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首页> 外文学位 >Defect structures in ordered intermetallics; grain boundaries and surfaces in FeAl, NiAl, CoAl and TiAl.
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Defect structures in ordered intermetallics; grain boundaries and surfaces in FeAl, NiAl, CoAl and TiAl.

机译：有序金属间化合物中的缺陷结构； FeAl，NiAl，CoAl和TiAl中的晶界和表面。

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摘要

Ordered intermetallics based on transition metal aluminides have been proposed as structural materials for advanced aerospace applications. The development of these materials, which have the advantages of low density and high operating temperatures, have been focused on the aluminides of titanium, nickel and iron. Though these materials exhibit attractive properties at elevated temperatures, their utilization is limited due to their propensity for low temperature fracture and susceptibility to decreased ductility due to environmental effects. A major embrittlement mechanism at ambient temperatures in these aluminides has been by the loss of cohesive strength at the interfaces (intergranular failure). This study focuses on this mechanism of failure, by undertaking a systematic study of the energies and structures of specific grain boundaries in some of these compounds.; The relaxed atomistic grain boundary structures in B2 aluminides, FeAl, NiAl and CoAl and L10 γ-TiAl were investigated using molecular statics and embedded atom potentials in order to explore general trends for a series of B2 compounds as well as TiAl. The potentials used correctly predict the proper mechanism of compositional disorder of these compounds. Using these potentials, point defects, free surface energies and various grain boundary structures of similar energies in three B2 compounds, FeAl, NiAl and CoAl were studied. These B2 alloys exhibited increasing anti-phase boundary energies respectively. The misorientations chosen for detailed study correspond to the Σ5(310) and Σ5(210) boundaries. These boundaries were investigated with consideration given to possible variations in the local chemical composition. The effects of both boundary stoichiometry and bulk stoichiometry on grain boundary energetics were also considered. Defect energies were calculated for boundaries contained in both stoichiometric and off-stoichiometric bulk. The surface energies for these aluminides were also calculated so that trends concerning the cohesive energy of the boundaries could be studied. The implications of stoichiometry, the multiplicity of the boundary structures and possible transformations between them for grain boundary brittleness are also discussed.
机译：已经提出了基于过渡金属铝化物的有序金属间化合物作为先进航空航天应用的结构材料。这些材料具有低密度和高工作温度的优点，其开发一直集中在钛，镍和铁的铝化物上。尽管这些材料在高温下表现出吸引人的性能，但是由于其易于发生低温断裂以及由于环境影响而易受延展性的影响，因此其使用受到限制。这些铝化物在环境温度下的主要脆化机理是界面处的内聚强度的损失（晶间破坏）。通过对这些化合物中某些化合物的特定晶界的能量和结构进行系统的研究，本研究集中于这种失效机理。利用分子静力学和嵌入原子势研究了B2铝化物，FeAl，NiAl和CoAl和 L 1 0 γ-TiAl中的弛豫原子晶界结构，以探索一般的一系列B2化合物以及TiAl的趋势。正确使用的电势可预测这些化合物组成紊乱的适当机制。利用这些电势，研究了FeAl，NiAl和CoAl三种B2化合物的点缺陷，自由表面能和相似能的各种晶界结构。这些B2合金分别显示出增加的反相边界能。选择用于详细研究的取向错误对应于Σ5（310）和Σ5（210）边界。考虑到局部化学成分的可能变化，研究了这些边界。还考虑了边界化学计量和体化学计量对晶界能量的影响。计算化学计量和非化学计量体积中包含的边界的缺陷能。还计算了这些铝化物的表面能，以便可以研究有关边界内聚能的趋势。还讨论了化学计量的含义，边界结构的多样性以及它们之间的可能转变对晶界脆性的影响。

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  • 作者

    Mutasa, Batsirai Manyara.;

  • 作者单位

    Virginia Polytechnic Institute and State University.;

  • 授予单位 Virginia Polytechnic Institute and State University.;
  • 学科 Engineering Materials Science.; Engineering Metallurgy.
  • 学位 Ph.D.
  • 年度 1997
  • 页码 133 p.
  • 总页数 133
  • 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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