Zr–Cu–Ni–Al bulk metallic glasses with superhigh glass-forming ability

Zr–Cu–Ni–Al quaternary amorphous alloy compositions with varying glass-forming ability are developed by an efficient method of proportional mixing of binary eutectics. The critical diameter of the glassy sample is improved from 6 mm for Zr₅₃Cu_18.7Ni₁₂Al_16.3 to 14 mm for Zr_50.7Cu₂₈Ni₉Al_12.3 by straightforwardly adjusting the eutectic unit’s coefficients. The drastic improvement in GFA is attributed to balancing the chemical affinities of the Zr, Cu, Ni and Al components in the melt prior to solidification which makes the precipitation of competing crystalline phases more difficult. As the glass-forming ability increases, the concentration of Cu in the alloys exhibits a same trend. Based on synchrotron radiation high-energy X-ray diffraction analysis and Miracle’s structural model, it is envisioned that the substitution of additional Cu atoms for Zr atoms in the investigated alloys stabilizes the efficient cluster packing structure of the amorphous alloys, leading to the pronounced increase in their glass-forming ability.     

Effect of addition of Be on glass-forming ability,plasticity and structural change in Cu–Zr bulk metallic glasses

The present study reports the effect of the addition of Be in Cu–Zr bulk metallic glass (BMG) on glass-forming ability (GFA), plasticity and structural change. Although Be has a negative enthalpy of mixing with all the constituent elements of these glasses, Cu_47.5Zr₄₀Be_12.5 alloy exhibits apparent double glass transitions (T_g) and enhanced plasticity as well as improved GFA. Intensive structural analysis using extended X-ray absorption fine structure suggests that a large difference in the enthalpy of mixing between atom pairs in multi-component BMGs can cause atomic scale structural inhomogeneity and/or locally favored structures in the amorphous matrix, resulting in enhanced compressive strains, although the enthalpies of mixing for atom pairs are all negative. This concept may shed light on the development of BMGs with large plasticity as well as high GFA.     

First-principles prediction of the glass-forming ability in Zr–Ni binary metallic glasses

In the present study, the atomistic approach, developed previously by hybridizing both internal energies and atomic-scale defect structures, is extended to predict the trend of glass forming ability (GFA) from the Zr–Cu binary alloy system with good GFA to the Zr–Ni binary system with relatively poor GFA. The predicted composition dependence of the GFA in the Zr–Ni alloy system is consistent with those obtained from experimental results, indicating the validity of the proposed atomistic approach in both of the alloy systems. The different GFAs in the Zr–Cu and Zr–Ni systems have been puzzled by the metallic glass community for quite a long time, and our study provides the physical reasons for the different glass forming behaviors of the two alloy systems in terms of both atomic configurations and relative stability of their intermetallic phases.     

Glass forming ability and mechanical properties of Nb-containing Cu–Zr–Al based bulk metallic glasses

Mechanical properties of (Cu₅₀Zr₄₃Al₇)_100-xNb_x (x=0,1,3,6,9) bulk metallic glasses rods with a diameter of 2.5～mm prepared by suction casting method were studied. The results of uniaxial compression tests at room temperture show that the best mechanical properties of 2.8% and 1.98 GPa for plastic strain and fracture strength, respectively, in the sample with x=3. Microstructure, fracture surface and shear bands of the samples were observed by SEM and XRD methods.     

Thermal stability,magnetic and mechanical properties of Fe–Dy–B–Nb bulk metallic glasses with high glass-forming ability

The effects of Dy addition on the thermal stability, glass-forming ability (GFA), magnetic and mechanical properties of quaternary (Fe_0.76−xDy_xB_0.24)₉₆Nb₄ (x = 0–0.07) bulk metallic glasses (BMGs) were investigated. Increasing Dy content from x = 0 to 0.05 extended the supercooled liquid region up to 112 K, allowing the fabrication by copper mold casting of BMGs rods with 5.5 mm in diameter. The high GFA was found to be related to the structure of primary crystalline phase. For the x = 0.05 alloy, the competitive formation process of the complex Fe₂₃B₆ and Dy₂Fe₁₄B phases enabled to obtain the largest GFA value. Moreover, the Fe–Dy–B–Nb BMGs exhibited good soft-magnetic properties, i.e., high saturation magnetization of 1.18–0.56 T and low coercive force of 1.9–21.6 A/m. In addition, the glassy alloy rods also showed high compressive fracture strengths of 4400–4150 MPa and high Vickers hardness of 1110–1090 kg/mm².     

