DOE OSTI2018
For the last decade, the use of microwave (MW) melting and casting technology for processing uranium (U) has been under development at Y-12 National Security Complex in Oak Ridge, TN [2] . Their objective has been to determine if MW is a viable option to replace conventional vacuum induction melting (VIM) for some U part types. Some of the benefits of using MW technology are minimizing processing steps and decreasing impurity content by changing crucible material, which will help to lower costs and improve machinability, respectively. While Y-12 has shown success using a MW melting and casting process to make U parts [4, 5], it is still a relatively new technology for casting metals, and there are several unknowns with respect to how the material properties compare to conventional VIM cast U. One major concern, associated with MW casting of metals, is superheating, which can cause arcing or plasma formation in a part and result in non-uniform material properties. Therefore, studying the anisotropy in MW cast metals in terms of pertinent properties is highly relevant. Specifically, the properties of interest here are deformation behavior and mechanical properties of U tested at different strain rates and weldability of thin wall sections. In order to address concerns about high strain rate mechanical properties, prototype MW-U parts (processed in 2009) were sent to LLNL in 2015 for advanced materials testing. The parts received had relatively thin walls (~6 mm), so Split Hopkinson Pressure Bar was selected as a method for dynamic mechanical testing (strain rate of ~103s-1) since most other high-rate (HR) tests require much larger sample dimensions. A VIM-U part from Y-12 was not available at the time of the study, so a VIM part from Idaho National Laboratory, cast into a rectangular block, was used here for comparison.