Anisotropic CMAS resistance in YSZ single crystals

We report a study on interactions between Yttria-stabilised zirconia (YSZ) single crystals and calcium-magnesium-alumino-silicate (CMAS), with a particular emphasis on the effect of crystallographic orientation on CMAS resistance. Crystals oriented in the (1 1 0) orientation exhibit reduced CMAS interaction depths due to the formation of reaction products, demonstrating its superior CMAS resistance compared to the (1 0 0) and (1 1 1) orientations. Contrary to the well-established ’dissolution-precipitation’ mechanism, these reaction products are directly formed within the infiltration channels in the crystals oriented in (1 1 0) following a mechanism of preferential growth. This growth mechanism is facilitated by the high structural compatibility between the (1 1 0)-orientated YSZ and the reaction products. As a result, the reaction layer maintains a crack-free microstructure with strong adhesion to the interior wall of the infiltration channels, which enhances the resistance to CMAS attack. This discovery introduces a new approach to thermal barrier coatings (TBCs) design through crystallographic engineering, leveraging the material’s intrinsic properties to expand the design possibilities for more resilient TBC materials.