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

几十年来，Fe-Al合金高达50 at。Al在无序的铁晶体结构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，因此对科学界和工业界具有潜在的兴趣。这种兴趣源于其固有的高耐腐蚀性和抗氧化性，以及与钢铁相比的重量优势。其缺点是高温强度适中，室温延展性低，限制了其应用能力。甚至更高的铝浓度超过50at。%（甚至更低的有利密度）存在几种金属间化合物，其稳定范围迄今尚未精确确定。特别是当浓度接近61at时。在1095℃下快速共晶反应，得到由FeAl和FeAl2组成的极细层状微观结构。这一发现是第一阶段资助的一个重要结果，并已在本项目中发表。提交的续篇提案的主要目标集中在详细表征和模拟全层状feal - feal2基合金的蠕变行为，该合金具有优异的抗蠕变性能，尽管微观结构不稳定。因此，我们将集中研究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相互作用。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了解来研究样品，这些共析反应遵循严格的、实验推导的和晶体学上可理解的取向关系。这一知识也在本提案的前身框架内建立和发表，并使该反应对定向（凝固和）转化方法的应用具有吸引力，并在抗蠕变方面具有进一步的潜在优势。这将最终导致能够描述基于单一层状群体的全层状Fe-61Al合金的取向依赖蠕变行为。为了实现这一目标，所选择的建模方法将纳入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，还可以提供在不同温度和应力下预测蠕变响应的能力。

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.