[en] Published in summary form only

[en] Reaction-bonded aluminum niobate-based (AlNbO₄-based) composites with tailorable microstructures were fabricated through controlled nucleation and growth of needlelike AlNbO₄ grains. Equiaxed to highly elongated grains were obtained by different heat treatments at 1,340 and 1,400 C in air. Scanning electron microscopy observations revealed that increasing the heating rate promoted the development of large, homogeneously distributed needlelike grains. Because of the elongated nature of the AlNbO₄ grains and the high residual stresses at the interface, enhanced crack wake bridging occurred. This bridging accounted for the observed increase of fracture toughness

[en] A novel pressureless reaction sintering process is presented for the fabrication of Al₂O₃ endash aluminide alloys (3A). Compacts of intensively milled metal oxide endash aluminum mixtures are heat-treated in vacuum or inert atmosphere such that the exothermic reactions take place in a controlled manner essentially at temperatures below the melting point of Al. Dense, homogeneous microstructures were obtained with a variety of Al₂O₃-matrix systems with interpenetrating networks of aluminides of Ti, Fe, Nb, Mo, Zr, Ni, etc. By adding modifiers in the form of oxides or metals, volume and phase composition as well as properties can be tailored in a wide range. copyright 1996 Materials Research Society

[en] Published in summary form only

[en] Crack velocity curves for Y-TZP and Al₂O₃-toughened Y-TZP were determined for long cracks in compact tension specimens with an in situ fracture device on the stage of an optical microscope. Indications for a crack velocity threshold were found for both materials. It is recognized that the dependence of the shielding term on the crack-tip stress field renders transformation-toughened materials particularly susceptible to stress-corrosion cracking. This interrelation leads to the definition of a steady-state velocity at constant applied stress intensity factor. This velocity is obtained in the situation where the shielding term is fully defined by the present crack-tip stress field, not depending on prior loading history

[en] Published in summary form only

[en] Orthorhombic zirconia was partially or totally stabilized with niobia by using a zirconium hydroxide gel and niobium ammonium oxalate. The Zr₈ Nb₂ O₂₁ superstructure type was obtained for 11.1 mol% of niobia. (author)

[en] Co-precipitation technique was used to stabilize zirconia with 1 to 100 mol % of ceria after calcination at temperature of 600_O C and 900_O C. Deconvolution method was used to determine the amount of tetragonal/cubic phases by X-ray diffraction. It was observed that both surface areas (determined by BET method) and phase compositions are affected by the ceria concentration and calcination temperature. (author)

No abstract available

No abstract available