| Single crystal nickel-base superalloys such as PWA 1484 exhibit superior performance compared to conventional superalloys, and are used extensively in turbine blade applications requiring high temperature mechanical strength and good hot corrosion resistance. The life of these blades is typically limited by cracks and erosion. Due to the high cost of these blades, welding techniques are being considered to weld/repair worn components, extending their useful lives and delaying the need for expensive replacement components. However, the sensitivities for solidification cracking and post weld heat treatment cracking are relatively high in these alloys. Electron Beam Welding (EBW) can deliver the most concentrated heat sources and has the potential to address these issues. Numerous welding trials and structural tests must be conducted to identify the optimum method and welding parameters.; In this thesis, welding and weldability are studied over a range of material conditions, welding parameters and directions. The influence of welding parameters on the fusion zone microstructure, and resultant weldability is investigated using combination of microscopic examination and micro-hardness testing. The effects of welding parameters on localized microstructural features, solidification cracking sensitivity, and mechanical properties of electron beam autogenously welded coupons of single crystal PWA 1484 are discussed as well. |
