Abstract
Competing microstructural evolution mechanisms can exist simultaneously when duplex stainless steels are operating for several decades in a high temperature service environment. Such competition between different microstructural evolution pathways can be difficult to ascertain using simple model alloy systems necessitating detailed microstructural analysis of phase transformation mechanisms in complex alloys. Thus, duplex stainless steels with complex but well understood chemistries were used to investigate the relative importance of different heterogeneous nucleation sites – specifically, spinodal decomposition and Cu clustering – on Ni-Si-Mn precipitation during thermal aging. Precipitation of Ni-Si-Mn particles in ferrite-bearing steels during thermal aging and irradiation can greatly change mechanical properties. Using duplex stainless steels with custom-modified compositions along with advanced microstructural characterization and first-passage kinetic Monte Carlo simulations, it is revealed that while the interface between Cr and Fe formed during spinodal decomposition can be a pathway for solute diffusion, it is not a preferred site for Ni-Si-Mn precipitation. Instead, the presence of a higher concentration of Cu leads to the formation of small Cu-rich clusters with high energy interfaces that act as nucleation sites for Ni-Si-Mn particles. These results will inform predictive models for the use of precipitation-hardened alloys for extended operation at high temperatures.
Original language | English |
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Pages (from-to) | 456-469 |
Number of pages | 14 |
Journal | Acta Materialia |
Volume | 196 |
DOIs | |
State | Published - Sep 1 2020 |
Funding
This research was partly sponsored by the Laboratory Directed Research and Development Program of Oak Ridge National Laboratory, managed by UT-Battelle, LLC, for the U. S. Department of Energy under contract number DE-AC05-00OR22725. The analysis was based upon the result of experiment research supported by the LWR Sustainability Program for the U.S. Department of Energy, Office of Nuclear Energy (LW-18OR040215) at Pacific Northwest National Laboratory (PNNL) operated by Battelle Memorial Institute for the U.S. Department of Energy under Contract No. DEAC05-76RL01830. APT was performed at PNNL's Environmental Molecular Sciences Laboratory, a Department of Energy - Office of Biological & Environmental Research national scientific user facility. Electron microscopy was performed at PNNL's Radiological Microscopy Suite at the Radiochemical Processing Laboratory using PNNL's Institutional Microscopy Tools. The authors also thank Dr. Shenyang Hu at Pacific Northwest National Laboratory, for numerous fruitful discussions regarding the computational modeling of Ni-Si-Mn cluster precipitation.
Keywords
- Atom probe tomography (APT)
- Duplex stainless steel
- Kinetic Monte Carlo
- Precipitation
- Thermal aging