A novel Bimodal Milling (BiM) approach to achieve harmonic structured SUS316L with controlled microstructure and outstanding mechanical performance

A novel systematic fabrication approach, called Bi-modal Milling (BiM), is proposed to prepare the austenitic steel (SUS316L) with peculiar Bimodal grain size structure, called Harmonic Structured (HS), with precisely controlled microstructural features of the fine-grained Shell and coarse-grained Core zones. The proposed technique consists of controlled mechanical milling of coarse- and fine-sized powders together to form the desired thickness of a layer of fine-sized powders over the coarse particles followed by consolidation of milled powders. The grain size and fraction of shell region were effectively controlled using different proportions (20–80%) of initial powders and milling time (36–180 ks) via producing milled powders with hierarchically distributed fine/coarse grains due to repeated coating of severe plastically deformed fine-grained powders to the coarse-grained powder particles. The BiM HS compacts exhibited considerably higher strength (σUTS), and ductility as compared to those with both heterogeneous and HS compacts having comparable fractions of Shell and Core.