Modeling the metastable phase formation of compositionally complex face-centered cubic Ti-V-Nb-Ta-Al-N thin films

在薄膜合成过程中，由于动力学限制，通常会得到亚稳态相，这使得其相形成的预测相当具有挑战性。最近，我们研究了AlN在面心立方（fcc） Ti1−xAlxN薄膜中的亚稳溶解度极限。在此基础上，我们提出用相关的实验和理论方法预测复合面心立方Ti-V-Nb-Ta-Al-N薄膜的亚稳相形成。多元素薄膜等高阶材料系统的使用，在某些情况下，提供了巨大的未开发的应用潜力，增强了热稳定性和优越的机械性能。我们的研究策略包括四元Ti-V-Al-N、四元Ti-V-X-Al-N （X = Nb或Ta）和四元Ti-V-Nb-Ta-Al-N薄膜的组合合成及其在组成和结构方面的实验表征。形成焓、晶格参数、弹性常数和表面和体扩散的活化能势垒将通过基于密度泛函理论的方法从头计算得到。结合实验和从头算数据作为输入，将使用CALPHAD方法获得组成复杂系统的热力学描述。这种方法——已经建立了三元氮化物——将在这些高度复杂的系统中进行严格的评估，得到TiN-VN-AlN， NbN-TiVN-AlN， TaN-TiVN-AlN和NbTaN-TiVN-AlN亚稳相形成图。我们期望这些亚稳相形成图将为未来合理指导结构复杂的面心立方薄膜材料的设计工作提供坚实的基础。

Metastable phases are commonly obtained during synthesis of thin films due to kinetically limited processes, which render the prediction of their phase formation rather challenging. Recently, the metastable solubility limits of AlN in face-centered cubic (fcc) Ti1−xAlxN thin films have been investigated by us. On this basis we propose to predict the metastable phase formation of compositionally complex face-centered cubic Ti-V-Nb-Ta-Al-N thin films using a correlative experimental and theoretical approach. Utilisation of such higher-order material systems as multi-element thin films provides, in some cases, enormous untapped application potential with respect to both, enhanced thermal stability and superior mechanical properties. Our research strategy comprises the combinatorial synthesis of thin films in the quaternary Ti-V-Al-N, quinary Ti-V-X-Al-N (X = Nb or Ta), and senary Ti-V-Nb-Ta-Al-N systems and their experimental characterization in terms of composition and structure. Enthalpies of formation, lattice parameters, elastic constants, and activation energy barriers for surface and bulk diffusion will be obtained from ab initio calculations for various compositions using density functional theory-based methods. Incorporating the experimental and ab initio data as input, thermodynamic descriptions of compositionally complex systems will be obtained using the CALPHAD approach. This methodology – already established for ternary nitrides – will be critically appraised for these highly complex systems, yielding TiN-VN-AlN, NbN-TiVN-AlN, TaN-TiVN-AlN, and NbTaN-TiVN-AlN metastable phase formation diagrams. We expect that these metastable phase formation diagrams will provide a solid basis for future rationally-guided design efforts for compositionally complex, face-centered cubic thin film materials.