Abstract

         Steels have important applications in current and advanced nuclear reactors, however, their irradiation tolerance and mechanical properties need to be improved. Bulk ultrafine-grained and nanocrystalline metals possess drastically higher strength than their conventional coarse-grained counterparts due to significant grain boundary strengthening, and are anticipated to have significantly enhanced irradiation tolerance owing to the role of grain boundaries as sinks for irradiation-induced defects. In our 7-year-long and multi-million-dollar DOE project, ultrafine-grained and nanocrystalline austenitic and ferritic steels were manufactured by equal-channel angular pressing (ECAP) and high-pressure torsion (HPT), respectively. The microstructure and mechanical behavior of the steels manufactured by ECAP and HPT were carefully studied. The thermal stability of the ultrafine-grained and nanocrystalline steels was also investigated. For ferritic FeCrAl alloys with different ranges of grain sizes, thermal aging was conducted to study thermally induced α’ Cr precipitation, which typically causes embrittlement. Neutron irradiation was performed to study irradiation behavior of the steels. Ion irradiation was also conducted to compare with the neutron irradiation. Results indicate that the ultrafine-grained and nanocrystalline steels manufactured by ECAP and HPT possess significantly improved hardness/strength compared to their conventionally manufactured coarse-grained counterparts. In FeCrAl alloys, with decreasing grain size, thermally induced α’ Cr precipitation was reduced. In 304 and FeCrAl steels, smaller grains possess reduced irradiation-induced hardening, segregation and precipitation compared to larger grains. Ultrafine-grained and nanocrystalline 304 steels have enhanced phase stability during irradiation compared to the coarse-grained counterpart. These results indicate enhanced irradiation tolerance of ultrafine-grained and nanocrystalline steels.

Bio

          Dr. Wen is an Assistant Professor in Department of Materials Science and Engineering and Department of Nuclear Engineering and Radiation Science at Missouri S&T. He obtained his PhD from University of California – Davis in 2012, and subsequently held postdoctoral appointments at Northwestern University and Idaho National Laboratory. Prior to joining Missouri S&T, he was a Research Assistant Professor at Idaho State University and a staff scientist at Idaho National Laboratory. Dr. Wen has extensive experience in research and development of advanced materials, including those for nuclear applications. He has been leading multiple research projects funded by Department of Energy, National Science Foundation, and Nuclear Regulatory Commission. Dr. Wen has authored or coauthored more than 65 peer-reviewed journal publications, with citations >3,200 and an h-index of 24. He serves on the Editorial Board of the journal Materials Science and Engineering A, and has served as the lead guest-editor of a special issue in AIMS Materials Science. He regularly reviews manuscripts for many journals and research proposals for DOE and NSF.