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 plasma spraying (APS).The stiffness and strength were measured for as-received and aged samples that were heat treated at 1000 °C, 1100 Lifestyle °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 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 Beauty microstructure that results from the plasma spray process.