Electronic structure based design of thermal shock resistant nanolaminates

当材料经受温度的快速变化时，会发生热冲击，导致工程部件内的热应力积聚，并最终导致其损坏和故障。尽管这在许多工程应用中出现，但关于这些材料的基于知识的设计的基础研究仍处于起步阶段。耐热冲击性可以通过热冲击参数来描述，热冲击参数包括弯曲强度、热导率、泊松比、线性热膨胀系数和弹性（杨氏）模量。为了提高抗热震性，必须使热冲击参数最大化，但这是非常具有挑战性的，因为这些特性通常是相互关联的，并且有各种外在因素影响它们。使用相关的实验和理论研究策略，我们试图建立热冲击参数，化学成分，和外在因素的Ti 2AlC，Zr 2AlC，Zr 3AlC 2，和Ta 4AlC 3之间的因果关系。因此，我们系统地研究了价电子浓度（来自IVB和VB族的过渡金属），尺寸效应（Ti 2AlC与Zr 2AlC）和堆叠顺序（Zr 2AlC和Zr 3AlC 2中的Zr-C和Al层的不同数量）对热震参数的影响。在这个项目中要研究的外在因素是晶粒尺寸，应力和大气暴露。我们将使用薄膜合成来探索化学变化对这些热机械性能的影响。施加衬底偏压和不同的衬底温度，成分的影响将从微观结构解耦。由于残余应力与热应力分量竞争，因此将获得残余应力数据，因为它们对于抗热震材料非常重要。我们将研究排气温度（以及相关的大气暴露引起的成分变化）对热机械性能的影响。这从来没有尝试过抗热震材料，但在一般情况下，修改表面化学的环境涂层相互作用是必不可少的理解的性能。所有的实验都将伴随着密度泛函理论的研究，旨在更深入地了解电子结构水平上建立的实验因果关系。所有理论数据将通过实验进行验证。几个开创性的步骤，如计算的线性热膨胀系数的Debye-Grüneisen理论内的这些阶段，这些低对称性系统的电子和声子水平上的热导率，并明确考虑的外在因素以及温度。本研究所得到的基本因果关系，可望为今后抗热震材料的量子力学设计提供坚实的基础。

Thermal shock occurs when materials are subjected to rapid changes in temperature, leading to thermal stress buildup within an engineering component and eventually to its damage and failure. Even though this arises in many engineering applications, fundamental studies regarding the knowledge based design of these materials is at infancy. The thermal shock resistance can be described by the thermal shock parameter, containing flexural strength, thermal conductivity, Poisson’s ratio, linear coefficient of thermal expansion, and elastic (Young’s) modulus. To increase the thermal shock resistance, the thermal shock parameter must be maximized, but this is very challenging as these properties are often interconnected and there are various extrinsic factors affecting them. Using a correlative experimental and theoretical research strategy, we seek to establish the causalities between thermal shock parameter, chemical composition, and extrinsic factors for Ti2AlC, Zr2AlC, Zr3AlC2, and Ta4AlC3. Hence, we systematically investigate the influence of valence electron concentration (transition metals from IVB and VB groups), size effects (Ti2AlC vs. Zr2AlC), and stacking sequence (different amount of Zr-C and Al layers in Zr2AlC and Zr3AlC2) on thermal shock parameter. The extrinsic factors to be investigated in this project are grain size, stress, and atmosphere exposure. We will use thin film synthesis to explore the chemical variation influence on these thermomechanical properties. Applying a substrate bias potential and different substrate temperatures, the compositional influence will be decoupled from microstructure. The residual stress data will be acquired as they are of importance for thermal shock resistant materials since the residual stress competes with the thermal stress components. We will investigate the effect of venting temperature (and the associated atmosphere exposure induced changes in composition) on the thermomechanical properties. This has never been attempted for thermal shock resistant materials, but in general ambient-coating interactions modifying the surface chemistry are essential for understanding the performance. All experiments will be accompanied by density functional theory investigations, aiming at deeper understanding of the established experimental causalities on the electronic structure level. All theoretical data will be validated experimentally. Several pioneering steps will be made, such as calculation of the linear coefficient of thermal expansion for these phases within the Debye-Grüneisen theory, the thermal conductivity on the electronic and phonon level for these low symmetry systems, and explicit consideration of the extrinsic factors as well as temperature. With the fundamental causalities obtained in this project, it is expected that a solid basis will be obtained for future quantum mechanical design of thermal shock resistant materials.