Piezo-spectroscopic characterization of alumina-aluminium titanate laminates

Abstract

A multilayered alumina-aluminium titanate composite was prepared by a colloidal route from aqueous suspensions. The structure of the laminate was symmetric and constituted of two external Al2O3 layers (width∼= 1750 m), one central Al2O3 layer (width∼= 1200 m) and two intermediate thin (width∼= 315–330 m) Al2O3–Al2TiO5 layers. Additional monolithic materials with the same compositions as those of the layers were fabricated as reference materials. Young’s modulus of the monoliths was determined by three point bending. Dilatometry determinations were performed on green specimens, following the same heating and cooling schedules as those used for sintering the laminate, in order to determine the actual dimensional changes on cooling after sintering. The dimensional changes of the sintered specimens on heating and on cooling were also determined. Microscopic distributions of residual stresses were evaluated by fluorescence piezo-spectroscopy, and they revealed the existence of weak tensile and compressive hydrostatic stresses in the aluminium titanate and alumina layers, respectively. The level and sign of these stresses was in good agreement with those predicted based on analysis of the Young’s modulus and the dimensional variations during cooling after sintering of the monoliths with the same compositions as those of the layers. Dimensional variations during cooling after sintering were different from those for sintered materials, which presented hysteresis between heating and cooling. In spite of the presence of compressive residual stresses in the external layers of the laminate, strength values of notched samples of the laminated specimens were lower than those for monoliths of the same composition as the external layers.