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. T.) have been extensively analyzed from a theoretical point of view. T.), and crack deflection toughening (C.D. stress-induced transformation toughening (T. It is now well recognized that dispersion of ZrO 2 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 toughening and strengthening effects are discussed on the basis of transformation of metastable zirconia particles depending on ZrO 2 and Y 2O 3 contents, on the particle size and on the temperature. At higher temperature, the composite properties decrease more slowly, with a higher critical temperature, than tetragonal zirconia materials (TZP). 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. The slow crack growth behaviour of ZTA composites was also studied at room temperature. The fracture strength and fracture toughness temperature dependence of zirconia toughened alumina materials (ZTA), prepared from Al 2O 3 and ZrO 2 raw powders by pressureless sintering and by hot pressing, was examined. Groupe d’Etudes de Métallurgie Physique et de Physique des Matériaux, (U.A.
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