钨丝增强ZrAlNiCuSi块体非晶复合材料及其塑性行为

采用渗流铸造法制备出了钨丝增强ZrAlNiCuSi块体非晶复合材料，在压缩条件下复合材料表现出弹性-完全塑性的应力-应变行为，和未复合的大块非晶相比，总应变量提高600%以上，非晶复合材料塑性提高的原因是钨丝阻碍了非晶基体剪切带的滑移，诱发多个剪切带的产生，同时滑移的面积增大的结果，复合材料的破坏方式与钨丝体积分数有关，在体积分数小于40%时一般为剪切破坏，大于60%时为纵向劈裂破坏，介于（40-60）%之间时，在钨丝与界面结合良好的情况下，趋于剪切破坏，否则为劈裂的破坏方式。     

Optimized interface and mechanical properties of W fiber/Zr-based bulk metallic glass composites by minor Nb addition

W fiber/Zr-based bulk metallic glass composites were prepared by melt infiltration casting and the interface reaction in composites was studied in detail. It was found that minor Nb addition to the matrix can suppress the interface peritectic reaction and optimize the interface structure in W fiber/Zr-based bulk metallic glass composites. Taking the interface characteristics of composites and glass forming ability of the matrix into account, an optimized alloy Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ was selected as a new metallic glass matrix. The interface in the W fiber/Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ bulk metallic glass composite has excellent interface bonding, and the compressive strength of 70% W fiber/Zr₄₇Ti₁₃Cu₁₁Ni₁₀Be₁₆Nb₃ metallic glass composite is 2.6 GPa, 58% higher than the unreinfored matrix. Multiple shear band formation in the matrix, which results from the interaction between W fiber and the matrix, can answer for the high ultimate fraction strength and excellent plastic deformation of the composite.     

Shear band evolution and hardness change in cold-rolled bulk metallic glasses

A systematic investigation of the shear band evolution and hardness change with deformation was performed on cold-rolled Zr_64.13Cu_15.75Ni_10.12Al₁₀ and Zr_46.5Cu₄₅Al₇Ti_1.5 bulk metallic glasses. It was found that primary shear bands reach saturation after 7% in thickness reduction and only primary shear bands exist below 20% in thickness reduction, based on statistical analyses of primary shear band spacing, angle and offset. Rolling creates more free volume, and deformation-induced residual stress distribution in a heavily rolled specimen relative to the as-cast specimen has been determined. Larger tensile residual stresses are generated on the side surface as compared with those on the top surface, while compressive residual stresses in the middle are induced. Such residual stresses strongly influence the hardness measured. It is also revealed that after stress relief, the hardness does not decrease considerably in heavily rolled/annealed specimens here as compared to as-cast/annealed specimens, probably due to low shear band density.     

Experimental characterization of plastic flow initiation in a bulk metallic glass via intermittent compression test

Intermittently plastic compression tests of the Zr_52.5Cu_17.9Ni_14.6Al₁₀Ti₅ bulk metallic glass were performed under a geometrically constrained condition at different cross-head displacement rates. A flow stress-overshoot phenomenon was observed during the macroscopically plastic deformation. It was found that there is a close correlation between the stress-overshoot intensity and the spatial density of shear bands. The stress-overshoot intensity can be used as a parameter to characterize the ability of plastic flow initiation caused by the spatial nucleation of shear bands in the bulk metallic glass. The micromechanisms of shear band multiplication were discussed.     

Effect of Ta on glass formation,thermal stability and mechanical properties of a Zr52.25Cu28.5Ni4.75Al9.5Ta5 bulk metallic glass

The effect of Ta on glass-forming ability, crystallization behavior and mechanical properties of Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ bulk metallic glass (BMG) is investigated. The solubility of Ta in the Zr-base BMG alloy depends on the arc melting conditions. 3.2 at.% Ta dissolve in the alloy inducing an increase of about 20 K in both glass transition temperature and crystallization temperature of the BMG. However, Ta does not significantly change the extension of the supercooled liquid region. The remaining Ta particles in the master alloy may induce a composition-segregation layer around the particles upon subsequent casting. This further induces the crystallization of Zr₂Cu that deteriorates the ductility of the samples. The compressive strength and ductility of the as-cast 3 mm diameter Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ samples are improved in comparison with the Zr₅₅Cu₃₀Ni₅Al₁₀ BMG alloy. The fracture plane of the present alloy has an angle of 31–33° with respect to the stress axis, which remarkably deviates from the maximum shear stress plane. The improvement of the mechanical properties and the peculiar fracture feature for the Zr_52.25Cu_28.5Ni_4.75Al_9.5Ta₅ BMG alloy can be attributed to the effect of dispersed Ta particles.     

