Effect of CaO Addition on Compressive Deformation of S ilicon N itride Ceramic with Y ‐ Mg ‐ Si ‐ O ‐ N Glassy System

Creep behavior of Si 3 N 4 polycrystals containing Y 2 O 3 ‐ MgO ‐ SiO 2 glass phase (with and without Calcium oxide [ CaO ] additive) was studied by compression tests between 1500 and 1700°C. We studied the effect of CaO additive on flow stress, microstructural evolutions, and thermal stability of the intergranular glass phase during deformation. While the addition of CaO did not affect grain size, the flow stress decreased with the amount of CaO . This result suggested that the addition of CaO reduced the viscosity of intergranular glass phase. The addition of CaO further improved the thermal stability of the glass phase by suppressing the evaporation at elevated temperatures.