Wang Zhaowei, Pei Haiqing, Shang Jing, Kou Liangzhi, Wen Zhixun, Li Chun
School of Mechanics, Civil Engineering and Architecture, Northwestern Polytechnical University, Xi'an 710129, China.
Phys Chem Chem Phys. 2019 Aug 21;21(33):18316-18327. doi: 10.1039/c9cp02824b.
Anti-oxidation is one of the significant properties of nickel-based superalloys useful for their potential applications in industry. However, previous research mainly focused on single-phase compounds of NiAl or Ni3Al. In the present study, first-principles density functional theory coupled with thermodynamics analysis are employed to investigate the atomistic oxidation behaviours of the Ni/Ni3Al composites systematically. An oxidation experiment with a DD6 alloy is conducted as well to further confirm the theoretical prediction. Initial surface formation energy analysis shows that the systems composed of Ni(111) and Ni3Al(100)/(111) surfaces are more stable and therefore are selected for further investigation. Thermodynamics calculations indicate that the Ni3Al phase is oxidized first, accompanied by Al-segregation on the top surfaces. This is followed by subsequent oxidation of the Ni phase. Surface oxidation diagrams with respect to the surface formation energies show that oxygen adsorption could enhance Al-segregation to the surface and Ni3Al(111) surfaces tend to be oxidized completely with slightly lower oxygen coverage. Oxidation at the interface is also investigated and the results show that oxygen atoms bind with the upper layers of the Ni3Al phase from the point of view of binding energy. The experimental results provide a reasonable explanation for the selective oxidation of Al atoms at the atomic-scale so as to form a dense anti-oxidation membrane. The present work could serve as a beneficial reference for subsequent investigations of oxidation or adsorption processes of two-phase composites.
抗氧化是镍基高温合金的重要性能之一，这使其在工业领域具有潜在的应用价值。然而，以往的研究主要集中在NiAl或Ni3Al的单相化合物上。在本研究中，采用第一性原理密度泛函理论并结合热力学分析，系统地研究了Ni/Ni3Al复合材料的原子尺度氧化行为。还进行了DD6合金的氧化实验，以进一步证实理论预测。初始表面形成能分析表明，由Ni(111)和Ni3Al(100)/(111)表面组成的体系更稳定，因此被选作进一步研究对象。热力学计算表明，Ni3Al相首先被氧化，同时在表面顶部出现Al偏析。随后是Ni相的氧化。基于表面形成能的表面氧化图表明，氧吸附可增强Al向表面的偏析，且Ni3Al(111)表面在稍低的氧覆盖度下倾向于被完全氧化。还研究了界面处的氧化情况，结果表明从结合能的角度来看，氧原子与Ni3Al相的上层结合。实验结果为原子尺度上Al原子的选择性氧化从而形成致密抗氧化膜提供了合理的解释。本工作可为后续两相复合材料氧化或吸附过程的研究提供有益参考。
