Al2O3-ZrO2 System Research Articles

A strong ceramic in the Al2O3-ZrO2-Y2O3 system

A highly dense ceramic based on the eutectic composition of the Al2O3-ZrO2 system was obtained using 3 mole % Y2O3 addition. The ceramic has a fine-grained structure and high hardness and strength.

Ion implanted precipitate microstructure and mechanical properties of ceramic surfaces

Microstructure of precipitates produced by annealing ion implanted surfaces have been investigated in the Al2O3-ZrO2 system and both microhardness and indentation fracture toughness have been measured for correlation with microstructure. Air annealing of 190 keV high dose implants of Al+ in yttriastabilized zirconia and Zr+ in AI2O3 have resulted in A12O3 and ZrO2 precipitates, respectively, as would be expected from phase equilibria. However, annealing schedules drastically alter precipitate microstructure (i.e., crystallite size, morphology, orientation), and changes in microstructure have produced significant variation of surface mechanical properties. Crystallization of the ZrO2 films on AI2O3 was observable by conventional XRD. The precipitated ZrO2 was in the monoclinic structure if the grain size was large or in the tetragonal state if grain size was small. Being able to produce tetragonal ZrO2 particles in A12O3 surfaces suggests the possibility of transformation toughening and strengthening.

Studies of the Systems Al<sub>2</sub>O<sub>3</sub>-ZrO<sub>2</sub> and Na<sub>2</sub>O-ZrO<sub>2</sub>

From the ceramic point of view the systems Al2O3-ZrO2 and Na2O-ZrO2 were studied. The results show that in the system Al2O3-ZrO2 there exists no compound as well as solid solution, and that a eutectic point is 1890°±5°C at the composition 45% Al2O3, 55% ZrO2.The rate of the growth of Al2O3 crystals is the highest at 80% Al2O3⋅20% ZrO3, and in this case, the transformation of ZrO2 from high to low temperature modification is kept in check most efficiently.In the system Na2O-ZrO2 there is a compound Na2O⋅ZrO2, and its temperature of formation is lower than the decomposition temperature of Na2CO3.The rate of reaction is expressed by{1-(1-α)1/3}2=-0.3715+0.0023tin which α is the rate of formation, and t is time. This compound melts incongluently at about 1180°C in which the quantity decomposed may be expressed by a logarithmic function of time.In Na2O-ZrO2 system the vapour pressure of Na2O which does not take part of the formation of compound is so large that it makes impossible to draw a melting curve.