Microstructure simulation of solidification in the weld

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As a flexible and contactless joining process, laser beam welding is becoming increasingly important. However, the processing of alloys with a large melting interval is a challenge, due to their solidification cracking tendency. Solidification cracks form due to critical stress and strain states of the dendritic microstructure with interdendritic melt. Despite the high industrial relevance, there have so far only been approaches that address sub-aspects of this problem - metallurgically or structurally. The research group "Solidification Cracks in Laser Beam Welding: High-Performance Computing for High-Performance Processes" aims to develop a quantitative process understanding of the mechanisms involved in the formation of solidification cracks and the connection with process parameters.Within the research group, the objective of this subproject is to determine the criteria and influencing factors of microstructural solidification crack formation, in order to be able to make reliable predictions about the solidification and segregation behaviour and the probability of solidification and segregation crack formation in metallic welds, under different process conditions. The research work lies in the modelling and simulation of the solidification process in a weld on austenitic stainless steel, with the solution of microstructural processes and the consideration of strongly coupled interactions of chemo-thermomechanical processes. In coupled phase field mechanical simulations, the different solidification stages of the primary dendrites, the dendrite blocking, the grain boundary formation and the complete solidification are calculated and the formation of possible microcracks, resulting from local stress peaks, is predicted. The chemomechanical simulations provide the concentration distributions, phase distributions and stress distributions and, in the future, will also provide the microcrack distributions during the solidification and segregation processes, while dissolving the microstructural structure and considering the local temperature distribution. In systematic studies, both process-related variables, such as the temperature gradient, the welding speed and the heat input, are varied and the influence on the susceptibility to crack formation at the dendritic, grain and phase boundaries in the heat-affected zone and in the melting range is analysed and finally passed on to the mesoscale, including the morphological information. The findings of the simulations on the microscale contribute to the classification of the metallurgically or mechanically induced hot crack formation on the mesoscale and are indispensable for further investigations within the research group.