Identification of the intrinsic deformation mechanisms of single phase body-centered cubic high entropy alloys

体心立方(BCC)耐火高熵合金(HEAs)由于具有优异的强度、良好的热稳定性和高温下的抗氧化性等优点，已成为高温应用的新型金属体系。到目前为止，耐火HEA领域的研究重点一直是开发和评价所产生的微观结构。然而，单相体心立方高能效应变器的内在变形机理仍存在争议。例如，平均场溶质强化模型严重低估了体心立方单相HEAs中位错运动的临界应力，而后者的溶质强化模型与面心立方单相HEAs的实验屈服强度一致。一般来说，体心立方HEA的力学行为取决于本征性质，如化学成分、微观结构、缺陷与不同微结构成分的相互作用，以及外部参数，如温度和应变率。拟议的项目旨在确定单相体心立方HEA的内在变形机制，并表征变形下的化学/微结构稳定性，目的是预测它们在室温和700K向高温区域的过渡过程中的结构完整性。确定了变形动力学和位错滑移系统，并将其与宏观韧性的Ta-Nb-Hf-Zr-TiHEA和宏观上明显脆性的Nb-Mo-Cr-Ti-Al HEA的特征变形特征联系起来。力学试验辅之以多尺度和扩展的空间分辨显微结构和化学分析。电子结构计算使用特殊的准随机结构来模拟显式无序的HEAs，并提供了对材料参数的本征涨落的化学精确预测，例如理想剪切强度和广义层错能。根据模拟得到的位错理论，确定了可能的滑移系和相应的螺旋/刃位错各向异性。发展了一种动力学蒙特卡罗方法来解释变形过程中特定元素的偏析趋势。模拟和实验相结合的ANSATZ将允许建立一个可验证的唯象模型，用于描述单相体心立方HEAS在室温下的变形过程。

Body-centered cubic (BCC) refractory high-entropy alloys (HEAs) have been studied as novel metallic systems for high-temperature applications due to their, for example, superior strength, excellent thermal stability, and oxidation resistance even at elevated temperatures. To date, the research emphasis in the field of refractory HEAs has been upon the development and evaluation of the resulting microstructure. However, the intrinsic deformation mechanisms of the single-phase BCC HEAs are still under debate. For example, a mean field solute-strengthening model severely underestimates the critical stresses for dislocation motion in single phase BCC HEAs, whereas the later solute-strengthening model is consistent with experimental yield strengths of face-centered cubic single phase HEAs. In general, the mechanical behavior of BCC HEAs depend on intrinsic properties, such as the chemical composition, microstructures, and the interaction of defects with the different microstructural components, as well as extrinsic parameters, such as temperature, and strain rate. The proposed project aims at determining the intrinsic deformation mechanisms of single-phase BCC HEAs and at characterizing the chemical/microstructural stability under deformation with the goal to predict their structural integrity at room-temperature and in the transition to the high-temperature regime at 700K. The deformation kinetics and dislocation slip systems are determined and linked to the characteristic deformation signatures of the macroscopically ductile Ta-Nb-Hf-Zr-Ti HEA and the macroscopically apparently brittle Nb-Mo-Cr-Ti-Al HEA in the proposed synergistic approach, which combines atomistic simulation methods and advanced temperature-dependent nano and micromechanical experiments. The mechanical tests are supplemented by multiscale and extended spatially-resolved microstructural and chemical analysis. Electronic structure calculations simulate explicitly disordered HEAs using special quasi-random structure and provide a chemical accurate prediction of the intrinsic fluctuations of materials parameter, e.g., ideal shear strength and generalized stacking fault energies. The possible slip systems and the associated screw/edge dislocation anisotropies are determined on the basis of simulation-informed dislocation theory. A kinetic Monte Carlo method is developed to elucidate element-specific segregation trends during deformation. The combined simulations-and-experiment ansatz will allow to formulate a verifiable phenomenological model for the deformation processes in single-phase BCC HEAs at room-temperature.