Unlike traditional crystalline metals, amorphous alloys exhibit a distinctive atomic arrangement characterized by short-range order and long-range disorder. Consequently, they lack dislocations, grain boundaries and other traditional crystalline defects, thus demonstrating very high strength and hardness. However, their plastic deformation is highly localized into nanoscale shear bands, which readily leads to catastrophic fracture and results in very poor room-temperature ductility. Forming crystalline-amorphous or amorphous-amorphous dual-phase structure is an effective strategy to solve the problems of the brittleness and limited plasticity of amorphous alloys. On the one hand, such heterogeneous architectures promote the formation of multiple shear bands, thereby dissipating energy and redistributing stress; on the other hand, when the amorphous phase size is reduced below roughly 100 nm, the glassy phase can be deformed by homogeneous flow, and the interactions between nanoscale amorphous regions and dislocation activity in the crystalline phase are conductive to more uniform macroscopic plasticity. Mechanical loading, heat treatment, and other processing routes can induce the transformation from crystalline single-phase or amorphous states to crystalline-amorphous or amorphous–amorphous dual-phase structures, thereby enabling the simultaneous attainment of ultrahigh strength and significant uniform plastic deformation. The resulting dual-phase alloys can retain the unique properties of amorphous alloys. Accordingly, this review summarizes recent advances in crystalline-amorphous and amorphous-amorphous phase- transformation behaviors below.1) Mechanical loading, such as friction and TRIP effects, can induce phase transformations. During frictional wear, materials experience large shear strains and stress concentrations; when combined with chemical reaction, these conditions can lead to the formation of crystalline-amorphous dual-phase structures at the surface. Under externally applied loads, phase transformations and microstructural reconfiguration occur; crystalline–amorphous and amorphous-amorphous TRIP effects become the primary mechanisms for energy dissipation, thereby delaying local stress concentration and improving ductility and fracture resistance.2) Thermal annealing above the glass transition temperature commonly induces crystallization of amorphous alloys, leading to in-situ precipitation of nanocrystals within the amorphous matrix. By controlling the annealing temperature and time, the size and volume fraction of the precipitates can be regulated, and more refined heat-treatment paths can even induce amorphous-amorphous transformation.3) Mixing enthalpy design and elemental partitioning play an important role in crystalline-amorphous and amorphous–amorphous phase behaviors. Elements with large negative mixing enthalpies tend to attract and enrich one another, whereas those with positive mixing enthalpies tend to repel; mechanical loading, thermal treatment and other external driving forces further promote atomic diffusion and elemental redistribution, which mediate the formation of crystalline-amorphous and amorphous-amorphous dual-phase structures.4) These unique structures endow crystalline-amorphous and amorphous-amorphous dual-phase alloys with excellent strength-ductility combinations as well as advantageous magnetic, hydrogen-storage, and catalytic properties. Future research should concentrate on three directions: Ⅰ) establishing a thermodynamic design framework centered on mixing enthalpy to clarify how compositional changes affect phase stability; Ⅱ) developing large-scale, and mass-producible routes for dual-phase materials; and Ⅲ) designing application-oriented dual-phase alloy systems that are low-cost, simple to fabricate, and have long service lives, thereby accelerating their industrial deployment in energy, precision machinery, electronics and communications, aerospace, and biomedical fields.
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