Preparation of fine powders of rare earth-cobalt by rapid quenching technique

The PrCo5and (MM)Co5powders obtained by splat cooling are found to have very large coercive forces. Small grains of 1-5 μm in size are produced in particles of 1-40 μm. Simple binding of these particles under ∼ 27 KOe leads to coercive fields as large as 9 KOe for PrCo5and 5 kOe for (MM)Co5, which are higher than the largest values reported for the conventionally fabricated magnets. The SmCo5powders made by this process, however, do not yield a larger coercive field. In splat cooling, particles are subject to much less surface defects than that encountered in the conventional grinding process. Also, some degree of preferential growth of the grains appears to result from the high thermal gradient between the liquid alloy and the substrait. In addition, a second phase was found to form surrounding the RCo5phase, which may have improved the surface properties of the RCo5phase. Since the presence of the second phase has been shown to have advantages to the sintering process for some high quality magnets of SmCo5and PrCo5, it is expected that liquid sintering of fine powders prepared by this new process would lead to greater improvement of magnetic properties.