REDISTRIBUTION OF A GRAIN-BOUNDARY GLASS PHASE DURING CREEP OF SILICON-NITRIDE CERAMICS

The compressive creep behavior of a high-purity silicon nitride cerami c with and without the addition of Ba was studied at 1400 degrees C, T wo distinct creep stages were observed during high-temperature deforma tion of both materials, Transmission electron microscopy (TEM) has bee n used to characterize the intergranular glass film thickness, Statist ical analysis of a number of grain-boundary films indicates that the f ilm thickness is confined to a narrow range in the as-sintered materia ls, However, the mean thickness is greater in the Ba-doped ceramic tha n in the undoped material, The standard deviation of the film thicknes s of a given material is considerably larger after creep than before, We conclude that the grain-boundary glass phase is redistributed durin g creep, suggesting that viscous flow of the glass phase is responsibl e for the first stage of the creep process.