Compared to traditional crystalline metal materials, amorphous alloys have unique physical and mechanical properties. However, the amorphous state is a complex structural disorder system that is energetically metastable. Under normal conditions, the amorphous alloy undergoes structural relaxation. This aging effect changes the physical and mechanical properties of the amorphous alloy, such as embrittlement and aging, which greatly limits the large-scale application of amorphous alloys. . How to overcome the relaxation and aging of amorphous materials has always been a bottleneck problem for amorphous materials. In recent years, research groups at home and abroad have tried to solve the problem of aging of amorphous alloys by surface shot peening, strong deformation and ion irradiation.
All of these methods can exert a certain degree of rejuvenation, so that some of the amorphous properties such as plastic deformation are improved to varying degrees. For example, the surface shot peening method jointly developed by the Wang Weihua research group of the Institute of Physics of the Chinese Academy of Sciences and Cambridge can greatly improve the plasticity of amorphous alloys [Nature Mater 5, 857-860 (2006)]; a simple room-temperature winding method developed by them can be convenient. Effectively modulating the concentration of the flow cell in the amorphous alloy enables room-temperature plastic deformation in an amorphous alloy [Phys. Rev. Lett. 113, 045501 (2014).]. However, shot peening and ion irradiation can only affect the performance of the amorphous alloy surface, and the strong deformation will introduce a large number of shear bands. These methods have limited industrial application due to their operability and process cost.
In recent years, experimental and computer simulations have found that there are some nanoscale liquid-like regions in amorphous alloys. Compared to the surrounding areas, liquid-like regions exhibit lower atomic packing density, lower hardness and modulus, higher energy states, and easier shear deformation and flow characteristics. Combining these research results, the Wang Weihua research group of the Institute of Physics of the Chinese Academy of Sciences/Beijing National Laboratory for Condensed Matter Physics proposed a flow units model to understand and explain the physical and mechanical problems of amorphous materials, The flow cell in the alloy resembles a defect in a crystalline material. The concentration, size and energy distribution of the alloy determine the mechanical properties of the amorphous alloy, aging and other properties, and can be effectively improved by regulating the flow cell in the amorphous alloy. Improve the mechanical properties of amorphous alloys. These work have a certain role in the regulation and modification of the properties and aging behavior of amorphous alloys.
Recently, the research group researchers Wang Weihua, Bai Hai, and PhD student Lu Zhen collaborated with the research group led by Professor AL Greer of the University of Cambridge and the research team led by DV Louzguine-Luzgin of Tohoku University in Japan to develop a simple amorphous alloy material. Thermal cycling process. This process involves soaking the amorphous alloy in liquid nitrogen or liquid helium for a few minutes, then rapidly warming to room temperature and holding it for several minutes. After dozens of cycles, it was found that the bulk energy of the amorphous alloy increased, showing that the relaxation peak of the structure before the crystallization of the amorphous alloy differential scanning calorimetry (DSC) curve was significantly enhanced.
Through mechanical tests, it was found that the hardness of the alloy after thermal cycling was significantly reduced; after compression testing by a mechanical tester, the thermal plasticity of the alloy increased to more than 7% after the thermal cycling, and the number of surface shear bands increased. The dynamic modulus tester (DMA) was used to measure the loss modulus of amorphous alloys under dynamic loading. It was found that the loss peaks moved to the low temperature region after thermal cycling, and the strength increased. These results all indicate that the number of rheological units increases significantly after thermal cycling, and the structure of the amorphous alloy is more non-uniform, resulting in a recovery effect of the alloy, that is, the aging resistance of the treated amorphous alloy is greatly enhanced. One of the manifestations of the anti-aging ability of amorphous alloys is that under the force conditions, more rheological units can evolve into shear bands, and shear bands are more easily generated in deformation. The macroscopic plastic deformation of amorphous is mainly determined by the number of shear bands, which can greatly improve the macroscopic plasticity of the amorphous alloy.
Compared with ion irradiation, surface shot peening, and strong deformation, the aging method of anti-amorphous alloys in cold and hot cycles has the characteristics of non-destruction, no change in shape, no limitation on sample size, no shear band, and more importantly, It is easy to implement in industry. Through these methods, the mechanical properties of the amorphous alloy can be effectively improved and the process treatment cost can be reduced, which can play an important role in promoting the industrial production and commercial application of the amorphous alloy.
The results were published in Nature, 524, 200â€“203 (2015). This work was supported by the National Natural Science Foundation of China, the â€œ973â€ Project and the Chinese Academy of Sciences.
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