Critical oxidation behavior of Ta-containing ZrB2 composites in the 1500–1650 °C temperature range

Abstract

The microstructure evolution of ZrB2 hot pressed with 15 vol% TaSi2 was studied in the as-sintered state and after oxidation for 15min at 1500 and 1650°C in stagnant air. In the pristine material, the original ZrB2 nuclei are surrounded by a mixed (Zr,Ta)B2 solid solution. Refractory Ta-compounds are located at triple junctions and wetted grain boundaries are distinctive of this ceramic. After oxidation, the solid solution evolves into ZrO2 grains encasing intragranular nano-structured TaB2 particles. Here we show that the operating limit temperature of this composite is related to the critical oxidation of TaB2 to Ta2O5 above 1600°C, accompanied by large volume expansion and local liquid formation, which ruptures the ZrO2 grains and structure.