Defect sinks, such as grain boundaries and phase boundaries, have been widely accepted to improve the irradiation resistance of metallic materials. However, free surface, an ideal defect sink, has received little attention in bulk materials as surface-to-volume ratio is typically low. Here by using in situ Kr ion irradiation technique in a transmission electron microscope, we show that nanoporous (NP) Ag has enhanced radiation tolerance. Besides direct evidence of free surface induced frequent removal of various types of defect clusters, we determined, for the first time, the global and instantaneous diffusivity of defect clusters in both coarse-grained (CG) and NP Ag. Opposite to conventional wisdom, both types of diffusivities are lower in NP Ag. Such a surprise is largely related to the reduced interaction energy between isolated defect clusters in NP Ag. Determination of kinetics of defect clusters is essential to understand and model their migration and clustering in irradiated materials.
Bibliographical noteFunding Information:
We acknowledge financial support by NSF-DMR-Metallic Materials and Nanostructures Program under grant no. 1304101. C. Sun was partially supported by DOE-NEUP under contract no. DE-AC07-05ID14517-00088120. Y. Chen was partially supported by US Army Research Office – Materials Science Division under contract no. W911NF-09-1-0223. We also thank Peter M. Baldo and Edward A. Ryan at Argonne National Laboratory for their help during in situ irradiation experiments. The IVEM facility at Argonne National Laboratory is supported by DOE-BES. Access to the DOE - Center for Integrated Nanotechnologies (CINT) at Los Alamos and Sandia National Laboratories and Microscopy and Imaging Center at Texas A&M University is also acknowledged.