Unravelling the mechanism of DBTT in chromium alloys via correlative microscopy: from atoms to dislocations

• Applicant: Dr. Subin Lee
• Subject Area: Mechanical Properties of Metallic Materials and their Microstructural Origins
• Term: since 2025
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 566981050

Gas turbines play a critical role in aerospace and power generation, driving continuous efforts to enhance efficiency, reduce CO₂ emissions, and extend the lifespan of key components. Ni-based superalloys, the dominant material for turbine blades, provide excellent mechanical properties at high temperatures due to their unique gamma/gamma prime microstructure. However, their relatively low melting point limits further temperature increases. To push operational limits beyond current Ni-based superalloys, alternative material systems with higher temperature stability are required. Chromium (Cr) alloys, with a melting point of approximately 1900 C, present a promising alternative due to their superior thermal stability, oxidation resistance, and lower density, which can improve turbine efficiency. However, their widespread application is hindered by an intrinsically high ductile-to-brittle transition temperature (DBTT), leading to room-temperature brittleness and limiting their structural reliability. While approaches such as microstructural refinement, alloying for example with rhenium (Re), and impurity control have demonstrated some success in reducing DBTT, the fundamental mechanisms governing Cr’s brittleness remain poorly understood. Key aspects, including solute interactions, dislocation behavior, and segregation effects, require in-depth investigation at the micro/nanoscale. This project aims to establish a fundamental understanding of the limited room-temperature ductility in Cr alloys through correlative defect analysis, micromechanical testing and advanced chemical characterization at the (sub)nanometer scale. The approach includes: Localized micro-mechanical testing coupled with quantitative defect analysis via controlled electron channeling contrast (ECCI), to assess dislocation behavior and plasticity. Site-specific segregation analysis using APT combined with ECCI, enabling nanoscale chemical insights at defect sites. Micromechanical testing at wide range of temperature cryogenic to the elevated temperature. In situ TEM deformation experiments, revealing dislocation glide mechanisms in real-time. A unique aspect of this study is the precise correlation between microstructural features and chemical segregation using controlled ECCI-supported APT sampling. This will enable a comprehensive understanding of how crystalline defects, solute interactions, and grain boundary effects contribute to Cr’s high DBTT. The insights gained will be directly applicable to alloy design strategies and modelling efforts, including dislocation core simulations via density functional theory or dislocation dynamics simulations. By bridging the gap between defect structure, mechanical performance and elemental segregation at nanoscale, this project will provide essential knowledge to enhance Cr alloys’ room temperature ductility and unlock their potential as next-generation high-temperature materials for gas turbine applications.

• DFG Programme: Research Grants
• International Connection: South Korea
• Partner Organisation: National Research Foundation of Korea, NRF
• Cooperation Partner: Professor Dr.-Ing. Pyuck-Pa Choi