The formation of coherent precipitates is often accompanied by large elastic mismatch stresses, which suppress phase separation. We discuss the presence of interfaces as a mechanism for stress relaxation, which can lead to preferred zones of precipitation. In particular, we discuss the proximity of free surfaces and shear-coupled grain boundaries, for which we can obtain a substantial local energy reduction and predict the influence on the local precipitation thermodynamics. The latter case is accompanied by morphological changes of the grain boundary, which are less suitable for large-scale descriptions. For that purpose, we develop an effective description through an elastic softening inside the grain boundary and map the microscopic grain boundary relaxation to a mesoscopic elastic and phase field model, which also allows generalizing the description to multi-phase situations.

We revisit recent findings on experimental and modeling investigations of bainitic transformations under the influence of external stresses and pre-strain during the press hardening process. Experimentally, the transformation kinetics in 22MnB5 under various tensile stresses are studied both on the macroscopic and microstructural level. In the bainitic microstructure, the variant selection effect is analyzed with an optimized prior-austenite grain reconstruction technique. The resulting observations are expressed phenomenologically using a autocatalytic transformation model, which serves for further scale bridging descriptions of the underlying thermo-chemo-mechanical coupling processes during the bainitic transformation. Using analyses of orientation relationships, thermodynamically consistent and nondiagonal phase field models are developed, which are supported by ab initio generated mechanical parameters. Applications are related to the microstructure evolution on the sheaf, subunit, precipitate and grain boundary level.

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For process monitoring and quality assurance of case-hardened components, the determination of the case-hardening depth in the manufacturing process after hardening of the subsurface layer is a quality verification that is often required in industry. Currently, these quality assurance tests can only be realized with destructive measures. During case-hardening, the essential microstructural formation, and thus the key component properties are developed during the heat treatment in the cooling section. The testing technique used in the present study is based on the analysis of harmonic signals of eddy current testing. The aim of this project was to achieve an early identification of incorrect cooling processes in the case of a known transformation behaviour of the components during cooling. The data collected in the industrial hardening process show that an evaluation of the carburizing process on the basis of the case-hardening depth can be carried out non-destructively during component cooling and in the cooled state with the use of eddy current technology.