微米级Co微粒的相稳定性研究

The Phase Stability of Micrometer Sized Co Particles

对两种微米尺度的初始微粒进行不同条件的退火处理,制备出不同晶体结构和不同尺寸大小的Co微粒。用X射线衍射仪和扫描电子显微镜分析了微粒的晶体结构和微观形貌变化。结果表明,选择合适的退火条件,可以得到几乎为单一FCC相的Co微粒。存在一个相稳定的临界尺寸,小于此尺寸的微粒,冷却过程中不发生FCC-HCP相变,高温相可以在室温下稳定存在。微粒的表面/界面状态影响临界尺寸的大小,表面/界面能越低,临界尺寸越小。从微粒所受的附加应力抑制了马氏体相变的角度,讨论了微粒尺寸和表面/界面状态对相稳定性的影响。

Two kinds of micrometer sized original particles were annealed in different conditions to pre- pare Co particles with different crystal structures and different particle sizes. The evolution of the crystal structures and morphologies of particles was analyzed by X-ray diffraction apparatus and scan- ning electron microscope. It is indicated that almost single FCC phase can be obtained if proper annea- ling conditions are involved during the annealing of Co particles. There is a critical size of phase stabil- ity, below which HCP-FCC transition of Co particles does not occur during cooling and high tempera- ture phase can stably exist at room temperature. The critical size is affected by the state of surface/in- terface, i.e. lower surface/interface energy gives rise to a smaller critical size. In the view of the sup- pression of martensitic transformation by extra pressure, the effect of the particle size and the state of surface/interface on the phase stability of Co particles is discussed.