Precipitation-site competition in duplex stainless steels: Cu clusters vs spinodal decomposition interfaces as nucleation sites during thermal aging

Journal Article · Sun May 17 04:00:00 EDT 2020 · Acta Materialia

DOI:https://doi.org/10.1016/j.actamat.2020.05.017· OSTI ID:1756022

Lach, Timothy G. ^[1]; Frazier, William E. ^[1]; Wang, Jing ^[1]; Devaraj, Arun ^[1]; Byun, Thak Sang ^[1]

---

1. BATTELLE (PACIFIC NW LAB)

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 structural and compositional analysis of phase transformation mechanisms in complex alloys Thus, in this study 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 precipitation of Ni-Si-Mn particles during long term thermal aging. Precipitation of Ni-Si-Mn particles in duplex stainless steels and ferritic steels during thermal aging and irradiation is known to have profound effect on mechanical properties. Using duplex stainless steels with custom modified compositions along with atom probe tomography characterization and first-passage kinetic Monte Carlo (FPKMC) simulations it is revealed that while the interface between Cr and Fe formed during spinodal decomposition can be a pathway for diffusion of Ni, Si, Mn, and Cu, it is not a site that encourages precipitation of Ni-Si-Mn rich particles. Instead, the presence of a higher concentration of Cu in these steels leads to formation of small Cu clusters with high energy interfaces that act as nucleation sites for Ni-Si-Mn particles because of its strong interaction particularly with Ni increasing the chemical driving force for precipitation. These results will help inform predictive models for the use of duplex stainless steels and other precipitation-hardened alloys for extended operation at high temperatures.

• Research Organization: Pacific Northwest National Laboratory (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1756022
• Report Number(s): PNNL-SA-143252
• Journal Information: Acta Materialia, Journal Name: Acta Materialia Vol. 196
• Country of Publication: United States
• Language: English

Related Subjects

Duplex stainless steel
Thermal aging
Precipitation
Cu co-precipitation
Spinodal decomposition
Atom probe tomography (APT)
Kinetic Monte Carlo