Abstract:

Nanocrystalline (NC) materials and high-entropy alloys (HEAs) have individually been sought for nuclear applications due to their exceptional mechanical and functional properties. Combinatorially, they (NC-HEAs) can provide vastly superior mechanical strength and heightened radiation tolerance than micro- and nano-crystalline traditional alloys. However, NC materials constitute a large high-energy grain boundary (GB) area that is prone to grain growth at low homologous temperatures. Such coarsening negates the benefits of utilizing their high density of defect sinks and mechanical properties in nuclear applications. As a result, both kinetic GB pinning and/or thermodynamic GB stabilization approaches are well-known adopted strategies to stabilize nanograin coarsening. Developing a novel NC-HEAs via mechanical alloying and subsequent heat treatment that drives solute/constituent HEA elements to GB to reduce the excess energy there, the effect of prior thermodynamic GB-decoration on the irradiation response of NC-AlCoCrFe-Zr in comparison with the as-milled counterpart is evaluated. Using Intermediate Voltage Electron Microscopy (IVEM)-Tandem facility at Argonne National Laboratory, a linear ion accelerator with a 911 Danfysik ion source coupled with a Hitachi 9000 TEM was used for simultaneous ion irradiation (up to 15dpa) and in-situ electron imaging, at room temperature. X-ray scattering experiments were performed at the 28-ID-2 X-ray Powder Diffraction (XPD) beamline of the National Synchrotron Light Source-II, Brookhaven National Laboratory, for post-irradiation examination of structural evolutions in irradiated doped/undoped NC-HEA samples. Using atom probe tomography for 3D evaluation of radiation-induced segregation at the atomic scale, this talk will focus on the observed suppressed grain growth rate and defect density/formation in NC-AlCoCrFe-Zr compared to those traditionally seen in literature for NC materials; GB segregation further suppresses irradiation damage compared to as-milled samples. Catalogued together, this work provides a pathway for accessing the technological benefits of GB-decorated NC-HEAs as a new concept for improving the radiation tolerance of materials for nuclear applications.

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Mr. Ben Hewitt