NSUF 24-4974: Direct Confirmation of Grain Boundary Roughening Using In Situ Irradiation

Molecular dynamics (MD) simulations are being carried out on grain boundaries (GBs) in Ni-Cr alloy with a wide range of characters (e.g., misorientation, tilt vs. twist, free volume) and under various radiation damage conditions as part of a separate work. These simulations will be used to identify the GBs most likely to roughen during in situ experimentation (i.e., GBs with minimal required dose for roughening). Electron transparent foils containing these ideal GBs will be irradiated in situ at the Intermediate Voltage Electron Microscope (IVEM) at Argonne National Laboratory using 500 keV Ne ions. High-resolution imaging of GBs before and after irradiation will be used to directly confirm and measure the degree of roughening, for use in a roughening vs. GB character data set, while in situ videos will be collected throughout the irradiations to better understand the evolution to steady state.

To date, GB roughening has been thought of and modeled as a high temperature phenomenon. This has led to few experimental studies analyzing these roughening transformations, despite the well-recognized changes in GB properties. However, consideration of driving forces such as point defect concentration gradients during irradiation leads to the potential for roughening at low homologous temperatures. While recent transmission electron microscopy (TEM) studies of GB evolution during room temperature, in situ irradiation have observed roughening of pre-existing GB facets, these works covered only three types of GBs and only to relatively small radiation doses. It is thus currently unknown how irradiation-induced roughening varies with GB character or whether the roughened state represents a new steady state GB phase which will survive greater damage. Further, such steady state GB phases are not expected to persist in the absence of irradiation, making ex situ study impractical. The existence of radiation-induced, steady state GB phases would be significant to our understanding of numerous GB phenomena under irradiation, including creep, radiation-induced segregation and precipitation, dislocation channeling, and irradiation-assisted stress corrosion cracking. Direct, in situ confirmation of GB roughening and any dependence on GB character will have implications for materials modeling, GB engineering for radiation environments, and current material lifetimes in nuclear energy systems and would prompt re-examination of well-studied materials – common and complex.

The total work – including sample preparation, IVEM experiments, image analysis, and manuscript preparation – is expected to last approximately five months. (The MD simulations are being performed as part of a separate work and will be completed prior to the estimated award date.) The work will produce a final report for NSUF RTE, at least one peer-reviewed journal publication, and a roughening vs. GB character data set from which the phenomenon can be modeled for future work.

추가 정보

필드	값
Award Announced Date	2024-05-28T17:12:42.37
Awarded Institution	Los Alamos National Laboratory
Facility Tech Lead	Wei-Ying Chen
Irradiation Facility
PI	Calvin Lear
PI Email	[email protected]
Project Type	RTE
RTE Number	None