A few days ago, Li Xiuyan, a researcher at Shenyang National Research Center for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, and others found that rapid heating can introduce annealing twins in nanocrystalline copper, thereby achieving "thermal relaxation" of nanocrystalline grain boundaries and improving nanocrystalline Thermal stability. The research results were published in "Science Progress" on April 24.
Relaxation refers to the process of gradually returning to equilibrium from a certain state in a certain gradual physical process. At present, the size of pure metal grains prepared by the common severe plastic deformation methods such as equal channel extrusion and lap rolling is usually in the submicron scale, and it is difficult to initiate the grain boundary relaxation mechanism during the processing. For example, the grain size of pure copper prepared by severe plastic deformation is mostly in the range of 100-200 nanometers, and its stability is poor. Its grain growth temperature is much lower than that of coarse grains.
To this end, the researchers adopted a rapid temperature increase method, which not only avoids the growth of grains, but also produces growth twins. The specific method is to heat the pure copper with a grain size of about 80 nanometers at a rate of 160 Kelvin / minute to 523 Kelvin for 15 minutes and then cool. The grain size of the material does not change significantly, and the number of twins increases significantly. Like deformed twins, these grown twins can also relax the grain boundaries and enhance the thermal stability of the nanocrystals. After heat treatment, the apparent growth temperature of the nanocrystals increased from below 393 Kelvin to above 773 Kelvin.
This method can be used to improve the stability of submicron and nanocrystals obtained by general severe plastic deformation, and is of great significance for the development of highly stable nanomaterials and the promotion of nanometal applications. (Reporter Shen Chunlei)
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