Owing to the superior mechanical and physical properties, metallic glasses (MGs) have attracted tremendous attention as promising candidates for structural and functional applications. Unfortunately, the ability to form uncontrollable glasses, the poor stability and the unpredicted catastrophic failure stemming from the disordered structure, as the Achilles' heel of MGs, severely restrict their large-scale applications. A number of phenomenological models, such as free volume model, shear transformation zone (STZ) model, flow unit model, etc., have been proposed, intending to relate microstructures to properties of MGs. However, few sophisticated structure-property relationships are established due to a poor understanding of the microstructure of MGs. Recently, heterogeneity is commonly believed to be intrinsic to MGs, and it can be used to establish the structure-property relationship of MGs. In this paper, we review the recent progress of MGs from the angle of heterogeneity, including the static heterogeneities and dynamic heterogeneities. The perspectives of the scientific problems and the challenges of metallic glass researches are also discussed briefly.
In recent decades, the positron annihilation spectroscopy technique has been used to characterize the microdefects of materials due to its advantages of non-destruction and high sensitivity on an atomic level. Positron annihilation spectroscopy technique is widely used in the microstructure study of thin film material surface and interface due to the rapid development of the slow positron beam technology. The slow positron beam technique can provide depth distribution information about material surface microstructure. Therefore, it is widely used to study the distributed defect concentrations in crystalline materials and the properties of thin films, surfaces and interfaces of layered materials. This article summarizes the slow positron beam technique applications and progress in the study of metal alloy materials. Firstly, this article introduces the slow positron beam technology development and application research achievement in detail. Secondly, it provides how to acquire the slow positron beam, introduces some kinds of and the principles of experimental measurements, and the major methods include Doppler bradening spectroscopy, coincidence Doppler broadening and PL. Thirdly, according to the defects induced by different ways, the latest experimental results about the material internal microdefect formation mechanism, evolution mechanism, defect feature research, such as microstructure, chemical environment, electron density and momentum distribution are introduced. The methods of inducing defects mainly include irradiation, physical deformation and chemical corrosion. Particles irradiation can be classified as four parts according to the different types of particles. In addition, monolayer and multilayer thin films have also been summarized. Finally, the new technique of thermal desorption spectroscopy and experimental measurements of age-momentum correlation are proposed. We can know that positron annihilation spectroscopy technology is a very special and effective nuclear spectroscopy analysis method in material microstructure study, and the slow positron beam technique makes it possible to study the depth distribution information about the thin film material surface microstructure. There is no doubt that this technique will play a huge role in the progress of material science and the creation of industrial material.
Owing to combining the properties of both metal and glass, metallic glasses exhibit superior physical and mechanical properties along with exotic phenomena, so they have a wide application prospect in many areas. In addition, their continuously adjustable composition and simple disordered atomic structure provide ideal model material systems for the study of fundamental questions commonly existing in glassy materials. The discovery of metallic glasses that can form bulk materials has pushed the relevant research to the frontier of condensed matter physics and material science. The EX4 group of the Institute of Physics, Chinese Academy of Sciences, has devoted to the study of glassy materials and physics for many years, and made important contributions to this field. In this paper, we summarize our recent progress of metallic glasses, including the relaxation behavior and stability, surface dynamics, materials functionalities, and new method on materials discovery.
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