Low Thermal Conductivity Yttrium Aluminum Garnet Thermal Barrier Coatings Made by the Solution Precursor Plasma Spray: Part II—Planar Pore Formation and CMAS Resistance
Abstract
Low thermal conductivity in yttrium aluminum garnet (YAG)-based thermal barrier coatings (TBCs) made by solution precursor plasma spray (SPPS) can be achieved by creating planar arrays of porosity called inter-pass boundaries (IPBs) as shown in Part I. In the current work, the mechanism of IPBs formation is studied through analysis of precursor entrainment and collection of single/raster step deposition patterns. It is concluded that the IPBs are formed by trapping precursor that under/over penetrates the plasma jet. CMAS interaction tests on SPPS YAG TBCs with heavy IPBs show an improvement of 123X and 15X over APS YSZ and SPPS YAG-light IPBs TBCs, respectively. It is demonstrated that the exceptional coating performance is because of the engineered heavy IPBs which branch out from the vertical cracks and run parallel to the surface. The CMAS melt gets drawn in the IPBs due to the capillary forces, leading to a shallow infiltration depth. The IPBs have a porosity of 70%, thus act as reservoirs for CMAS. Based on the favorable results, an alternate CMAS mitigation strategy is proposed that solely relies on microstructural features instead of the conventional approach where a vigorous reaction between CMAS-TBCs is desirable to form secondary phases.
- Publication:
-
Journal of Thermal Spray Technology
- Pub Date:
- June 2018
- DOI:
- 10.1007/s11666-018-0727-x
- Bibcode:
- 2018JTST...27..794K
- Keywords:
-
- enhanced CMAS resistance;
- intern pass boundaries;
- microstructural optimization;
- planar porosity formation;
- solution precursor plasma spray;
- thermal barrier coatings;
- yttrium aluminum garnet