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

The compressive creep behaviours of a silicon nitride ceramic densified wit h yttria and alumina and of the same material containing 10 wt% SiC nanopar ticles are compared in the 1250-1450 degrees C temperature range under stre sses ranging from 45 to 180 MPa. The stress exponents are similar to 0.8 an d 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 obser ved. For both materials grain boundary sliding accommodated by diffusion th rough the intergranular glass phase is considered as the primary steady-sta te creep mechanism. The higher creep resistance of the composite is connect ed to the presence of intergranular SiC nanoparticles which limit grain bou ndary sliding and to the difference in chemical composition of the intergra nular glass phase.