NSUF 23-1862: Deconvoluting Void and Bubble Effects on Deformation-Induced Martensitic Transformations in Austenitic Stainless Steel Using 4D STEM Strain Mapping
The objective of this project is to deconvolute the effects of voids from bubbles, on deformation-induced martensitic transformations in irradiated austenitic stainless steels (SS). Deformation-induced martensitic transformations are diffusionless, solid-state, and highly localized phase transformations from fcc austenite to hcp and/or bcc martensite in SS. These martensites compromise the structural integrity of nuclear components because they lead to embrittlement and increased corrosion susceptibility. Cavities (i.e., voids and bubbles) promote martensitic transformations because their internal surface energy reduces the externally applied strain energy required to exceed the critical transformation energy and trigger the transformation. Martensites tend to be associated with cavities in irradiated SS, possibly due to their offsetting compressive (martensite) and tensile (cavities) strains. However, researchers have been unable to distinguish the role of voids from that of bubbles. We hypothesize that voids and bubbles will have markedly different effects on the transformation due to their differences in surface energy, which is sensitive to cavity shape, void facets, and bubble gas pressure.
Our approach will determine strain distributions around voids and bubbles with varying surface energy (i.e., shapes and sizes), and link these strains to phase transformability. Work will involve three key tasks: (1) irradiation, (2) nanoindentation, and (3) transmission electron microscopy (TEM). Ion irradiations at Texas A&M University will create void- or bubble-dominated microstructures in 304L SS to isolate the effects of voids from bubbles, as compared to our reference specimen that contains both voids and bubbles (304L SS hex block 3A2 irradiated in EBR-II to 23 dpa, 3 appm He, 415ºC; EBR-II-HEX-008). Nanoindents on ion- and reference neutron-irradiated materials will be dissected into TEM lamellae. Finally, we will conduct 4-dimensional (4D) scanning TEM (STEM) strain mapping around voids and bubbles having varying surface energies. This work is timely because it has just been made feasible in NSUF through the recent installation of the ThermoFisher Spectra 300 STEM with electron microscope pixel array detector (EMPAD) at the Center for Advanced Energy Studies (CAES). The expected period of performance is within 9 months of award.
Additional Info
| Field | Value |
|---|---|
| Abstract | The objective of this project is to deconvolute the effects of voids from bubbles, on deformation-induced martensitic transformations in irradiated austenitic stainless steels (SS). Deformation-induced martensitic transformations are diffusionless, solid-state, and highly localized phase transformations from fcc austenite to hcp and/or bcc martensite in SS. These martensites compromise the structural integrity of nuclear components because they lead to embrittlement and increased corrosion susceptibility. Cavities (i.e., voids and bubbles) promote martensitic transformations because their internal surface energy reduces the externally applied strain energy required to exceed the critical transformation energy and trigger the transformation. Martensites tend to be associated with cavities in irradiated SS, possibly due to their offsetting compressive (martensite) and tensile (cavities) strains. However, researchers have been unable to distinguish the role of voids from that of bubbles. We hypothesize that voids and bubbles will have markedly different effects on the transformation due to their differences in surface energy, which is sensitive to cavity shape, void facets, and bubble gas pressure. Our approach will determine strain distributions around voids and bubbles with varying surface energy (i.e., shapes and sizes), and link these strains to phase transformability. Work will involve three key tasks: (1) irradiation, (2) nanoindentation, and (3) transmission electron microscopy (TEM). Ion irradiations at Texas A&M University will create void- or bubble-dominated microstructures in 304L SS to isolate the effects of voids from bubbles, as compared to our reference specimen that contains both voids and bubbles (304L SS hex block 3A2 irradiated in EBR-II to 23 dpa, 3 appm He, 415ºC; EBR-II-HEX-008). Nanoindents on ion- and reference neutron-irradiated materials will be dissected into TEM lamellae. Finally, we will conduct 4-dimensional (4D) scanning TEM (STEM) strain mapping around voids and bubbles having varying surface energies. This work is timely because it has just been made feasible in NSUF through the recent installation of the ThermoFisher Spectra 300 STEM with electron microscope pixel array detector (EMPAD) at the Center for Advanced Energy Studies (CAES). The expected period of performance is within 9 months of award. |
| Award Announced Date | 2023-02-08T10:50:08.163 |
| Awarded Institution | None |
| Facility | None |
| Facility Tech Lead | Lin Shao, Yaqiao Wu |
| Irradiation Facility | Accelerator Laboratory |
| PI | Keyou Mao |
| PI Email | [email protected] |
| Project Type | RTE |
| RTE Number | 4546 |