Preliminary studies in the processing and characterization of Al2O3/SnO2 laminated composites

Abstract

All oxide composites (reinforcement and matrix both being oxides) exhibit high temperature oxidation resistance in addition to high strength and hardness. A major drawback of these materials is that the oxide fiber and oxide matrix tend to react, which strengthens the interface and therefore drastically reduces the damage tolerance. To overcome this problem, a mechanically weak interphase material, which also serves as a diffusion barrier, is generally used. One such materials system is tin dioxide (SnO₂) in alumina-based composites. Previous attempts to fabricate such alumina matrix composites have been unsuccessful due to the higher temperatures needed to densify Al₂O₃ coupled with the fact that SnO₂ decomposes to SnO in reducing environments. SnO has a relatively low melting point (1125 °C). In this paper we report the successful fabrication of Al₂O₃/SnO₂, laminated composites and some observations on microstructural and mechanical characterization of the laminates. As expected from the phase diagram, no chemical compound formation was observed between Al₂O₃ and SnO₂ which means that no primary chemical bonding developed between individual laminae. TEM observations showed, however, a strong mechanical interlocking at the SnO₂/Al₂O₃ interfaces. In spite of the relatively strong interfacial bond, cracks did deflect. Our microstructural studies showed that SnO₂ served as a weak interphase material.