Superplasticity in a fine-grained beta-silicon nitride ceramic containing a transient liquid Original Research Article

Compressive deformation in a dense fine-grained β-Si3N4 sintered with 7 wt% cordierite was investigated over a wide range of temperatures (1450–1650°C) and strain rates (1×10−5–1×10−3/s). The superplastic characteristics and the results of microstructural examination are presented. These indicate that: (a) fine-grained β-Si3N4 ceramics are capable of high rates of deformation (about 10−5–10−4/s) at 1550°C without strain hardening occurring; (b) remarkable phase and microstructural evolutions, such as formation of elongated and strongly textured Si2N2O grains occurred during deformation; (c) a transient liquid phase present in this material system which facilitated the formation of Si2N2O grains enhanced the superplastic flow, and well-aligned Si2N2O grains formed in situ did not have a detrimental impact on the superplasticity; and (d) the mechanism of deformation is grain boundary sliding accommodated by diffusion-controlled solution–precipitation creep.