EFFECT OF Gd ADDITION ON THE GLASS FORMING ABILITY AND MECHANICAL PROPERTIES IN A Zr–BASED BULK AMORPHOUS ALLOY

适量的Gd掺杂可提高Zr_50.7Cu₂₈Ni₉Al_12.3块体非晶合金的玻璃形成能力, 当Gd元素掺杂量 (原子分数) 为1%时, 即(Zr_50.7Cu₂₈Ni₉Al_12.3)₉₉Gd₁, 柱状非晶合金直径可达16 mm (不掺杂时为14 mm). 稀土Gd掺杂降低了锆基块体非晶合金的断裂强度与塑性 变形能力. 随着Gd含量的增加, 其断裂方式由单一的剪切断裂转变为剪切断裂与破碎断裂的复合形式, 且含Gd元素掺杂的非晶合金断口呈现了脉状纹络与纳米周期性条纹共存的特征.     

Effect of cold rolling on compressive and tensile mechanical properties of Zr52.5Ti5Cu18Ni14.5Al10 bulk metallic glass

The effect of cold-rolling on structure, thermal stability, and compressive and tensile mechanical properties of the Zr_52.5Ti₅Cu₁₈Ni_14.5Al₁₀ bulk metallic glass has been investigated. The results reveal that cold-rolling does not influence the thermal stability of the material. However, the small plastic deformation induced by cold-rolling is very effective for improving the room temperature plastic strain of the glass: the compressive plastic strain increases from 1.1% for the as-cast material to 2.6% for the cold-rolled sample and the tensile ductility increases from 0% for the as-cast glass to 0.8% for the cold-rolled sample. Hardness measurements indicate that cold rolling creates a heterogeneous microstructure consisting of hard and soft regions. Most likely, the soft regions are preferred locations for shear band formation and propagation, whereas the hard regions may act as obstacles for shear band propagation, effectively limiting shear bands from propagating catastrophically and, consequently, enhancing the room temperature plastic deformation of the glass.     

Machining of a Zr–Ti–Al–Cu–Ni metallic glass

Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ metallic glass machining chips were characterized using SEM, X-ray diffraction and nano-indentation. Above a threshold cutting speed, oxidation of the Zr produces high flash temperatures and causes crystallization. The chip morphology was unique and showed the presence of shear bands, void formation and viscous flow.     

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.     

Microstructure and electrochemical behavior of Ti-coatedZr55Al10Ni5Cu30 bulk metallic glass

In this study, pure Ti was coated on Zr₅₅Al₁₀Ni₅Cu₃₀ bulk metallic glass (BMG) using a physical vapour deposition (PVD) technique with magnetron sputtering. Microstructures of Ti coating, BMG substrate and interface were investigated by conventional and high-resolution transmission electron microscopy (TEM and HREM). The electrochemical behavior of Ti-coated Zr₅₅Al₁₀Ni₅Cu₃₀ BMG was studied by potentiodynamic polarization curves and electrochemical impedance spectroscopy (EIS) in Hanks' solution. Scanning electron microscopy (SEM) was used to characterize the surface morphology of the coating after electrochemical testing. HRTEM observation reveals that the sputtering Ti coating consists of α-Ti nano-scale particles with the size about 10 nm. The polarization curves revealed that the open-circuit potential shifted to a more positive potential and the passive current density was lower after Ti coating was applied in comparison with that of the monolithic Zr₅₅Al₁₀Ni₅Cu₃₀ BMG. Electrochemical impedance spectroscopy (EIS) measurements showed that the Bode plots of Ti-coated Zr₅₅Al₁₀Ni₅Cu₃₀ BMG presented one time constant for 1 h and 12 h immersion and two time constants after 24 h immersion. The good bonding condition between Ti coating and Zr₅₅Al₁₀Ni₅Cu₃₀ BMG substrate may be responsible for the high corrosion resistance of Ti-coated Zr₅₅Al₁₀Ni₅Cu₃₀ BMG.     

