Progress in Dynamic Deformation Mechanism of High-Strength High-Durability Metals with Multi-Structure Structures

The multi-level structure has mechanical properties superior to that of the uniform structure under quasi-static conditions, so does it also have superior mechanical properties under dynamic conditions? How does the various levels of structure and its coordinated deformation affect dynamic mechanical properties? Dynamic deformation behavior of multi-stage structures What is the microstructure mechanism? Recently, researchers from the Institute of Mechanics at the Chinese Academy of Sciences, North Carolina State University and Johns Hopkins University have made progress in the research of the above scientific issues.

For gradient structures, researchers have designed a new set of dynamic shear testing methods that for the first time revealed the dynamic shear deformation mechanism of gradient nanostructures: Additional processing occurs due to strain distribution during dynamic deformation between layers. Hardening can delay the initiation of shear bands on the surface of nanocrystals, and limit the propagation of shear bands from the surface to the core (its propagation speed is an order of magnitude lower than that of homogeneous structures). Gradient nanostructure metals can achieve a homogeneous structure Superior dynamic shear performance, while finding that the well-known maximum shear stress initiation criterion is no longer applicable in gradient structures.

Through cold rolling and short-time annealing at low temperatures, the researchers obtained multi-scale grain structure in entropy alloys in low-level fault-tolerant metals. The study found that the deformation coordination and strain distribution between multi-scale grains can promote work hardening, during dynamic deformation. Grain refinement occurred, which delayed the initiation of shear bands, promoted dynamic shear plasticity, and achieved the most superior dynamic shear properties reported so far. It was also found that at low temperatures, multi-stage twinning can be promoted. Change, the initiation and interaction of intragranular defects such as dislocation locks, improves the work hardening capacity, and leads to superior dynamic performance. This study provides ideas for improving the energy absorption efficiency and protective effect of metallic materials under impact conditions, and can provide High-strength, high-toughness metal for applications in extreme environments (eg energy-absorbing structures in the automotive industry, military protective structures, etc.).

Relevant research results were published on Materials Research Letters and Acta Materialia. The research was funded by the National Natural Science Foundation of China, the National Key Research and Development Program Nanoscale Project, and the Chinese Academy of Sciences Strategic Leading Technology Program (Class B).

Figure 1. Dynamic shear deformation mechanism of gradient nanostructures

Figure 2. Microstructure mechanism of superior dynamic properties and dynamic deformation of entropy alloys in multi-scale grain structure