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Noburnium: Systems design of niobium superalloys.

机译：burn：铌高温合金的系统设计。

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摘要

A systems-based approach, integrating quantum mechanical calculations with efficient experimentation, was employed to design niobium-based superalloys. The microstructural concept of gamma-gamma' nickel-based superalloys was adopted, where, the coherent gamma ' aluminides act both as the strengthening phase and a source of aluminum for Al2O3 passivation. Building on previous research, the selected bcc-type ordered aluminide was L2 1 structured Pd2HfAl phase. Comprehensive phase relations were measured on Nb-Pd-Hf-Al prototype alloys, and key tie-tetrahedra were identified. Aluminide precipitation in a bcc matrix was demonstrated in designed Nb+Pd2HfAl alloys. Thermodynamic databases were developed by integrating first-principles calculations with measured phase relations. Atomic volume models were developed for the bcc matrix and the Pd2HfAl phase and matrix elements which would reduce lattice misfit were identified. An experimental 2-phase alloy demonstrated a misfit of 3%.; A modified Wagner's model was used to predict the required transient properties to form external Al2O3. The principal oxidation design goal was to decrease the oxygen permeability ( NSOx DO ) divided by the aluminum diffusivity (DAl) by 5 orders of magnitude. A multicomponent mobility database was developed to predict the diffusivities. Guided by first-principles calculations the effect of alloying elements on the oxygen diffusivity in Nb was measured, and the mobility database was experimentally validated.; Based on the mobility database, it was found that increasing Al solubility in the bcc matrix greatly increased Al diffusivity. Alloying elements were identified that would increase Al solubility in the bcc matrix. Prototype alloys were prepared and the best oxidation performance was exhibited by a bcc+Nb2Al Nb-Hf-Al alloy, which exhibited parabolic oxidation behavior at 1300°C. The alloy was shown to have achieved the required 5 orders of magnitude reduction in the design parameter. The oxidation performance of the Nb-Hf-Al alloy achieved the IHPTET Phase III oxidation goals. However, the alloy failed to form a continuous Al2O3 scale, due to formation of stable HfO2 and observed NbAlO4, which was shown to be metastable by first-principles calculations. This implies that catalytic formation of Al2O3 is still thermodynamically possible in these systems. A new design strategy is also proposed which exploits fast yttrium diffusion in Nb to form a protective YAG scale.
机译：一种基于系统的方法将量子力学计算与有效的实验相结合，用于设计基于铌的高温合金。采用了γ-γ'镍基高温合金的微观结构概念，其中，相干的γ'铝化物既充当了强化相，又充当了Al2O3钝化的铝源。在先前的研究基础上，选定的bcc型有序铝化物为L2 1结构的Pd2HfAl相。在Nb-Pd-Hf-Al原型合金上测量了全面的相关系，并确定了关键的四面体连接。在设计的Nb + Pd2HfAl合金中证实了bcc基质中的铝化物沉淀。热力学数据库是通过将第一性原理计算与测得的相关系相结合而开发的。开发了用于bcc基质的原子体积模型，并确定了Pd2HfAl相和可减少晶格失配的基质元素。实验性2相合金的失配率为3％。修改后的Wagner模型用于预测形成外部Al2O3所需的瞬态特性。氧化的主要设计目标是将氧气渗透率（NSOx DO）除以铝扩散率（DAl）5个数量级。开发了多组分流动性数据库来预测扩散率。以第一性原理计算为指导，测量了合金元素对Nb中氧扩散率的影响，并通过实验验证了迁移率数据库。根据迁移率数据库，发现增加的铝在bcc基质中的溶解度大大提高了铝的扩散率。合金元素被确定会增加Al在bcc基质中的溶解度。制备了原型合金，bcc + Nb2Al Nb-Hf-Al合金表现出最佳的氧化性能，该合金在1300°C下表现出抛物线的氧化行为。结果表明，该合金的设计参数已降低了所需的5个数量级。 Nb-Hf-Al合金的氧化性能达到了IHPTET III期的氧化目标。但是，由于形成稳定的HfO2和观察到的NbAlO4，该合金未能形成连续的Al2O3氧化皮，这通过第一性原理计算已证明是亚稳态的。这意味着在这些系统中仍然可以在热力学上催化形成Al2O3。还提出了一种新的设计策略，该策略利用钇在Nb中的快速扩散来形成保护性YAG氧化皮。

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  • 作者

    Misra, Abhijeet.;

  • 作者单位

    Northwestern University.;

  • 授予单位 Northwestern University.;
  • 学科 Engineering Materials Science.; Engineering Metallurgy.
  • 学位 Ph.D.
  • 年度 2005
  • 页码 204 p.
  • 总页数 204
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 工程材料学;冶金工业;
  • 关键词

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