Abstract
In aluminized CoCrAlY coatings used for oxidation tests and for in-service gas turbine blades, a boundary diffusion layer is found at the boundary between the coating and the substrate. The square of the layer thickness is roughly proportional to time. By means of this relationship, there is a possibility that the temperature at any observed area of a blade can be estimated by measuring the layer thickness. However, application of this temperature estimation is limited due to change of diffusion behavior. Regardless of operating time and of observed locations in gas turbine blades, Al-content in the coating decreases almost proportionally to the thickness of the boundary diffusion layer. From this relationship, by finding the time when the boundary diffusion layer reaches the thickness corresponding to an Al-content equal to that in substrate, there is a possibility to predict the time when the Al-content in the coating decreases below that in the substrate. An estimation of Al-content was tried by examining two blades with different operating hours. As a result, the estimated Al-contents are almost equal to the measured ones. As for aluminized CoNiCrAlY coating, the behavior of the Al-content in the coating and of the boundary diffusion layer was examined in oxidation tests, and the possibility of estimating temperature and predicting Al-content is also shown.