Correlation between mechanical behavior and glass forming ability of Zr–Cu metallic glasses

A series of Zr–Cu glassy ribbons were fabricated, and the compositional dependence of microhardness in the as-quenched and annealed state was systematically investigated. The as-quenched microhardness exhibits a positive deviation from linearity at the compositions which correspond to local maximum in glass forming ability (GFA). Upon annealing, the microhardness change is relatively smaller for the high GFA compositions. High atomic packing density at the special compositions should be responsible for the microhardness behavior.     

Composition optimization of the Al–Co–Zr bulk metallic glasses

Composition optimization for locating the composition with the largest glass forming ability in the Al–Co–Zr system is attempted in this investigation. The criteria that we have developed are respectively related to a specific conduction electron concentration, termed the e/a-constant criterion, and to a specific cluster structure, termed the e/a-variant criterion. For this system, the two criteria are incarnated into the composition line with constant e/a=1.5 and the Co₄Zr₉–Al composition line. Bulk metallic glasses are obtained by suction casting for compositions with e/a=1.3–1.5, with their thermal stabilities and glass forming abilities being increased with increasing e/a ratios. The crossing point of the e/a=1.5 line and the Co₄Zr₉–Al line gives the composition Al_23.5Co_23.5Zr₅₃ with the largest GFA (e.g. T_g/T_m=0.637), superior to the reported Al₂₀Co₂₅Zr₅₅ alloy with T_g/T_m=0.621.     

Formation and properties of Ti-based Ti–Zr–Cu–Fe–Sn–Si bulk metallic glasses with different (Ti + Zr)/Cu ratios for biomedical application

Ti-based Ti–Zr–Cu–Fe–Sn–Si bulk metallic glasses (BMGs) free from highly toxic elements Ni and Be were developed as promising biomaterials. The influence of (Ti + Zr)/Cu ratio on glass-formation, thermal stability, mechanical properties, bio-corrosion resistance, surface wettability and biocompatibility were investigated. In the present Ti-based BMG system, the Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy exhibited the highest glass forming ability (GFA) corresponding to the largest supercooled liquid region, and a glassy rod with a critical diameter of 3 mm was prepared by copper-mold casting. The Ti-based BMGs possess high compressive strength of 2014–2185 MPa and microhardness of 606–613 Hv. Young's modulus of the Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy was about 100 GPa, which is slightly lower than that of Ti–6Al–4V alloy. The Ti₄₇Zr_7.5Cu₄₀Fe_2.5Sn₂Si₁ glassy alloy with high GFA exhibited high bio-corrosion resistance, and good surface hydrophilia and cytocompatibility. The mechanisms for glass formation as well as the effect of (Ti + Zr)/Cu ratio on bio-corrosion behavior and biocompatibility are discussed.     

Effect of addition of Zn and Al elements on glass-forming ability and thermal stability of Mg-Cu-Y bulk metallic glasses

After substituting partial Cu and Mg with Zn or Al elements for Mg65Cu25Y10 alloy, respectively, the metallic glass plate samples with thickness of 2-3 mm were prepared by water-quenching, their respective glass-forming ability and thermal stability were studied by using differential thermal analysis （DTA） and X-ray diffraction （XRD）. Using Kissinger equation, the activation energies of crystallization of these metallic glasses heated with a constant rate were calculated. The results show that Al element is greatly harmful to the glass-forming ability of Mg-Cu-Y alloys and cannot acquire bulk amorphous alloys; nevertheless, the effect of Zn element addition is indeterminate for various components. The magnitudes of thermal stability are also revealed.     

Mg–Ni–Gd–Ag bulk metallic glass with improved glass-forming ability and mechanical properties

The improvement of glass-forming ability (GFA) and mechanical properties by using Ag to substitute Mg in the Mg–Ni–Gd bulk metallic glass (BMG) were studied. The Mg₆₉Ni₁₅Gd₁₀Ag₆ bulk metallic glass (BMG) could be cast into glassy rod up to 7 mm. The activation energies of Mg₆₉Ni₁₅Gd₁₀Ag₆ metallic glass were calculated by the Kissinger’s method to be E_g = 2.24 eV, E_x = 1.65 eV, E_p1 = 1.36 eV, E_p2 = 1.59 eV, E_p3 = 1.26 eV and E_p4 = 1.99 eV. The compressive fracture strength and the plastic strain of Mg₆₉Ni₁₅Gd₁₀Ag₆ BMG reached 846 MPa and 0.37% respectively.     

