Study On The Synthesis And Properties Of The Co-rich Metastable Phase In Samarium-Cobalt Alloy

Sm-Co alloys are widely used as high-temperature magnets due to the good stability at high temperatures and the high Curie temperature. The Curie temperature and the saturated magnetization of the Sm-Co compounds increase with the increase of Co content. Therefore, exploring Co-rich Sm-Co compounds is a promising way for the development of high-temperature magnets. The nanocrystalline Sm-Co metastable alloys with element dopping were prepared by a new method in the present study. The effect of element dopping on the permanent magnetic properties, the high-temperature stability and the phase transformation along with the grain growth were studied systematically.The ingots and the nanocrystalline SmCo9.8-xSix alloys were prepared. The SmCo9.8-x Six ingots consist of Sm2Co17(R) phase and Co phase, while the nanocrystalline alloy has only the single phase of SmCo9.8(H). The saturated magnetization of the ingots declines with the increase of Si content. The greatly increased coercivity, remanence and maximum energy product are obtained in the nanocrystalline SmCo9.8-xSix alloy with increasing the Si content, together with the decreased saturation magnetization and the Curie temperature. The contraction of the lattice parameters and the increase in the phase stability were detected during addition of Si content.A systematic study was carried out on the phase transformation and corresponding magnetic properties of the metastable SmCo8.9Si0.9 phase. With the increase of the heat-treatment temperature, the nanocrystalline SmCo8.9Si0.9 alloy transformed from the SmCo9.8(H) phase to the Sm2Co17(H) and Co(FCC) phases and the coercivity was improved. The mechanism was that the precipitated fine Co phase enhanced the pinning effect. With a further increase in temperature, the Sm2Co17(H) phase transformed into Sm2Co17(R) accompanied with an evident grain growth and an inhomogeneous grain size distribution, leading to the decrease in the magnetic properties.The preparation of the nanocrystalline SmCo13-x Six alloy with higher Co content was investigated based on the effect of Si-dopping on the phase stability found in the SmCo8.9Si0.9 alloy. A ternary compound was found in the ingot with increasing the Si content, which is hardly to be milled to transform to amorphous and remains in the nanocrystalline alloy. The SmCo13-x Six alloy ingot was formed by Sm2Co17(R) phase and Co phase which are all the high temperature phase in the Sm-Co system. The super paramagnetic phenomenon emerges due to the ultrafine grains of the nanocrystalline SmCo11Si2 alloy.