Comportement mécanique de composites céramiques à dispersoïdes

Abstract

The fracture strength and fracture toughness temperature dependence of zirconia toughened alumina materials (ZTA), prepared from Al2 O3 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 Y2 O3 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 Al2 O3 composites of different compositions. Some experimental results of the study are presented in this paper.