In situ formation of ZrB2–ZrO2 ultra-high-temperature ceramic composites from high-energy ball-milled ZrB2 powders

The in situ formation is reported of a fine-grained ZrB2 ultra-high-temperature ceramic (UHTC) containing evenly distributed ZrO2 of uniform size located at triple joints and grain boundaries of the ZrB2 grains, discovered during the spark-plasma sintering of ZrB2 powders subjected to high-energy ball-milling in air. It is found that this type of microstructure forms because the oxide film of ZrO2, developed on the surface of the ZrB2 particles during the high-energy ball-milling in air, creeps towards the ZrB2 multigrain joints under the application of pressure during sintering, and then crystallizes there during the fast cooling down to room-temperature. Together with the mechanism by which these dense ZrB2–ZrO2 UHTC composites form, it is also shown that they are simultaneously harder and much tougher than their ZrB2 monolith counterpart.

► The in situ formation of fine-grained ZrB2–ZrO2 composites is reported. ► A route to process ZrB2–ZrO2 composites with new microstructures is presented. ► A method to process engineered ZrB2–oxide composites controllably is described.