Two Contributions to Advancing Superalloy Research at Superalloys 2024 and one poster award
In collaboration with WW1 and Ruhr-Universität Bochum, the Institute of Micro and Nanostructure Research (IMN)/CENEM is proud to announce two paper contributions to the 15th International Symposium on Superalloys, taking place from September 8th-12th, 2024, in Seven Springs, Pennsylvania (USA). Both contributions focus on improving our understanding of stacking faults, a key feature in the high-temperature deformation of superalloys.
One of them was even awarded a poster price: IMN/CENEM researcher Nicolas Karpstein received one of only two Best Interactive Presentation Awards for his poster presentation on the topic “Temperature and Time Dependence of Elemental Segregation at Stacking Faults in Ni- and Co-base Superalloys”. We congratulate Nicolas for this outstanding achievment!
Both contributions are explained in the following in more detail:
The first contribution addresses analyzing stacking fault structures in the L1₂-ordered γ′ phase through high-resolution Scanning Transmission Electron Microscopy (STEM). Traditionally, such analyses are performed in the [110] projection, which allows for distinguishing between intrinsic and extrinsic stacking faults and determining the projected Burgers vectors of dislocations. However, this projection alone cannot reliably identify whether a stacking fault is complex or not, which is a crucial factor in understanding deformation mechanisms, including atomic-scale reordering processes.
To overcome this limitation, our team developed a method to tilt the fault structure by 30° into a neighboring [211] projection, enabling the identification of complex faults and the precise determination of Burgers vectors. We demonstrated the effectiveness of this approach through two key examples:
- Experimental verification of the Kolbe mechanism for SESF formation in a Co-base superalloy.
- Microscopic insights into the shear-based phase transformation from the γ′ phase to the χ phase, commonly observed in Co-base superalloys within the Co-Al-W ternary system.
This new method promises to enhance our understanding of deformation at the microscopic scale in superalloys and other materials.
The second contribution explores the elemental segregation at stacking faults in the γ′ phase of superalloys, a process that can significantly influence the mechanical behavior of the alloy. This segregation can either degrade or improve the alloy’s mechanical properties depending on the local composition at the fault. Our study investigates the time and temperature dependence of elemental segregation at extrinsic stacking faults in both Ni-base and Co-base superalloys. We measured fault compositions immediately after deformation and after additional load-free annealing at various temperatures and durations.
Key findings from this study include:
- Elemental segregation is dynamic and continues to evolve after fault formation.
- Lower temperatures promote a more γ-like fault composition, which weakens the alloy, while higher temperatures promote an η-like composition, which strengthens it through a process known as “local phase transformation strengthening.”
These insights could be instrumental in further optimizing superalloy compositions and heat treatment processes for enhanced performance.
Both contributions were presented at the Superalloys 2024 conference and have been published in the conference proceedings. They can be accessed via the following links:
The papers will soon be available via the Superalloys Proceedings Archive on the TMS website: Superalloys Proceedings Archive