Oxidation resistance and creep behaviour of a silicon nitride ceramic densified with Y2O3 |
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Authors: | A Bouarroudj P Goursat J L Besson |
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Affiliation: | (1) Laboratoire des Céramiques Nouvelles, LA CNRS 320, U.E.R. Sciences, 87060 Limoges Cedex, France;(2) Laboratoire des Matériaux Céramiques, LA CNRS 320, E.N.S.C.I., 87065 Limoges Cedex, France |
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Abstract: | The corrosion resistance and creep behaviour in air of hot-pressed materials with a composition of 70 Si3N4-25 SiO2-5 Y2O3 (mol%) has been studied. Kinetics data and microstructural changes in the 1180 to 1650° C temperature range indicate the presence of two oxidation mechanisms. Between 1180 and 1420° C, the preferential oxidation of the intergranular phase containing nitrogen is interpreted in terms of an inward diffusion of ionic oxygen. At temperatures higher than 1420° C, the degradation of the material is the sum of many processes (solution of silicon nitride, migration of oxygen and yttrium and release of nitrogren) but the diffusion to the nitride-oxide interface of a complex combination of yttrium and nitrogen in the boundary phase seems to be the limiting step. The three-point bending creep is discussed in relation to the evolution of the secondary intergranular phases in an oxidizing environment. The creep deformation is the sum of a viscoelastic component and a diffusional component characterized by the same activation energy (720 kJ mol–1). |
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