Abstract
FeCr based steels, widely deployed for various industrial applications, are prone to embrittlement from Cr-rich alpha prime (α’) precipitation. However, experimental α/α + α’ phase boundary assessments at low-to-intermediate temperatures are challenging due to slow Cr diffusivity below 450 °C, and existing CALPHAD predictions are inaccurate. To overcome these limitations, proton irradiations were used to enhance diffusion in Fe-(5–18)%Cr at 250–450 °C, and thermal aging was performed at 450–500 °C for up to one year. The resulting precipitate morphology and composition were examined using atom probe tomography, with supporting analysis from scanning-transmission-electron-microscopy (STEM). In Fe-18Cr, thermal aging resulted in α’ formation across all temperatures. Proton irradiation produced precipitate morphologies comparable to those observed after aging, indicating radiation-enhanced precipitation. In the less concentrated FeCr alloys, radiation-enhanced α’ formed in Fe-10Cr at 350 °C. At 250 °C, Fe-5Cr exhibited radiation-induced Cr precipitation (attributed to segregation of Cr to dislocation loops), whereas radiation-enhanced and −induced precipitation both occurred in Fe-(8–10)Cr. Despite mild ballistic mixing and radiation-induced segregation, a reasonable equilibrium phase boundary was established using a modified regular solution equation. This experimental Cr solvus line can guide alloy design to mitigate α’-related embrittlement, and benchmark thermodynamic calculations of FeCr system.
| Original language | English |
|---|---|
| Article number | 114280 |
| Journal | Materials and Design |
| Volume | 256 |
| DOIs | |
| State | Published - Aug 2025 |
Funding
The authors thank Mr. James P. Burns from ORNL for helping with APT data acquisition, Qinyun Chen and Zehui Qi for valuable discussions, and Dr. Zhijie Jiao and the MIBL team for performing the ion irradiations. Funding: This research was sponsored by the Office of Fusion Energy Sciences , U.S. Department of Energy under grant # DE-SC0023293 with the University of Tennessee (YZ, YL, SJZ) and contract DE-AC05–00OR22725 with UT-Battelle, LLC (AB). The authors acknowledge funding from the State of Tennessee and the Tennessee Higher Education Commission (THEC) through their support of the Center for Materials Processing. The fabrication of the Fe-Cr binary alloys was carried out within the framework of the EUROfusion Consortium and received funding from the Euratom research and training program 2019–2020 under Grant Agreement No. 633053 . APT research was supported by the Center for Nanophase Materials Sciences (CNMS), which is a US Department of Energy , Office of Science User Facility at Oak Ridge National Laboratory .
Keywords
- Iron-chromium alloys
- Phase diagram
- Precipitate nucleation and growth
- Thermal aging
- Vickers microhardness