Three-Dimensionally Gradient and Periodic Harmonic Structure for High Performance Advanced Structural Materials

Abstract

Creation of a unique Harmonic Structure (HS) with controlled bimodal grain size distribution in metals and alloys is a new material design paradigm allowing the improved mechanical performance of structural materials via enhancing strength without sacri cing ductility. A well designed powder metallurgy based processing approach has been developed to create such a controlled microstructure which consists of controlled mechanical milling (MM) of powder particles to create powder particles with bimodal grain size distribution, with a peculiar coreshell structure, followed by their hot consolidation. In the present study, full density compacts with HS were prepared and the effect of such a bimodal microstructure on the mechanical properties of commercially pure Ti with hexagonal close packed (HCP) crystal structure was investigated. The HS pure Ti exhibited considerably higher strength values, without sacri cing ductility, as compared to their coarse-grained (CG) counterparts. The numerical simulation results revealed that the initial stages of deformation and strength of the HS are governed by the characteristics of the interconnected network of the strong ne-grained (FG) shell regions whereas the extent of uniform deformation and overall ductility is governed by the ductile CG core region. It was also demonstrated that the unique HS design promotes uniform deformation very ef ciently by avoiding strain localization during plastic deformation.

Elaboration of Metallic Materials by SPS: Processing, Microstructures, Properties, and Shaping

“…Incidentally, these results indicate that a removal of the superficial oxide layers by electric arcs and/or plasma, as proposed in several studies [4][5][6][7], does not seem to operate. Finally, original harmonic microstructures consisting in nanograins surrounding large grains could be stabilized with β-Ti due to the rapidity of the SPS process ( Figure 10) [46][47][48][49]. These materials exhibited enhanced resistance under monotonic solicitation [46,47] and fatigue [48,49].…”

“…Finally, original harmonic microstructures consisting in nanograins surrounding large grains could be stabilized with β-Ti due to the rapidity of the SPS process ( Figure 10) [46][47][48][49]. These materials exhibited enhanced resistance under monotonic solicitation [46,47] and fatigue [48,49].…”

Local Deformation Behavior of the Copper Harmonic Structure near Grain Boundaries Investigated through Nanoindentation

“…The fabrication of a bimodal microstructure called the “harmonic structure,” which consists of a coarse-grained “core” surrounded by a three-dimensional continuously connected fine-grained “shell,” was proposed by Ameyama et al It has been reported that this microstructure possesses both higher strength and ductility compared with homogenous coarse-grained and fine-grained counterparts in various materials [ 1 , 2 , 3 , 4 , 5 ].…”

Multiscale analysis of mechanical behavior of multilayer steel structures fabricated by wire and arc additive manufacturing

“…Heterogeneous structure design has been recognized as an effective approach to overcome this dilemma as it avoids the localization of stress or strain [ 1 , 2 ]. In this context, various metallic materials containing a heterogeneous structure have been developed such as bimodal grain size structure [ 3 , 4 ], ultrafine fibrous grain structure [ 5 ], harmonic structure [ 6 – 8 ], Van Gogh’s sky structure [ 9 , 10 ], and the multilayer structure [ 11 ]. Bimodal grain-size structure [ 3 , 4 ] and ultrafine fibrous grain structure [ 5 ] were fabricated by severe plastic deformation processes; hence, the size and shape are limited.…”

“…Bimodal grain-size structure [ 3 , 4 ] and ultrafine fibrous grain structure [ 5 ] were fabricated by severe plastic deformation processes; hence, the size and shape are limited. Although harmonic structure [ 6 – 8 ] which is shell-core bimodal grain size structure is capable of near-net-shape manufacturing using powder metallurgy, it is difficult to fabricate big components. Van Gogh’s sky structure [ 9 , 10 ] based on segregation of alloy element appears in only a special alloy system; therefore, the applicability is very limited.…”