钐钴永磁的Sm2Co17R/SmCo5共格界面迁移及塑性变形机制

The goal of this investigation is to deal with the poor plastic deformation ability and the low mechanical strength of the current Sm2Co17-based rare earth permanent magnets. This is achieved via the decrease of the thickness of SmCo5 cell boundary phase, which subsequently initiates migration of Sm2Co17R/SmCo5 cellular coherent boundary, by adjusting the annealing treatment parameters. The correlation between the cell size and the microstructural parameters, such as the dislocation alignment, the dislocation density, atomic bonding at the Sm2Co17R/SmCo5 interface and relevant crystalline orientations, are elucidated in addition to the fracture behaviour and deformation mechanisms of the alloy. The interactions between coherent boundary and dislocations are examined associated with the initiation and distribution of the slip systems and interface migration. A shear stress model related to the SmCo5 cell phase thickness is established based on molecular dynamics. This demonstrates the critical thickness and shear stress value to begin the coherent boundary migration process and its behind mechanisms. More importantly, the involved physics such as the plastic deformation, failure and toughening in the rare earth permanent magnets are clearly explained. As such, ultimately the optimised mechanical and magnetic properties of the studied alloys can be anticipated via the obtained microstructural parameters in our work.

针对本征脆性Sm2Co17型稀土永磁塑性变形能力差、强度低的核心问题，通过调节时效处理工艺来减少SmCo5胞壁相厚度以启动Sm2Co17R/SmCo5胞状共格界面迁移，来提高变形过程中位错运动和储存能力，使合金获得高的强度和良好的塑性。研究合金的断裂行为和变形机制与胞状结构的尺寸及其内部位错组态和位错密度、Sm2Co17R/SmCo5界面原子结合及晶体学位向关系等微观结构参量的相关性；研究合金在变形过程中胞状共格界面与位错的相互作用、滑移系的开动和分布特征、界面的迁移。结合分子动力学模拟，建立与SmCo5胞壁相厚度相关的临界剪切应力的模型，探明启动胞状共格界面迁移的胞壁相厚度和临界剪切应力的大小及界面迁移微观机制，揭示Sm2Co17型稀土永磁的塑性变形机理、失效规律和强韧化机制，最终达成微观结构参数的最优化以获得优良的力学性能和磁性能。

针对Sm2Co17型稀土永磁塑性变形能力差、强度低的核心问题，本项目采用粉末冶金法制备了具有高强度和良好磁性能的Sm2Co17型稀土永磁材料：Br=10.96−11.07kOe、Hcj=17.39−24.14kOe、 (BH)max =25.75−30.00MGOe，σb=168.23−293.1MPa， KIC=1.60−3.20 MPa•m1/2。研究发现，合金的断裂呈典型的穿晶解理脆性断裂。但是在小位移量时合金体现出塑性变形特征，高强度的合金塑性变形量显著。合金的磁性能和力学性能与胞状结构密切相关。胞状结构中，Sm2Co17R相与SmCo5相具有极低能量的共格界面，且两相的(0001)面相互平行、<11-20>方向相互平行。研究发现合金的胞状结构是通过Sm2Co17H过饱和固溶体的调幅分解来形成的。调幅分解产生的晶格缺陷（位错、小角度晶界等）和细晶强化是材料强韧化的主要机制。在加载过程中，在SmCo5/Sm2Co17R界面处产生应力集中，当应力集中到孪生所需的临界切应力时，在应力集中处通过形成富Zr的片状相进行均匀切变，产生孪生变形，使合金发生塑性变形。 第一性原理计算结果进一步证明了SmCo5能够与其厚度相当的Sm2Co17R相（n≤3)产生孪生变形，导致材料具有较大能量的释放，从而具有一定的塑性。该研究结果对于指导解决本征脆性稀土永磁塑性变形能力差、强度低的工程应用问题具有重要意义。