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Recently, Li Xiuyan and others at the Nano Metal Scientist Studio, Shenyang National Research Center for Materials Science, Institute of Metal Research, Chinese Academy of Sciences have found that rapid heating can introduce annealing twins into nanocrystalline copper, thereby achieving "thermal relaxation" of the nanocrystalline grain boundaries To improve the thermal stability of nanocrystals. The results were published in the "Science" sub-sector "Science Progress" on April 24.
The study found that the thermal relaxation method of rapid temperature increase to improve the stability of nanocrystals can be used to improve the stability of submicrometers and nanocrystals obtained by general severe plastic deformation, which is useful for the development of highly stable nanomaterials and the promotion of nanometal applications. Significance.
Based on the Kissinger effect, the researchers proposed that increasing the heating rate can increase the grain growth temperature without affecting the twinning growth temperature. Therefore, rapid temperature rise not only avoids grain growth, but also produces growth twins. The pure copper with a grain size of about 80 nanometers was rapidly heated to a temperature of 523 kelvins at a rate of 160K (on) / minute and then cooled for 15 minutes. The grain size of the material did not change significantly, but the number of twins increased 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.
At present, the commonly used severe plastic deformation methods such as pure metal prepared by equal channel extrusion, lap rolling and other processes have grain sizes usually in the submicron scale, and it is difficult to initiate the grain boundary relaxation mechanism during processing, such as severe plastic deformation The size of the prepared pure copper grains is mostly between 100 and 200 nanometers, and the stability is poor. The grain growth temperature is much lower than the coarse grains.
The Nano Metal Scientist Studio of the Shenyang National Research Center for Materials Science has conducted systematic research on the stability of nano metals in recent years. In 2018, they discovered the abnormal grain size effect of thermal stability of nanocrystals in nanocrystalline pure copper and pure aluminum prepared by plastic deformation. In 2019, they found in their research that despite the difference in the internal mechanism of grain boundary migration under heating, the mechanical stability of nanocrystals under stress also has this abnormal grain size effect.