【摘要】：金屬間化合物FeAl合金具有優(yōu)異的抗氧化硫化性能、耐腐蝕性好、比強度高等被廣泛應(yīng)用,是一種良好的新型結(jié)構(gòu)材料。但材料在工藝生產(chǎn)及加載過程中不可避免的與氫、硫、碳元素反應(yīng),導(dǎo)致材料室溫延展性降低并發(fā)生脆性斷裂與失效。微量(100ppm)的B能顯著提高合金的塑性和耐磨性。FeAl合金中點缺陷的類型及其擴散與合金的蠕變、燒結(jié)、固態(tài)相變等性能密切相關(guān)。因此理論研究雜質(zhì)原子在合金中的擴散規(guī)律及擴散影響因素對改善材料性能具有重要的指導(dǎo)意義。本文采用原子相互作用勢(EAM勢)通過分子靜力學(xué)方法模擬B、C、H雜質(zhì)原子在FeAl合金中的缺陷性質(zhì)與擴散行為。首先,分別通過分子靜力學(xué)計算了B2-FeAl的晶格常數(shù)、結(jié)合能、熔點和彈性常數(shù),結(jié)果與實驗值和他人的計算值一致,可見本文選用的EAM勢模型是合理的。接著,采用該模型計算雜質(zhì)原子B、C、H在FeAl合金塊體中的缺陷類型與擴散機制,研究表明：B原子容易取代Al位,C原子容易取代Fe位,而H原子不能形成穩(wěn)定的取代缺陷,易形成四面體間隙缺陷；塊體里雜質(zhì)原子所有的擴散機制中間隙擴散激活能最低,且H原子擴散最快,B次之,最后是C原子。其次,計算FeAl合金(100)-Al、(110)及(111)-Al的表面能,并計算B、C、H在這三個表面上的吸附與擴散情況,結(jié)果發(fā)現(xiàn)：(110)面排列最緊密,表面能最低；研究的雜質(zhì)原子中,H吸附能最低,吸附能力最強,B原子次之；此外,雜質(zhì)在表面上的擴散比塊體中的擴散容易,H原子最容易擴散,擴散速度最快。最后,本文還研究B、C、H在FeAl合金Σ5(310)[001]界面上的點缺陷及擴散性質(zhì)。結(jié)果發(fā)現(xiàn)：H形成取代缺陷不穩(wěn)定,雜質(zhì)原子形成In3間隙類型的形成能低于其他間隙缺陷與取代缺陷,且B、C原子的形成是一個放熱過程。取代位擴散計算發(fā)現(xiàn)B、C原子遷移至界面Al2位的能量最低,雜質(zhì)原子從塊體中傾向于以第一近鄰擴散機制(Fe位至Al位)遷移至晶界。
[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.
【學(xué)位授予單位】：廣西大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2016
【分類號】：TG111.6

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