Dmitri V. Louzguine-Luzgin

Nearly full density Ni52.5Nb10Zr15Ti15Pt7.5 bulk metallic glass obtained by spark plasma sintering of gas atomized powders

Ni-based bulk metallic glasses (BMGs) with a large size were fabricated by spark plasma sintering (SPS) of a gas-atomized Ni52.5Nb10Zr15Ti15Pt7.5 glassy alloy powder. The structure and thermal stability of the sintered specimens as well as the interface characteristics between powder particles were investigated. The sintered glassy specimens with nearly 100% relative density were obtained by the SPS process at a sintering temperature of 773K with a loading pressure of 600MPa. It was achieved using relatively low sintering temperature, short holding time, and rapid cooling during the SPS process. The results suggest that the BMGs fabricated by the SPS process opens possibilities of application as structural materials offering excellent properties and satisfying large-size requirements.

An assessment of binary metallic glasses: correlations between structure, glass forming ability and stability

Abstract This manuscript explores the influence of atomic structure on glass forming ability and thermal stability in binary metallic glasses. A critical assessment gives literature data for 628 alloys from 175 binary glass systems. The atomic structure is quantified for each alloy using the efficient cluster packing model. Comparison of atomic structure with amorphous thickness and thermal stability gives the following major results. Binary glasses show a strong preference for discrete solute to solvent atomic radius ratios R*, which give efficient local atomic packing. Of 15 possible R* values, only five are common and only four represent the most stable glasses. The most stable binary glasses are also typically solute rich, with enough solute atoms to fill all the solute sites and roughly one-third of the solvent sites. This suggests that antisite defects, where solutes occupy solvent atom sites, are important in the glass forming ability of the most stable glasses. This stabilising effect results from an increase in the number of more stable solute-solvent bonds in solute rich glasses. Solute rich glasses also enable efficient global atomic packing. Together, these structural constraints represent only a narrow range of topologies and thus give a useful predictive tool for the exploration and discovery of new binary bulk metallic glasses (BMGs).

Excellent capability in degrading azo dyes by MgZn-based metallic glass powders

The lack of new functional applications for metallic glasses hampers further development of these fascinating materials. In this letter, we report for the first time that the MgZn-based metallic glass powders have excellent functional ability in degrading azo dyes which are typical organic water pollutants. Their azo dye degradation efficiency is about 1000 times higher than that of commercial crystalline Fe powders, and 20 times higher than the Mg-Zn alloy crystalline counterparts. The high Zn content in the amorphous Mg-based alloy enables a greater corrosion resistance in water and higher reaction efficiency with azo dye compared to crystalline Mg. Even under complex environmental conditions, the MgZn-based metallic glass powders retain high reaction efficiency. Our work opens up a new opportunity for functional applications of metallic glasses.

Heating of metallic powders by microwaves: Experiment and theory

It is known that bulk metallic samples reflect microwaves while powdered samples can absorb such radiation and be heated efficiently. In the present work we studied heating mechanisms of metallic powders in a multimode 2.45 GHz microwave applicator. The present paper shows direct evidence of penetration of a layer of metallic powder by microwave radiation and provides theoretical explanation of such behavior.The most effectively heated powder is Fe because both eddy current loss (in alternating H-field) and magnetic reversal loss (in alternating E-field) mechanisms act in case of such metal. Diamagnetic metals Sn and Cu are heated better than paramagnetic Ti while Au is also only slightly heated. Cu- and Ni-based metallic glassy powders are also moderately heated. Weak heating of Au powder (which is a noble metal) can be explained by the absence on the particles of the oxide layer (shell), which allows eddy currents flowing through larger area compared to other metals, and reflection mechanism works much ...

Atomic structure of Zr–Cu glassy alloys and detection of deviations from ideal solution behavior with Al addition by x-ray diffraction using synchrotron light in transmission

The atomic structure of Zr–Cu binary amorphous alloys was studied using real space pair distribution functions derived from x-ray diffraction. The structure can be modeled by an ideal solution approximation because of relatively weak Cu–Zr atomic interactions. Addition of Al to Zr–Cu metallic glasses modifies the atomic structure in the short and medium range order because of the strongly attractive interaction between Al and Zr atoms. These interactions generate strong deviations from the ideal solution behavior.

