Temperature‐dependent mechanical and oxidation behavior of in situ formed ZrN/ZrO 2 ‐containing Si 3 N 4 ‐based composite

In this work, Si 3 N 4 and Zr(NO 3 ) 4 were used as raw materials to prepare ZrN/ZrO 2 ‐containing Si 3 N 4 ‐based ceramic composite. The processing, phase composition, and microstructure of the composite were investigated. Hardness and fracture toughness of the ceramics were evaluated via Vickers indentation in Ar at 25°C, 300°C, 600°C, and 900°C. During spark plasma sintering, Zr(NO 3 ) 4 was transformed into tetragonal ZrO 2 , which further reacted with Si 3 N 4 , resulting in the formation of ZrN. The introduction of ZrN enhanced the high‐temperature mechanical properties of the composite, and its hardness and fracture toughness reached 13.4 GPa and 6.1 MPa·m 1/2 at 900°C, respectively. The oxidation experiment was carried out in air at 1000°C, 1300°C, and 1500°C for 5 h. It was shown that high‐temperature oxidation promoted the formation and growth of porous oxide layers. The microstructure and phase composition of the formed oxide layers were investigated in detail. Finally, it was identified that the obtained composite exhibited a higher thermal diffusivity than that of monolithic Si 3 N 4 in the temperature range of 100°C–1000°C.