利用密度泛函理論探討鐵合金中間隙元素的影響;Studying the Effect of Interstitial Elements in Fe-based Alloys Using Density Functional Theory

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Title:	利用密度泛函理論探討鐵合金中間隙元素的影響;Studying the Effect of Interstitial Elements in Fe-based Alloys Using Density Functional Theory
Authors:	朱郁民;Chu, Yu-Min
Contributors:	化學工程與材料工程學系
Keywords:	密度泛函理論;抗腐蝕;奧斯田鐵;間隙碳;間隙氮;DFT;corrosion resistance;austenite;interstitial carbon;interstitial nitrogen
Date:	2023-08-03
Issue Date:	2024-09-19 14:47:48 (UTC+8)
Publisher:	國立中央大學
Abstract:	不鏽鋼材料因其具有良好的抗腐蝕性，因而在工業界被廣泛使用。在製造不鏽鋼的過程中，通常會添加少量的間隙原子 (碳與氮) 以增強材料抗腐蝕性能，目前對於這些微量元素如何影響不鏽鋼抗腐蝕性的了解仍相當有限，且較少研究探討原子尺度下，間隙碳和間隙氮的協同效應對不鏽鋼抗腐蝕性能的影響，然而該特性對於設計良好的抗腐蝕不鏽鋼材料可能扮演重要角色。因此，本研究利用密度泛函理論計算方法探討間隙碳及間隙氮原子對不鏽鋼耐腐蝕性的影響。在本研究中使用多種分析方法，包括:鍵序鍵能 (Bond-order bond energy, BOBE) 模型、能態密度（Density of states, DOS）分析、晶體軌域漢密爾頓（Crystal orbital Hamilton populations, COHP）分析、電荷密度差異、電荷分析 (Bader charge analysis) 等，以探索間隙碳和間隙氮在不鏽鋼中的效應。利用鍵序鍵能模型得到金屬-金屬鍵、碳-金屬鍵和氮-金屬鍵的鍵能，並發現間隙碳和間隙氮對合金系統的總能量皆表現出局部影響特性。另一方面，由電荷密度差異及 Bader charge analysis 發現碳原子的周圍有明顯的電子累積現象，電子由周邊的金屬原子轉移至碳原子上，在間隙氮原子上也觀察到同樣的現象。此外，利用能態密度分析也證實了間隙碳原子與氮原子對於系統電子結構的局部影響特性。進一步使用晶體軌域漢密爾頓分析發現氮與周圍金屬原子成鍵並且具有共價鍵特徵，與間隙碳和間隙氧與金屬間的鍵結特性相似。儘管分析結果皆顯示碳與氮並不直接影響對方的電子結構，但從電荷密度差異可以觀察到，當碳、氮互為對方的第二鄰近間隙原子時，電子累積表現出方向性，碳和氮的周圍電子更傾向累積在共用金屬原子和碳之間，以及共用金屬原子和氮之間，顯示間隙碳和間隙氮以間接方式影響對方電子結構的可能性。;Stainless steels are widely used in industry because of their excellent corrosion resistance. In the process of manufacturing stainless steels, a small amount of interstitial carbon (C) or nitro gen (N) is often added to enhance the corrosion resistance. Currently, our understanding of how these tiny elements affect the corrosion resistance is not comprehensive. Limited knowledge is achieved on the synergistic effects of interstitial C and N at the atomic scale on the corrosion resistance of stainless steels. However, this is crucial for designing stainless steels with high corrosion resistance for specific applications. Therefore, in this study, the density functional theory (DFT) calculation is applied to explore the influence of interstitial C and N atoms on the corrosion resistance of stainless steels. Several analysis methods were utilized, including the bond-order bond energy (BOBE) model, density of states (DOS) analysis, crystal orbital Hamil ton population (COHP) analysis, charge density difference and Bader charge analysis, to explore the synergistic effects of interstitial C and N. By decomposing the bond energy of metal-metal bonds, carbon-metal bonds, and nitrogen-metal bonds using the BOBE model, it is observed that both C and N exhibit local influences on the total energy of the alloy system. From the charge density difference and Bader charge analysis, significant electron accumulation around C and N, and electrons transfer from the metal ions to C and N. Additionally, DOS analysis reveals an overlap of C and its first nearest neighboring metal atoms, which is also found in N and its first nearest neighboring metal atoms. However, no significant interaction was found between C and N, indicating local effects of interstitial atoms. Furthermore, the COHP analysis sug gests covalent bonding features between N and first nearest neighboring metal atoms. Although the analysis indicates that C and N do not directly affect their electronic structure. In addition, charge density difference shows that when C and N are within the distance of the second nearest interstitial position, a directionality of electron accumulation occurs. Electrons around C and N tend to accumulate between C and the shared metal atom, as well as between N and the shared metal atom.
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