Friction Stir Welding of Zr_(55)Al_(10)Ni_5Cu_(30) Bulk Metallic Glass to Crystalline Aluminum

The Zr55Al10Ni5Cu30 bulk metallic glass plate were successfully welded to crystalline aluminum plates by using a friction stir welding (FSW) method. The welded zone was examined. No defects, cracks or pores were observed and no other crystalline phases except for aluminum were found in the welded joint. The strength of the joint is higher than that of aluminum. The glassy phase in the stir zone keeps the amorphous state, showing a successful welding. The storage modulus softens over the glass transition. An...     

Effect of Minor Alloying on Crystallization Behavior and Thermal Properties of Zr_(64.5)Ni_(15.5)Al_(11.5)Cu_(8.5) Bulk Amorphous Alloy

Minor alloying plays an important role in the synthesis and improvement of thermal stability of bulk metallic glasses(BMGs).The present study was conducted to investigate the effect of minor additions of Y,Ti and Nb on the crystallization behavior and the thermal properties of Zr64.5Ni15.5Al11.5Cu8.5 alloy.Thermal parameters and the activation energies for crystallization were calculated for four(Zr0.645Ni0.155Al0.115-Cu0.085)100-xMx(M=Y,Ti and Nb,while x=0,2 at.) alloys.The present alloys have wide supercooled liquid region of ≥87 K.Maximum activation energy was found to be greater than 300 kJ/mol for the base alloy.Four crystalline phases were identified in the samples annealed at 823 K for 20 min.Reduced glass transition temperature(Trg) and other thermal parameters such as γ,δ and β were improved by Y and Ti addition.Nb addition resists crystallization below annealing temperature 713 K,however,its effect on thermal properties is not very promising.     

Crystallization Study of Cu_(56)Zr_7Ti_(37) Metallic Glass by Electrical Resistivity Measurement

In this paper,the crystallization behaviour of amorphous Cu56Zr7Ti37 alloy using thermal electrical resistivity(TER) and differential scanning calorimetry(DSC) studies has been described.Isochronal TER and DSC measurements indicate that crystallization occurs in two stages.Isothermal crystallization studies of the alloy by TER show that the kinetics conforms to Johnson-Mehl-Avrami model.Avrami exponents derived from kinetics,between 1.1 and 1.2,imply that the crystallization processes are diffusion controlled with near zero nucleation.Activation energy has been found to increase with the transformed volume fraction.A plausible explanation has been presented by separating the contributions due to nucleation and crystal growth towards total activation energy.     

Deformation Behavior of the Zr_(53.5)Cu_(26.5)Ni_5Al_(12)Ag_3 Bulk Metallic Glass Over a Wide Range of Strain Rate and Temperatures

The stress–strain relations for the Zr53.5Cu26.5Ni5Al12Ag3 bulk metallic glass(BMG) over a broad range of temperatures(room temperature to its supercooled liquid region) and strain rates(10-4to 10-1s-1) were established in uniaxial compression using a thermal-mechanical simulation system. The superplastic flow was seen above its glass transition temperature(Tg = 694 K) and strain rates of up to 10-1s-1from the variation of stress–strain curves. A deformation map of strain rate vs temperature of Zr53.5Cu26.5Ni5Al12Ag3 was obtained, which was mainly composed of homogeneous and inhomogeneous deformation regions,the former featuring either Newtonian or non-Newtonian flow while the latter characterizing linear elastic behavior followed by shear localization, respectively. A phenomenological constitutive equation used to describe a master curve of viscosity with respect to the strain rate was obtained by fitting the experimental results, which determines the viscosity of the present alloy at the temperature near and above Tg. The results show the Zr53.5Cu26.5Ni5Al12Ag3 BMG is the subject suitable for net shape forming process at the supercooled liquid region.     

W丝增强块状非晶基复合材料单轴压缩形变的研究

利用扫描电子显微镜和透射电子显微镜，研究了室温单轴压缩下W丝增强块状非晶基复合材料的形变特征，结果表明：非晶基体内产生了大量的剪切带，剪切带分布特征与W丝密切相关；非晶基体的微观结构发生了改变，局域内自由体积显著增加。     

Thermal Relaxation and High Temperature Creep of Zr55Cu30Al10Ni5 Bulk Metallic Glass

The free volume model is applied to isothermal relaxation and hightemperature creep. For this analysis, the time dependent flow behaviourof Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass (BMG) near the glass transition temperature (T _g ) is expressed as a trade off between stress inducedgeneration and diffusion controlled annihilation of free volume. Thestrain rate-stress relation over a wide strain rate-range (10^–7to 10^–2 s^–1) was established for three different temperatures near T _g . It was found that the thermal relaxation behaviour and creep kinetics arecontrolled by the mobility of atoms with an activation energy of 161 kJ/mol.     

Pressure Effect on Crystallization of Zr55Cu30Al10Ni5 Bulk Metallic Glass

The effect of pressure on the variation of the crystallization phases of the Zr55u30Al10Ni5 bulk glass and its thermal stability under high pressure annealing was investigated by X-ray diffraction (XRD)and differential scanning calorimeter(DSC).The mode of crystallization and products of crystallization of the Zr55Cu30Al10Ni5 bulk glass were quite different pressure.At ambient pressure,the crystallization products consisted of NiZr2 and CuZr2,while at pressure of 1 Gpa and 3 Gpa,the alloys crystallized into NiZr2 and Cu10Zr7,respectively.The alloy was nearly not crystallized and only a small amount of Cu10Zr7 was precipitated under 5 Gpa.DSC proved that the mode of the crystallization under high pressure was different from that at ambient pressure.     

