Preliminary Evaluation of NDE Techniques for Structural Ceramics
A preliminary evaluation of several nondestructive testing methods for flaw detection in high-temperature structural ceramic components is being carried out. The ceramics components being investigated include silicon carbide heat-exchanger tubes and silicon nitride rotors. The nondestructive evaluation techniques under consideration include dye-enhanced radiography, holographic interferometry, infrared scanning, acoustic microscopy, acoustic-emission monitoring, acoustic-impact testing, and conventional ultrasonic testing. The capability of each technique to detect critical-size flaws will be discussed. Preliminary results to date' have shown that (a) dye-enhanced radiographic techniques are capable of detecting tight cracks missed with conventional x-ray methods, (b) acoustic microscopy techniques may be useful in detecting and establishing the size of subsurface defects in reaction-bonded silicon nitride, (c) holographic interferometry techniques should be valuable in locating surface cracks in silicon nitride/silicon carbide components, and (d) the results from various silicon carbide tubes suggests that infrared scanning techniques may reveal changes in heat-flow patterns which are related to variations in physical properties. The results for the other techniques mentioned will be discussed. Future efforts in this program, will be directed toward in-depth investigations of the most useful nondestructive techniques.