In situ formation of metal-ceramic microstructures, including metal-ceramic composites, using reduction reactions

Abstract

Partial reduction reactions were used to form a metallic phase either around or inside oxide grains in polycrystals in the FeMnO system. By suitable choice of oxide composition, partial pressure of oxygen, annealing time and temperature, it is possible to control the nucleation and growth of the metallic phase to produce a wide range of metal-ceramic microstructures. These include ceramic grains with a thin layer of metallic phase at their boundaries; ceramic grains with a thick layer 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 metal-ceramic microstructures with respect to that of the pure ceramic, with the largest increase observed for the metal-ceramic composite. It is believed that the principles established by studying the FeMnO system can be used on more practical mixed oxide systems to produce metal-ceramic microstructures, which in some cases are unique, and in particular, if the starting oxide material is in the form of plate- or rod-shaped crystals, to produce metal-ceramic composites in situ.