First-principle study of the effect of cerium on the modification and corrosion of nonmetal inclusions in steel
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摘要: 通過原位腐蝕觀察和基于密度泛函理論的第一性原理計算方法,從微觀角度研究了稀土元素鈰(Ce)對J5不銹鋼中夾雜物的改性和夾雜物誘導腐蝕的機理。采用掃描電子顯微鏡與能譜分析了稀土元素Ce改性夾雜物的過程中夾雜物成分和類型的變化,觀察到的代表夾雜物為CeAlO3?Ce2O2S、Ce2O3?Ce2O2S、MnS等。根據形成能計算,經稀土元素Ce處理后,生成了穩定的Ce2O3、Ce2O2S、CeAlO3夾雜物。通過表面能判斷了晶面的穩定性,Fe(100)-2面的表面能經收斂測得為2.4374 J·m?2,該晶面的功函數為4.7352 eV。通過對比夾雜物與鋼基體的功函數與計算電勢差,分析了不同含Ce夾雜物誘導點蝕的趨勢,探討了不同原子位置、原子數量和不同slab模型對功函數的影響。研究表明,與Fe (100)-2面的電子功函數相比,MnS以及改性后3種夾雜物CeS、Ce2O3和Ce2O2S電勢差大多小于0,CeAlO3的電勢差在0 eV左右。夾雜物不同晶面對功函數影響很大,O、S等非金屬原子數量多的晶面功函數平均值較高,添加稀土元素Ce可以有效降低晶面功函數。5種夾雜物和鋼基體的平均功函數大小順序為CeAlO3>Fe>MnS>CeS>Ce2O2S>Ce2O3。結合不銹鋼中復合夾雜物的實驗結果可知,Ce2O3誘導點蝕發生的概率最高,CeAlO3可以有效提高鋼的耐腐蝕能。Abstract: Nonmetallic inclusions in steel significantly influence the steel life, quality, toughness, and corrosion resistance. Pitting corrosion is the most common type of localized corrosion in stainless steel. Rare-earth elements, which are key materials in the metallurgical sector, largely influence the modification of sulfur (S) and oxygen (O) inclusions in steel. Numerous experimental studies have been conducted on the corrosion of the rare-earth metal cerium (Ce); however, studies on the microscopic-scale mechanism are few. In this study, in situ corrosion observation and the first-principle calculations based on density functional theory were applied to investigate the effects of the rare-earth element cerium on inclusions in J5 stainless steel and the inclusion-induced corrosion process. The changes in the inclusion composition and the primary types of inclusions in the steel were investigated by scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. The results show that CeAlO3?Ce2O2S, Ce2O3?Ce2O2S, and MnS are representative inclusions. MnS and other oxide inclusions in stainless steel were treated with Ce to generate stable Ce2O3, Ce2O2S, and CeAlO3 inclusions, according to formation energy calculations. The surface energy of the Fe (100)-2 plane is measured as 2.4374 J·m?2, and the work function of this crystal plane is predicted to be 4.7352 eV. The crystal plane stability was examined according to the surface energy. The work functions and potential differences between the inclusion and the steel matrix were analyzed to compare the trend of pitting corrosion induced by different Ce-containing inclusions, and the influences of different atomic positions, atomic numbers, and different slab models on the work function were explored. Compared with the electronic work function of the Fe (100)-2 surface, the potential difference between MnS and the three modified inclusions CeS, Ce2O3, and Ce2O2S is typically less than zero, and the potential difference of CeAlO3 is about 0 eV. The average work function of the crystal plane with a large number of nonmetal atoms such as O and S is higher. Ce addition reduces the work function of the crystal plane, and the molecular mechanism of pitting corrosion according to different crystal planes and termination planes of inclusions is revealed. The five types of inclusions and the steel matrix are in the following order: CeAlO3>Fe>MnS>CeS>Ce2O2S>Ce2O3. The experimental findings on composite inclusions in stainless steel reveal that Ce2O3 has the highest chance of pitting corrosion, and CeAlO3 can significantly improve steel corrosion resistance.
