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

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 degrees 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. (C) 1999 Kluwer Academic Publishers.