Unique Mechanical Properties of Harmonic Structure Designed Materials

Abstract

Harmonic Structure (HS) 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 HS is heterogeneous on micro- but homogeneous on macro-scales. The most unique feature of HS is its continuously connected UFG Shell structure. In the present work, the HS design has been applied to pure metals and alloys via SPD powder metallurgy 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 is essentially related to the ability of the HS to promote a large strain hardening and uniform distribution of strain during plastic deformation, leading to improved mechanical properties by avoiding or delaying localized plastic instability. Such outstanding mechanical properties of HS materials are attributed to the continuously connected UFG-Shell structure. This unique microstructure provides stress partitioning in the micro scale and stress dispersion in the macro scale.

Tensile test results of a homogeneous (A) and harmonic structure (B, C, D) compacts. (a): Stress-strain curves and (b): relationship between UTS and tensile toughness. B, C and D corresponds to the microstructures (a), (b) and (c) in Fig.1, respectively.