Thermo-chemo-mechanical coupling during thermomechanical processing of microalloyed steels

由于热激活和/或机械诱导过程引起的热化学机械相互作用支配着金属合金在生产和使用过程中的本构行为。了解这些机制及其对材料行为的影响对于设计新合金和相应的热机械加工路线具有非常重要的意义。除了直接的相互作用，例如由于塑性变形期间的耗散而导致的温度升高，进而导致材料的软化，还发生了进一步的间接耦合现象。在金属材料的情况下，这种进一步的现象包括再结晶、晶粒粗化、相变和沉淀物形成。根据优先方案的要求，该项目提案的中心目标是对应用材料中的强热-化学-机械耦合现象进行化学上一致的建模和模拟。具体而言，本建议的目的是开发用于描述基于位错的塑性、回复、再结晶、晶粒粗化、基体相的转变和钢中第二相沉淀物的形成之间的复杂耦合的物理一致的模型。在正在进行的第一个资助期间，在Dierk Raabe和Dirk Helm小组之间富有成效的合作中，已经构建了一个基本的热力学框架，并开发了用于表示金属中热化学机械耦合过程的物理一致模型。更具体地说，空间分辨模型和平均场模型，都描述了塑性，恢复，再结晶，晶粒粗化和析出物的演变之间的相互关系已制定和实施。在第二阶段，我们的目标是提高本构模型，并纳入额外的影响，如铁素体和奥氏体之间的相变和更复杂的沉淀物的形成，这是重要的应用在钢。如第一阶段所示，建模工具的开发大大受益于与定义明确的实验的比较。因此，我们计划继续我们的准原位实验，以高空间分辨率在高温下绘制所考虑的模型材料的微观结构演变，以提供实验基准解决方案。最后，成熟的模型将使我们能够将它们应用于材料科学和工程中具有挑战性的问题的数值和实验研究。其中一个具有挑战性的问题是发展的成核标准的再结晶的热化学机械状态的材料的依赖。

Thermo-chemo-mechanical interactions due to thermally activated and/or mechanically induced processes govern the constitutive behaviour of metallic alloys during production and in service. Understanding these mechanisms and their influence on the material behaviour is of very high relevance for designing new alloys and corresponding thermomechanical processing routes. Besides direct mutual interactions, such as the temperature increase due to dissipation during plastic deformation, in turn leading to softening of the material, further indirect coupling phenomena take place. In the context of metallic materials, such further phenomena comprise recrystallization, grain coarsening, phase transformation and precipitate formation. According to the call of the Priority Programme, the central goal of the project proposal is the thermodynamically consistent modelling and simulation of strong thermo-chemo-mechanical coupling phenomena in applied materials. Specifically, the aim of this proposal is to develop thermodynamically consistent models for describing the complex coupling between dislocation-based plasticity, recovery, recrystallization, grain coarsening, transformations of the matrix phases and formation of second phase precipitates in steels. During the ongoing first funding period, in a fruitful collaboration between the groups of Dierk Raabe and Dirk Helm, a fundamental thermodynamic framework has been constructed and thermodynamically consistent models for representing thermo-chemo-mechanically coupled processes in metals have been developed. More specifically, a spatially resolved model and a mean-field model, both describing the interrelation between plasticity, recovery, recrystallization, grain coarsening and the evolution of precipitates have been formulated and implemented. In the second period, we aim at enhancing the constitutive models and incorporating additional effects such as phase transformation between ferrite and austenite and the formation of more complex precipitates, which are important for the application in steels. As demonstrated in the first period, the development of modelling tools benefits significantly from the comparison to well-defined experiments. We therefore plan to continue our quasi-in-situ experiments mapping the microstructure evolution of the considered model material during elevated temperatures at high spatial resolution to provide experimental benchmark solutions. Finally, maturing the models will enable us to apply them to numerical and experimental investigations of challenging questions in materials science and engineering. One of such challenging questions is the development of nucleation criteria for recrystallisation in dependence of the thermo-chemo-mechanical state of the material.