Structural origins for the high plasticity of a Zr–Cu–Ni–Al bulk metallic glass

The structural origins for the high plasticity of a Zr₅₃Cu_18.7Ni₁₂Al_16.3 (at.%) bulk metallic glass are explored. Under plastic flow conditions, in situ synchrotron high-energy X-ray diffraction reveals that the atomic strain saturates to the closest packing in the longitudinal direction of the applied load while atoms yield in the transverse plane. Scanning electron microscopy investigation reveals that global plasticity benefits from abundant shear band multiplication and interactions. Atomic level flows are seen to accompany profuse shear bands. The plasticity enhancement of this metallic glass benefits from such atomic level flows. Atomic level flow facilitates the activation of shear transformation zones that further self-assemble to promote shear band multiplication. On the other hand, it also mitigates the shear band propagation that prevents catastrophic shear band extension.     

Corrosion behavior of Zr–Cu–Ni–Al bulk metallic glasses in chloride medium

Polarization and passivation behavior of three Zr-based BMGs, i.e. Zr_58.3Al_14.6Ni_8.3Cu_18.8, Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 were investigated in 3% NaCl aqueous solution. Electrochemical investigations were carried out by potentiodynamic polarization method at room temperature. The corroded sample surfaces were examined using scanning electron microscope having energy dispersive spectroscopy (EDS) attachment. The results of the present investigation revealed that Zr₅₈Al₁₆Ni₁₁Cu₁₅ and Zr_57.5Al_17.5Ni_13.8Cu_11.3 BMGs having relatively larger supercooled liquid region (ΔT_x) and pitting overpotential (η_pit) values exhibit low corrosion current density (i_corr) and corrosion penetration rate (CPR) values.     

Thermodynamic modeling and composition design for the formation of Zr–Ti–Cu–Ni–Al high entropy bulk metallic glasses

This work explores the idea of predicting metallic glass forming composition in a multi component alloy for which an equilibrium phase diagram is yet to be deciphered. Deep eutectic regions in a quaternary alloy (Zr–Ti–Cu–Ni) have been extrapolated to the quinary Zr–Ti–Cu–Ni–Al system for designing a potential bulk glass forming composition. P_HSS parameter which is the product of mixing enthalpy, mismatch entropy and configurational entropy of an alloy, has been utilized for thermodynamic modeling. P_HSS values are computed through substitution of Al into the each of the fifteen quaternary eutectics that have been reported in the literature in the Zr–Ti–Cu–Ni system. A good correlation of P_HSS range between modeled alloys and established glass formers indicates the subtle efficacy of this method for high entropy amorphous alloy design through a rationale thermodynamic approach.     

Effects of rare-earth elements on the glass-forming ability and mechanical properties of Cu46Zr47-xA17Mx （M = Ce, Pr, Tb, and Gd） bulk metallic glasses

Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr, Tb, and Gd) bulk metallic glassy (BMG) alloys were prepared by copper-mold vacuum suction casting. The effects of rare-earth elements on the glass-forming ability (GFA), thermal stability, and mechanical properties of Cu₄₆Zr_47−x Al₇M _x were investigated. The GFA of Cu₄₆Zr_47−x Al₇M _x (M = Ce, Pr) alloys is dependent on the content of Ce and Pr, and the optimal content is 4 at.%. Cu₄₆Zr_47−x Al₇Tb _x (x = 2, 4, and 5) amorphous alloys with a diameter of 5 mm can be prepared. The GFA of Cu₄₆Zr_47−x Al₇Gd _x (x = 2, 4, and 5) increases with increasing Gd. T _x and T _p of all decrease. T _g is dependent on the rare-earth element and its content. ΔT _x for most of these alloys decreases except the Cu₄₆Zr₄₂Al₇Gd₅ alloy. The activation energies ΔE _g, ΔE _x, and ΔE _p for the Cu₄₆Zr₄₂Al₇Gd₅ BMG alloy with Kissinger equations are 340.7, 211.3, and 211.3 kJ/mol, respectively. These values with Ozawa equations are 334.8, 210.3, and 210.3 kJ/mol, respectively. The Cu₄₆Zr₄₅Al₇Tb₂ alloy presents the highest microhardness, Hv 590, while the Cu₄₆Zr₄₃Al₇Pr₄ alloy presents the least, Hv 479. The compressive strength (σ _c.f.) of the Cu₄₆Zr₄₃Al₇Gd₄ BMG alloy is higher than that of the Cu₄₆Zr₄₃Al₇Tb₄ BMG alloy.     

Formation and mechanical properties of bulk Cu-Ti-Zr-Ni metallic glasses with high glass forming ability

Bulk amorphous Cu52.5Ti30Zr11.5Ni6 and Cu53.1Ti31.4Zr9.5Ni6 alloys with a high glass forming ability can be quenched into single amorphous rods with a diameter of 5 mm, and exhibit a high fracture strength of 2 212 MPa and 2 184 MPa under compressive condition, respectively. The stress—strain curves show nearly 2% elastic strain limit, yet display no appreciable macroscopic plastic deformation prior to the catastrophic fracture due to highly localized shear bands. The present work shows clearly evidence of molten droplets besides well-developed vein patterns typical of bulk metallic glasses on the fracture surface, suggesting that localized melting induced by adiabatic heating may occur during the final failure event.     

