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

由热激活和/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，对于设计新的合金和相应的热机械加工路线具有很高的相关性。除了直接的相互作用，如塑性变形过程中耗散引起的温度升高，进而导致材料的软化，还会发生进一步的间接耦合现象。在金属材料的背景下，这种进一步的现象包括再结晶、晶粒粗化、相变和析出形成。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强烈的热-化学-机械耦合现象进行热力学上的一致建模和模拟。具体地说，这一建议的目的是建立热力学上一致的模型，用于描述钢中位错基塑性、回复、再结晶、晶粒粗化、基质相转变和第二相析出物形成之间的复杂耦合。在正在进行的第一个资助期内，Dierk Raabe和Dirk Helm两个小组进行了卓有成效的合作，建立了一个基本的热力学框架，并开发了描述金属中热-化学-机械耦合过程的热力学一致性模型。更具体地说，建立并实现了描述塑性、回复、再结晶、晶粒粗化和析出相演化之间相互关系的空间分辨模型和平均场模型。在第二阶段，我们的目标是改进本构模型，并考虑其他效应，如铁素体和奥氏体之间的相变和更复杂的析出物的形成，这些对钢的应用是重要的。正如第一阶段所表明的那样，模型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现场实验，绘制所考虑的模型材料在高空间分辨率下的高温过程中的微观结构演变，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。这些具有挑战性的问题之一是根据材料的热-化学-机械状态制定再结晶的形核标准。

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.