NSUF 20-4112: Ion irradiation and examination of metastability engineered stainless high entropy alloy
Stainless steels are extremely relevant for current and next generation reactors. The strength levels of stainless steels vary significantly and high-strength variants, like A286 and 17-4 PH, are usually attained through precipitation strengthening. To enhance the long-term viability and competitiveness of the existing fleet and to develop an advanced reactor pipeline, it is essential to utilize advanced materials for nuclear applications. This proposal is centered towards advanced metastable stainless alloy that integrate two emerging/innovative concepts, (a) expansion of alloying space through high entropy alloys (HEAs) approach (also referred as complex concentrated alloys), and (b) strengthening of alloys by engineering coherent interfaces at the nanoscale. Recently, metastable high entropy alloys have exploited the composition dependence of stacking fault energy (SFE) to activate deformation-induced twinning in the f.c.c. phase, deformation-induced γ-f.c.c. → ε-h.c.p. transformation and deformation-induced twinning in the ε-h.c.p phase. We have recently developed a Fe40Mn20Cr15Co20Si5 alloy (CS-HEA) with superior properties (yield strength of ~700 MPa, ultimate tensile strength of ~1175 MPa, ductility of >35%, and corrosion resistance comparable to 304 & 316 stainless steels). The SFE of the CS-HEA has been determined to be ~6.31 mJ m-2. Additionally, the ε-h.c.p. phase exhibited unique stress-induced decrease of c/a ratio (from ~1.619 to 1.588 Å), which was accompanied by activation of non-basal deformation modes, such as deformation twinning and pyramidal slip. However, the irradiation response of this metastable high entropy alloy is not known. HEAs are being considered for nuclear applications due to their promising mechanical properties and corrosion resistance. For nuclear applications, it is essential to understand the microstructural evolution and the concomitant changes in mechanical properties after irradiation. We will use the CS-HEA sheet with grain size of 6 µm. It is hypothesized that radiation induced transformation would be reversed by thermally induced reverse transformation in this metastable stainless HEA with very low SFE and this could lead to reduced irradiation damage. Heavy-ion irradiations will be performed to identify maximum swelling temperature and rate, swelling incubation period and predict swelling behaviors at ultra-low dpa rate typical of reactor environment. Samples will be irradiated at 3.0 MV NEC tandem accelerator at TAMU by 5 MeV Fe self-ions for doses equivalent to 25, 50 and 100 dpa at 350C, 400C, 450C and 500C. The doses will be determined by using SRIM code under KP mode. The PIE plan includes nanoindentation and TEM characterization of ion irradiated CS-HEA alloy at CAES. The project performance (sample preparation, ion irradiation and PIE) is expected to take place during July-September 2020. Successful completion of the proposed study will lead to key knowledge regarding (1) impact of irradiation on defect generation at γ/ε interfaces, (2) influence of irradiation on c/a ratio change in the ε phase, and (3) effect of irradiation on radiation induced transformation and reverse thermal transformation.
추가 정보
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| Abstract | Stainless steels are extremely relevant for current and next generation reactors. The strength levels of stainless steels vary significantly and high-strength variants, like A286 and 17-4 PH, are usually attained through precipitation strengthening. To enhance the long-term viability and competitiveness of the existing fleet and to develop an advanced reactor pipeline, it is essential to utilize advanced materials for nuclear applications. This proposal is centered towards advanced metastable stainless alloy that integrate two emerging/innovative concepts, (a) expansion of alloying space through high entropy alloys (HEAs) approach (also referred as complex concentrated alloys), and (b) strengthening of alloys by engineering coherent interfaces at the nanoscale. Recently, metastable high entropy alloys have exploited the composition dependence of stacking fault energy (SFE) to activate deformation-induced twinning in the f.c.c. phase, deformation-induced γ-f.c.c. → ε-h.c.p. transformation and deformation-induced twinning in the ε-h.c.p phase. We have recently developed a Fe40Mn20Cr15Co20Si5 alloy (CS-HEA) with superior properties (yield strength of ~700 MPa, ultimate tensile strength of ~1175 MPa, ductility of >35%, and corrosion resistance comparable to 304 & 316 stainless steels). The SFE of the CS-HEA has been determined to be ~6.31 mJ m-2. Additionally, the ε-h.c.p. phase exhibited unique stress-induced decrease of c/a ratio (from ~1.619 to 1.588 Å), which was accompanied by activation of non-basal deformation modes, such as deformation twinning and pyramidal slip. However, the irradiation response of this metastable high entropy alloy is not known. HEAs are being considered for nuclear applications due to their promising mechanical properties and corrosion resistance. For nuclear applications, it is essential to understand the microstructural evolution and the concomitant changes in mechanical properties after irradiation. We will use the CS-HEA sheet with grain size of 6 µm. It is hypothesized that radiation induced transformation would be reversed by thermally induced reverse transformation in this metastable stainless HEA with very low SFE and this could lead to reduced irradiation damage. Heavy-ion irradiations will be performed to identify maximum swelling temperature and rate, swelling incubation period and predict swelling behaviors at ultra-low dpa rate typical of reactor environment. Samples will be irradiated at 3.0 MV NEC tandem accelerator at TAMU by 5 MeV Fe self-ions for doses equivalent to 25, 50 and 100 dpa at 350C, 400C, 450C and 500C. The doses will be determined by using SRIM code under KP mode. The PIE plan includes nanoindentation and TEM characterization of ion irradiated CS-HEA alloy at CAES. The project performance (sample preparation, ion irradiation and PIE) is expected to take place during July-September 2020. Successful completion of the proposed study will lead to key knowledge regarding (1) impact of irradiation on defect generation at γ/ε interfaces, (2) influence of irradiation on c/a ratio change in the ε phase, and (3) effect of irradiation on radiation induced transformation and reverse thermal transformation. |
| Award Announced Date | 2020-07-14T14:06:48.227 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Lin Shao, Yaqiao Wu |
| Irradiation Facility | Accelerator Laboratory |
| PI | Rajiv Mishra |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4112 |