质子辐照对永磁合金微观结构演化的研究

钐钴和钕铁硼稀土永磁合金已经广泛应用于粒子加速器的波荡器和其他器件中,作为加速器的重要组成部分,永磁合金在辐照环境中长期服役会出现磁性能损失的现象,这会影响束流的品质.为了探讨产生这个现象的微观机理,采用透射电镜对质子辐照前后的钐钴和钕铁硼稀土永磁合金进行了微观结构演化的表征和分析,统计了由辐照析出的纳米晶体积密度和粒径分布,并讨论了微观结构演化对宏观磁性能损失的影响.结果表明,随着质子辐照损伤程度的增加,永磁合金的微观结构从单晶结构转变为纳米晶多晶结构,且纳米晶和基体的晶体结构相同.钕铁硼的纳米晶体积密度先增大后减小,粒径分布先增大后不变;钐钴的纳米晶体积密度逐渐减小,粒径逐渐增大.在2 dpa的质子辐照损伤程度下,钕铁硼稀土永磁合金比钐钴永磁合金的非晶化趋势更明显.

Effect of proton irradiation on microstructure evolution of permanent magnet

Nd₂Fe₁₄B rare earth and Sm₂Co₁₇ type permanent magnets have been widely used in the third generation of synchronous radiation light source and free electron laser facility in undulators and other components of particle accelerators. In addition, the permanent magnets are used in the radiation treatment system for cancer as a beam line component. Compared with Sm₂Co₁₇ type permanent magnet, Nd₂Fe₁₄B rare earth permanent magnet has the characteristics of large magnet energy product, rich starting materials and low price. Although its Curie point and coercive force are lower than those of Sm₂Co₁₇ type of permanent magnet, Nd₂Fe₁₄B rare earth permanent magnet is still widely used. As an important part of the accelerator, the magnetic loss phenomenon appears when permanent magnet is used in long-term irradiation environments, which affects the stability and quality of the beam. Therefore, it is important to investigate the magnet demagnetization induced by photon irradiation. Recently, there have appeared many researches of the phenomena of demagnetization for the permanent magnets under the irradiation of various kinds of particles. By using different research methods and experimental conditions, single particle irradiation is performed and then the effect of irradiation on magnetic loss is investigated by comparing the macro magnetic properties (such as magnetic flux loss rate, saturation magnetization, etc.). However, there are not any available reports on the microstructure investigations of permanent magnets after irradiation. Microstructure affects macroscopic magnetic properties. In order to discuss the microscopic demagnetization mechanism, the transmission electron microscope is used to characterize and analyze the microstructure evolutions of Sm₂Co₁₇ type permanent magnet and Nd₂Fe₁₄B rare earth permanent magnet before and after proton irradiation. The evolution of the number density of nanocrystal and its size distribution induced by proton irradiation are calculated. Moreover, the effect of microstructure evolution on macroscopic magnetic loss is discussed. The results indicate that the microstructure of permanent magnet transforms from single crystal structure to polycrystalline structure with the increase of the proton irradiation damage level. Nanocrystal and the matrix of permanent magnet have the same crystal structure. With the irradiation damage level increasing, the nanocrystal density of Nd₂Fe₁₄B first increases and then decreases, while the particle size distribution first increases and then keeps constant; the number density of nanocrystal of Sm₂Co₁₇ type permanent magnet gradually decreases, while particle size gradually increases, and comparing with Sm₂Co₁₇ type permanent magnet, the crystal structure of Nd₂Fe₁₄B permanent magnet shows an obvious tendency to be amorphous in 2 dpa irradiation damage level.