Combustion synthesis of ferromagnetic Al₂O₃-based cermets in thermal explosion mode

The ferromagnetic Al₂O₃-based cermets with different ratios of Co and Co–50Ni alloys were successfully prepared by combustion synthesis in thermal explosion (TE) mode. The reaction process, microstructure, and magnetic property of cermets were investigated. The relative density of cermets can be over 95% via uniaxial loading at the time of ignition when the cermets are hot and ductile. In Al₂O₃–Co cermets, β-Co and α-Co co-exist at room temperature with average size of less than 10 μm and disperse homogeneously in the matrix, while in Al₂O₃–(Co–50Ni) cermets, the network-like Co–50Ni alloy can infiltrate into the boundary gaps of Al₂O₃ particles. The ferromagnetic Co and Co–50Ni alloys are responsible of the magnetic properties of Al₂O₃-based cermets. The saturation magnetization strongly depends on the magnetic characteristics and ratios of ferromagnetic phases. Al₂O₃–(Co–50Ni) cermets have soft magnetic properties with high magnetic susceptibility and low coercive force.