Cold spray manufacturing of oxide-dispersion strengthened (ODS) steels using gas-atomized and ball-milled 14YWT powders

Abstract

The cold spray deposition process has been investigated for the manufacture of 14YWT oxide-dispersion strengthened (ODS) steel, a nanostructured ferritic alloy (NFA), using gas-atomized and ball-milled feed-stock powders. Cold spraying of the gas-atomized powder resulted in a thick dense deposit, but an-nealing them above 900 degrees C induced grain growth and heterogeneous precipitation of nanoparticles, thus resulting in lower hardness ( - 170 HV) compared to 14YWT ODS steel manufactured by the conventional method. The ball-milled powder (Fe-14Cr-3W-0.4Ti-0.2Y-0.125O) was cryomilled in liq-uid N 2 to achieve small particle sizes followed by annealing in a H2/Ar environment at 10 0 0 degrees C and 1100 degrees C to reduce the hardness from -8 GPa to -5 GPa. Both smaller particle sizes and lower hardness of annealed powders made them amenable to the cold spray deposition process, result-ing in thick and dense deposits, while retaining the favorable fully solutionized microstructure of the ball-milled powders. The microstructure of the as-deposited ODS exhibited very fine grain sizes (50- 250 nm) with a uniform dispersion of Y-Ti-O nanoprecipitates in the ferritic steel matrix. The hard-ness values of the cold spray deposits using the powders annealed at 10 0 0 degrees C and 110 0 degrees C was 770 HV and 496 HV, respectively. Post-heat treatment of the as-deposited material up to 1100 degrees C showed a high-density microstructure with uniformly dispersed nanoscale oxide particles. The hard-ness of the annealed deposits up to 10 0 0 degrees C had a notably higher hardness than bulk 14YWT ODS steel manufactured by conventional methods. The study demonstrates that cold spray deposition of the microstructurally-tailored feedstock powders can be used to successfully manufacture ODS steel with mi-crostructure and properties comparable to those produced by the conventional methods, while provid-ing for an attractive option for the more rapid and cost-effective manufacturing of ODS steel cladding tubes.