Starting with a mixture of ultrafine beta-Si3N4 and a SiO2-containing addit
ive, a superplastic Si3N4-based composite was developed, using the concept
of a transient liquid phase. Significant deformation-induced phase and micr
ostructure evolutions occurred in the nonequilibrium, fine-grained Si3N4 ma
terial, which led to the in situ development of a Si3N4 22-vol%-Si2N2O comp
osite and strong texture formation. The unusual ductility of the composites
with elongated Si2N2O grains was attributed to the fine-grained microstruc
ture, the presence of a transient liquid phase, and the alignment of the el
ongated Si2N2O grains, The mechanical properties of the resultant composite
were enhanced rather than impaired by superplastic deformation and subsequ
ent heat treatment; the resultant composite exhibited both high strength (9
57 MPa) and high fracture toughness (4.8 MPa.m(1/2)).