High temperature plastic deformation of multilayered YTZP/ZTA composites obtained by tape casting

Laminar composites containing layers of 3 mol% yttria-stabilized tetragonal ZrO2 (YTZP) and a mixture of Al2O3/3YTZP (60/40 vol.%) have been fabricated via a tape casting process that allowed formation of multilayers 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 1,200 and 1,400 C with the stress axis both parallel and perpendicular to the layer interfaces. Microstructural observations of strained composites indicated that deformation is achieved primarily by grain boundary sliding. The stress exponent n and the activation energy for flow Q decrease from 2 to 1 and from 650 to 550 kJ/mol, respectively, with increasing stress. Such a trend has already been observed in the monolithic constituents, suggesting that the same rate controlling mechanisms may operate in the composites. The creep behavior of the softer phase (YTZP) is strongly influenced by the laminar microstructure, increasing the flow stress with respect to the bulk material