The effect of segregated sp-impurities on grain-boundary and surface structure, magnetism and embrittlement in nickel
The effect of segregated sp-impurities on grain-boundary and surface structure, magnetism and embrittlement in nickel
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DOI：
10.1016/j.pmatsci.2011.01.008
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发表时间：
2011-08
影响因子：
37.4
通讯作者：
M. Všianská;M. Šob
中科院分区：
文献类型：
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作者：
M. Všianská;M. Šob
本文对面心立方铁磁镍中第3、4、5周期sp元素（Al、Si、P、S、Ga、Ge、As、Se、In、Sn、Sb、Te）在晶界的偏聚和强化/脆化能进行了详细的理论研究。为了比较，我们还研究了这些杂质在（210）自由表面（FS）的偏析。在从头算电子结构计算的基础上，对无杂质和有杂质的GB和FS的几何构型进行了全弛豫，并分析了杂质对磁矩分布的影响。而有一个轻微的增强磁化在干净的GB和FS相对于散装镍（3 - 7%和24%，分别），研究的杂质完全杀死或强烈减少铁磁性在GB和其紧邻，使磁死层形成。由于杂质sp态和镍d态的杂化，这种效应在杂质修饰的（210）FS处甚至更加明显。我们确定的首选偏析网站在1005（210）GB的sp-杂质的研究，他们的偏析heteropies和强化/脆化的能量与他们的化学和机械成分的分解。我们发现，在镍中，晶界偏聚的Si是GB内聚增强剂，置换偏聚的Al和晶界偏聚的P没有或只有最小的强化效果，晶界偏聚的S、Ge、As、Se和置换偏聚的Ga、In、Sn、Sb和Te是GB脆化剂。由于GB偏析镍的实验信息很少，目前的结果大多是理论预测，可能会激励未来的实验工作。
We present a detailed theoretical study of segregation and strengthening/embrittling energy of sp-elements from the 3rd, 4th and 5th period (Al, Si, P, S, Ga, Ge, As, Se, In, Sn, Sb and Te) at the Σ5(210) grain boundary (GB) in fcc ferromagnetic nickel. For comparison, we investigate also the segregation of these impurities at the (210) free surface (FS). On the basis of ab initio electronic structure calculations, full relaxation of the geometric configuration of the GB and FS without and with impurities is performed and the effect of impurities on the distribution of magnetic moments is analysed. Whereas there is a slight enhancement of magnetization at the clean GB and FS with respect to bulk nickel (3–7% and 24%, respectively), the studied impurities entirely kill or strongly reduce ferromagnetism at the GB and in its immediate neighbourhood so that magnetically dead layers are formed. This effect, which is due to the hybridization of the impurity sp-states and nickel d-states, is even more pronounced at the impurity-decorated (210) FS. We determine the preferred segregation sites at the Σ5(210) GB for the sp-impurities studied, their segregation enthalpies and strengthening/embrittling energies with their decomposition into the chemical and mechanical components. We find interstitially segregated Si as a GB cohesion enhancer, substitutionally segregated Al and interstitially segregated P with none or minimum strengthening effect and interstitially segregated S, Ge, As, Se and substitutionally segregated Ga, In, Sn, Sb and Te as GB embrittlers in nickel. As there is very little experimental information on GB segregation in nickel most of the present results are theoretical predictions which may motivate future experimental work.