Densification and mechanical properties of hot-pressed ZrN ceramics doped with Zr or Ti

The densification of hot-pressed ZrN ceramics doped with Zr or Ti have been investigated at 1500–1700 °C. It is shown that either Zr or Ti additive can facilitate the densification process. ZrN with 20 mol% Zr or Ti (named ZNZ and ZNT) sintered at 1700 °C can achieve above 98% relative densities whereas densification temperature up to 2000 °C is necessary for pure ZrN. The densification improvements are attributed to solid solution of Zr or Ti into ZrN to form non-stoichiometric ZrN1−x or (Zr, Ti)N1−x. The microstructures and mechanical properties of ZNZ and ZNT samples have been examined. Large grain size and flat fracture surface existed in ZNT sample sintered at 1700 °C, which lead to poor toughness as low as 2.3 MPa m1/2. On the contrary, the fracture toughness of ZNZ sample sintered at 1700 °C was up to 5.9 MPa m1/2, attributed to fine and uniform grain size distribution.