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首页> 外文期刊>Physical review >First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel
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First-principles study of helium, carbon, and nitrogen in austenite, dilute austenitic iron alloys, and nickel

机译：奥氏体，稀奥氏体铁合金和镍中氦，碳和氮的第一性原理研究

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An extensive set of first-principles density functional theory calculations have been performed to study the behavior of He, C, and N solutes in austenite, dilute Fe-Cr-Ni austenitic alloys, and Ni in order to investigate their influence on the microstructural evolution of austenitic steel alloys under irradiation. The results show that austenite behaves much like other face-centered cubic metals and like Ni in particular. Strong similarities were also observed between austenite and ferrite. We find that interstitial He is most stable in the tetrahedral site and migrates with a low barrier energy of between 0.1 and 0.2 eV. It binds strongly into clusters as well as overcoordinated lattice defects and forms highly stable He-vacancy (V_mHe_n) clusters. Interstitial He clusters of sufficient size were shown to be unstable to self-interstitial emission and VHe_n cluster formation. The binding of additional He and V to existing V_mHe_n clusters increases with cluster size, leading to unbounded growth and He bubble formation. Clusters with n/m around 1.3 were found to be most stable with a dissociation energy of 2.8 eV for He and V release. Substitutional He migrates via the dissociative mechanism in a thermal vacancy population but can migrate via the vacancy mechanism in irradiated environments as a stable V_2He complex. Both C and N are most stable octahedrally and exhibit migration energies in the range from 1.3 to 1.6 eV. Interactions between pairs of these solutes are either repulsive or negligible. A vacancy can stably bind up to two C or N atoms with binding energies per solute atom up to 0.4 eV for C and up to 0.6 eV for N. Calculations in Ni, however, show that this may not result in vacancy trapping as VC and VN complexes can migrate cooperatively with barrier energies comparable to the isolated vacancy. This should also lead to enhanced C and N mobility in irradiated materials and may result in solute segregation to defect sinks. Binding to larger vacancy clusters is most stable near their surface and increases with cluster size. A binding energy of 0.1 eV was observed for both C and N to a [001] self-interstitial dumbbell and is likely to increase with cluster size. On this basis, we would expect that, once mobile, Cottrell atmospheres of C and N will develop around dislocations and grain boundaries in austenitic steel alloys.
机译：为了研究He，C和N溶质在奥氏体，稀Fe-Cr-Ni奥氏体合金和Ni中的行为，已进行了大量的第一性原理密度泛函计算，以研究它们对显微组织演变的影响。辐射下奥氏体钢合金的制造。结果表明，奥氏体的行为与其他面心立方金属非常相似，特别是镍。在奥氏体和铁素体之间也观察到很强的相似性。我们发现间隙He在四面体部位最稳定，并以0.1至0.2 eV之间的低势垒能迁移。它牢固地结合到簇以及过度配位的晶格缺陷中，并形成高度稳定的He-空位（V_mHe_n）簇。已显示足够大的间隙He团簇对自间隙发射和VHe_n团簇形成不稳定。额外的He和V与现有V_mHe_n簇的结合随着簇大小的增加而增加，从而导致无限制的增长和He气泡的形成。发现n / m约为1.3的团簇最稳定，He和V释放的解离能为2.8 eV。替代性He通过热空位种群中的解离机制迁移，但可以在辐射环境中以稳定的V_2He络合物通过空位机制迁移。 C和N都是八面体最稳定的，并且迁移能在1.3至1.6 eV的范围内。这些溶质对之间的相互作用是排斥的或可忽略的。空位可以稳定地最多结合两个C或N原子，每个溶质原子的结合能对于C高达0.4 eV，对于N高达0.6 eV。但是，Ni的计算表明，这可能不会导致像VC和VC那样导致空位俘获VN复合物可以与隔离空位相媲美的势垒能量协同迁移。这也应导致被辐照材料中C和N的迁移率提高，并可能导致溶质偏析到缺陷阱中。与较大的空位簇的结合在其表面附近最稳定，并随簇大小的增加而增加。 C和N与[001]自间隙哑铃的结合能均为0.1 eV，并且可能随簇的大小而增加。在此基础上，我们希望，一旦移动，奥氏体钢合金中的位错和晶界周围就会形成C和N的Cottrell气氛。

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