Li Yan;Jian Meichen;Gao Yunhe;Wang Yepei;Liu Wenlin;Huang Yue;Liu Yizhou;Huo Juntao;Wang Junqiang;Gao Meng;

• 1:Ningbo Institute of Materials Technology and Engineering
• 2: Chinese Academy of Sciences
• 3:School of Materials Science and Chemical Engineering
• 4: Ningbo University

Abstract：

Amorphous alloys stand out in the material science landscape due to their distinctive atomic arrangement: a structure featuring long-range disorder yet short-range order. This structural hallmark endows amorphous alloys with a suite of exceptional properties that have garnered significant attention across industries. They exhibit ultrahigh strength, high elastic strain limit, large toughness, and excellent soft magnetic properties. Additionally, their chemical homogeneity-free from grain boundaries that act as corrosion initiation sites-grants them superior resistance to oxidation and wear. These attributes position amorphous alloys as game-changing materials in aerospace, renewable energy and precision engineering. However, a critical limitation has hindered their widespread adoption: poor macroscopic ductility at room temperature. While they may exhibit moderate plasticity in compression, tensile stress often triggers sudden, catastrophic brittle fracture. This behavior stems from the unique deformation mechanism of amorphous alloys, which is dominated by localized shear banding. These shear bands form when local atomic rearrangements coalesce under stress; once formed, they propagate rapidly due to adiabatic heating, leading to immediate fracture. Overcoming this "plasticity bottleneck" thus hinges on understanding and controlling the kinetics of shear band nucleation. This work systematically reviewed the research progress on shear band nucleation kinetics during plastic deformation of amorphous alloys, with emphasis placed on the microscopic origin of shear band nucleation, regulatory methods, and their correlation with macroscopic mechanical properties. Shear band nucleation kinetics usually included four key parameters: the distribution patterns of nucleation sites, nucleation sites density, nucleation rate, and energy barrier. These parameters dictated whether a material would form a single dominant shear band(leading to brittle fracture) or multiple, interacting shear bands(enabling ductile deformation). Traditional experimental methods, such as compression or tensile testing combined with high-resolution electron microscopy, struggled to capture these kinetic processes because nucleation in disordered systems was rapid, stochastic, and spatially heterogeneous. This challenge had been addressed by a groundbreaking approach based on nanoindentation technology, which had revolutionized the field. A key observation was that the first sudden displacement jump, termed a "pop-in" event during indentation, directly corresponded to the nucleation of the first shear band. By statistically analyzing hundreds of such first pop-in events across a material's surface, researchers could extract quantitative data on nucleation kinetics. At the microscopic level, shear band nucleation was deeply rooted in the structural heterogeneity of amorphous alloys. Despite appearing macroscopically uniform, these materials contained nanoscale regions of varying atomic packing density and mobility: "liquid-like" regions with high free volume and low elastic modulus, dispersed within a "solid-like" matrix with tighter packing and higher rigidity. These liquid-like regions acted as "flow unit defects"-analogous to dislocations in crystals-where atomic rearrangements were more easily activated under stress. Controlling nucleation kinetics to enhance plasticity had been achieved through several strategic approaches, each targeting the structural heterogeneity that drove nucleation. First, tuning intrinsic relaxation behavior was proven effective. Second, microalloying by adding small amounts of elements like erbium to Zr-based alloys optimized free volume distribution. Third, manipulating cooling rates during fabrication modulated the number of frozen liquid-like regions. Finally, controlling structural relaxation through annealing adjusted metastable energy states. These findings collectively highlighted that nucleation kinetics parameters served as the critical bridge between microstructure and macroscopic performance. By tailoring these parameters, researchers could guide amorphous alloys from single shear band-dominated brittleness to multiple shear band-enabled ductility. Looking forward, three directions would accelerate progress: first, developing quantitative models that linked alloy composition, processing conditions, and nucleation parameters enabled the predictive design of high-plasticity amorphous alloys. Second, advancing cross-scale in-situ characterization, such as combining nanoindentation with synchrotron X-ray diffraction or atomic-resolution electron microscopy, to track atomic rearrangements during nucleation in real time. Third, exploring nucleation behavior under extreme conditions-high temperatures, cyclic loading, or corrosive environments-to address the needed of harsh engineering applications like aerospace engines or deep-sea equipment. Ultimately, mastering shear band nucleation kinetics would unlock the full potential of amorphous alloys. By balancing their exceptional strength with ductility, these materials would transition from laboratory curiosities to indispensable components in next-generation technology, driving innovation in high-performance engineering and sustainable energy systems.

Key Words： amorphous alloys;shear bands;nucleation kinetics;structural heterogeneity;mechanical properties

Abstract:

Keywords:

Foundation: 国家自然科学基金面上项目（52471187）资助

Authors: Li Yan;Jian Meichen;Gao Yunhe;Wang Yepei;Liu Wenlin;Huang Yue;Liu Yizhou;Huo Juntao;Wang Junqiang;Gao Meng;

DOI: 10.13373/j.cnki.cjrm.XY25080004

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