NSUF 18-1262: In Situ Straining of 10-dpa Neutron Irradiated Austenitic Stainless Steels using Scanning Electron Microscope Electron Backscatter Diffraction
The proposed experiment will consist in manufacturing and preparing three irradiated tensile specimens of the irradiated alloy with the custom-made in-situ-suitable geometry (gauge dimensions 2 x 0.8 x 0.4 mm) with LAMDA CNC machine. The specimens will be machined from a fragment of a tested round compact tension (RCT) specimen produced, irradiated, and tested in the framework of the Cooperative Irradiation-Assisted Stress Corrosion Cracking Research Program. At the moment, manufacturing irradiated tensile object is well-established and risk-free procedure at LAMDA; the irradiated material is available in the sufficient quantity, and no shipping is required since the original material is stored at LAMDA. The tensile specimens will be strained in the FEI Versa 3D SEM equipped with the Kammrath/Weiss Tech. miniature tensile frame. The loading schemes will be designed so as to be close to the testing conditions of the preliminary in situ neutron diffraction tests. Specimens will be tested in load-control mode up to 80% of the expected yield stress, and then in displacement-control mode. Two specimens will be strained to 20% with two different strain rates (0.001 and 0.0001 s-1). The third specimen will be low-cycle fatigue tested to investigate micro-plasticity below the engineering yield point. For all specimens, the following EBSD maps will be collected after each stress/strain increment: i) three moderate resolution EBSD maps at 0.5 micron step size to capture multiple grain orientations, ii) three high-resolution EBSD maps at 125 150 nm step size on regions of interest such as dislocation channel/grain boundary intersections. All tests will be replicated with the three unirradiated specimens of the same geometry prepared by EDM. The combined in situ neutron diffraction straining (already completed) and in-situ SEM EBSD characterization results would allow assessing the fundamental aspects of plasticity in neutron-irradiated austenitic stainless steel, in particular in comparison with unirradiated stainless steel. As it was recently shown that grain orientation is likely of paramount importance in irradiation-assisted stress corrosion cracking, results would likely be instrumental in developing models and strategies to prevent IASCC. In addition to oxidation, a growing body of evidence identified localized deformation as a primary contributor to IASCC. In high-dose AustSS, most plastic deformation is localized within dislocation channels, which are regions almost clear of radiation defects. The interactions of these channels with grain and twin boundaries are likely of paramount importance to the development of intergranular cracks. AustSS are known to be highly anisotropic in unirradiated conditions, both in the elastic and plastic regimes. Previous observations show that irradiated AustSS conserve some anisotropy, but quantitative data on orientation-dependent load partitioning, dislocation density, and dislocation channeling in irradiated AustSS is required. The orientation-dependence of twinning is also of interest, since twinning leads to forming additional grain (twin) boundaries. They would lead to interpret a set of key laboratory results that do not fit with the current state of knowledge - neutron irradiation has no effect on the hardening in true stress/true strain and on the true stress for plastic instability, yet it dramatically impacts the microstructure.
Additional Info
| Field | Value |
|---|---|
| Abstract | The proposed experiment will consist in manufacturing and preparing three irradiated tensile specimens of the irradiated alloy with the custom-made in-situ-suitable geometry (gauge dimensions 2 x 0.8 x 0.4 mm) with LAMDA CNC machine. The specimens will be machined from a fragment of a tested round compact tension (RCT) specimen produced, irradiated, and tested in the framework of the Cooperative Irradiation-Assisted Stress Corrosion Cracking Research Program. At the moment, manufacturing irradiated tensile object is well-established and risk-free procedure at LAMDA; the irradiated material is available in the sufficient quantity, and no shipping is required since the original material is stored at LAMDA. The tensile specimens will be strained in the FEI Versa 3D SEM equipped with the Kammrath/Weiss Tech. miniature tensile frame. The loading schemes will be designed so as to be close to the testing conditions of the preliminary in situ neutron diffraction tests. Specimens will be tested in load-control mode up to 80% of the expected yield stress, and then in displacement-control mode. Two specimens will be strained to 20% with two different strain rates (0.001 and 0.0001 s-1). The third specimen will be low-cycle fatigue tested to investigate micro-plasticity below the engineering yield point. For all specimens, the following EBSD maps will be collected after each stress/strain increment: i) three moderate resolution EBSD maps at 0.5 micron step size to capture multiple grain orientations, ii) three high-resolution EBSD maps at 125 150 nm step size on regions of interest such as dislocation channel/grain boundary intersections. All tests will be replicated with the three unirradiated specimens of the same geometry prepared by EDM. The combined in situ neutron diffraction straining (already completed) and in-situ SEM EBSD characterization results would allow assessing the fundamental aspects of plasticity in neutron-irradiated austenitic stainless steel, in particular in comparison with unirradiated stainless steel. As it was recently shown that grain orientation is likely of paramount importance in irradiation-assisted stress corrosion cracking, results would likely be instrumental in developing models and strategies to prevent IASCC. In addition to oxidation, a growing body of evidence identified localized deformation as a primary contributor to IASCC. In high-dose AustSS, most plastic deformation is localized within dislocation channels, which are regions almost clear of radiation defects. The interactions of these channels with grain and twin boundaries are likely of paramount importance to the development of intergranular cracks. AustSS are known to be highly anisotropic in unirradiated conditions, both in the elastic and plastic regimes. Previous observations show that irradiated AustSS conserve some anisotropy, but quantitative data on orientation-dependent load partitioning, dislocation density, and dislocation channeling in irradiated AustSS is required. The orientation-dependence of twinning is also of interest, since twinning leads to forming additional grain (twin) boundaries. They would lead to interpret a set of key laboratory results that do not fit with the current state of knowledge - neutron irradiation has no effect on the hardening in true stress/true strain and on the true stress for plastic instability, yet it dramatically impacts the microstructure. |
| Award Announced Date | 2018-02-01T14:19:22.547 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Kory Linton |
| Irradiation Facility | None |
| PI | Jean Claude van Duysen |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 1262 |