Harmonic Structure Design for High Strength and High Ductility Materials Production

Abstract

Harmonic structure has three dimensional gradient microstructure. The harmonic structure has a heterogeneous microstructure consisting of bimodal grain size together with a controlled and specific topological distribution of fine and coarse grains. In other words, the harmonic structure is heterogeneous on micro- but homogeneous on macro-scales. The harmonic structure design has been applied to structural metallic materials, such as ferrous and non-ferrous materials, via a powder metallurgy route consisting of controlled severe plastic deformation of the corresponding powder and subsequent sintering process. At a macro-scale, the harmonic structure materials exhibited significantly better combination of strength and ductility, as compared to their homogeneous microstructure counterparts. This behavior was essentially related to the ability of the harmonic structure to promote the uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability. In addition, the harmonic structure materials also showed many unique deformation behaviors.