Wróbel J S, Nguyen-Manh D, Kurzydłowski K J, Dudarev S L
CCFE, UK Atomic Energy Authority, Culham Science Centre, Abingdon, Oxon OX14 3DB, United Kingdom. Faculty of Materials Science and Engineering, Warsaw University of Technology, Wołoska 141, 02-507 Warsaw, Poland.
J Phys Condens Matter. 2017 Apr 12;29(14):145403. doi: 10.1088/1361-648X/aa5f37. Epub 2017 Feb 8.
The occurrence of segregation in dilute alloys under irradiation is a highly unusual phenomenon that has recently attracted attention, stimulated by the interest in the fundamental properties of alloys as well as by their applications. The fact that solute atoms segregate in alloys that, according to equilibrium thermodynamics, should exhibit full solubility, has significant practical implications, as the formation of precipitates strongly affects physical and mechanical properties of alloys. A lattice Hamiltonian, generalizing the so-called 'ABV' Ising model and including collective many-body inter-atomic interactions, has been developed to treat rhenium solute atoms and vacancies in tungsten as components of a ternary alloy. The phase stability of W-Re-vacancy alloys is assessed using a combination of density functional theory (DFT) calculations and cluster expansion (CE) simulations. The accuracy of CE parametrization is evaluated against the DFT data, and the cross-validation error is found to be less than 4.2 meV/atom. The free energy of W-Re-vacancy ternary alloys is computed as a function of temperature using quasi-canonical Monte Carlo simulations, using effective two, three and four-body interactions. In the low rhenium concentration range (<5 at.[Formula: see text]Re), solute segregation is found to occur in the form of voids decorated by Re atoms. These vacancy-rhenium clusters remain stable over a broad temperature range from 800 K to 1600 K. At lower temperatures, simulations predict the formation of Re-rich rhenium-vacancy clusters taking the form of sponge-like configurations that contain from 30 to 50 at.[Formula: see text]Re. The anomalous vacancy-mediated segregation of Re atoms in W can be rationalized by analyzing binding energy dependence as a function of Re to vacancy ratio as well as chemical Re-W and Re-vacancy interactions and short-range order parameters. DFT calculations show that rhenium-vacancy binding energies can be as high as 1.5 eV if the rhenium/vacancy ratio is in the range from 2.4 to 6.6. The predicted Re clustering agrees with experimental observations of precipitation in self-ion irradiated W-2[Formula: see text] Re alloys and neutron-irradiated alloys containing 1.4 at.[Formula: see text]Re.
在辐照下稀合金中发生的偏析是一种非常不寻常的现象，最近受到了关注，这既源于对合金基本性质的兴趣，也源于其应用方面的兴趣。溶质原子在合金中发生偏析，而根据平衡热力学，这些合金本应表现出完全互溶性，这一事实具有重大的实际意义，因为析出物的形成会强烈影响合金的物理和力学性能。一种晶格哈密顿量已被开发出来，它推广了所谓的“ABV”伊辛模型，并包括集体多体原子间相互作用，用于将铼溶质原子和钨中的空位作为三元合金的组分来处理。使用密度泛函理论（DFT）计算和团簇展开（CE）模拟相结合的方法来评估W-Re-空位合金的相稳定性。根据DFT数据评估CE参数化的准确性，发现交叉验证误差小于4.2毫电子伏/原子。使用有效的二体、三体和四体相互作用，通过准经典蒙特卡罗模拟计算W-Re-空位三元合金的自由能随温度的变化。在低铼浓度范围（<5原子分数的Re）内，发现溶质偏析以由Re原子修饰的空位形式出现。这些空位-铼团簇在800 K至1600 K的宽温度范围内保持稳定。在较低温度下，模拟预测形成富含Re的铼-空位团簇，其形式为海绵状构型，含有30至50原子分数的Re。通过分析结合能随Re与空位比以及化学Re-W和Re-空位相互作用和短程序参数的变化，可以解释W中Re原子异常的空位介导偏析。DFT计算表明，如果铼/空位比在2.4至6.6范围内，铼-空位结合能可高达1.5 eV。预测的Re团簇与自离子辐照的W-2原子分数的Re合金以及含1.4原子分数的Re的中子辐照合金中析出的实验观察结果一致。
