Prediction of the temperature-dependent cracking behavior of CrAlN-coated high-speed steels for warm forming tools

• Applicants: Professorin Dr.-Ing. Kirsten Bobzin; Professor Dr.-Ing. Christoph Broeckmann
• Subject Area: Coating and Surface Technology ; Primary Shaping and Reshaping Technology, Additive Manufacturing
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 567806430

Warm forming tools are subjected to high cyclic thermomechanical stresses, which may lead to micro- and consequently macro-scale crack growth on the tool surface. This can significantly limit the tool service life. The cracking behavior of warm forming tools with physical vapor deposition (PVD) coatings is not sufficiently understood. Current investigations mostly focus on the effect of elastic-plastic properties as well as the architecture and residual stress state of the coating on deformation behavior and crack susceptibility of the compounds under monotonic loading at room temperature. The coating and substrate dependent factors, that may significantly influence crack formation in compounds under monotonic and cyclic loads at higher temperatures, have not been thoroughly investigated with microstructure consideration and fully identified with experiments or simulations. The main goal of the research project is development of a knowledge-based approach to increase the crack resistance of CrAlN-coated plasma-nitrided high-speed steels for warm forming tools. For this purpose, micromechanical models, for description of crack growth in compounds under thermomechanical loading, will be realized. At the start, CrAlN coatings with CrAl interlayer, with varying coating thickness, will be deposited on high-speed steel PM HS6-5-3C with and without plasma nitriding. Subsequently, the microstructure of the compound boundary zone will be characterized and thermomechanical properties of the coating, substrate and compound will be determined. The meso-scale modeling of the compounds will be carried out using representative volume elements (RVE) approach and the results from the compound characterization. The deformation behavior of the compounds as well as of the uncoated substrates will be characterized by instrumented indentation tests with monotonic and cyclic loading at higher temperatures. The cracking behavior will be investigated through in-depth electron microscopy analysis of the indent imprints. In order to realize micromechanical simulations based on RVE models, a fully coupled thermomechanical modeling approach and measurement data from indentation tests will be used. The simulative predictions of integral damage in the compounds due to the thermomechanical loading will be experimentally validated. Finally, meso-scale microstructural parameters as well as macro-scale parameters like coating thickness of the compound will be systematically varied in the validated simulation models. The influence of the varied parameters on temperature-dependent deformation and cracking behavior of the compound will be determined through sensitivity analysis. The findings from experimental investigations as well as the simulation models will enable the formulation of the knowledge-based approach to increase the temperature-dependent crack resistance of the compounds.

• DFG Programme: Research Grants