Lamellar Fe-Al in situ composite materials: microstructure and mechanical properties

几十年来，Al含量高达50at.%的Fe-Al合金引起了科学界和工业界的潜在兴趣，因为它们在无序的体心立方结构的铁以及有序的金属间化合物D03和B2中对Al具有很大的溶解度。之所以引起人们的兴趣，是因为它们固有的高耐腐蚀性和抗氧化性，以及与钢相比的比重优势。作为缺点，中等的高温强度和较低的室温延展性限制了它们的应用能力。在更高的Al浓度超过50at.%(和更低的有利密度)时，存在一些金属间化合物，到目前为止还没有准确地确定稳定范围。特别是，在非常接近61at.%的浓度下，在1095°C非常快速的共析反应产生了由FeAl和FeAl2组成的非常细小的片层组织。这一调查结果是第一期资金的一个重要结果，并已在该项目内公布。提交的延续提案的主要目标是详细描述和模拟全片层FeAl-FeAl2基合金的蠕变行为，这些合金虽然微观结构不稳定，但具有优异的抗蠕变性能。因此，我们将集中讨论蠕变速率与诸如片层间距、片层相对于加载轴的取向以及片层集落大小等参数的复杂交互作用。为了表征这些微观结构参数的影响，必须了解材料内部的作用机制。因此，我们将利用我们对共析反应性质的知识，在一个菌落内研究具有特殊排列的片层的样品，该反应遵循严格的、实验推导的和结晶学上可理解的取向关系。这一知识也是在这一建议的前身框架内建立和发表的，使这一反应对定向(凝固和)转变方法的应用具有吸引力，并在蠕变抗力方面有进一步的潜在好处。这将最终导致能够描述基于单个片层团的全片层Fe-61Al合金的取向相关蠕变行为。为了实现这一目标，所选择的建模方法将包含所有相关的微观结构机制，从而不仅可以根据现有的实验蠕变曲线确定作用的蠕变机制，还可以预测在不同温度和应力状态下的蠕变响应，这是迄今为止实验尚未研究过的。

Since decades Fe-Al alloys with up to 50 at.% Al are potentially interesting for the scientific and industrial community, as they possess a large solubility for Al in the disordered bcc crystal structure of iron as well as in the ordered intermetallic compounds D03 and B2. The interest stems from their intrinsically high corrosion and oxidation resistances as well as from the specific weight advantage as compared to e.g. steel. As a drawback, moderate high temperature strength and low room temperature ductility limit their application capabilities. At even higher Al concentrations beyond 50 at.% (and even lower advantageous densities) several intermetallic compounds exist with so far not precisely determined stability ranges. In particular, at concentration very close to 61 at.% an very rapid eutectoid reaction at 1095°C yields an extremely fine lamellar microstructure consisting of FeAl and FeAl2. This finding was one essential result of the first period of funding and already published within this project. The major goal of the submitted continuation proposal focuses on the detailed characterization and modelling of the creep behaviour of fully lamellar FeAl-FeAl2-based alloys which exhibit excellent creep resistances albeit being microstructural instable. Therefore, we will concentrate on the complex interaction of creep rate with parameters such as lamellar spacing, lamellar orientation with respect to the loading axis as well as size of lamellar colonies. In order to characterize the impact of these microstructural parameters, it is mandatory to understand the mechanisms acting within the material. Samples will thus be investigated with specially aligned lamellae within one colony using our knowledge about the nature of the eutectoid reaction which follows a strict, experimentally derived and crystallographically understandable orientation relation. This knowledge was also established and published within the frame of the predecessor of this proposal and makes this reaction attractive for the application of the method of directional (solidification and) transformation with a further potential benefit in creep resistance. This will eventually lead to being able to describe the orientation dependent creep behaviour of fully lamellar Fe-61Al alloy based on a single lamellar colony. To aid this goal, the modelling approach chosen will incorporate all relevant microstructural mechanisms and thus serve to determine not only the acting creep mechanisms based on existing experimental creep curves but also provide the capability to predict creep response at different temperature and stress regimes not investigated by experiment so far.