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

The microstructure evolution of ZrB2 hot pressed with 15 vol% TaSi2 was studied in the as-sintered state and after oxidation for 15 min at 1500 and 1650 degrees C in stagnant air. In the pristine material, the original ZrB2 nuclei are surrounded by a mixed (Zr,Ta)B-2 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 degrees C, accompanied by large volume expansion and local liquid formation, which ruptures the ZrO2 grains and structure. (C) 2017 Elsevier Ltd. All rights reserved.