Creep deformation behavior during densification of ZrB₂-SiBCN ceramics with ZrO₂ additive

ZrB₂-SiBCN ceramics with ZrO₂ additive are hot-pressed under a constant applied pressure. The densification behavior of the composites is studied in a view of creep deformation by means of the Bernard-Granger and Guizard model. With determination of the stress exponent (n) and the apparent activation energy (Q_d), the specific deformation mechanisms controlling densification are supposed. Within lower temperature ranges of 1300-1400 ℃, the operative mechanism is considered to be grain boundary sliding accommodated by atom diffusion of the polymer-derived SiBCN (n = 1, Q_d = 123±5 kJ/mol) and by viscous flow of the amorphous SiBCN (n = 2, Q_d = 249±5 kJ/mol). At higher temperatures, the controlling mechanism transforms to lattice or intra-granular diffusion creep (n = 3-5) due to gradual consumption of the amorphous phase. It is suggested that diffusion of oxygen ions inside ZrO₂ into the amorphous SiBCN decreases the viscosity, modifies the fluidity, and contributes to the grain boundary mobility.