Redistribution of a Grain‐Boundary Glass Phase during Creep of Silicon Nitride Ceramics

The compressive creep behavior of a high‐purity silicon nitride ceramic with and without the addition of Ba was studied at 1400°C. Two distinct creep stages were observed during high‐temperature deformation of both materials. Transmission electron microscopy (TEM) has been used to characterize the intergranular glass film thickness. Statistical analysis of a number of grain‐boundary films indicates that the film thickness is confined to a narrow range in the as‐sintered materials. However, the mean thickness is greater in the Ba‐doped ceramic than in the undoped material. The standard deviation of the film thickness of a given material is considerably larger after creep than before. We conclude that the grain‐boundary glass phase is redistributed during creep, suggesting that viscous flow of the glass phase is responsible for the first stage of the creep process.