Metastable phase formation and high coercivity of Nd₉₀F ₁₀ by gas flow type levitating process

In the last decades, Nd-Fe amorphous alloys have been studied by many methods because of high coercivity at room temperature and relation to Nd-Fe-B permanent magnets. In this study, we examined the effect of the containerless process for high undercooling and the metastable phase formation in detail. In the gas levitating process, undercooling of Nd₉₀Fe₁₀ samples increased with cooling rate. Undercooling of Nd₉₀Fe ₁₀ sample solidified at 268 K/s is ΔT= 35 K. The primary α-Nd phases were surrounded by fine metastable phases. And the intergranular eutectic-like areas were comprised of α-Nd phase and metastable phase. In contrast, the sample with low undercooling was comprised of α-Nd phases and rod-like Nd₂Fe₁₇ phases among primary α-Nd phases. In Nd₉₀Fe₁₀ samples with undercooling of Δ T= 35 K, coercivity of Nd₉₀Fe₁₀ samples is about 4.5 kOe at room temperature. This high coercivity is caused by fine crystallization of matastable phases.