Improved Attachment Design for Ceramic Turbine Blades Via Hybrid Concepts

This proposal presents a hybrid metal-CMC turbine blade. A SiC/SiC CMC airfoil section will be bonded to a single crystal superalloy root section in order to mitigate risks associated with an all-CMC blade inserted in a superalloy disk. This allows current blade attachment technology (SX blade with a dovetail attachment to a slotted Ni disk) to be used with a ceramic airfoil. The bond between the CMC and single crystal will be primarily mechanical in nature, and enhanced with clamping arising from thermal expansion mismatch. Two single crystal root sections will be bonded to each other using diffusion bonding and/or transient liquid phase bonding at temperatures near 2200 0F. The single crystals will form a clam shell around the CMC, with little or no gap between the metal and ceramic. Upon cooling, the metal will shrink around the CMC spar to firmly clamp it. Single crystals will resist stress relaxation at an operating temperature of 1500 0F, thus maintaining clamping loads for long lives. The use of an inter layer ("compliant layer") between the CMC and the single crystal may also be entertained. 1500 0F is a reasonable upper limit for chemical reactivity issues between the metal and ceramic.