In situ formation of metal-ceramic microstructures in the NiAlO system by partial reduction reactions

Abstract

Metal-ceramic microstructures were obtained by partial reduction of the spinel compound NiAl 2O 4. Electron microscopy studies were performed for microstructural characterization, phase identification and chemical analysis. Depending on the reduction temperature, two different morphologies of nearly pure Ni particles, equiaxed and rod-like, form within a ceramic matrix. The equiaxed Ni particles (0.02–0.5 μm in diameter) are embedded in α-Al 2O 3, while the rod-like Ni particles (∼ 5 μm in length and ∼ 0.1 μm in diameter) are in a metastable “defect spinel” containing much less Ni than NiAl 2O 4. The fracture toughness of the NiAl 2O 3 mixture was significantly improved with respect to that of the original spinel phase.