2003 Volume 44 Issue 4 Pages 794-797
The deformation behavior of Si–C–N ceramics derived from polyvinylsilazane polymer precursor has been investigated by compression tests at elevated temperatures. The dense Si–C–N ceramic monolith was fabricated by hot isostatic pressing of a compact prepared from pyrolyzed powders at 1500°C and at 950 MPa without any sintering additives. The microstructure of the ceramic monolith was a nano-composite structure consisting of α-Si3N4 crystalline grains and turbostratic graphite-like phases. Only slight plastic deformation was observed at 1500°C in spite of high compressive stress over 1000 MPa. On the other hand, the sample showed plastic flow at 1600 and 1700°C. A compressive strain of about 11% was obtained at 1700°C and 4×10−5 s−1. The feature of the microstructure was maintained after the compressive deformation, although the grains were coarsened during the deformation. The strain rate exponent of the compressive stress during the deformation at 1600 and 1700°C was about 0.1. The deformation mechanism of the ceramic material is thought to be different from those of creep deformation in amorphous Si–C–N ceramics and of superplastic deformation in silicon nitride ceramics containing glassy grain boundary phases.
