NSUF 17-1029: Irradiation responses of ultrastrong nano precipitation martensite steel
The objective of this proposal is to study irradiation responses of a recently developed (S. Jiang, et al., Nature 544, 2017, p. 460) ultrastrong nano-precipitation maraging martensite steel, especially the evolution of nano-precipitates with irradiation temperature and precipitation/solute segregation behavior. Due to the inherently strong resistance to irradiation effects (in particular void swelling) and intergranular stress corrosion cracking (IGSCC), martensite steels have been considered as important structural materials for Gen IV nuclear reactors and may also be appealing candidates for accident tolerant fuel cladding in current light water reactors. Martensite nano-precipitation steels, combining a martensite matrix with extremely high density nanoprecipitates, are an interesting new class of high-strength materials. Their outstanding strength originates from semi-coherent precipitates, and the ultra-high density nano precipitates introduce numerous interfaces that can serve as sinks for annihilation of radiation-induced defects and thereby enhance irradiation tolerance. Therefore, the martensite nano-precipitation steels have remarkable potential for application in advanced nuclear reactors. To date, however, irradiation responses of these nano-precipitation martensite steels have not been reported. Here, we study a martensite nano-precipitation steel with composition Fe-18Ni-3Al-4Mo-0.8Nb-0.08C-0.01B (wt%). After solution annealing at 950 oC and aging for 3 h at 500 oC, a high density of nano-precipitates with B2 structure and enriched with Ni, Fe and Al is found, and these highly dispersed, fully coherent nano-precipitates (average density of 4×1024/m3 and size diameter ~2.7 nm), showing low lattice misfit with the matrix and high anti-phase boundary energy, strengthen the alloy without sacrificing ductility (room temperature strength ~2 GPa and moderate ductility ~8% total, 4% uniform elongation). These ultra-high particle densities are even higher than reported in the best oxide dispersion strengthened ferritic/martensitic steels. Ion irradiation experiments were performed using 5 MeV Fe at 250, 350, 500 and 650 °C in our home institution to a fluence of 4×1016 cm-2 (~14 dpa at a midrange depth of 750 nm). Irradiation-induced defects and the precipitation behavior in the matrix will be characterized by TEM. Nano indentation will be used to measure the hardness and modulus after ion irradiation. Since both the mechanical properties and irradiation tolerance of the martensite nano-precipitation steel are related with the high density nano-precipitates, the evolutions of these nano precipitates under high temperature ion irradiation are significant for its performance. Therefore, Atom Probe Tomography (APT) characterizations are proposed to be performed in the Microscopy and Characterization Suite (MaCS) at the Center for Advanced Energy Studies (CAES) to study the evolutions of these nano precipitates at different ion irradiation temperatures, which includes the variations of the nano-precipitate sizes, compositions and locations. Furthermore, since APT is a very sensitive characterization approach, we can also obtain the quantitative precipitation/solute segregation behavior, including potential Cr enrichment at dislocation loops and alpha prime precipitation at 250 and 350 °C. Based on the various characterization results, we will obtain a comprehensive understanding of the irradiation responses of the nano-precipitation martensite steel and provide reliable evidences for its application in advanced reactors.
Additional Info
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| Abstract | The objective of this proposal is to study irradiation responses of a recently developed (S. Jiang, et al., Nature 544, 2017, p. 460) ultrastrong nano-precipitation maraging martensite steel, especially the evolution of nano-precipitates with irradiation temperature and precipitation/solute segregation behavior. Due to the inherently strong resistance to irradiation effects (in particular void swelling) and intergranular stress corrosion cracking (IGSCC), martensite steels have been considered as important structural materials for Gen IV nuclear reactors and may also be appealing candidates for accident tolerant fuel cladding in current light water reactors. Martensite nano-precipitation steels, combining a martensite matrix with extremely high density nanoprecipitates, are an interesting new class of high-strength materials. Their outstanding strength originates from semi-coherent precipitates, and the ultra-high density nano precipitates introduce numerous interfaces that can serve as sinks for annihilation of radiation-induced defects and thereby enhance irradiation tolerance. Therefore, the martensite nano-precipitation steels have remarkable potential for application in advanced nuclear reactors. To date, however, irradiation responses of these nano-precipitation martensite steels have not been reported. Here, we study a martensite nano-precipitation steel with composition Fe-18Ni-3Al-4Mo-0.8Nb-0.08C-0.01B (wt%). After solution annealing at 950 oC and aging for 3 h at 500 oC, a high density of nano-precipitates with B2 structure and enriched with Ni, Fe and Al is found, and these highly dispersed, fully coherent nano-precipitates (average density of 4×1024/m3 and size diameter ~2.7 nm), showing low lattice misfit with the matrix and high anti-phase boundary energy, strengthen the alloy without sacrificing ductility (room temperature strength ~2 GPa and moderate ductility ~8% total, 4% uniform elongation). These ultra-high particle densities are even higher than reported in the best oxide dispersion strengthened ferritic/martensitic steels. Ion irradiation experiments were performed using 5 MeV Fe at 250, 350, 500 and 650 °C in our home institution to a fluence of 4×1016 cm-2 (~14 dpa at a midrange depth of 750 nm). Irradiation-induced defects and the precipitation behavior in the matrix will be characterized by TEM. Nano indentation will be used to measure the hardness and modulus after ion irradiation. Since both the mechanical properties and irradiation tolerance of the martensite nano-precipitation steel are related with the high density nano-precipitates, the evolutions of these nano precipitates under high temperature ion irradiation are significant for its performance. Therefore, Atom Probe Tomography (APT) characterizations are proposed to be performed in the Microscopy and Characterization Suite (MaCS) at the Center for Advanced Energy Studies (CAES) to study the evolutions of these nano precipitates at different ion irradiation temperatures, which includes the variations of the nano-precipitate sizes, compositions and locations. Furthermore, since APT is a very sensitive characterization approach, we can also obtain the quantitative precipitation/solute segregation behavior, including potential Cr enrichment at dislocation loops and alpha prime precipitation at 250 and 350 °C. Based on the various characterization results, we will obtain a comprehensive understanding of the irradiation responses of the nano-precipitation martensite steel and provide reliable evidences for its application in advanced reactors. |
| Award Announced Date | 2017-09-20T12:36:12.227 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Yaqiao Wu |
| Irradiation Facility | None |
| PI | Steven Zinkle |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1029 |