Magnetic Sintering of Ferromagnetic Metal Powder Compacts

Magnetic sintering of ferromagnetic metal powder compacts has been carried out aiming at precise control of microstructures in polycrystalline materials. Powder compacts of carbonyl iron and cobalt were subjected to magnetic sintering in a direct-current magnetic field ranging up to 1.2 MA/m at temperatures in both the ferromagnetic and the paramagnetic regions. We have found that a magnetic field can enhance the densification and grain growth of iron powder compacts in the ferromagnetic state and in the paramagnetic one. The higher became the magnetic field strength, the more the densification during sintering proceeded. The observed magnetic field effects seemed to be most significant in the intermediate stage of sintering. The observations suggested that a magnetic field was responsible for an increase in the driving force for grain boundary migration that would play an important role in the densification during sintering. In contrast to iron powder compacts, the densification of cobalt powder compacts were suppressed by a magnetic field.