An in situ powder neutron diffraction study of nano-precipitate formation during processing of oxide-dispersion-strengthened ferritic steels

The evolution of phases in a Fe-14Cr-10Y2O3 (wt.%) oxide-dispersion-strengthened ferritic steel during mechanical alloying (MA) and subsequent annealing was studied by high resolution powder neutron diffraction, with emphasis on the kinetics of oxide-based nanoprecipitate formation. Y2O3 particles were almost dissolved into the ferritic matrix during MA. The formation of nano-precipitates was then observed by in-situ thermo-diffraction experiments during annealing of as-milled powder above 900oC, supported by scanning electron microscopy. This revealed nano-precipitate coarsening with increasing annealing temperature. Powder microhardness was measured at various processing stages, and hardness changes are discussed in terms of the measured phase fractions, crystallite size and lattice strain at different temperatures and times.