The effects of hydrogen on viscoelastic relaxation in Zr–Ti–Ni–Cu–Be bulk metallic glasses: implications for hydrogen embrittlement

The effects of hydrogen on the viscoelastic relaxation behavior of a Zr–Ti–Ni–Cu–Be bulk metallic glass have been investigated in an attempt to elucidate hydrogen-affected flow and fracture behavior. Dynamic mechanical testing was performed to study relaxation behavior near the glass transition temperature. Relaxation time constants were increased in the presence of hydrogen with a concomitant increase of thermal activation energy. In addition, the glass transition temperature was increased and crystallization kinetics retarded in the presence of hydrogen leading to enhanced thermal stability. Positron annihilation spectroscopy was employed to study the interaction of hydrogen and open-volume regions. While hydrogen charging was found to decrease the open-volume regions in the amorphous phase, an increase in free volume was observed in the crystalline counterpart. The amorphous phase was found to have a greater hydrogen absorption capacity compared to its crystalline counterpart. Relaxation behavior, crystallization kinetics and the interaction of hydrogen with the amorphous microstructure are discussed. Finally, the effects of retarded relaxation processes on fracture resistance are considered.     

Effect of Nb content on the microstructures and mechanical properties of Zr–Ti–Cu–Be–Nb glass-forming alloys

(Zr₃₅Ti₃₀Be_27.5Cu_7.5)_100?xNb_x (x = 0, 5, 8, 10, 12, 15 at.%) glass-forming alloys were prepared by copper-mould suction casting. The alloys with different Nb contents exhibited different microstructures and mechanical properties. The proper addition of Nb (x = 5, 8 at.%) to the Zr–Ti–Be–Cu system could ensure the formation of mostly amorphous phase. And excessive amount of Nb favored the formation of the bcc β-Zr solid solution. The alloys with Nb contents of 8 at.%, 10 at.%, and 12 at.% displayed the distinguished plasticity of 11.1%, 7.6%, and 11.0%, respectively.     

Finite element simulation and experimental investigation of forming micro-gear with Zr–Cu–Ni–Al bulk metallic glass

Bulk metallic glasses exhibit some unique physical properties as compared to their corresponding crystalline alloys. Due to the superplasticity by behaving like a Newtonian fluid in their supercooled liquid region, the bulk metallic glasses can be used to make high strength microparts by net-shape forming. In this paper, the compressive tests of Zr–Cu–Ni–Al metallic glass are performed with different strain rates at a temperature of 683 K. According to the experimental results, the forming evolution of a metallic glass micro-gear is simulated using a finite element simulation software DEFORM 3D, and the forming load is predicted at different processing parameters. Meanwhile, the filling stages of bulk metallic glass in the micro-gear mold cavity are investigated by finite element simulation and experiment. The predicted workpiece geometry shows good agreement with experimental result. The forming experiments for micro-gear of Zr–Cu–Ni–Al metallic glass are carried out by hot embossing process, and the amorphous micro-gears are obtained successfully. It is found that the finite element simulation results are in reasonable agreement with the experimental observation.     

Remarkable effect of Ce base element purity upon glass forming ability in Ce–Ga–Cu bulk metallic glasses

Raw Ce element materials of eleven different purities are used to prepare bulk metallic glasses with the same nominal composition of Ce₇₀Ga₈Cu₂₂ (at.%). In the high-purity regime of Ce (98.13–99.87wt.%), three distinct peaks are observed in the curve plotting the purity vs. the glassy rod critical diameter (D_c); and with ∼0.11 wt.% decrease in purity, the D_c can increase sharply from 1 to 10 mm. In the relatively low-purity regime of 96.15–98.13 wt.%, the low material purity is found to be beneficial for glass formation; and with a ∼0.61 wt.% decrease in purity, the D_c increases dramatically from 1.5 mm to at least 20 mm. Such a sensitive and systematic purity-dependent glass-forming ability has rarely been reported before in metallic glasses. It is also suggested that the high stability of the competing crystalline phases results from the mixture effect via addition of multiple impurity elements into the matrix glass-forming alloys, and that this addition of impurity elements may be the dominant factor responsible for their intrinsic glass-forming ability of these alloys. The results provide systematic evidence for the strong purity and composition effects that are present in glass formation, and can be used to shed light on scientific research and industrial applications in the field of metallic glasses.