In situ study on medium-range order evolution during the polyamorphous phase transition in a Pd-Ni-P nanostructured glass

Engineering multiscale structural hierarchies in glassy alloys enable a broad spectrum of potential applications.Metallic glasses were born in hierarchical structures from atomic-to-nanometer scales.However,the frozen-in structures in traditional metallic glasses prepared by rapid quenching techniques are challenging to tailor.Here,we show that a PdNiPbulk nanostructured glass of polyamorphous interfacial structures was prepared by inert-gas condensation with a laser evaporation source,and its multiscale structures could be engineered.In-situ scattering experiment results reveal polyamorphous phase transitions occurred in the interfacial regions,which are accompanied by the evolution of medium-range order and the nanoscale heterogeneous structures during the condensation process of glassy nanoparticles under high pressure and the following heating process.Moreover,changes in the cluster connectivity resulting from repacking of the local ordering induced by pressure and temperature could be observed.The thermophysical and mechanical properties,including boson peaks,hardness,and elasticity modulus,could be changed as a function of heat-treatment parameters.Our findings would shed light on the synthesis of bulk nanostructured glassy alloys with tailorable thermodynamic and dynamical behavior as well as mechanical properties based on the understanding of metastability for polyamorphous interfacial phases.

Polyamorphism mediated by nanoscale incipient concentration wave uncovering hidden amorphous intermediate state with ultrahigh modulus in nanostructured metallic glass

Comprehending the pressure-/temperature-induced structural transition in glasses,as one of the most fascinating issues in material science,is far from being well understood.Here,we report novel polyamorphic transitions in a Cu-based metallic glass(MG)with apparent nanoscale structural heterogeneity relating to proper Y addition.The low-density MG compresses continuously with increasing pressure,and then a compression plateau appears after∼8.1 GPa,evolving into an intermediate state with an ultrahigh bulk modulus of∼467 GPa.It then transforms to a high-density MG with significantly decreased structural heterogeneity above∼14.1 GPa.Three-dimensional atom probe tomography reveals concentration waves of Cu/Zr elements with an average wavelength of∼5-6 nm,which promote the formation of interconnected ringlike networks composed of Cu-rich and Zr-rich dual-glass domains at nanometer scale.Our experimental and simulation results indicate that steplike polyamorphism may stem from synergic effects of the abnormal compression of the Zr-Zr bond length at the atomic scale and the interplay between the applied pressure and incipient concentration waves(Cu and Zr)at several nanometer scales.The present work provides new insights into polyamorphism in glasses and contributes to the development of high-performance amorphous materials by high-pressure nanostructure engineering.

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.