Effect of overheating-induced minor addition on Zr-based metallic glasses

Melt treatment is well known to have an important influence on the properties of metallic glasses(MGs).However,for the MGs quenched from different melt temperatures with a quartz tube,the underlying physical origin responsible for the variation of properties remains poorly understood.In the present work,we systematically studied the influence of melt treatment on the thermal properties of a Zr50Cu36Al14 glass-forming alloy and unveiled the microscopic origins.Specifically,we quenched the melt at different temperatures ranging from 1.1Tl to 1.5Tl(Tl is the liquidus temperature)to obtain melt-spun MG ribbons and investigated the variation of thermal properties of the MGs upon heating.We found that glass transition temperature,Tg,increases by as much as 36 K,and the supercooled liquid region disappears in the curve of differential scanning calorimetry when the melt is quenched at a high temperature up to 1.5Tl.The careful chemical analyses indicate that the change in glass transition behavior originates from the incorporation of oxygen and silicon in the molten alloys.The incorporated oxygen and silicon can both enhance the interactions between atoms,which renders the cooperative rearrangements of atoms difficult,and thus enhances the kinetic stability of the MGs.

Corrosion and in vitro cytocompatibility investigation on the designed Mg-Zn-Ag metallic glasses for biomedical application

In the present work,seven Mg-Zn-Ag alloys with the nominal composition of Mg_(96-x)Zn_(x)Ag_(4)(x=17,20,23,26,29,32,35 in at.%)were prepared by induction melting and single-roller melt-spinning.The X-ray diffraction(XRD)analyses indicate the metallic glasses with three composition of Mg_(73)Zn_(23)Ag_(4),Mg_(70)Zn_(26)Ag_(4),and Mg_(67)Zn_(29)Ag_(4)were obtained successfully.The differential scanning calorimetry(DSC)measurement was used to obtain the characteristic temperature of Mg-Zn-Ag metallic glasses for the glass-forming ability analysis.The maximum glass transition temperature(Trg)was found to be 0.525 with a composition close to Mg_(67)Zn_(29)Ag_(4),which results in the best glass-forming ability.Moreover,the immersion test in simulated body fluid(SBF)demonstrate the relative homogeneous corrosion behavior of the Mg-Zn-Ag metallic glasses.The corrosion rate of Mg-Zn-Ag metallic glasses in SBF solution decreases with the increase of Zn content.The sample Mg_(67)Zn_(29)Ag_(4)has the lowest corrosion rate of 0.19mm/yr,which could meet the clinical application requirement well.The in vitro cell experiments show that the Madin-Darby canine kidney(MDCK)cells cultured in sample Mg_(67)Zn_(29)Ag_(4)and its extraction medium have higher activity.However,the Mg-Zn-Ag metallic glasses exhibit obvious inhibitory effect on human rhabdomyosarcoma(RD)tumor cells.The present investigations on the glass-forming ability,corrosion behavior,cytocompatibility and tumor inhibition function of the Mg-Zn-Ag based metallic glass could reveal their biomedical application possibility.

Unveiling the early stage evolution of local atomic structures in the crystallization process of a metallic glass

The early stage evolution of local atomic structures in a multicomponent metallic glass during its crystallization process has been investigated via molecular dynamics simulation.It is found that the initial thermal stability and earliest stage evolution of the local atomic clusters show no strong correlation with their initial short-range orders,and this leads to an observation of a novel symmetry convergence phenomenon,which can be understood as an atomic structure manifestation of the ergodicity.Furthermore,in our system we have quantitatively proved that the crucial factor for the thermal stability against crystallization exhibited by the metallic glass is not the total amount of icosahedral clusters,but the degree of global connectivity among them.

Magnetic and magnetocaloric effect of Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass

Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass exhibited excellent magnetic refrigeration material with a wide temperature range and high refrigeration capacity(RC)was reported.Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass was observed with typical spin glass behavior around 15.5 K.In addition,we find that the magnetic entropy change(-△S_(M))originates from the sample undergoing a ferromagnetic(FM)to paramagnetic(PM)transition around 20 K.Under a field change from 0 T to 7 T,the value of maximum magnetic entropy change(-△S_(M)^(max))reaches 12.5 J/kg·K,and the corresponding value of RC reaches 487.7 J/kg in the temperature range from 6 K to 60 K.The large RC and wide temperature range make the Er_(20)Ho_(20)Dy_(20)Cu_(20)Ni_(20)high-entropy metallic glass be a promising material for application in magnetic refrigerators.

