Application of the glass-ceramic process for the fabrication of whisker reinforced celsian-composites

Abstract

The glass-ceramic process has been investigated as an alternative route to the common ceramic process for the formation of whisker reinforced ceramic composites. In the BaSiAlTiO system composites have been prepared with celsian (BaAl₂Si₂O₈) as the matrix and hollandite (Ba_1.23Al_2.46Ti_5.54O₁₆) as the reinforcement. Different starting materials have been subjected to a thermal treatment, and the product samples have been studied with respect to their microstructures and the crystalline phases present. By annealing pellets of a finely powdered, quenched melt containing Ba, Si, Al and O, to which crystalline TiO₂ was added, a complete transformation of hexacelsian, formed in a first step, into celsian was achieved at 1000°C. In the celsian matrix, needle-shaped hollandite crystals precipitate, which are distributed homogeneously over the matrix phase. In these dense composites, typical reinforcement mechanisms, such as crack deflection and whisker pull-out have been observed.