杂质原子在B2-FeAl合金中扩散性质的理论研究

发布时间：2018-12-15 14:39

【摘要】：金属间化合物FeAl合金具有优异的抗氧化硫化性能、耐腐蚀性好、比强度高等被广泛应用,是一种良好的新型结构材料。但材料在工艺生产及加载过程中不可避免的与氢、硫、碳元素反应,导致材料室温延展性降低并发生脆性断裂与失效。微量(100ppm)的B能显著提高合金的塑性和耐磨性。FeAl合金中点缺陷的类型及其扩散与合金的蠕变、烧结、固态相变等性能密切相关。因此理论研究杂质原子在合金中的扩散规律及扩散影响因素对改善材料性能具有重要的指导意义。本文采用原子相互作用势(EAM势)通过分子静力学方法模拟B、C、H杂质原子在FeAl合金中的缺陷性质与扩散行为。首先,分别通过分子静力学计算了B2-FeAl的晶格常数、结合能、熔点和弹性常数,结果与实验值和他人的计算值一致,可见本文选用的EAM势模型是合理的。接着,采用该模型计算杂质原子B、C、H在FeAl合金块体中的缺陷类型与扩散机制,研究表明：B原子容易取代Al位,C原子容易取代Fe位,而H原子不能形成稳定的取代缺陷,易形成四面体间隙缺陷；块体里杂质原子所有的扩散机制中间隙扩散激活能最低,且H原子扩散最快,B次之,最后是C原子。其次,计算FeAl合金(100)-Al、(110)及(111)-Al的表面能,并计算B、C、H在这三个表面上的吸附与扩散情况,结果发现：(110)面排列最紧密,表面能最低；研究的杂质原子中,H吸附能最低,吸附能力最强,B原子次之；此外,杂质在表面上的扩散比块体中的扩散容易,H原子最容易扩散,扩散速度最快。最后,本文还研究B、C、H在FeAl合金Σ5(310)[001]界面上的点缺陷及扩散性质。结果发现：H形成取代缺陷不稳定,杂质原子形成In3间隙类型的形成能低于其他间隙缺陷与取代缺陷,且B、C原子的形成是一个放热过程。取代位扩散计算发现B、C原子迁移至界面Al2位的能量最低,杂质原子从块体中倾向于以第一近邻扩散机制(Fe位至Al位)迁移至晶界。
[Abstract]:Intermetallic compound FeAl alloy has been widely used in many fields, such as excellent oxidation resistance, good corrosion resistance and high specific strength, so it is a good new structural material. However, in the process of production and loading, the material inevitably reacts with hydrogen, sulfur and carbon elements, which leads to the reduction of ductility at room temperature and the occurrence of brittle fracture and failure. The ductility and wear resistance of the alloy can be significantly improved by 100ppm. The type and diffusion of point defects in FeAl alloy are closely related to the creep, sintering, solid phase transformation and other properties of the alloy. Therefore, it is important to study the diffusion law of impurity atoms in alloy and the influence factors of diffusion to improve the properties of materials. Atomic interaction potential (EAM potential) was used to simulate the defect properties and diffusion behavior of impurity atoms in FeAl alloys by means of molecular statics. Firstly, the lattice constants, binding energy, melting point and elastic constants of B2-FeAl are calculated by molecular statics, respectively. The results are in agreement with the experimental values and the calculated values of others. It can be seen that the EAM potential model selected in this paper is reasonable. Then, the defect types and diffusion mechanism of impurity atom BX CnH in FeAl alloy bulk are calculated by using this model. The results show that B atom is easy to replace Al site, C atom is easy to replace Fe site, and C atom is easy to replace Fe site. The H atom can not form a stable substitution defect, and it is easy to form a tetrahedron gap defect. Among the diffusion mechanisms of impurity atoms in bulk, the gap diffusion activation energy is the lowest, and H atom diffusion is the fastest, B is the second and C atom is the last. Secondly, the surface energy of FeAl alloy (100)-Al, (110) and (111)-Al were calculated, and the adsorption and diffusion of Al on these three surfaces were calculated. The results show that: (1) the surface energy of (110) alloy is the most compact and the surface energy is the lowest; Among the impurity atoms studied, the adsorption energy of H is the lowest, the adsorption ability is the strongest, and B atom is the second. In addition, the diffusion of impurity on the surface is easier than that in bulk, and the diffusion rate of H atom is the fastest. Finally, the point defects and diffusion properties of FeAl alloy 危 5 (310) [001] have been studied. The results show that the formation of substitution defects in H is unstable, and the formation of In3 gap type of impurity atoms is lower than that of other interstitial defects and substitution defects, and the formation of C atoms is an exothermic process. The substitution site diffusion calculation shows that the energy of the Al2 site is the lowest and the impurity atoms tend to migrate to the grain boundary by the first nearest neighbor diffusion mechanism (Fe site to Al site) from the block.
【学位授予单位】：广西大学
【学位级别】：硕士
【学位授予年份】：2016
【分类号】：TG111.6

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