Effect of high-energy Ne ions irradiation on mechanical properties difference between Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5)metallic glass and crystalline W

In this paper,high-energy Ne ions were used to irradiate Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) metallic glass(MG)and crystalline W to investigate their difference in mechanical response after irradiation.The results showed that with the irradiation dose increased,the tensile micro-strain increased,nano-hardness increased from 7.11 GPa to 7.90 GPa and 8.62 GPa,Young’s modulus increased,and H3/E2 increased which indicating that the plastic deformability decreased in crystalline W.Under the same irradiation conditions,the Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG still maintained the amorphous structure and became more disordered despite the longer range and stronger displacement damage of Ne ions in Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG than in crystalline W.Unlike the irradiation hardening and embrittlement behavior of crystalline W,Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG showed the gradual decrease in hardness from 6.02 GPa to 5.89 GPa and 5.50 GPa,the decrease in modulus and the increase in plastic deformability with the increasing dose.Possibly,the irradiation softening and toughening phenomenon of Zr_(63.5)Cu_(23)Al_(9)Fe_(4.5) MG could provide new ideas for the design of nuclear materials.

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.

Crystallization of Mg-based bulk metallic glass

Mg-based bulk metallic glass fabricated by conventional copper mould method was aged at different temperatures. X-ray diffractometry(XRD), scanning electron microscopy(SEM), atomic force microscopy(AFM) and focused ion beam(FIB) miller were employed to examine specimens obtained under different conditions. The crystallization of Mg-based bulk metallic glass depends upon both the aging temperature and the aging time. As temperature increases or the holding time increases, the microstructure of the aged specimen varies from glassy one to crystalline one plus glassy phase and then to absolutely multiphase crystalline one. From the FIB images, it is clear that Mg-based bulk metallic glass could not only crystallize completely but also display dendrite-like growth style. From the AFM images, there are not only significant variations of microstructures but also surface morphology of specimens obtained under different conditions. It is proposed that the surface morphology varies as the treating temperature increases. The Vickers hardness of different specimens increases as the fraction of crystalline phase (s) increases.

Mg-based bulk metallic glasses:A review of recent developments

Metallic biomaterials have been widely used in the field of medical implants for replacement purposes and/or for regeneration of tissue.Metals such as stainless steel(316 L),cobalt-chromium alloys and titanium alloys(Ti-6Al-4 V)are widely used as metallic implants today.However,they often exhibit unsatisfactory results such as stress shielding,the release of toxic ions and are often permanent and invasive–where a second surgery is required to remove the implant once the bone is fully healed.Magnesium as a biomaterial have attracted much attention recently due to its excellent biocompatibility,similar mechanical properties to bone and biodegradability.Unlike other metals and bio ceramics,the ability for magnesium alloys to undergo biodegradation eliminates the requirement for a second surgery to remove the implant.Additionally,the degradation of magnesium releases Mg2+ions,which stimulates metabolism as they are a cofactor in numerous numbers of enzymes.Despite the advantages of magnesium alloys,the rapid degradation of magnesium proved to be challenging as the implant is unable to retain its structural integrity sufficiently enough to act as an implant.To improve the corrosion resistance of magnesium alloys,researchers have been working on the synthesis and characterization of Mg-based bulk metallic glasses,which can significantly improve the corrosion resistance of Mg-based alloys.This paper is a comprehensive review that compiles,analyzes and critically discusses the recent literature on the latest understanding of the processing,mechanical and biological characteristics of Mg-based bulk metallic glasses.

A group of ductile metallic glasses prepared by modifying local structure of icosahedral quasicrystals

Inspired by research into the association between icosahedral local orders and the plasticity of metallic glasses(MGs),beryllium(Be) is added to the icosahedral quasi-crystal forming alloy Zr40Ti40Ni20. In this way, bulk metallic glasses(BMGs) with favorable compressive plasticity are fabricated. Therein, the icosahedral quasi-crystalline phase is the main competing phase of amorphous phases and icosahedral local orders are the main local atomic motifs in amorphous phases.The alloys of(Zr40Ti40Ni20)76Be24and (Zr40Ti40Ni20)72Be28with their greater plastic strain capacity show similar characteristics to highly plastic amorphous systems: The serrated flow of compression curves always follows a near-exponential distribution. The primary and secondary shear bands intersect each other, bifurcate, and bend. Typical vein patterns are densely distributed on the fracture surfaces. The relaxation enthalpy of four MGs is linearly correlated with the plastic strain, that is, the greater the relaxation enthalpy, the larger the plastic strain.

Structural origin for composition-dependent nearest atomic distance in Cu–Zr metallic glass

We systematically investigate the structures of Cu–Zr metallic glass(MG) by varying the Cu concentration in classic molecular-dynamics simulation. From the pair distribution functions(PDFs), it is found that the nearest atomic distance between Zr atom and Zr atom increases significantly after adding Cu, which is related to the composition-dependent coordination behavior between Cu atom and Zr atom in the nearest neighbors. The portion of PDF related to the nearest connection is decomposed into the contributions from quadrilateral structure, pentagonal structure, hexagonal structure,and heptagonal bipyramid structure. Although the population of denser structures, i.e. 5-, 6-, and 7-number sharing ones,increases with Cu addition increasing, the connection distances between the central atoms in all these bipyramids increase for Zr–Zr pairs, leading to the expansion of Zr–Zr nearest atomic distance. These results unveil the effect of the interplay between chemical interaction and geometric packing on the atomic-level structure in Cu–Zr metallic glasses.

