Superplastic behavior of fine-grained beta-silicon nitride material under compression

The deformation behavior of a hot-pressed, fine-grained beta-Si3N4 ceramic was investigated in the temperature range 1450 degrees-1650 degrees C, unde r compression, and the results for strain rate and temperature dependence o f the flow stress are presented here. The present results show that the mat erial is capable of high rates of deformation (similar to 10(-4)-10(-3) s(- 1)) within a wide range of deformation temperatures and under a pressure of 5-100 MPa; no strain hardening occurs in the material, even at slow deform ation rates, because of its stable microstructure; Newtonian flow occurs, w ith a stress exponent of approximately unity; and the material has activati on energy values for flow in the range 344-410 kJ . mol(-1). Grainboundary sliding and grain rotation, accommodated by viscous flow, might be the mech anisms of superplasticity for the present material.