DEFORMATION BEHAVIOR AND CONSTITUTIVE EQUATION FOR Zr55Cu30Al10Ni5 BULK METALLIC GLASS IN SUPERCOOLED LIQUID REGION

Zr₅₅Cu₃₀Al₁₀Ni₅块体非晶合金(BMG)在过冷液态区内的单向压缩实验表明: 材料在过冷液态区内的形变行为强烈依赖于温度和变形速率. 随着应变速率的增加, 材料的流变特征由Newtonian流变转变为非Newtonian流变.利用扩展指数本构方程模型建立了非晶合金的流变应力、应变速率和温度的关系.     

Plasticity improvement of (Cu43Zr48Al9)98Y2 bulk metallic glass composites by dispersed Ta particles

(Cu₄₃Zr₄₈Al₉)₉₈Y₂-based bulk metallic glass composites (BMGCs) with dispersed Ta particles (3vol.%, 6vol.%, 9vol.%) were successfully fabricated through suction casting. The thermal properties, microstructure, and mechanical properties of the BMGCs were systematically investigated. Ta particles are homogeneously dispersed in the amorphous matrix. Ta particle reinforced BMGCs exhibit similar thermal properties and glass-forming ability with the (Cu₄₃Zr₄₈Al₉)₉₈Y₂ base BMG. Compression test results show that the BMGC with 9vol.% Ta particles has superior mechanical performance with up to 15.7% compressive plastic strain, 2,216 MPa yield strength, and 2,260 MPa fracture strength at room temperature. These homogeneously distributed Ta particles act as discrete obstacles in the amorphous matrix, restricting the highly localized shear band. This results in the formation of multiple shear bands around the Ta-rich particles, which lowers the stress concentration, allowing the shear band to propagate further and improve plasticity.

     

Partial crystallization of as-quenched Zr55Cu30Al10Ni5 bulk metallic glass induced by oxygen

Dendritic crystals, randomly distributed into the as-quenched Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass were characterized by optical microscopy, electron probe microanalysis, X-ray diffraction and electron backscattering diffraction. Oxygen enrichment is observed into these crystallites (formula: Zr₇Cu₄Al₃O, space group: Fd m, cell parameter: 5.70 Å) demonstrating the negative effect of oxygen, inducing partial crystallization during casting.     

High strength ductile Cu-base metallic glass

Usually, bulk metallic glasses exhibit strength values superior to conventional crystalline alloys, often combined with a large elastic limit and rather low Young's modulus. This combination of properties renders such alloys quite unique when compared to commercial materials. However, the major drawback for engineering applications is their limited room temperature ductility and toughness due to the localized deformation processes linked to shear banding, where high plastic deformation is accumulated in a very narrow region without contributing to macroscopic deformation, work hardening or yielding. In this work we report on a new class of metallic glass in a simple Cu-base alloy. Addition of 5 at.% Al increases the glass-forming ability of binary Cu₅₀Zr₅₀. The resulting Cu_47.5Zr_47.5Al₅ glass exhibits high strength (2265 MPa) together with large room temperature ductility up to 18%. After yielding a strong increase in the flow stress is observed during deformation. The structure of the metallic glass exhibits atomic-scale heterogeneities that enable easy nucleation and continuous multiplication of shear bands. The interaction and intersection of shear bands increases the flow stress of the material with further deformation, leading to a ‘work hardening’-like behavior and yields a continuous rotation of the shear angle up to fracture resulting in a high compressive ductility.     

Mechanical properties of monolithic Zr62Al8Ni13Cu17 bulk metallic glass

We present mechanical properties of monolithic bulk metallic glass (BMG) Zr₆₂Al₈Ni₁₃Cu₁₇ under uniaxial compression and tensile tests. It is found that the Zr₆₂Al₈Ni₁₃Cu₁₇ BMG exhibits pronounced plasticity of nearly 14% without catastrophic failure upon compression. However, it is destroyed under tension in a brittle manner. High energy X-ray diffraction has been used to detect the structural change in this BMG during both conditions. No deformation-induced nanocrystallization is detected in a 55% strained sample under compression while it only appears in the fracture-affected region upon tension. No excess free volume is obviously found in the fractured samples. We suggest that monolithic BMG alloys with small differences in atomic affinity and atomic sizes among components might have high plasticity under compression.     