Corrosion Behavior of Mg_(65)Cu_(25-x) Zn_xGd_(10)(x=0, 5) Metallic Glass

The effect of substitutional element Zn on corrosion behavior of Mg65Cu25Gd10 glass was investigated. The amorphous structure of Mg65Cu25-xZnxGd10 （x=0,5） alloys were examined by X-ray diffractometry and differential scanning calorimetry （DSC）. The dissolution rates of Mg65Cu25-xZnxGd10 （x=0, 5） metallic glasses in a 5 wt% NaCl solution with pH value of 7 were determined by a hydrogen evolution testing method. The corrosion behavior of these alloys was characterized using dipping tests with 5 wt% NaCl, in combination with electrochemical measurements and scanning electron microscopy （SEM）. Results show that the anti-corrosion ability of Mg65Cu25Gd10 alloy is significantly improved due to the addition of Zn. Possible mechanism responsible for the improvement is discussed.

Structure Relaxation of Mg_(65)Cu_(25)Gd_(10) Metallic Glass and Its Effect on Strength

To identify the re-arrangement of constituent atoms of an amorphous Mg65Cu25Gd10 alloy happened with annealing, structure relaxation of the alloy was investigated as a function of an- nealing time at 373 K through extended X-ray absorption fine structure （EXAFS） analysis procedures. To understand the effect of structure relaxation on strength, compression tests were conducted for both the as-cast and the annealed Mg65Cu25Gd10 samples. It is found that short range order around Cu and Gd atoms exhibits different variation trends with increasing annealing time at 373 K, though the structure of the alloy still remains to be amorphous. Based on the fact that the strength of the alloy first exhibits a reduction and then a recovery with annealing time, it is suggested that the enhancement of short range order around Cu should be responsible for the strength reduction, while the enhancement of short range order around Gd should be responsible for the strength recovery.

Role of yttrium in glass formation of Ti-based bulk metallic glasses

Starting with Zr of two different purities, Ti-based bulk metallic glasses （BMGs） with a nominal composition of Ti40Zr25Cu12Ni3Be20 were prepared. The effect of the addition of yttrium at levels of 0.2 at.%, 0.4 at.%, 0.5 at.%, 0.6 at.%, and 1 at.% on the glass forming ability （GFA） of the alloy has been investigated by means of metallography, X-ray diffraction, and differential scanning calorimetry. Experimental data in-dicates that high impurity content dramatically reduces the glass forming ability. Microalloying with 0.5 at.% Y is effective in suppressing the crystalline phase formation and alleviating the detrimental effect of oxygen in the low-purity alloy. On the contrary, in the alloy contain-ing high-purity element, the effective yttrium addition is less than 0.4 at.%. The results indicate that the beneficial effect of the optimum dopants is mainly due to scavenging the oxygen impurity via the formation of innocuous phase.

Kinetics of Glass Transition and Crystallization in Carbon Nanotube Reinforced Mg-Cu-Gd Bulk Metallic Glass

Mg65Cu25Gd10 bulk metallic glass and its carbon nanotube reinforced composite were prepared. Differential scanning calorimeter （DSC） was used to investigate the kinetics of glass transition and crystallization processes. The influence of CNTs addition to the glass matrix on the glass transition and crystallization kinetics was studied. It is shown that the kinetic effect on glass transition and crystallization are preserved for both the monothetic glass and its glass composite. Adding CNTs in to the glass matrix reduces the influence of the heating rate on the crystallization process. In addition, the CNTs increase the energetic barrier for the glass transition. This results in the decrease of GFA. The mechanism of the GFA decrease was also discussed.

Effect of Nb on the corrosion behavior of continuous bulk metallic glass-coated steel wire composites

（Zr41.2Ti13.sCu12.sNi10Be22.5）100-~Nb~ （at%, x=0 and 8） bulk metallic glasses （BMGs） were coated on the surface of Q195 steel wires by a continuous coating process. The potentiodynamic polarization tests of these BMGs were conducted in 3.5wt% NaC1 aqueous solution. It is found that the addition of 8at% Nb into Zr41.2Ti13.sCu12.sNi10Be22.5 alloy results in the improvement of corrosion resistance with the pitting potential of -52 mV, the open circuit potential of-446 mV, and the corrosion current density of 9.86x 10-6 mA/cm2. This may be attributed to that Nb is beneficial to passivate and stabilize Zr and Ti.

