Abstract
(Fe, Co)-B and Ni-B ultrafine powders were prepared by chemical reduction of metal ions in aqueous solutions. The obtained powders have a spherical morphology with diameter of about 100 nm and amorphous structure. Electro-discharge sintering (EDS) of the powders were conducted. The gas evolution in EDS was much greater than that of resistance sintering alone, indicating that EDS contributes to cleaning of powder surfaces and reduces the oxygen content of sintered alloy. The higher was the sintering temperature during EDS or resistance sintering immediately after EDS, the higher was the density of sintered alloy. Applied pressure during EDS and subsequent resistance sintering had a great effect on density at low temperature showing that the large pores among agglomerated particles could be eliminated by high pressure. However, the effect of pressure on the sintered density was small at high temperature. It was also observed that mixed structure consisting of amorphous and crystalline phases could be obtained above crystallization temperature by EDS and subsequent rapid resistance sintering. In addition, the sintered density increased only slightly as the pulse time decreases in EDS during the above process.
