How to improve the strength of materials without losing their plasticity? This is the main challenge faced by many materials scientists. Recently, Lu Ke and Lu Lei, researchers from Shenyang National (Joint) Laboratory of Materials Science, Institute of Metals, Chinese Academy of Sciences, cooperated with S.Suresh, a professor at Massachusetts Institute of Technology, to complete a new principle and method of material strengthening.

That is, using nano-scale lattice interface to strengthen materials can strengthen metal materials and improve toughness and plasticity at the same time. On April 17, Science published a special summary paper, which elaborated the research results in detail.

It is understood that improving the strength of materials has been the core issue of material research for centuries. Up to now, the ways to strengthen materials can be divided into four categories: solid solution strengthening, second phase dispersion strengthening, processing (or strain) strengthening and grain refinement strengthening. The essence of these strengthening techniques is to prevent dislocation movement by introducing various defects (point defects, line defects, surface defects and bulk defects, etc.). ), making it difficult for the material to produce plastic deformation and improving the strength. However, the strengthening of materials is often accompanied by a sharp decline in plasticity or toughness, resulting in insufficient plasticity and toughness of high-strength materials, while the strength of high-plasticity and toughness materials is often very low. For a long time, the inverse ratio of strength and toughness of this material has become a major scientific problem in the field of materials and an important bottleneck restricting the development of materials.

Experts say that traditional material strengthening technology mostly uses ordinary non-lattice grain boundaries or phase boundaries to hinder dislocation movement to improve strength. When a large number of non-grain boundaries are introduced into the material, the strength is significantly improved (for example, the strength of nanocrystalline materials is one order of magnitude higher than that of coarse-grained materials). However, with more and more "obstacles" of dislocation movement (that is, non-* * lattice boundaries), lattice dislocation movement is seriously hindered or even completely suppressed, making materials brittle.

Lu Ke et al. found that the nanometer twin interface has three basic structural characteristics of strengthening interface: (1) there is a lattice relationship between the interface and the matrix; (2) The interface has good thermal stability and mechanical stability; (3) The characteristic dimensions of the interface are in the order of nanometers (

It should be understood that nano-scale twin grain boundaries in materials can be obtained by various preparation techniques. The results show that the faster the deposition rate, the thinner the twin layer. Twining induced by plastic deformation is very common in middle and low-grade materials (such as copper, copper alloy and stainless steel). Increasing strain rate or lowering deformation temperature is helpful to the formation of twins.

Lu Ke said that the recently developed dynamic plastic deformation (DPD) technology can form a large number of nano-twin grain boundaries in materials, which is an effective way to prepare bulk nano-twin structures. The use of nano-scale lattice grain boundary strengthening materials can also bring excellent electrical properties. The results show that the ultra-high strength nano-twin copper sample has the same high conductivity as oxygen-free high-purity copper, and can achieve high strength and high conductivity at the same time. Nano-twin structure can effectively reduce the diffusion mobility of electro-induced atoms in Cu, thus greatly reducing the electromigration effect, and finding a new solution to reduce the electromigration damage of copper wires in microelectronic devices. Some scholars also found that nano-twin structure can effectively improve the damping properties of materials, which opened up a new way for developing high-performance damping materials.

Researchers at the Institute of Metals, Chinese Academy of Sciences said that strengthening materials with nano-scale lattice interfaces has become a new way to improve the comprehensive properties of materials. Although there are still many challenges in the preparation technology, growth control, physical and chemical properties, mechanical properties and service behavior of nano-scale lattice interface, this new strengthening approach shows great development potential and broad application prospects in improving the comprehensive properties of engineering materials.

—— (transferred from: Xinhuanet)