The goal of the proposed rapid turnaround experiment (RTE) led by the University of Wisconsin, Madison (UW) is to perform comparative microstructural study on irradiation response of ODS steel produced by two distinct manufacturing routes using advanced TEM examination. The proposed research would provide extended data showing the stability of oxide nanoclusters in the cold spray produced ODS steel materials with regards to the number density, size, and composition under heavy ion irradiation as compared to ODS steel materials fabricated by conventional mechanical alloying methods. In the proposal, six days of instrument time is requested on the TEM characterization and four days of associated FIB time at the Irradiated Materials Characterization Laboratory (IMCL) in Idaho National Laboratory (INL). During the cold spray process, pre-alloyed 14YWT powder particles containing oxide nanoparticles are propelled at supersonic velocities through a converging-diverging nozzle system by pre-heated, pressurized gas onto a substrate to form a deposit. The particle temperature is low and deposition occurs by severe plastic deformation. While UW has successfully demonstrated a manufacturing route for ODS steel cladding tubes using the cold spray process under an ongoing NEET project, comprehensive microstructural analysis using the TEM is required to quantify the evolution of the nano-oxide particles and radiation-induced defects in the irradiated ODS steel materials. The size, size distribution, number density, and the composition of the oxide nanoparticles, which dictate the high temperature strength of ODS steels, as well as a radiation sink strength of the oxide nanoparticles will be evaluated.
The first question this RTE will seek to answer is about evaluation of the stability of oxide nanoparticles during the cold spray process and their reprecipitation during ion-irradiation. It is hypothesized that the high velocity impact of the oxide nanoparticles in the powder particle during the cold spray process results in oxide particle dissolution into the ferritic steel matrix, analogous to the high energy ball milling process used in the conventional methods of preparing ODS. Subsequent heavy ion irradiation of the supersaturated solid-solution matrix can potentially lead to reprecipitation of the oxide nanoparticles. Investigation of this hypothesis requires TEM examination of as-deposited ODS steel and its ion-irradiated counterpart.
The second question this RTE will seek to answer is how cold spray manufactured ODS steel behaves under radiation as compared to conventionally manufactured ODS steel with respect to distribution of radiation-induced defects and characteristics of the oxide nanoparticles.
Both the above scientific questions in our opinion are most conclusively addressed by the state-of-the-art TEM facility at the Idaho National Laboratory.
Supporting work (outside RTE proposal): (i) Ion irradiation of cold spray produced ODS steel samples performed at UW’s accelerator facilities using 3.7 MeV Fe+2 ions to a maximum damage level of 110 dpa. (ii) Continued SEM characterization of oxide nanoparticles in the ODS steels (produced by both cold spray and conventional methods) at the UW’s Materials Science Center.