Structural and magnetic properties of (In1−xFex)2O3 (0.0⩽x⩽0.25) system: Prepared by gel combustion method

(In1-xFex)2O3 polycrystalline samples with x = (0.0, 0.05, 0.10, 0.15, 0.20 and 0.25) have been synthesized by a gel combustion method. Reitveld refinement analysis of X raydiffraction data indicated the formation of single phase cubic bixbyite structure without any parasitic phases. This observation is further confirmed by high resolution transmission electron microscopy (HRTEM) imaging, and indexing of the selected-area electron diffraction (SAED) patterns, X-ray Absorption Spectroscopy (XAS) and Raman Spectroscopy. DC Magnetization studies as a function of temperature and field indicatethat they are ferromagnetic with Curie temperature (TC) well above room temperature.

Large-size ultrahigh strength Ni-based bulk metallic glassy matrix composites with enhanced ductility fabricated by spark plasma sintering

Ni-based bulk glassy alloy composites (GACs) simultaneously with ultrahigh strength and enhanced ductility and satisfying large-size requirements were fabricated by spark plasma sintering of gas-atomized Ni52.5Nb10Zr15Ti15Pt7.5 glassy alloy powder blend with ceramic or metal powders. No crystallization of metallic glassy matrix and good bonding state between the particles are responsible for good mechanical properties of the fabricated bulk GACs. The improvement of plastic ductility of the fabricated bulk GACs originates from the structural inhomogeneity caused by the particles inclusion. The additional particulates act as a resisting media causing deviation, branching, and multiplication of shear bands.

Comparative analysis of glass-formation in binary, ternary, and multicomponent alloys

In the present work we analyze the composition ranges over which bulk metallic glasses (BMGs) are produced in ternary, quaternary, and quinary amorphous alloys. The maximum diameter of the sample over which an amorphous structure can be retained, referred to as the critical diameter, Dc, is consistently large over specific composition ranges. For ternary BMGs, these most stable glasses are centered around the compositions, in decreasing order of accompanying Dc: A44B38C18, A44B43C13, A65B25C10, A56B32C12, A55B28C17, A70B20C10, and A65B20C15. As a general trend, the most stable glasses have the lowest concentrations of solvent atoms. Structural analysis using the efficient cluster packing model suggests that the best ternary glasses are near the isostructural composition, which represents the maximum degree of atomic confusion. Both Dc and ΔTx=Tx−Tg, the difference between the crystallization and glass transition temperatures, are larger in quaternary and quinary systems relative to typical values for tern...

High-strength and ductile glassy-crystal Ni–Cu–Zr–Ti composite exhibiting stress-induced martensitic transformation

We present a Ni-based crystal-glassy composite material having superior strength paired with a considerable ductility of 15%. The formation of a metastable crystalline phase in a glassy matrix during solidification has been proven capable of promoting a strain-induced martensitic transformation leading to enhanced plasticity under compression at room temperature. Underlying mechanisms of plastic deformation are discussed in terms of the interplay between dislocation slip in the crystalline phase and shear deformation in the glassy matrix. We suppose that the strain-induced martensitic inclusions serve as strong barriers for shear band propagation, promoting shear band branching and multiple shear band formation, thus extending the ductility and preventing a premature brittle fracture. The acoustic emission technique has been employed to clarify the kinetics of transformation and stages of plastic deformation.

Reduced electronegativity difference as a factor leading to the formation of Al-based glassy alloys with a large supercooled liquid region of 50K

The influence of the electronegativity difference among the constituent elements on the stability of the supercooled liquid in two Al-based glassy alloys is studied. A record-large value of the supercooled liquid region of about 50K is obtained based on the electronegativity difference concept within a certain composition range.