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

• Applicants: Dr.-Ing. Dirk Helm; Professor Dr.-Ing. Dierk Raabe
• Subject Area: Thermodynamics and Kinetics as well as Properties of Phases and Microstructure of Materials ; Mechanics
• Term: from 2014 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 257204851

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.

• DFG Programme: Priority Programmes
• Subproject of: SPP 1713: Strong Coupling of Thermo-Chemical and Thermo-Mechanical States in Applied Materials
• International Connection: Austria, Czech Republic, USA
• Cooperation Partners: Professor Dr. Ernst Kozeschnik; Professor Dr. Ricardo Anibal Lebensohn; Dr. Jiri Svoboda