The inherent instability of nano-grain materials limits its application. The traditional method is to add alloys to stabilize, but this makes the cost of materials continue to rise, and the performance improvement rate slows down. Academician Lu Ke's team has been devoted to grain boundary control in recent years to achieve material characterization. Material materialization aims to improve material performance through cross-scale material organization control, replace alloying, and reduce the use of alloying elements. However, the thermal stability of nano-metallic materials is poor, which makes it difficult to materialize. Academician Lu Ke's team previously found that grain boundary relaxation can effectively stabilize the pure metal of nano-grains, which provides a new method for improving the mechanical stability of nano-crystals, making it possible to materialize. On April 24th, the team of Academician Lu Ke published another article in the top journal, and found that rapid heating may trigger strong grain boundary relaxation of pure copper nanocrystals up to submicron in size, providing a new method for stabilizing nanostructured materials.
Poor thermal stability is a key issue in ultrafine-grained and nano-structured crystalline materials. It is also one of the reasons that hinders its application and is a current research hotspot. Recently, the Israel Institute of Technology and the Karlsruhe Institute of Technology in Germany have discovered that the surface layer of copper ultrafine particles treated by high-pressure torsion has extremely high thermal stability. The related paper was published in Scripta Materialia. The study found that the phenomenon of capturing N2 molecules from the atmosphere in severely deformed metals was ignored in previous studies. Therefore, designing nanopores filled with different gases can be used as a tool to improve the thermal stability of ultrafine grains and nanostructured metal materials. (New discovery! Inflatable pores can improve the stability of ultra-fine grain structure)
As early as 2017, "Scicence" published a paper by Academician Lu Ke as the corresponding author online. The study found that the grain boundary segregation through appropriate alloying elements can improve the grain boundary stability, which can greatly adjust the strength of nanometals. This discovery reveals the nature of softening and hardening behaviors in nanomaterials and clarifies the debate on this issue over the past three decades (Academician Lu Ke of Science found that the stability of grain boundaries can regulate the properties of nanometals, clarifying more than 30 Years of controversy!).
However, alloying has caused the cost of materials to continue to rise, the performance improvement has slowed down, and recycling is more difficult. More and more attention is paid to the sustainable development of materials. In 2019, at the invitation of "Science", Academician Lu Ke and Researcher Li Xiuyan wrote a prospective paper about grain boundary control to achieve material characterization. Material materialization aims to improve material performance through cross-scale material organization control and replace alloying. Reduce the use of alloy elements and promote material recycling and reuse. Although this concept is feasible in principle, the instability of nanostructures leads to poor thermal stability of nanometallic materials, which makes it difficult to materialize. (Lu Ke & Li Xiuyan's "Science"! Grain boundary control realizes materialization)
In March 2019, the results of academician Lu Ke and others on grain boundary relaxation were published in Physical Review Letters, and it was found that grain boundary relaxation can effectively stabilize the pure metal of nano-grains. This finding shows that it is similar to the grain boundary segregation effect , The grain boundary relaxation effect related to the grain size can obviously inhibit the mechanically driven grain boundary migration, which provides a new method for improving the mechanical stability of nanocrystals, and also provides an important reference for the development of nanocrystal preparation processes. , Making materialization possible. (Top Journal: Lu Ke et al. Another Disruptive Discovery in Nano Metals!)
Materialization has attracted more and more attention. Recently, Chen Hao and others of Tsinghua University used a planar defect that has not been deeply studied, that is, the chemical interface, to obtain a new layered heterogeneous structure composed of nano lath martensite and nano twin austenite. The low-carbon medium-manganese steel has a tensile strength of more than 2.0 GPa and has high ductility (> 20%). It does not require the addition of high carbon content or expensive alloying elements. The related paper was published in Science Advances, which opened up a new method to replace the grain boundary engineering. (Important breakthrough! Tsinghua University uses a new method to obtain 2GPa low-cost ultra-high-strength steel!)
On April 24, 2020, Li Xiuyan, Lu Ke and others published a paper in Science Advances with the title "Rapid heating induced ultrahigh stability of nanograined copper", and found that rapid heating may trigger strong crystals of pure copper nanocrystals up to submicron in size. Boundary relaxation, pure copper nanocrystals have obvious instability in metals. The rapidly heated copper nanocrystals remain stable at temperatures up to 0.6 times the melting point, which is even higher than the recrystallization temperature of deformed coarse-grained copper. The thermally induced grain boundary relaxation caused by the generation of high-density nano twins provides a new method for stabilizing nano-structured materials.