Crack Growth Tests in Air Plasma-Sprayed Yttria Coatings for Alumina Ceramic Matrix Composites

Crack Growth Tests in Air Plasma-Sprayed Yttria Coatings for Alumina Ceramic Matrix Composites

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Yttria coatings for all-oxide combustor walls were tested for their crack-growth behavior.These environmental and thermal barrier Y2O3-coatings were processed by atmospheric Digestive Supplements plasma spraying (APS).The stiffness and strength were measured for as-received and aged samples that were heat treated at 1000 °C, 1100 °C and 1200 °C for a 10 h dwell time.

The results show a clear development with respect to the aging conditions.The changes of the modulus and the bending strength indicate that the microstructural changes are not completed, even after aging at 1200 °C for 10 h.The fracture toughness was tested for different orientations on samples aged at 1200 °C.

Bending tests as well as Connectors indentation experiments were conducted.Furthermore, a bending device was designed to observe the crack-growth in situ.The device had to be rigid and is driven by a piezo stack.

The crack growth resistance shows differences in the rise of the R-curves for different orientations of the crack propagation.This is in agreement with the microstructure that results from the plasma spray process.