Mechanisms of self and impurity diffusion in Fe-Al intermetallic compounds

合金的扩散数据，如空位形成能、迁移能、扩散激活能和尝试频率等，是材料设计和材料加工的基本信息。对于几种纯金属，已经用实验和理论的方法研究了相关的机理。然而，对于金属间化合物，从实验和理论的角度研究自扩散和杂质扩散的机制是具有挑战性的。因此，只有有限的知识存在，特别是关于这些材料中原子沿晶界的扩散。拟议的联合项目致力于研究Fe-Al合金中的自扩散和杂质扩散机制。一方面，利用X射线衍射仪、电阻率测量和正电子寿命谱对缺陷类型和缺陷微结构进行表征。另一方面，Fe-Al金属间化合物中点缺陷的浓度和稳定构型将由第一性原理计算得到，并将用于优化EAM原子间相互作用势。此外，第一性原理方法也将被用来确定自扩散和杂质扩散激活能/系数。相应的数据将与基于EAM的分子动力学计算得到的经验结果进行比较。在这些广泛的有效性检验的基础上，将使用经验势来模拟不同原子在所研究化合物中沿典型晶界的扩散行为。由此得到的铁铝化物的动力学数据将被用来推导一个扩散模型，该模型包含了在完美的晶格结构内和沿选定的晶界扩散的影响。通过这种方式，该项目的目的是了解和量化作为温度和组成函数的相关扩散机制，并为优化铁铝化物中各种元素的原子迁移率提供想法。

The diffusion data of alloys, such as vacancy formation energies, migration energies, diffusion activation energies and attempt frequencies, are basic information for materials design and materials processing. For several pure metals the involved mechanisms have already been studied using both experimental and theoretical methods. However, for intermetallic compounds the investigation of the mechanism of self- and impurity diffusion is challenging from experimental and theoretical point of view. Consequently, only limited knowledge exists in particular about atomic diffusion along grain boundaries in these materials. The proposed joint project is devoted to the investigation of self- and impurity diffusion mechanisms in Fe-Al alloys. On the one hand, the defect types and the defect micro-structures will be characterized by XRD, resistivity measurements and positron lifetime spectroscopy. On the other hand, the concentration and stable configurations of point defects in Fe-Al intermetallic compounds will be derived from first-principles calculations and will be used to optimize EAM interatomic potentials. Furthermore, first principles methods will also be used to determine self- and impurity diffusion activation energies/coefficients. The corresponding data will be compared with empirical results obtained from EAM based molecular dynamics calculations. Based on these extensive validity checks, the diffusion behavior of different atoms along typical grain boundaries within the investigated compounds will be simulated employing the empirical potentials. The resulting kinetic data for iron aluminides will be used to derive a diffusion model, which incorporates the effects of diffusion within a perfect lattice structure and along selected grain boundaries. In this way the project aims at understanding and quantifying the relevant diffusion mechanisms as a function of temperature and composition and at providing ideas to optimize atomic mobilities of various elements in iron aluminides.