Friction Stir Welding of Titanium Composites

Composite materials consisting of a titanium alloy reinforced with continuous silicon carbide fibres, called TISIC are currently being investigated to enhance performance for applications where titanium alloys are used. The silicon carbide fibres are stronger and stiffer, thereby offering the possibility of weight savings when manufacturing structural components. These composites exceed the performance of many high strength titanium alloys, are corrosion resistant and are 30% to 70% lighter than conventional metal parts, with excellent fatigue properties and crack arrest capabilities. However the joining of such composites to manufacture components is challenging. Conventional fusion welding techniques create difficulties due to the detrimental impact of high temperature on the fibre/metal interfaces and cause loss of joint strength. These problems have hindered the practical application of these composites. Therefore alternate joining techniques are being sought. The stationary shoulder friction stir welding (SSFSW) technique has been successfully used to join TISIC components, to monolithic titanium, avoiding much of the technical limitations usually reported for the case of fusion welding. A range of process parameters were assessed. The results showed a very small heat affected zone and no damage to the fibres due to the welding process. Microscopic investigations showed flaw free welding, until the SSFSW tool started to mechanically interact with the SiC fibres. When subjected to tensile testing, the weld properties were superior to the parent monolithic titanium. The technical details and results will be presented and potential advantages will be discussed.