Si3N4/SiCN nanocomposites:: Influence of SiC nanoprecipitates on the creep behaviour

The compressive creep behaviours of a silicon nitride ceramic densified with yttria and alumina and of the same material containing 10 wt% SiC nanoparticles are compared in the 1250-1450 degrees C temperature range under stresses ranging from 45 to 180 MPa. The stress exponents are similar to 0.8 and 1 and the apparent activation energies are 514 and 590 kJ mol(-1) for the monolith and the composite, respectively. No signs of cavitation are observed. For both materials grain boundary sliding accommodated by diffusion through the intergranular glass phase is considered as the primary steady-state creep mechanism. The higher creep resistance of the composite is connected to the presence of intergranular SiC nanoparticles which limit grain boundary sliding and to the difference in chemical composition of the intergranular glass phase.