Preparation and Mechanical Properties of Misch Metal Based Bulk Metallic Glasses

The formation, thermal stability and mechanical properties of Misch metal （Mm）-based alloy bulk metallic glasses （BMGs） with composition of Mm55Al25Cu10Ni5Co5 were investigated by means of X-ray diffraction, differential scanning calorimetry, differential thermal analysis and compression test. The results indicate that the Mm-based BMGs exhibit a distinct glass transition and a wide supercooled liquid region Δ Tx（ 〉 60 K） before crystallization. The alloy can be fabricated into bulk glassy form of 3 mm in diameter by copper mold casting methods. Compared with the La55Al25Cu10 Ni5Co5 BMG, the Mm55Al25Cu10Ni5Co5 BMG shows higher compression fracture strength and lower cost. A new parameter γ and melting temperature Tl are closely correlated with the glass forming ability （GFA） of Mm-based alloys.

Porous bulk metallic glass fabricated by powder hot pressing

A synthesis method for the production of porous bulk metallic glass (BMG) was introduced. This method utilizes the su- perplastic forming ability of amorphous powder in the supercooled liquid (SCL) state and intenerating salt mixture as a placeholder to produce BMG foam by using a hot die pressing method. Scanning electron microscope (SEM), X-ray diffraction (XRD) and dif- ferential scanning calorimetry (DSC) were employed to characterize the morphologies of foaming structure, the crystallization and the percentage of crystallization of the as-produced porous BMG. The results suggested that the formation of porous structure by su- perplastic forming process is feasible. Good bonding effect was observed between amorphous powder particles. Less than 6.5% of crystalline phases were formed during hot pressing, and less than 5.5% of residual salt was enclosed in the foam. To remove any re- sidual salt particles, salt preforms with three-dimensional network and good connectivity is necessary.

Deformation and fracture of a Zr-Al-Cu metallic glass ribbon under tension near glass transition temperature

The high temperature tensile and fracture behavior of Zr_(50)Al_(40)Cu_(10) metallic glass at the temperature range in the vicinity of glass transition were investigated. Tensile tests were carried out at room temperature, 350-420 ℃, and in the supercooled liquid region temperature range, respectively. Obvious plastic deformation was initiated at temperature about 80 ℃ lower than the glass transition temperature. The ultimate tensile strength decreases with the increase of testing temperature and the ductility increases with temperature. At temperature higher than Tg, viscous fl ow of Non-Newtonian fl uid led to super plastic deformation behavior. The deformation process under tension was inhomogeneous, and remarkable serrations were observed on the stress-strain curve near glass transition temperature.

Formation and corrosion properties of Fe-based bulk metallic glasses

Bulk metallic glass （BMG） formation was explored in the Fe-B-Si-Nb alloy system though combined use of the atomic cluster line approach and the minor alloying strategy. The basic ternary compositions in the Fe-B-Si system were determined by the intersection points of two cluster lines, namely, Fe-B cluster to Si and Fe-Si cluster to B. 3at% -4at% Nb was added to the quaternary Fe-B-Si-Nb alloy. The casting experiments revealed that good glass-forming ability （GFA） occurred at the （Fe73.4Si8.2B18.4）96Nb4 composition, and 3-mm diameter BMG samples were made. The glass transition temperature （Tg）, crystallization temperature （Tx）, and supercooled liquid region （△Tx=Tx-Tg） of this BMG were measured to be 866, 889, and 23 K, respectively. The BMG shows a high Vickers hardness of about Hv 1164, a Young＇s modulus of 180 GPa, and a good corrosion resistance in the solutions of 1 mol/L HCl and 3wt% NaCl.

Ballistic performance of tungsten particle/metallic glass matrix composite long rod

In the present manuscript numerical analysis on the ballistic performance of a tungsten particle/metallic glass matrix(WP/MG) composite rod is conducted by integrating with related experimental investigations. In the corresponding finite element method(FEM) simulations a modified coupled thermomechanical constitutive model is employed to describe the mechanical properties of metallic glass(MG)matrix, and geometrical models of the WP/MG composite rod are established based on its inner structure. The deformation and failure characteristics of the rod and target materials are analyzed in detail,and the influences of various factors on the ballistic performance of the WP/MG composite long rod are discussed. Related analysis demonstrates that the penetrating performance of the WP/MG rod is similar to that of the tungsten fiber/metallic glass matrix(WF/MG) composite long rod, i.e., a "self-sharpening" behavior also occurs during the penetration process, and correspondingly its penetrating capability is better than that of the tungsten heavy alloy(WHA) rod. However, the mass erosion manner of the WP/MG rod is different and the erosion is relatively severe, thus its penetrating capability is a little lower compared with that of the WF/MG one. Moreover, the impact velocity and the target strength have significant influences on the ballistic performance of the WP/MG composite rod, whereas the effect of initial nose shape is very little.