Non-destructive CMAS-infiltration characterization of thermal barrier coatings
The present invention provides a non-destructive method of characterizing CMAS infiltration and CMAS assisted damage in thermal barrier coatings (TBCs). Such approach is especially relevant for determining the lifetime of coatings on e.g. turbines or parts of the turbines such as blades or in-liners of the combustion chambers. The turbines can be gas turbines or high-pressure turbines or others and may be stationary or used for example in aviation.
1. A non-destructive method of determining any CaO—MgO—Al 2 O 3 —SiO 2 (CMAS) infiltration in barrier coatings on a metallic substrate comprising:
i. providing a metallic substrate coated with a barrier coating potentially exposed and infiltrated by CMAS,
ii. analyzing the metallic substrate and barrier coating with Raman mapping, and
iii. determining if the barrier coating has experienced a phase change initiated by infiltration of CMAS of the barrier coating that is detectable by the Raman mapping.
2. The method according to claim 1 , wherein the Raman mapping is 3D Raman mapping.
3. The method according to claim 2 wherein the 3D Raman mapping consists of a) surface Raman mapping and
b) depth-profiling and x and y mapping.
4. The method according to claim 3 wherein step a) consists in scanning the surface of the sample in an x and y plane.
5. The method according to claim 3 or 4 wherein step b) is a collection of Raman spectra point by point along an axis normal to the surface of the sample (z-axis).
6. The method according to claim 1 further comprising the step of
iv. correlating the phase change of the barrier coating of any other phase present in the coating material that undergoes a phase change initiated by CMAS and that is detectable by the Raman technique from the depth of the samples to the CMAS infiltration damage.
7. The method according to claim 6 , wherein step iv is:
iv. correlating the phase change from the tetragonal phase to the monoclinic phase in 7YSZ in the depth of the samples to the CMAS infiltration damage.
8. The method according to claim 1 wherein the means consists essentially of a high-temperature resistant material.
9. The method according to claim 8 wherein the high-temperature resistant material is selected from Ni-based superalloys or oxide-based or SiC-based ceramic matrix composits.
10. The method according to claim 1 wherein the metallic substrate is located on a turbine, gas turbine, high-pressure turbine, or parts of the high-pressure gas turbine, such as turbine blade, or inliner of a combustion chamber.
11. The method according to claim 1 wherein the barrier coating is a thermal barrier coating or an environmental barrier coating.
12. The method according to claim 11 , wherein the thermal barrier coating is a 7% Yttria-Stabilized-Zirconia coating or any TBC system that gives that undergoes a phase change initiated by CMAS and that is detectable by the Raman technique.
13. The method according to claim 11 wherein the environmental barrier coating is selected from rare earth (RE) mono-silicate, or disilicate.
14. The method according to claim 1 wherein step iii is:
iii. determining the concentration of tetragonal phase peaks and monoclinic phase peaks of 7YSZ damaged by CMAS and thereby collecting information about the phase change initiated by CMAS from the tetragonal phase to the monoclinic phase.
15. The method according to claim 1 wherein the damage evolution of barrier coatings is monitored based on the detection of the phase change.
16. The method according to claim 15 wherein the monitoring of the phase change is made with respect to the depth of the barrier coating.