Creep in Silicon Nitride at High Temperatures.

Creep experiments on reaction-sintered and hot-pressed silicon nitride were carried out at temperatures of 1200 to 1400 degree C using a four-point bending apparatus. The initially high rate of creep falls with reaction-sintered Si//3N//4 more rapidly it does with the hot-pressed material, so that the former shows a better creep behavior at temperatures of 1200 degree C and above. Higher MgO contents have a harmful effect. Grain-boundary sliding or viscous flow of the glassy phase present between grains is assumed to be the predominant mechanism of high-temperature deformation of hot-pressed silicon nitride.