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<p>Thermal barrier coatings (TBCs) have been used extensively in gas-turbine engines to protect hot section components from harsh operating environments at elevated temperatures. Thermally grown oxide (TGO) in TBCs exerts significant influence on TBCs durability and life span, and this influence is primarily controlled by doping less than 1 wt pct of reactive elements (REs) in the TBCs bond coat. This phenomenon is significant as it considerably delays the failure of TBCs and extends the lifetime of gas turbine engines. However, the mechanisms behind how the REs affect TGO are not fully understood. Therefore, it is necessary to better understand the RE effect's underlying mechanisms to improve TBC durability further. In this paper, focusing on <i>α</i>-Al<sub>2</sub>O<sub>3</sub>-TGO, <i>ab initio</i> density functional theory (DFT) calculations were performed to examine the influence of singly and co-doped Hf, Y, and Zr at a Σ3 twin grain boundary (GB) and a Σ13 twin GB in <i>α</i>-Al<sub>2</sub>O<sub>3</sub>. Five energetically favourable GB models with different RE additions were constructed for each GB. The impact of dopants on the electronic structure of these GB models, as well as the segregation of oxygen vacancy (V<sub>O</sub><sup>2+</sup>) and aluminum vacancy (V<sub>Al</sub><sup>3−</sup>), was investigated. Our results show that some dopants and co-dopants changed the electronic structure of the GBs and the segregation of vacancies at those regions remarkably, which can be correlated to experimental observations of suppressed oxide growth by the same REs. The findings in this work suggest that REs modify the segregation energies of V<sub>O</sub><sup>2+</sup> by altering the electronic structure and the electrostatic interactions around GBs. On the other hand, more studies are needed to explain the changes brought by REs on the segregation of V<sub>Al</sub><sup>3−</sup>, suggesting that it is likely affected by other factors, such as interactions between ions and strain effect. To summarize, this work demonstrates that the electronic properties of GBs are important characteristics for gaining insight into the effect of REs on the growth of TGO GBs.</p>

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Ab Initio Thermodynamics Study of α-Al2O3 Grain Boundaries Doped with Reactive Elements

  • 期刊论文

  • 发表日期：

    2025年3月1日

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  • Chuyang Li,
  • Kuiying Chen,
  • Qiwen Qiu,
  • Jun Song

摘要

Thermal barrier coatings (TBCs) have been used extensively in gas-turbine engines to protect hot section components from harsh operating environments at elevated temperatures. Thermally grown oxide (TGO) in TBCs exerts significant influence on TBCs durability and life span, and this influence is primarily controlled by doping less than 1 wt pct of reactive elements (REs) in the TBCs bond coat. This phenomenon is significant as it considerably delays the failure of TBCs and extends the lifetime of gas turbine engines. However, the mechanisms behind how the REs affect TGO are not fully understood. Therefore, it is necessary to better understand the RE effect's underlying mechanisms to improve TBC durability further. In this paper, focusing on α-Al2O3-TGO, ab initio density functional theory (DFT) calculations were performed to examine the influence of singly and co-doped Hf, Y, and Zr at a Σ3 twin grain boundary (GB) and a Σ13 twin GB in α-Al2O3. Five energetically favourable GB models with different RE additions were constructed for each GB. The impact of dopants on the electronic structure of these GB models, as well as the segregation of oxygen vacancy (VO2+) and aluminum vacancy (VAl3−), was investigated. Our results show that some dopants and co-dopants changed the electronic structure of the GBs and the segregation of vacancies at those regions remarkably, which can be correlated to experimental observations of suppressed oxide growth by the same REs. The findings in this work suggest that REs modify the segregation energies of VO2+ by altering the electronic structure and the electrostatic interactions around GBs. On the other hand, more studies are needed to explain the changes brought by REs on the segregation of VAl3−, suggesting that it is likely affected by other factors, such as interactions between ions and strain effect. To summarize, this work demonstrates that the electronic properties of GBs are important characteristics for gaining insight into the effect of REs on the growth of TGO GBs.