纳米晶SmCo7合金的相稳定性、相变行为及其对磁性能的影响

以纳米晶单相SmCo7合金块体为初始原料,通过系列退火系统研究了随着晶粒长大其物相组成和显微组织的演变特征。研究发现纳米晶SmCo7相从室温至600℃都能保持很好的相稳定性(晶粒长大十分缓慢)。而且研究发现纳米晶SmCo7相的失稳分解和晶粒的突发长大会同时发生。值得注意的是分解形成的Sm2Co17相大部分是以显微孪晶的形式存在,而SmCo5相则是呈圆形均匀分布于合金中。另外通过对具有不同晶粒尺寸和物相组成的纳米晶SmCo7合金的室温磁性能细致表征,发现单相SmCo7合金都具有非常优异的磁性能。而其中平均晶粒尺寸为33nm的单相SmCo7合金具有最高矫顽力,达到1164.54kA/m;平均晶粒尺寸为29nm的单相SmCo7合金具有最高的磁能积,达到95.65kJ/m3。

Phase Stability and Phase Transformation of Nanocrystalline SmCo7 Alloy and Their Effects on the Magnetic Performance

The evolutions of the phase composition and the microstructure, as well as their effects on the magnetic performance, were investigated with a series of annealing processes using the prepared nanocrystalline single-phase SmCo7 alloy as the starting material. The SmCo7 (1:7H) phase is discovered to have a good single-phase stability from the room temperature up to 600 °C. A discontinuous nanograin growth takes place in nanocrystalline SmCo7 alloy, accompanied with the destabilization of the single 1:7H phase, resulting in the formation of the Sm2Co17 (2:17R) and SmCo5 (1:5H) phases, which exist in a form of the phase-transformation twins and the particulate precipitates respectively. The optimum magnetic performance is obtained in the nanocrystalline 1:7H single-phase alloys, and the maximum intrinsic coercivity 1164.54 kA/m and energy product 95.65 kJ/m3 are archived in SmCo7 alloys with the mean grain size of 33 nm and 29 nm, respectively.