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随着航空航天、能源化工等领域的快速发展, 人们对高温合金的性能提出了更高的期望. Inconel 718 (简称IN 718)是目前用量最大的镍基高温合金, 目前国内外关于Si对IN 718合金组织与性能影响的研究, 尤其是在微观尺度上的研究, 还存在大量空白. 本文从第一性原理计算出发研究了Si掺杂对IN 718合金中 γ相的影响, 计算了Si掺杂前后 γ相的晶格常数、总能量、缺陷形成能、形成热、结合能、态密度和差分电荷密度, 并进行了布居分析. 同时利用等离子熔覆的方法制备了IN 718涂层以及Si质量分数为2%的IN 718涂层, 并对其进行显微组织及相结构的分析. 计算结果表明, Si的掺杂改变了体系内原子的交互作用, 影响了原子之间的价电子数量、电荷密度分布及原子之间键合的强度, 从而扩大了 γ相的晶胞体积, 同时降低了 γ相的稳定性. 实验结果表明, Si掺杂会使得IN 718合金涂层组织发生由柱状晶向等轴晶的转变, 并降低IN 718合金中 γ相的体积分数, 同时, Si掺杂会加剧合金组织内Nb和Cr元素的偏析.
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关键词:
- Inconel 718合金/
- 第一性原理/
- γ相/
- Si掺杂
Inconel 718 (IN 718) is the most widely used nickel-based high-temperature alloy today. It is widely adopted in important fields such as aerospace, energy and chemicals, and is also one of the few high-temperature alloys, of which some can be fabricated by using additive manufacturing. There is a lack of research on the effect of Si on the structure and properties of IN 718 alloy on a microscopic scale. In this paper, the effect of Si doping on the γ phase in IN 718 alloy is investigated by first-principles calculations through using the CASTEP package. The lattice constants, total energy, defect formation energy, formation enthalpy, cohesive energy, density of states, and electron density difference of the γ phase are calculated before and after Si doping, and population analysis is performed. The calculation of the lattice constant reveals that the doping of Si atoms expands the cell volume of the γ phase supercell, which contributes to a certain solution strengthening effect, and is conducive to the improvement of the hardness of the alloy. The energy and electronic structure calculations show that the Si atoms prefer to occupy the Ni atomic positions in the γ phase. The number of valence electrons between the atoms, the distribution of the charge density, and the strength of the bonds between the atoms also change with Si doping, thus modifying the interaction of the atoms within the γ phase, reducing the stability of the γ phase, and favouring the precipitation of the second phase. Besides, uniform and dense IN 718 coatings with low-coat Si doping are successfully fabricated by using plasma cladding. The experimental results demonstrate that Si doping has no significant effect on the type of matrix structure of IN 718 coatings, but causes a slight expansion of the lattice of the alloy, which is consistent with the calculation result. The addition of Si can result in a transformation of the alloy coating from columnar crystal to equiaxed crystal, refining the grain size of the alloy, while reducing the volume fraction of the γ phase and increasing the volume fraction of the second phase. Moreover, the addition of Si exacerbates the segregation of Nb and Cr elements in the IN 718 coatings.-
Keywords:
- Inconel 718/
- first principles/
- γ phase/
- Si doping
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System Site a/nm b/nm c/nm α/(°) β/(°) γ/(°) V/nm3 Ni19Fe6Cr6Nb — 0.71345 0.72715 0.70223 90.000 90.000 90.000 0.3643 Ni18Fe6Cr6NbSi Ni Site 0.71915 0.71859 0.71627 90.000 90.000 90.000 0.3701 Ni19Fe5Cr6NbSi Fe Site 0.73543 0.73499 0.68475 90.000 90.000 90.314 0.3702 Ni19Fe6Cr5NbSi Cr Site 0.70478 0.73256 0.70599 89.592 89.991 90.003 0.3645 Ni19Fe6Cr6Si Nb Site 6.99468 7.26214 7.01313 90.000 90.000 90.001 0.3562 
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System Site Ef/eV H/(eV·atom–1) E/(eV·atom–1) Etotal/eV Ni19Fe6Cr6Nb — — –0.213127 –2.929875 –47447.72376 Ni18Fe6Cr6NbSi Ni Site –1.339744 –0.256865 –2.915375 –46241.16350 Ni19Fe5Cr6NbSi Fe Site –1.322440 –0.255194 –2.880194 –46754.74620 Ni19Fe6Cr5NbSi Cr Site –1.226650 –0.252200 –2.892825 –45218.05041 Ni19Fe6Cr6Si Nb Site –1.112683 –0.248639 –2.948639 –45961.73644 下载:
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System Species s p d f Total Charge Ni19Fe6Cr6Nb Ni 0.48 0.83 8.65 0 9.96 0.031 Cr 2.58 6.77 4.96 0 14.32 –0.31 Fe 0.50 0.70 6.72 0 7.92 0.08 Nb 2.26 6.02 3.93 0 12.21 0.79 Ni18Fe6Cr6NbSi Ni 0.49 0.83 8.65 0 9.97 0.02 Cr 2.57 6.77 5.00 0 14.33 –0.33 Fe 0.49 0.67 6.74 0 7.90 0.11 Nb 2.26 6.04 3.94 0 12.24 0.76 Si 1.21 2.61 0.00 0 3.83 0.17 下载:
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System Bond Population Length/nm Ni19Fe6Cr6Nb Fe—Ni 0.06 0.360847 Cr—Fe –0.07 0.350106 Cr—Ni –0.03 0.359244 Ni—Ni –0.03 0.375966 Fe—Nb –0.10 0.434654 Ni—Nb –0.13 0.364001 Cr—Nb –0.46 0.340342 Cr—Cr –0.16 0.419928 Fe—Fe –0.07 0.427230 Ni18Fe6Cr6NbSi Fe—Ni 0.06 0.363710 Cr—Fe –0.12 0.351112 Cr—Ni –0.04 0.363071 Ni—Ni 0.03 0.373913 Fe—Nb –0.13 0.434897 Ni—Nb –0.13 0.356309 Cr—Nb –0.40 0.338983 Cr—Cr –0.33 0.422106 Fe—Fe –0.06 0.418588 Ni—Si 0.02 0.386153 下载:
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System Measurement results Converted results α/(°) β/(°) γ/(°) a/nm b/nm c/nm V/nm3 a/nm b/nm c/nm V/nm3 IN 718 0.36028 0.36021 0.35848 0.0465 0.72056 0.72042 0.71696 0.3721 90.000 90.000 90.000 2Si-IN 718 0.35970 0.35960 0.36114 0.0467 0.71940 0.71920 0.72228 0.3737 90.000 90.000 90.000 下载:
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Coating Area Ni Fe Cr Nb Mo Ti Al Si IN 718 Matrix 40.85 38.46 17.42 0.53 1.14 — 1.28 0.32 Second phase 36.08 28.42 14.33 6.89 2.89 1.46 0.56 9.33 2Si-IN 718 Matrix 38.95 40.42 16.06 0.43 1.13 0.69 0.99 1.33 Second phase 34.1 23.6 10.4 12.8 2.73 1.54 0.53 14.3 下载:
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