From embryos to precipitates: A study of nucleation and growth in a multicomponent ferritic steel

The nucleation and growth of nanoscale precipitates in a new class of high-strength, multicomponent, ferritic steels has been studied with complementary state-of-the-art microstructural characterization techniques of atom probe tomography for individual embryos and precipitates and small-angle neutron scattering for their statistical averages. Both techniques revealed a bimodal size distribution, with subnanometer embryos, and nanoscale precipitates. The embryos, which have a radius of similar to 0.4 nm, are enriched in Cu and served as preferential sites for nucleation. The critical radius for nucleation was determined to be similar to 0.7 nm. Subsequent growth of the precipitates is dictated by volumetric diffusion, as predicted by the Lifshitz-Slyozov-Wagner theory.