Amorphous alloy, also known as metallic glass, is a new alloy material that combines the excellent mechanical, physical, and chemical properties of general metals and glass. The disordered atomic structure of amorphous alloys makes it a new type of structural material with a series of excellent mechanical properties such as high strength, high toughness and high elasticity. Unlike crystalline alloys, which have deformed crystal defects such as dislocations and grain boundaries, the room-temperature deformation of amorphous alloys is highly concentrated in nano-scale shear bands. The softening and expansion of local shear bands ultimately lead to amorphous materials. Instability fracture. Shear band is the carrier of deformation and rheology of amorphous materials. Understanding and regulating the shear band is the key to breaking the brittle bottleneck of glass system. However, as there are no visible deformation units similar to crystal dislocations, it is unclear whether the physical image of the formation and evolution mechanism of the shear bands in the amorphous alloy and whether the shear bands interact with each other.
The process of forming a shear band by plastic deformation of an amorphous alloy is regarded as the activation and cooperative rearrangement of a series of shear transition zones (STZs). The internal structure of the shear band has undergone huge changes relative to the surrounding parent body, and the formation and expansion of the shear band It is often accompanied by novel physical phenomena such as stick-slip motion, adiabatic heating, and nanocrystallization. However, researchers have not reached a consensus on the basic problem of the specific thickness of the shear band. Earlier, transmission electron microscopy revealed that the intuitive thickness of the shear band is a rearranged region of the atomic structure of tens of nanometers. In recent years, a series of experimental methods such as nano-indentation, radiotracer, nano-beam X-ray diffraction, and X-ray photon correlation spectroscopy have found that there is a more widely distributed influence zone around the shear zone. At the same time as the formation of the central shear band, a certain range of precursors around it also participate in deformation and structural rearrangement, which forces people to re-understand the strain localization and plastic deformation mechanism of amorphous alloys. However, due to the differences in resolution and sensitivity, the width of the shear zone influence zone obtained by different experimental methods varies widely, and the scale spans from nanometers to submicrons. New experimental methods are urgently needed to comprehensively and accurately reveal the influence of the shear zone. Area.
Recently, Shen Laiquan, a Ph.D. student in the Wang Weihua research group of the Key Laboratory of Extreme Condition Physics, Institute of Physics, Chinese Academy of Sciences / Beijing National Research Center for Condensed Matter Physics, under the guidance of Researcher Wang Weihua, Researcher Liu Yanhui and Researcher Sun Baoan, used a magnetic iron-based amorphous alloy as a model In the system, the magnetic domain measurement originating from magnetoelastic coupling is used to intuitively reveal the influence zone of the shear band of the amorphous alloy, and through the analysis of the magnetic domain structure, the cutting-edge issues such as the structure, expansion and interaction of the shear band A systematic study was carried out and a new understanding of shear bands was obtained. Unlike anisotropic magnetic structures caused by the long-range ordered lattice structure of crystalline materials, iron-based amorphous alloys have long-range disordered atomic arrangements, exhibiting excellent soft magnetic properties, and their magnetic moment distributions are coupled to magnetoelasticity. The effect is very sensitive. Therefore, magnetic domains can be used as "microscopes" that reflect the local deformation of amorphous alloys after plastic deformation. The measurement of magnetic domains at various shear band locations using a magnetic microscope with nano-scale resolution shows that micro-scale magnetic domain distributions are common on both sides of the shear band (Figure 1), indicating that the total amount of plastic deformation when forming a shear band A micro-scale shear band influence zone forms a strain gradient field around the shear band; the magnetic domain structure of multiple distributed shear bands indicates that multiple shear bands interact through the overlap of effective deformation zones (Figure 3 In addition, the gradient magnetic domain distribution extending around the long-range extension of the shear band indicates that there may also be a stress-graded long-range elastic region extending by several hundred micrometers around the shear band (Figure 2). Combined with the experimental results, they gave a complete physical image of the shear band structure (Figure 4). Based on this image and the results, they can well explain the relevant physical and mechanical phenomena in the amorphous materials previously reported, such as amorphous after deformation. The additional energy state of the alloy increases the structure relaxation. The above research results provide an important basis for comprehensive understanding of the shear band and plastic deformation mechanism of amorphous systems.