Thermal fracture of ceramic thermal barrier coatings under high heat flux with time-dependent behavior. Part 1. Experimental results

The objective of this research was to study the thermal fracture of ceramic thermal barrier coatings under high heat flux laser heating and investigate the effect of time-dependent behavior of the ceramic. Continuously plasma-sprayed zirconia coatings with thicknesses varying from 0.26 to 1.5 mm were heated with a CO2 laser to maximum surface temperatures varying from 700 to 1700 degreesC. Temperature differences from 600 to 1300 degreesC across the ceramic coating were applied. High heat flux heating was found to cause changes in the material, leading to a denser microstructure and relaxation of compressive stresses. These changes lead to the development of surface and interface cracks during ambient air cooling following laser heating. Increasing the coating thickness was found to decrease the number of surface cracks developed and increase the distance between cracks. Surface cracks were found to extend further into thin coatings than thick coatings. Increasing the maximum surface temperature was found to increase the surface crack length. The thinnest and thickest coatings developed fewer and shorter interface cracks than coatings with intermediate thicknesses. (C) 2001 Elsevier Science B.V. All rights reserved.