Analysis of the Stability of High Entropy Alloys by Dewetting of Thin Films

高熵合金（HEAs）是一类新型材料，具有实现传统合金无法实现的机械，电气和热性能的卓越组合的潜力。它们含有大约等量的至少五种元素，并且可以令人惊讶地结晶为单一的fcc或bcc固溶体。更好地了解这些材料的冶金和物理行为是了解其性能组合的先决条件。最终，它将促进可靠的HEA薄膜的开发，用于创新技术驱动器，如微电子工业和散装HEA。由于HEA稳定性强烈依赖于材料缺陷，一个专家联盟将通过系统地操纵1D和2D缺陷来解决HEA薄膜的相稳定性。膜中的缺陷密度将通过以下方式来控制：（i）纳米/微米级变形以在位错密度中引入梯度，（ii）通过采用非晶和单晶衬底来改变界面结构，以及（iii）改变膜生长和处理条件以操纵晶粒尺寸。法德联合团队融合了四个互补合作伙伴在材料科学不同领域的公认专业知识（组合薄膜合成，微观结构物理，热力学和材料力学）研究HEA薄膜的以下基本问题：（i）HEA相稳定性，（ii）相演变和相应的动力学，包括组成、缺陷和/或热稳定性的影响。（iii）晶粒生长和织构，（iv）去湿动力学和形态，（v）温度和微观结构应力演变，（vi）塑性变形，（vii）热机械疲劳机制和寿命。AHEAD将重点关注bcc-AlCrFeCoNi和fcc-MnCrFeCoNi薄膜，作为两种不同晶体结构的通用示例。薄膜合成是一个关键问题，将由一个合作伙伴通过组合沉积进行。其他三个合作伙伴将解决控制HEA薄膜在等温和循环热机械退火过程中的相，微观结构和形态稳定性的机制，作为其厚度，成分和缺陷结构的函数。先进的实验工具-从组合薄膜沉积和高通量表征到多尺度定量微结构分析和小型化机械技术-将与四个合作伙伴的互补专业知识相结合，首次提供关于热力学，机械，两种HEA薄膜的微观结构和形态稳定性。在AHEAD项目中，2名博士生和2名博士后将受益于多学科的工作条件和国际交流。

High-Entropy Alloys (HEAs) are a new class of materials, with the potential to realize exceptional combinations of mechanical, electrical and thermal properties unachievable by conventional alloys. They contain about equal amounts of at least five elements, and can surprisingly crystallize as single fcc or bcc solid solutions. A better knowledge of the metallurgical and physical behavior of those materials is a prerequisite to understand their property combinations. Eventually it will foster the development of reliable HEA thin films for innovative technology drivers such as the microelectronic industry, and of bulk HEAs. Since HEA stability is suggested to depend strongly on material defects, a consortium of experts will address HEA thin film phase stability by systematically manipulating 1D and 2D defects. The defect density in the films will be controlled by (i) nano-/microscale deformation to introduce gradients in the dislocation density, (ii) altering the interface structure by employing amorphous and single crystalline substrates and (iii) varying film growth and processing conditions to manipulate the grain size. The joint French-German team merges the recognized expertise in different fields of materials science of four complementary partners (combinatorial thin film synthesis, microstructure physics, thermodynamics and mechanics of materials) to investigate the following fundamental issues on HEA films: (i) HEA phase stability, (ii) phase evolution and corresponding kinetics including influence of composition, defects (dislocations, interfaces, grain boundaries) and dimensional constraints (film thickness, patterning) on phase stability, (iii) grain growth and texture, (iv) dewetting kinetics and morphologies, (v) temperature and microstructure-stress evolution, (vi) plastic deformation, (vii) thermo-mechanical fatigue mechanisms and lifetimes. AHEAD will focus on thin films of bcc-AlCrFeCoNi and fcc-MnCrFeCoNi as generic examples for two different crystal structures. Film synthesis, a key issue, will be performed by combinatorial deposition by one partner. The three other partners will address the mechanisms controlling the phase, microstructure and morphological stability of the HEA films during isothermal and cyclic thermo-mechanical annealing as a function of their thickness, composition and defect structure. Advanced experimental tools - from combinatorial thin film deposition and high-throughput characterization to multiscale quantitative microstructure analysis and miniaturized mechanical techniques - will be used and combined with the complementary expertise of the four partners, to provide for the first time a large and consistent data set on the thermodynamic, mechanical, microstructural and morphological stabilities of two types of HEA films.Within the AHEAD project, 2 PhD students and 2 postdoctoral fellows will benefit from a multidisciplinary working conditions, and international exchanges.