High-strength ZrB2-based ceramics prepared by reactive pulsed electric current sintering of ZrB2–ZrH2 powders

Fully densified ZrB2-based ceramic composites were produced by reactive pulsed electric current sintering (PECS) of ZrB2–ZrH2 powders within a total thermal cycle time of only 35 min. The composition of the final composite was directly influenced by the initial ZrH2 content in the starting powder batch. With increasing ZrH2 content, ZrB2–ZrO2, ZrB2–ZrB–ZrO2 and ZrB2–ZrB–Zr3O composites were obtained. The ZrB2–ZrB–ZrO2 composite derived from a 9.8 wt% ZrH2 starting powder exhibited an excellent flexural strength of 1382 MPa combined with a Vickers hardness of 17.1 GPa and a fracture toughness of 5.0 MPa m1/2. The high strength was attributed to a fine grain size and the removal of B2O3 through reaction with Zr. Higher ZrH2 content starting powders were densified through solution-reprecipitation resulting in the formation of coarser angular ZrB2–ZrB composites with a Zr3O grain boundary phase with a fracture toughness of 5.0 MPa m1/2 and an acceptable strength in the 852–939 MPa range.