Use of ceramic components in the hot section of gas-fired microturbines would allow higher operating temperatures and thus better operating efficiencies. However, the cost of such ceramic components is an issue for commercial-scale production. Costs can be reduced, in part, through improving fabrication yields. Use of nondestructive evaluation (NDE) methods in early stages of fabrication will support the development process to improve yields and subsequently reduce costs by rejecting flawed components prior to final processing and proof testing. An NDE approach using high-speed 3D X-ray tomographic imaging has been investigated. A large (40 × 40 cm), flat-panel, amorphous silicon X-ray detector, together with fast image processing, has been shown to allow full-volume X-ray imaging with detection of internal features in full-size as-cast parts. Gelcast radial-flow microturbine rotors, ≈23 cm in diameter, have been studied for internal defects with this 3D X-ray imaging method. Internal cracks, voids, and other variations in density within the rotors have been detected. Data acquisition speeds of 3 full frames per second have been achieved with reconstruction times of individual cross-sections of less than 1 second. This paper presents details of the 3D X-ray imaging method and results achieved on full-size microturbine rotors.
Ceramic Applications in Turbine Engines (CATE) Development Testing
