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

在过去的十年中，被称为复杂浓缩或成分复杂合金（CCAs）的分支得到了迅速的发展。这些合金在成分超空间中含有高浓度的全部或大部分成分。由于其成分的强原子相互作用，CCAs在腐蚀性环境下具有降低扩散速度的潜力，并且在机械载荷下具有增加的硬化行为。因此，在高温承载应用范围内对更强抗氧化材料的需求为开发基于耐火材料（rcca）的cca打开了一扇窗。虽然rCCAs通常具有脆性室温行为的特征，但最近开发的合金AlMo0.5NbTa0.5TiZr的抗压强度比大多数等效的商用ni基高温合金提高了两倍，同时仍保持10%的断裂伸长率。与工业合金相比，AlMo0.5NbTa0.5TiZr rCCA合金在1200℃时具有较高的抗压强度和塑性。尽管AlMo0.5NbTa0.5TiZr rCCA具有理想的低密度（=7.4 g/cm3）和在恶劣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。本项目旨在提高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知识。更具体地说，旨在研究1)在氧化环境和2)在机械载荷下发生的初始高温损伤机制。因此，将研究具有燃气轮机工业代表性的受控气氛下氧化的早期阶段，即潮湿空气，以及蠕变和高温张力下的变形机制。为了解决这些条件下的微观结构发展，将实施广泛的表征方法，如高温氧化时的原位x射线衍射，残余应力分析，以及通过自行开发的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.