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表 1 Fe與夾雜物晶體結構參數
Table 1. Inclusion crystal structure parameters
Material Space ground Atom positions Lattice parameters Fe Im$\overline{3} $m (299) Fe (0,0,0) a=b=c=0.283 nm
α=β=γ=90°MnS Fm$\overline{3} $m (225) Mn (0,0,0)
S (0.5,0.5,0.5)a=b=c=0.522 nm
α=β=γ=90°CeS Fm$\overline{3} $m (225) Ce (0,0,0)
S (0.5,0.5,0.5)a=b=c=0.568 nm
α=β=γ=90°Ce2O3 P$\overline{3} $m1 (164) Ce (0.33,0.67,0.25)
O (0.33,0.67,0.64)a=b=0.383 nm
c=0.607 nm
α=β=90°,γ=120°Ce2O2S P$\overline{3} $m1 (164) Ce (0.33,0.67,0.28)
O (0.33,0.67,0.63)
S (0,0,0)a=b=0.395 nm
c=0.680 nm
α=β=90°, γ=120CeAlO3 R$\overline{3} $c (164) Ce (0,0,0.25)
Al (0,0,0)
O (0.519,0,0.25)a=b=0.539 nm
c=1.139 nm
α=β=90°, γ=120°表 2 J5不銹鋼化學成分(質量分數)
Table 2. Chemical composition of J5 stainless steel
% C Si Mn P S Cr Ni N 0.13 0.51 10.05 0.045 0.0019 13.37 0.93 0.15 表 3 含Ce夾雜物的形成能
Table 3. Formation energy of inclusions
eV·atom?1 Ce2O3 Ce2O2S CeAlO3 CeS Ce2S3 Ce3S4 ?3.33192 ?3.20334 ?3.22015 ?2.38639 ?2.43052 ?2.41476 表 4 Fe不同終止面的電子功函數與表面能
Table 4. Electronic work function and surface energy of different termination surfaces of Fe matrix
Surface Terminated plane Work function/eV Surface energy/(J·m?2) This work Experiment Calculation This work Experiment Calculation 100 1 4.7433 4.67[23] 4.65[18] 2.7405 2.41[24] 2.463[25] 2 4.7352 2.4374 110 1 4.7367 4.5[23, 26] 2.4443 2.41[24] 2.48[26] 2 4.7368 2.4431 111 1 3.8098 4.81[23] 2.7111 2.41[24] 2.658[27] 2 3.8105 2.7113 3 3.8182 2.7111 表 5 MnS不同終止面的電子功函數
Table 5. Electronic work function of different termination surfaces of MnS
Surface Terminated plane Work function/eV 100 1 4.11 2 4.10 110 1 4.14 2 4.13 111 1 3.36 2 5.82 3 3.39 4 5.82 5 3.38 6 5.81 表 6 CeS不同終止面的電子功函數
Table 6. Electronic work function of different termination surfaces of CeS
Surface Terminated plane Work function/eV 100 1 2.34 2 2.32 110 1 2.42 2 2.42 111 1 3.16 2 5.33 3 3.15 4 5.34 5 3.15 6 5.34 表 7 Ce2O3不同終止面的電子功函數
Table 7. Electronic work function of different termination surfaces of Ce2O3
Surface Terminated plane Work function/eV 100 1 3.08 2 2.05 3 2.45 4 3.09 5 2.05 6 2.44 110 1 1.87 2 1.85 111 1 upper plane 2.49 1 lower plane 2.12 2 upper plane 2.42 2 lower plane 4.72 3 upper plane 2.74 3 lower plane 2.58 4 upper plane 4.09 4 lower plane 2.22 5 upper plane 2.19 5 lower plane 3.08 6 upper plane 2.46 6 lower plane 2.12 7 upper plane 2.41 7 lower plane 4.74 8 upper plane 2.72 8 lower plane 2.59 9 upper plane 4.09 9 lower plane 2.23 10 upper plane 2.21 10 lower plane 3.13 表 8 Ce2O2S不同終止面的電子功函數
Table 8. Electronic work function of different termination surfaces of Ce2O2S
Surface Terminated plane Work function/eV 100 1 4.52 2 2.11 3 2.52 4 4.51 5 2.14 6 2.53 110 1 2.13 2 2.13 111 1 upper plane 3.44 1 lower plane 2.00 2 upper plane 2.35 2 lower plane 4.72 3 upper plane 2.42 3 lower plane 2.75 4 upper plane 3.84 4 lower plane 2.17 5 upper plane 2.11 5 lower plane 3.53 6 upper plane 3.56 6 lower plane 2.03 7 upper plane 2.33 7 lower plane 4.69 表 9 CeAlO3不同終止面的電子功函數
Table 9. Electronic work function of different termination surfaces of Ce2O3
Surface Terminated plane Work function/eV 100 1 4.20 2 1.96 3 1.96 4 4.64 5 6.50 110 1 3.89 2 2.73 3 1.28 4 5.94 5 6.42 111 1 4.19 2 5.18 3 4.19 4 4.01 www.77susu.com -
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