Abstract
At high temperature conditions relevant to fossil and nuclear energy plants, Laves phase (Fe2X, X=Mo, W) precipitation is observed in common ferritic martensitic (FM) structural steels, with various reported effects on creep behavior. Despite being valuable metrics to correlate with mechanical properties and other precipitate phases, the volume fraction and number density of Laves phase precipitates has been difficult to quantify accurately using common techniques such as transmission electron microscopy (TEM) due to the relatively large size (∼0.25 μm) and low number density (∼1011 cm−3) of Laves precipitates. To address this characterization challenge, we developed and demonstrated a high-throughput and widely accessible method to quantify the volume fraction and number density of the Laves phase based on scanning electron microscope (SEM) images with a backscattered electron signal and the information depth (ID) of backscattered electrons. We applied this new technique in creep ruptured Grade 92 FM steel to study the effect of Laves phase on creep properties and determine the influence of stress on Laves phase precipitation. The quantitative accuracy of the SEM-based volume fraction and number density values was verified using synchrotron high energy X-ray diffraction and serial sectioning tomography. Stress did not significantly affect the Laves phase size or volume fraction during creep testing at 550 – 650°C and stress levels of 90 – 260 MPa (vs. unstressed conditions). Conversely, a moderate but statistically significant stress-enhanced increase in Laves phase number density, corresponding to an increase in nucleation rate, occurred during creep exposure above 110 MPa.
| Original language | English |
|---|---|
| Article number | 121559 |
| Journal | Acta Materialia |
| Volume | 301 |
| DOIs | |
| State | Published - Dec 1 2025 |
Funding
The authors wish to acknowledge Lizhen Tan for his visionary inspiration to develop a novel, accessible SEM-based precipitate characterization method to improve mechanistic understanding of precipitate evolution processes on thermal creep. His scientific mentorship is greatly missed due to his untimely passing. The authors would also like to thank Yanli Wang for her assistance with creep data procurement. Electron microscopy instrument access was provided by the Institute for Advanced Materials & Manufacturing (IAMM) at the University of Tennessee, Knoxville. The Electron Microscopy Laboratory (EML) at Los Alamos National Laboratory hosted the acquisition of the serial sectioning data. Funding: This material is based upon work supported under a Department of Energy, Office of Nuclear Energy University Nuclear Leadership Program Graduate Fellowship (EP). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the Department of Energy Office of Nuclear Energy. This research was sponsored in part by the DOE Office of Science Fusion Energy Sciences Program (WZ, LT; SJZ: DOE DE-SC0023293), the DOE Office of Nuclear Energy, and the FY 2017 Consolidated Innovative Nuclear Research Nuclear Science User Facilities program and the Light Water Reactor Sustainability program (WZ, LT), under Contract no. DE-AC05-00OR22725. Part of these experiments and analysis were supported by the DOE Office of Fusion Energy Sciences (DJS, LLS) under grant DESC0018322 with the Research Foundation for the State University of New York at Stony Brook. This research used The Pair Distribution Function beamlines of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science (DJS, LLS) by Brookhaven National Laboratory under Contract No. DE-SC0012704. Part of these experiments and analysis were supported by the DOE Office of Fusion Energy Sciences (DJS, LLS) under grant DESC0018322 with the Research Foundation for the State University of New York at Stony Brook. This research used The Pair Distribution Function beamlines of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science (DJS, LLS) by Brookhaven National Laboratory under Contract No. DE-SC0012704. Funding: This material is based upon work supported under a Department of Energy, Office of Nuclear Energy University Nuclear Leadership Program Graduate Fellowship (EP). Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the Department of Energy Office of Nuclear Energy. This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan ( http://energy.gov/downloads/doe-public-access-plan ). This research was sponsored in part by the DOE Office of Science Fusion Energy Sciences Program (WZ, LT; SJZ: DOE DE-SC0023293), the DOE Office of Nuclear Energy, and the FY 2017 Consolidated Innovative Nuclear Research Nuclear Science User Facilities program and the Light Water Reactor Sustainability program (WZ, LT), under Contract no. DE-AC05-00OR22725.
Keywords
- Creep
- Electron microscopy
- Laves phases
- Precipitate quantification
- Steel