Superplastic Behavior of Fine-Grained β-Silicon Nitride Material under Compression

The deformation behavior of a hot-pressed, fine-grained β-Si₃N₄ ceramic was investigated in the temperature range 1450°—1650°C, under compression, and the results for strain rate and temperature dependence of the flow stress are presented here. The present results show that the material is capable of high rates of deformation (∼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 deformation rates, because of its stable microstructure; Newtonian flow occurs, with a stress exponent of approximately unity; and the material has activation energy values for flow in the range 344—410 kJ·mol⁻¹. Grain-boundary sliding and grain rotation, accommodated by viscous flow, might be the mechanisms of superplasticity for the present material.