Additive Manufacturing of ODS Steel Claddings with an Integral Diffusion Barrier

Oxide dispersion strengthened (ODS) steels are desired for Generation IV reactor core applications such as thin-walled claddings due to their improved elevated temperature strength and radiation properties. The high temperature resistance of the ODS steels is a result of uniformly dispersed oxide nanoparticles in a ferritic matrix. The oxide nanoparticles prevent grain boundary movement and pin dislocations at elevated temperatures, while the ferritic matrix minimizes radiation induced swelling. In addition, the high concentration of grain boundaries acts as sinks for radiation induced defects, which enhances radiation damage resistance. However, the utilization of ODS steels has been limited due to the inability to form the desired microstructure using traditional fabrication techniques. For example, costly and low production volume mechanical alloying methods have been needed to produce the ODS steel feedstock powder and then consolidation has been performed using powder metallurgy methods to prevent coarsening of the oxide nanoparticles. In addition, fabrication of thin walled tubes then requires multiple drawing and annealing steps, which further increases the cost for large-scale production and makes lining the cladding with diffusion barrier layers very challenging. Recently, a novel, net-shape fabrication method using cold spray processing and removable mandrels was demonstrated as a viable manufacturing method for producing ODS steel tubes. Therefore, during this effort, cold spray processing techniques will be developed for producing additively manufactured thin wall ODS steel claddings. Because the claddings will be built from the inside to the outside on a removable mandrel, the ability to produce a thin diffusion barrier on the internal surface of the ODS claddings will be developed. To further reduce the cost of producing ODS steels, the direct addition of oxide nanoparticles to commercially available ferritic steel powders will be evaluated along with the traditional route of in-situ formation of the oxide dispersoids. Samples will be produced for microstructural examination and preliminary mechanical properties testing. To perform the detailed microstructural characterization and preliminary mechanical testing, Plasma Processes will partner with MIT. During Phase II, the techniques for producing full length ODS steel claddings using cold spray additive manufacturing will be developed. The cold spray processing techniques developed during this effort will be applicable to ductile metallic materials and other dispersion strengthened alloys for producing large, additively manufactured, multilayered components for government and commercial applications. These include aerospace, defense, propulsion, power generation, medical, electronic, and corrosion protection coatings.