Multiscale thermodynamics: From the atomic world to the real life application, how to get it all?

在现代社会，铝合金、镍高温合金和钢等金属材料被广泛应用于各种高性能应用中：它们用于汽车、飞机、桥梁和发动机。根据应用的不同，它们的高比机械性能、它们在使用中的潜在耐高温性能或它们对高腐蚀性环境的耐受性可能是它们比其他材料更受欢迎的几个原因之一。大多数金属和合金的高回收潜力也是选择理想材料时要考虑的一个重要方面，特别是在航空航天和汽车行业，金属合金与复合材料竞争。有几种加工方法来加工金属合金，并将其转化为金属产品，如梁、螺栓、框架、轴和链轮。绝大多数金属材料都会在其使用寿命内发生演变。有些材料会发生腐蚀，其表面成分会发生变化；有些材料会经历纳米颗粒的动态沉淀并硬化；而另一些材料会在高温的影响下看到其本体微结构的演变。所有这些现象的驱动力都与物质的实际状态和平衡状态之间的自由能差有关。事实上，只要平衡条件不变，达到平衡状态的物质就不应该再演化。因此，通常使用松弛金属材料的热处理来确保它们在使用中的稳定性。正如这里所强调的，材料的微观结构将调节其热物理性能。能够预测材料的初始微结构以及其在使用过程中的演变是科学家和工程师试图从数值模拟中获得的两个基本方面。所有现有的模拟材料微观结构演化的数值方法都需要一个关键因素，那就是热力学驱动力的精确评估。这项研究计划旨在提供下一代金属固溶体热力学模型，该模型将考虑所有基本的能量贡献，即原子振动、每个原子周围的化学环境和每个相互作用的化学性质，并定义溶液的自由能。因此，能够预测主相的晶格参数、局部晶格扭曲、储存的弹性能、热膨胀、表面能以及电子和光学性质的高度预测的热力学模型将被集成在用于预测金属材料微观结构演变的复杂方法中。这将为科学家和工程师设计新的高性能金属材料提供新的机会。

Metallic materials such as aluminum alloys, nickel super-alloys and steel are used in a panoply of high performance applications in our modern societies: they are used in cars, in aircrafts, in bridges, in engines. Depending on the application, their high specific mechanical properties, their potential resistance to high temperature in service or their resistance to highly corrosive environment might be one of the several reasons why they are preferred to other materials. The high recycling potential of most metals and alloys is also an important aspect to consider when choosing the ideal material, especially in the aerospace and automotive industries where metallic alloys compete with composite materials.There exist several processing routes to elaborate metallic alloys and as many to transform them into metallic products such as beams, bolts, frames, shafts and sprockets. The vast majority of the metallic materials will evolve during their useful life. Some materials will corrode and their surface composition will change; some materials will experience dynamic precipitation of nanoparticles and will harden; while some other will see their bulk microstructure evolves by the effect of high temperatures. The driving force for all these phenomena is linked to the free energy difference between the actual state of a material and its equilibrium state. In fact, a material that reached its equilibrium state should not evolve anymore as long as the equilibrium conditions are not changed. For that reason heat treatments that relax metallic materials are typically used to ensure their stability in service.As highlighted here, the microstructure of a material will modulate its thermo-physical properties. Being able to predict the initial microstructure of a material as well as its evolution in service are two fundamental aspects scientists and engineers are trying to obtain from numerical simulations. All the available numerical approaches that model the microstructural evolution of materials require a key ingredient which is the precise evaluation of the thermodynamic driving force.This research program is intended to provide the next generation of thermodynamic models of metallic solid solutions that will account for all the fundamental energetic contributions that are the atomic vibration, the chemical environment surrounding each atom and the chemical nature of each interaction into the definition of the free energy of a solution. As a result, highly predictive thermodynamic models able to predict the lattice parameter of a primary phase, local lattice distortions, stored elastic energy, thermal expansion, surface energies as well as electronic and optic properties will be integrated in complex approaches used to predict the microstructural evolution of metallic materials. This will open new opportunities for scientists and engineers to design new highly performant metallic materials.