Creep mechanism of gas-pressure-sintered silicon nitride polycrystals II. Deformation mechanism

Abstract

As reported in the companion paper, part I, the creep behaviour of two silicon nitride ceramics is governed by a stress exponent n = 0.6 ± 0.1. It is known that, under certain conditions, silicon nitride ceramics may undergo a transition n = 1 → n<1 (the ‘shear-thickening transition’) at a well-defined stress σ*. This transition has not been observed, which, together with considerations regarding the value of the transition stress σ*, leads us to reject the shear-thickening phenomenon as an explanation for the creep behaviour of the materials investigated. Instead, it may be understood in terms of a particular grain boundary sliding mechanism accommodated by solution–precipitation.

Acknowledgements

This work was supported by the Brite–Euram Project BE97-4544, during the stay of J.J.M.-M at the University of Seville. The authors wish to thank Professor F. Wakai for fruitful discussions. One of the authors (J.J.M.-M) wishes to thank Dr Naoki Kondo (Synergy Materials Center, Agency of Industrial Science and Technology, Nagoya, Japan) for his comments and for providing copies of his papers.

Notes

Present address: Departamento de Física. Universidad de Extremadura, Avenida de Elvas, s/n 06071, Badajoz, Spain.

Additional information

Notes on contributors

A. Domínguez-Rodríguez ‡

Present address: Departamento de Física. Universidad de Extremadura, Avenida de Elvas, s/n 06071, Badajoz, Spain.