Development of oxidation protective coatings on ZrB2 based UHTC materials: Current status and implications

Kurzfassung

The oxidation of ZrB2 based Ultra-High Temperature Ceramics (UHTCs) leads to the formation of liquid B2O3 and porous ZrO2. Increased evaporation of B2O3 above 1500°C restricts the usage of ZrB2 for long term applications. Overlay coatings for oxidation protection has been explored for the first-time using various approached. Coatings such as HfO2, Gd2O3, Al2O3 and metallic Nb are applied on top of ZrB2 and high temperature oxidation tests up to 1700°C are conducted for various times. The application of protective coatings has proven the increased oxidation resistance of ZrB2 at the studied temperatures and times. The underpinning oxidation mechanisms are understood and identified as 1) Formation of a liquid solution with B2O3 and decreasing its evaporation rate and 2) Densification of ZrO2 scale by means of liquid phase sintering or solid solution formation.