Fractographic Observations of Sapphire Whisker Reinforced Alumina

Abstract

Fiber reinforcement of ceramics has generally been limited to metallic fibers. Metallic fibers have improved the thermal properties of ceramics but have generally been ineffective in promoting increased strengthening. Discontinuous ceramic fiber reinforced ceramics have demonstrated increased strenghtening both in flexure and impact. This investigation was limited to studying reinforcement of an alumina matrix with sapphire whisker fibers.In an attempt to correlate the morphology of the fracture faces of the sapphire whisker reinforced ceramic composites with fabrication and composition parameters; two-stage replicas, cellulose acetate film—carbon film -30° chromium shadow, were prepared from the samples utilized for mechanical testing. The mode of fracture of the samples was generally intergranular as shown in Fig. 1. Trans-granular fracture of the samples was, however, observed and its occurrence became more frequent as firing time and whisker content were increased. Fig. 2 is a fractograph of a twenty percent 3B sapphire whisker-alumina composite which was hot-pressed and subsequently fired at 1315°C.