate fracture toughness. American Research Company of Virginia (ARCOVA) proposes four technical objectives to demonstrate the capability to produce strong welds and the ability to predict ultimate fracture toughness in the welded joints. Specifically, in Phase I of the program ARCOVA will determine the laser process parameters for welding Beta 21S, fabricate a series of test samples using a fast-axial flow CO2 laser, characterize and test the samples, and model fracture toughness parameters using fuzzy logic expert systems.