Creep deformation behavior during densification of ZrB2-SiBCN ceramics with ZrO2additive

ZrB2-SiBCN ceramics with ZrO(2)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 degrees C, 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 ZrO(2)into the amorphous SiBCN decreases the viscosity, modifies the fluidity, and contributes to the grain boundary mobility.