Three-Dimensional FIB/EBSD Characterization of Irradiated HfAl_3-Al Composite

摘要

A thermal neutron-absorbing composite comprised of 28.4 vol% HfAl_3 intermetallic particles in an Al matrix, developed for use in a conductively cooled thermal neutron filter, will enable fast flux irradiation of materials and fuels in an existing pressurized water test reactor In this paper, an EBSD-FIB characterization approach is used to observe the microstructural changes of the HfAl_3-Al composite in response to simulated long-term neutron irradiation. Using a focused ion beam (FIB), the sample was fabricated to 25um x 25um x 20 μm and mounted on a transmission electron microscopy (TEM) grid. A series of operations were carried out repeatedly on the sample's top surface to prepare it for scanning electron microscopy (SEM) First, a ~100-nm layer was removed by high voltage FIB milling. Then, several cleaning passes were performed on the newly exposed surface using low voltage FIB milling to improve the SEM image quality. The surface was then scanned by Electron Backscattering Diffraction (EBSD) to obtain a two-dimensional image. After 50 to 100 two-dimensional images were collected, the images were stacked to reconstruct a three-dimensional model using DREAM 3D software Two such reconstructed three-dimensional models were obtained from samples of the original and post-irradiation HfAl_3-Al composite, from which the most significant microstructural change caused by neutron irradiation appears to be the size reduction of both HfAl_3 and Al grains Possible causes include thermal expansion and related thermal strain from thermal neutron capture.