The project was inspired by Tsuji’s recent idea, that is, balancing both high strength and large ductility of structural metallic materials through a sequential nucleation (activation) of different deformation modes and regeneration of strain-hardening ability. A schematic illustration showing this concept, for example, a sequential nucleation of new deformation modes from grain boundaries in ultrafine-grained metallic materials is shown in Fig. 1. [2]. In particular, both the strength (the yield strength) and the tensile ductility (the uniform elongation) show a grain size dependence, however, it has been extremely challenging to design a microstructure having both high strength and large ductility. This collaborative (team) research effort tackles the strength-ductility paradox, by revisiting several basic and well-known materials science concepts; some of major keywords in here are i) plastic instability, ii) strain hardening regeneration, and iii) grain refinement. Although these appear to be proverbial words; the mechanisms of enhanced strain-hardening have not yet been exactly clarified even for the conventional TWIP and TRIP phenomena, widely used for advanced industrial structural materials.
Tsuji and Inui have recently proposed the “Plaston” concept, which attempts to understand materials’ fundamental plastic deformation behaviors from a collective activation and motion of small localized groups of atoms viewpoint. The formation and migration of a local defective zone in which atoms are “excited” could be an essential structure that leads to a plastic strain by its migration. Atomistic structure of a dislocation core is one of such localized defective zones. More details of the Plaston concept can be found in these articles:
- The Plaston Concept: Plastic Deformation In Structural Materials (open access)
- Strategy for managing both high strength and large ductility in structural materials–sequential nucleation of different deformation modes based on a concept of plaston
In summary, this on-going research project aims to collect mechanistic understanding of materials’ fundamental plastic deformation behaviors from atomic to continuum scale by taking the maximum advantage of collective expertise of the research team, consisting of world-class experts of experimental and computational materials science. More specifically, the research firstly clarifies the mechanism for the nucleation of various deformation modes from grain boundaries and interfaces in the metallic materials having highly controlled nano-/micro-structures. Then, the mechanism for the regeneration of strain-hardening ability by the nucleation of different deformation modes is fundamentally studied. Based on the obtained results, the team tries to realize advanced structural metals having both high strength and large ductility, through designing and processing the nano-/micro-structures of materials in which different deformation modes can be sequentially activated. Using state-of-the-art methods in both experiments and calculations, deformation mechanism in nanoscales is correlated with macroscopic deformation behaviors.
