Comportement mécanique de composites céramiques à dispersoïdes^*

Cas du renforcement par dispersion de zircone

Thermomechanical properties of zirconia toughened alumina materials : effect of microstructure and temperature on toughening mechanisms

Groupe d’Etudes de Métallurgie Physique et de Physique des Matériaux, (U.A. CNRS 341), INSA, Villeurbanne

Abstract

The fracture strength and fracture toughness temperature dependence of zirconia toughened alumina materials (ZTA), prepared from Al₂O₃ and ZrO₂ raw powders by pressureless sintering and by hot pressing, was examined. The slow crack growth behaviour of ZTA composites was also studied at room temperature.

Zirconia toughened alumina composites present well improved machanical properties at ambiant temperature related to pure alumina ; improvement in sub-critical crack growth resistance is significant. At higher temperature, the composite properties decrease more slowly, with a higher critical temperature, than tetragonal zirconia materials (TZP).

The toughening and strengthening effects are discussed on the basis of transformation of metastable zirconia particles depending on ZrO₂ and Y₂O₃ contents, on the particle size and on the temperature. It is now well recognized that dispersion of ZrO₂ particles or precipitates in a ceramic matrix can produce a new class of materials having improved mechanical properties and which go by the name of “Zirconia Toughened Ceramics” (Z.T.C.). The different toughening mechanisms e.g. stress-induced transformation toughening (T. T.), microcrack toughening (M. T.), and crack deflection toughening (C.D. T.) have been extensively analyzed from a theoretical point of view. The effective toughening effects operating in these composite materials is determined by the microstructural characteristics and the environmental conditions (temperature, loading rate, etc.) of test/preparation.

We have been studying the microstructure and the mechanical behaviour of Zirconia toughened dense Al₂O₃ composites of different compositions. Some experimental results of the study are presented in this paper.