Structural effects of shot-peening in bulk metallic glasses

Shot-peening induces surface compressive stresses in bulk metallic glass components, improving their plasticity. Structural changes in the peened surface of fully glassy and partially crystalline Zr₅₅Al₁₀Cu₃₀Ni₅ are studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. An earlier study is extended by examining the effect of sample temperature. While fully glassy samples show no phase change under peening, partially crystalline samples show either amorphization or crystallization depending on temperature. Peening can induce very large stored energy in metallic glasses rendering them susceptible to crystallization below room temperature, a result which may be relevant for improving the plasticity of these materials.     

W丝增强含Co锆基非晶复合材料的变形行为与力学性能

采用渗流铸造方法制备了W丝增强Zr-Ti-Cu-Be-Co非晶基复合材料，研究了复合材料的变形方式及力学性能。结果表明：W丝增强复合材料在准静态压缩条件下不仅保持了Zr-Ti-Cu-Be-Co非晶基体高的强度，而且表现出很高的塑性。与纯非晶相比提高了900％。随着W丝体积分数的增加，复合材料的变形方式由剪切滑移转变为W丝的弯曲和劈裂。复合材料的宏观塑性变形量与压缩过程中产生的剪切带数量成正比。W丝对非晶基体单一剪切带滑移的阻碍，促进多重剪切带的产生和扩展是复合材料产生大量塑性变形的微观机理。     

Electron irradiation induced nano-crystallization in Zr66.7Ni33.3 amorphous alloy and Zr60Al15Ni25 metallic glass

Electron irradiation induced phase transformation behavior of an amorphous phase in Zr_66.7Ni_33.3 alloy, and an amorphous phase or supercooled liquid in Zr₆₀Al₁₅Ni₂₅ alloy was investigated. The amorphous phase could not maintain the original glassy structure under electron irradiation at 298 K, and f.c.c.-solid solution precipitated under electron irradiation in both alloys. The precipitation of C16-Zr₂Ni, big-cube (metastable f.c.c.-based Zr₂Ni intermetallic compound), Zr₆Al₂Ni and Zr₅AlNi₄ crystalline phases from an amorphous phase was not observed during electron irradiation induced crystallization. The amorphous phase in Zr₆₀Al₁₅Ni₂₅ metallic glass shows the highest phase stability against electron irradiation induced crystallization among Zr_66.7Cu_33.3, Zr_66.7Ni_33.3, Zr₆₅Al_7.5Ni_27.5, Zr₆₀Al₁₅Ni₂₅ and Zr₆₅Al_7.5Ni₁₀Cu_17.5 alloys. In Zr₆₀Al₁₅Ni₂₅ metallic glass, electron irradiation promoted the precipitation of f.c.c.-solid solution and Zr₆Al₂Ni crystalline phases from the supercooled liquid.     

Bulk metallic glasses in the Zr-Al-Ni-Cu system

Electron concentration and atomic size rules are important criteria for bulk metallic glass formation. According to these rules, a series of new Zr-Al-Ni-Cu amorphous alloys with a constant e/a ratio of 1.4 and an average atomic size of 0.1496 nm was designed. All the alloys have high glass forming abilities, large supercooled liquid regions ΔT_x, and large reduced glass transition temperatures T_rg. The best glass forming composition is located near Zr_63.8Al_11.4Ni_17.2Cu_7.6. Its glass forming ability is higher than that of the Inoue alloy Zr₆₅Al_7.5Ni₁₀Cu_17.5.     

Effect of pre-existing shear bands on the tensile mechanical properties of a bulk metallic glass

Bulk Zr_64.13Cu_15.75Ni_10.12Al₁₀ metallic glass has been rolled at room temperature in two different directions, and the dependences of microstructure and tensile mechanical property on the degree of deformation and rolling directions have been investigated. No deformation-induced crystallization occurs except for shear bands. Shear band formation in conjugated directions is achieved in the specimen rolled in two directions, while rolling in one direction induces shear band formation only in a single direction. Pre-existing properly spaced soft inhomogeneities can stabilize shear bands and lead to tensile plastic strain, and the efficient intersection of shear bands in conjugated directions results in work-hardening behavior, which is further confirmed by in situ tensile scanning electron microscopic observation. Based on the experimental results obtained in two different specimen geometries and finite element analysis, it is deduced that a normal-stress-modified maximum shear stress criterion rather than a shear plane criterion can describe the conditions for the formation of shear bands in uniaxial tension.