Effect of annealing on the microstructure, room-temperature strength, and fracture toughness of Al2O3−ZrO2−TiN ceramics
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The microstructure, phase composition, room-temperature flexural strength, and fracture toughness of Al2O3−ZrO2−TiN (AZT) ceramics were studied on specimens annealed in air at 1000, 1200, and 1400°C. The strength of the ceramics decreased with annealing temperature. The degradation in strength was caused by defects formed on or near the surface of the ceramics during oxidation of TiN which started at 600–700°C. The surface defects after annealing are influenced by the formation of rutile (TiO2) at 1000 and 1200°C, aluminum titanate (Al2TiO5), and titanium suboxide Ti5O9 at 1400°C as well as by diffusion processes associated with ZrO2. If the annealing of smooth AZT specimens in air resulted in lower strength, specimens in the form of single-edge notched beam (SENB) exhibited a considerable increase in fracture toughness (K Ic) with annealing temperature. Such behavior was caused by the formation of an oxide layer which hindered the propagation of the main crack from the notch base. Thermal treatment of the smooth AZT specimens and further edge notching and testing did not result in a change of K Ic values. The Al2O3 and Al2O3−ZrO2 ceramics were also tested for comparison.
KeywordsFracture Toughness Rutile Tungsten Oxide Main Crack Titanium Nitride
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