HIGH-TEMPERATURE PLASTIC-DEFORMATION OF MULTILAYERED YTZP ZTA COMPOSITES OBTAINED BY TAPE CASTING/

Laminar composites containing layers of 3 mol% yttria-stabilized tetra gonal ZrO2 (YTZP) and a mixture of Al2O3/3YTZP (60/40 vol.%) have been fabricated via a tape casting process that allowed formation of multi layers with strong and sharp interfaces. Compressive tests at constant strain rate and constant load were carried out on these materials in air at temperatures between 1200 and 1400 degrees C with the stress ax is both parallel and perpendicular to the layer interfaces. Microstruc tural observations of strained composites indicated that deformation i s achieved primarily by grain boundary sliding. The stress exponent II and the activation energy for flow Q decrease from 2 to 1 and from 65 0 to 550 kJ/mol, respectively, with increasing stress. Such a trend ha s already been observed in the monolithic constituents, suggesting tha t the same rate controlling mechanisms may operate in the composites. The creep behavior of the softer phase (YTZP) is strongly influenced b y the laminar microstructure, increasing the flow stress with respect to the bulk material. (C) 1998 Acta Metallurgica Inc.