An Alternate Approach to Fabricating Strengthened Steel

The Science

Potential fusion power plants require materials capable of withstanding extreme conditions. Oxide dispersion strengthened (ODS) steel represents a top candidate material, but current production is labor and cost intensive. Researchers combined cold spray deposition and friction stir processing to create an alternative route to generate ODS steel plates. They found that the plates are fully dense with practical levels of strength and ductility. Microstructural analysis revealed the presence of a significant quantity of nano-sized oxide particles.

The Impact

ODS steels are a promising class of structural materials for use in fusion power plants due to their strength and durability. ODS steel plates are traditionally fabricated through a series of complex labor- and cost-intensive steps and processes. This work provides a proof-of-concept for fabricating ODS steel through a significantly more straightforward process that should lead to lower overall manufacturing costs and higher-quality materials. Cold spray deposition can enable easier scale up, but often leads to materials with rough surfaces and less desirable microstructures. Friction stir processing of the deposited materials refines the microstructure of the ODS steel and increases its favorable physical properties.

Summary

Producing ODS steels has typically required forming a bulk material, followed by a complicated series of rolling and thermal treatment steps to reach a plate or sheet of steel. The numerous steps and complex nature procedures often lead to a final product with nonuniform microstructures, undependable physical properties, and high costs. The potential for ODS steel applications in future fusion plants has led to research interest in identifying alternative manufacturing routes to produce these materials. Researchers developed a new approach to creating ODS steel plates by combining cold spray deposition and friction stir processing. Cold spray deposition uses powder prepared by gas atomization reaction synthesis directly, with no prior ball milling steps necessary. After initial formation, friction stir processing then consolidates the slightly porous material and refines the microstructure. In-depth analysis revealed a fully dense final ODS steel with a favorable trade-off between strength and ductility. Examination of the microstructure showed a significant density of nano-sized oxide particles, which are known to strengthen ODS steel plates. Initial work exploring the scalability of the new process is promising, providing a proof-of-concept for larger-scale plate fabrication.

PNNL Contact

Wahyu Setyawan, Pacific Northwest National Laboratory, wahyu.setyawan@pnnl.gov 

Funding

This research is funded by the Department of Energy, Fusion Energy Sciences program under contract DE-AC05-76RL01830 (FWP 13784). This work was performed in part at EMSL, the Environmental Molecular Sciences Laboratory, a national scientific user facility sponsored by the Department of Energy, Biological and Environmental Research program.