INSITU FORMATION OF METAL-CERAMIC MICROSTRUCTURES, INCLUDING METAL-CERAMIC COMPOSITES, USING REDUCTION REACTIONS

Partial reduction reactions were used to form a metallic phase either around or inside oxide grains in polycrystals in the Fe-Mn-O system. B y suitable choice of oxide composition, partial pressure of oxygen. an nealing time and temperature, it is possible to control the nucleation and growth of the metallic phase to produce a wide range of metal-cer amic microstructures. These include ceramic grains with a thin layer o f metallic phase at their boundaries; ceramic grains with a thick laye r of metallic phase at their boundaries -essentially, a metal ceramic composite; and ceramic grains containing a fine distribution of metal particles-essentially, a ductile phase toughened ceramic. The presence of the metallic phase increases the fracture toughness of all the met al-ceramic microstructures with respect to that of the pure ceramic, w ith the largest increase observed for the metal ceramic composite. It is believed that the principles established by studying the Fe-Mn-O sy stem can be used on more practical mixed oxide systems to produce meta l ceramic microstructures, which in some cases are unique, and in part icular, if the starting oxide material is in the form of plate- or rod -shaped crystals, to produce metal ceramic composites in situ.