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

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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.