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

体心立方（BCC）难熔高熵合金（HEAs）由于其优异的强度、优异的热稳定性和即使在高温下也能抗氧化等优点，已被研究作为高温应用的新型金属体系。迄今为止，难熔HEAs领域的研究重点一直是对所得微观结构的开发和评价。然而，单相BCC HEAs的固有变形机制仍存在争议。例如，平均场溶质强化模型严重低估了单相BCC 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，BCC HEAs的力学行为取决于内部性能，如化学成分、微观结构、缺陷与不同微观结构组分的相互作用，以及外部参数，如温度和应变速率。该项目旨在确定单相BCC HEAs的固有变形机制，并表征其在变形下的化学/微观结构稳定性，以预测其在室温和700K高温状态下的结构完整性。采用原子模拟方法和先进的温度相关纳米和微观力学实验相结合的协同方法，确定了变形动力学和位错滑移系统，并将其与宏观上具有延展性的Ta-Nb-Hf-Zr-Ti HEA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。力学测试由多尺度和扩展的空间分辨微观结构和化学分析补充。电子结构计算利用特殊的准随机结构模拟显式无序HEAs，并提供对材料参数（如理想剪切强度和广义层错能）的内在波动的化学精确预测。在模拟信息位错理论的基础上，确定了可能的滑移系统和相应的螺/边位错各向异性。建立了一种动力学蒙特卡罗方法来阐明变形过程中元素的特定偏析趋势。模拟和实验相结合的分析将允许为单相BCC HEAs在室温下的变形过程制定一个可验证的现象学模型。

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.