The thermal stability of copper nanocrystals can be greatly improved by rapid heating

    Li Xiuyan et al. found that annealing twins could be introduced into nanocrystalline copper by rapid heating, so as to achieve "thermal relaxation" of nanocrystalline grain boundary and improve the thermal stability of nanocrystalline.The results were published April 24 in science Advances, a subsidiary of Science.

    It is found that the thermal relaxation method of increasing the stability of nanocrystals can be used to improve the stability of submicron and nanocrystals obtained by severe plastic deformation, which is of great significance for the development of highly stable nanomaterials and the application of nanocrystals.

    Based on the Kissinger effect, the researchers proposed that increasing the rate of warming would increase the grain growth temperature without affecting the twin growth temperature.Therefore, rapid heating can not only avoid grain growth, but also produce growth twins.The pure copper with a grain size of about 80 nanometers was rapidly heated to 523 open at a rate of 160K (open)/min for 15 minutes and then cooled. The grain size of the material did not change significantly, while the number of twins increased significantly.Like deformation twins, these growth twins can relax grain boundaries and enhance the thermal stability of nanocrystals.After heat treatment, the growth temperature of nanocrystals increased from below 393 kelvin to above 773 kelvin.

    At present, the commonly used method of severe plastic deformation such as channel such as extrusion, pack rolling process of the preparation of pure metal, the grain size is usually in the submicron scale, it is hard to start the grain boundary relaxation mechanism in the process, such as severe plastic deformation of the preparation of pure copper grain size in 100 ~ 200 nm, poor stability, the grain growth is far lower than the coarse grain temperature.

    In recent years, the Nanometer metal Scientists' Workshop of Shenyang National Research Center for Materials Science has carried out systematic research on the stability of nanometer metals.In 2018, they found anomalous grain size effects on the thermal stability of nanocrystals in pure copper and aluminum prepared by plastic deformation.In 2019, their study found that although the intrinsic mechanism of grain boundary migration under heating is different, the mechanical stability of nanocrystals under stress also has this anomalous grain size effect.