Thermochemical compatibility between alumina and ZrO2–GdO3/2 thermal barrier coatings

Abstract Gd 2 Zr 2 O 7 and Gd co-doped zirconias are notable examples of materials under consideration for the next generation of thermal barrier coatings, wherein thermochemical and thermomechanical compatibility are critical to the durability of the system. The thermochemical compatibility of GdO 1.5 –ZrO 2 compositions with Al 2 O 3 has been investigated using powder compacts and diffusion couples. A tentative isothermal section for the AlO 1.5 –GdO 1.5 –ZrO 2 system at 1200 °C is reported, with additional discussion of the ordering transformation between the fluorite and pyrochlore phases. New light is shed on the long-standing uncertainty on the latter issue. It is shown that addition of GdO 1.5 to ZrO 2 above ∼32% results in the formation of a GdAlO 3 interphase, with convoluted morphology and a Gd-depleted fluorite layer above it. The results provide guidelines for the compositional design of emerging thermal barrier materials.