Incipient Oxidation and Deformation Mechanisms of the Complex Concentrated Alloy AlMo0.5NbTa0.5TiZr in the High Temperature Regime

在过去的十年里，被称为复杂的浓缩或成分复杂的合金(CCA)的分支有了迅速的发展。这些合金在成分超空间中含有高度集中的全部或大部分存在的成分。CCAS具有在腐蚀性环境下表现出降低的扩散速度的潜力，以及如果机械加载则表现出更强的硬化行为的潜力，这是由于其组件的强烈的原子相互作用。因此，在高温承重应用范围内对更强的抗氧化材料的需求为开发基于耐火元素(RCCA)的CCA打开了窗口。虽然RCCA通常具有脆性的室温行为，但最近开发的AlMo0.5NbTa0.5TiZr合金显示出比大多数同等的商业镍基高温合金提高两倍的压缩强度，同时仍保持10%的断裂伸长率。与商业合金相比，AlMo0.5NbTa0.5TiZr RCCA的抗压强度和延性均保持在1200°C以下。尽管AlMo0.5NbTa0.5TiZr RCCA具有理想的低密度(=7.4g/cm3)和在侵蚀性环境下形成保护性氧化铝层的潜力，但压缩测试仍然是迄今为止评估的唯一性能。本项目旨在增进对AlMo0.5NbTa0.5TiZr RCCA在与高温应用领域相关的化学和机械载荷条件下的响应的了解。更具体地说，它旨在研究1)在氧化环境中和2)在机械载荷下发生的初始高温损伤机制。因此，将研究以燃气轮机工业为代表的受控气氛下氧化的早期阶段，即潮湿空气，以及在蠕变和高温拉伸下发现的变形机制。为了解决这些条件下的显微组织发展问题，将采用多种表征方法，如高温氧化过程中的原位X射线衍射、残余应力分析，以及利用自主开发的STEM立体程序对晶体缺陷进行三维观察和重建。

The branch known as complex concentrated ‒or compositionally complex‒ alloys (CCAs) has seen a rapid development within the last ten years. These alloys contain high concentrations of all ‒or most‒ present constituents in the compositional hyperspace. CCAs have the potential for showing reduced diffusion velocities under corrosive environments, as well as an increased hardening behavior if mechanically loaded, due to the strong atomic interaction of its components. Thus, the need for stronger oxidation resistant materials in the range of high temperature load-bearing applications has opened a window for developing CCAs based on refractory elements (rCCAs). While rCCAs are usually characterized by brittle room temperature behavior, the recently developed alloy AlMo0.5NbTa0.5TiZr shows a two-fold increase of compression strengths than most equivalent commercial Ni-base superalloys, while still retaining a 10% fracture elongation. The higher compression strength and ductility of the AlMo0.5NbTa0.5TiZr rCCA are kept up to 1200°C, relative to the commercial alloys. Although coupled with a desired low density (=7.4 g/cm3) and a potential to form a protective Aluminum oxide layer under aggressive environments, compression tests remain the sole property assessed so far for the AlMo0.5NbTa0.5TiZr rCCA. The present project aims at advancing the knowledge on the response of the AlMo0.5NbTa0.5TiZr rCCA under chemical and mechanical loading conditions relevant for the high temperature realm of applications. More specifically, it is intended to study the initial high temperature damage mechanisms that occur 1) in oxidizing environments and 2) under mechanical loads. Thus, the early stages of oxidation under a controlled atmosphere representative for the gas turbine industry will be studied, i.e., humid air, as will be the deformation mechanisms found under creep and high temperature tension. In order to tackle the microstructural development under these conditions, a wide range of characterization methods will be implemented such as in-situ X-ray diffraction during high temperature oxidation, residual stress analysis, and 3D observation and reconstruction of crystalline defects by self-developed STEM stereoscopic procedures.