Phase selection rule of high-entropy metallic glasses with different short-to-medium-range orders

When an equiatomic multi-component alloy is quenched from its molten state down to room temperature,either a solid solution crystalline alloy or a metallic glass is formed.The former is called a high-entropy alloy,whereas the latter is referred as a high-entropy metallic glass(HE-MG).In such multicomponent alloys,thermodynamic parame-ters,e.g.,the mixing entropy,the mixing enthalpy and other parameters such as atomic size mismatch,determine the resulting phases.

In situ scattering study of multiscale structural evolution during liquid–liquid phase transition in Mg-based metallic glasses

The glass-forming ability of Mg-Cu-Gd alloys could be significantly promoted with the addition of Ag.A calorimetric anomaly could be observed in the supercooled liquid region of the Mg-Cu-Ag-Gd metallic glass,indicating the occurrence of a liquid-state phase transition driven by entropy.However,the underlying mechanism of the polyamorphous phase transition remains unsettled.In the paper,in situ scattering techniques were employed to reveal multiscale structure evidence in a Mg65Cu15Ag10Gd10metallic glass with an anomalous exothermic peak upon heating.Resistivity measurements indicate a reentrant behavior for the Mg-Cu-Ag-Gd metallic glass in the anomalous exothermic peak temperature region during heating.In situ synchrotron diffraction results revealed that the local atomic structure tends to be ordered and loosely packed first,followed by reentering into the initial state upon heating.Moreover,time-resolved small-angle synchrotron X-ray scattering(SAXS) results show an increase in nanoscale heterogeneity first followed by a reentrant supercooled liquid behavior.A core-shell structure model has been used to fit the SAXS profiles when polyamorphous phase transition occurs.In contrast,there is no structure anomaly for the reference Mg-Cu-Gd alloy system.The detailed multiscale structural evidence suggests the occurrence of a liquid-liquid phase transition followed by a reentrant behavior in the MgCu-Ag-Gd metallic glass.Our results deepen the understanding of the structural origin of the glass-forming ability and shed light on the possibility of tuning the physical and mechanical properties by heat-treatment in the supercooled liquid region of Mg-based metallic glasses.

Phase transformation behavior of a dual-phase nanostructured Fe-Ni-B-Si-P-Nb metallic glass and its correlation with stress-impedance properties

A study of the phase transformation process of a Fe-Ni-B-Si-P-Nb metallic glass using a suite of advanced characterization tools is reported.Transmission electron microscopy(TEM)and small angle neutron scattering(SANS)experiments show that the as-spun metallic glass ribbon has a dual-phase structure with bcc nanoclusters of a size of 2-3 nm.In situ high-energy X-ray diffraction(XRD)reveals a three-stage crystallization process when heating the metallic glass into supercooled liquid states.The isothermal annealing experiment shows the nanoclusters grow instantly without incubation.The easy formation and phase stability of the nanoclusters are due to the low interfacial energy between the amorphous matrix and clusters,as real space analysis shows that the nanoclusters and the amorphous matrix share similar short-to-mediumrange orders.We further find that the dual-phase structure reduces local magneto-anisotropy and enhances effective magnetic permeability,resulting in an excellent stressimpedance effect without sacrificing coercivity.Our work sheds light on the structure-property engineering of soft magnetic metallic glasses and provides a foundation for developing novel magnetic functional materials with nanostructured dual-phases.

Effects of casting current on structure and properties of a nanostructured Zr-Cu-Fe-Al bulk metallic glass

The effects of casting currents on the thermophysical behaviors, atomic and nanoscale structure, and mechanical properties of two Zr-based-bulk metallic glasses, i.e., Zr59Cu33A18 and Zr59（Cuo.55Feo.45）33A18, were studied by using differential scanning calorimetry, wide-angle X-ray diffraction, and small-angle X-ray scattering, as well as compression tests. The casting currents can be tuned to change the casting initiative temperature. Results revealed that there is no anomalous structural change for the Zr59Cu33A18 molten liquid before crystallization during cooling with different casting currents. In contrast, liquid-state phase separation was suggested to occur in the Zr59（Cuo.55Feo.45）33A18 molten liquid prepared using lower casting current before crystallization during cooling. The position shift of the first sharp diffraction peak for the diffraction pattern of Zr59（Cuo.55Feo.45）33A18 shows that the density of the molten liquid may decrease upon cooling at different casting currents. The small-angle X-ray scattering results indicate that the heterogeneity of the Zr59（Cuo.55- Feo.gs）33A18 metallic glasses increases with decreasing the casting temperature. As a result, the metallic glasses with a liquid-state phase separation possess better mechanical properties, including higher-yielding stress and more significant compressive ductility. The increase in degree of heterogeneity formed by nanoscale liquid-state phase separation and their interactions with the shear bands for the Zr-Cu-Fe-Al bulk metallic glasses were suggested to be responsible for the enhanced mechanical properties.