Microstructure and Wear Behavior of FeBSiNbCr Metallic Glass Coatings

In this paper,FeBSiNbCr metallic glass coatings were prepared onto AISI 1045 steel substrate by using wire arc spraying process.The phase and structure of the coating were characterized by transmission electron microscopy(TEM),X-ray diffraction(XRD)and scanning election microscopy(SEM)equipped with energy dispersive X-ray analysis(EDX).The microstructure of the coating consists of full amorphous phase.The coating has high hardness and low porosity.Full density and little oxides are detected in the coating.T...     

Zr65Al7.5Ni10Cu15Co2.5合金的玻璃转变温度

根据Ｚｒ６５Ａｌ７。５Ｎｉ１０Ｃｕ１５Ｃｏ２。５合金的纳米晶，晶体，液体和玻璃比热的测量结果，研究了合金的玻璃转变温度与全金的热力学函数，动力学参数以及加热速度的关系。结果表明，非晶态合金玻璃转变所需转变激活能很小，玻璃转变温度实际上是由于加热速度引起的不同状态的玻璃与液体的热力学平衡温度。     

Effect of Aspect Ratio on the Evolution of Shear Bands in Zr_(61.7)Al_8Ni_(13)Cu_(17)Sn_(0.3) Bulk Metallic Glass

Zr_(61.7)Al_8Ni_(13)Cu_(17)Sn_(0.3) bulk metallic glass samples with different aspect ratios in the range of 0.25–2.25 were deformed by compression,and the effect of aspect ratio on the evolution of shear bands was investigated.It is found that for the deformed Zr_(61.7)Al_8Ni_(13)Cu_(17)Sn_(0.3) bulk metallic glass,the average shear band spacing decreases and the shear band density increases monotonically as the aspect ratio increases from 0.25 to 2.25.A minimal average shear band spacing of 0.478 μm is achieved for the sample with an aspect ratio of 2.25.In addition,the fractions of shear bands with spacings below 100 and 50 nm are about 12.84% and 6.76%,respectively,for the sample with an aspect ratio of 2.25.The reason for the formation of a higher density of shear bands can probably be attributed to the increase of the driving force for the sample with a larger aspect ratio.     

Tensile Elastic Behavior of a Zr-Cu-Ag-Al Bulk Metallic Glass

Tensile elastic behavior of bulk Zr46（Cu4.5/5.5Ag1/5.5）46Al8 metallic glass was experimentally investigated. It exhibited linear and non-linear time-independent elastic deformation with a demarcative stress of approximately 500 MPa within the timescale in the present work, and repeated loading-unloading before yielding did not alter stress-strain relationship. The pure linear elastic strain limit is 0.6%, significantly lower than 2% as generally reported, but still much higher than 0.1% observed for typical crystalline alloys. Deviation from linear elastic behavior at stresses higher than 500 MPa is explained here as a macroscopic manifestation of local fluctuations in elastic strain, which becomes pronounced at stresses higher than the critical value. The occurrence of non-linear elasticity is possibly also related to the sinusoidal relationship between shear stress and atomic displacement.     

金属玻璃Pd_(77.5)Ni_(6.0)Si_(16.5)的晶化过程

本文报道了三元金属玻璃Pd_(77·5)Ni_(5·)Si_(·5)经不同温度退火后的透射电子显微镜观察结果。初步确定了Pd_(77·5)Ni_(6·)Si_(16·s)的晶化过程和亚稳相的结构。由于Ni元素的加入,使其晶化过程相对于二元金属玻璃Pd_(su)Si_(2u)变得更加复杂。     

块状非晶合金室温单轴压缩过程中孔洞的形成及其微观机制

利用扫描电子显微镜（SEM）、透射电子显微镜（TEM）对室温单轴压缩断裂后块状非晶Zr55Al10Ni5Cu30的微观结构进行了研究。经观察断裂面具有典型的脉纹状结构，且断裂面上和靠近断裂面附近的区域有孔洞形成。研究结果表明：由于塑性形变集中块状非晶形成了局部软化区，软化区内自由体积的成核、生长、合并是形成孔洞的根本原因。     

Constitutive description of Bulk Metallic Glass composites at high homologous temperatures

Experimental stress–strain responses of La-based in situ Bulk Metallic Glass (BMG) composites within the supercooled liquid region reveal initial post-yield hardening, followed by softening and subsequent strain-hardening. This behavior contrasts with that of monolithic La-based BMGs, which reach a steady stress level after an initial overshoot. XRD analysis of BMG composites shows the formation of intermetallic compounds during compressive deformation. These intermetallic compound formation/interactions are associated with storage of energy in the material and affect the stress–strain response. In this study, an elastic–viscoplastic, three-dimensional, finite deformation constitutive model is also established to describe the behavior of a recently developed La-based in situ BMG (La–Al–Cu–Ni) composite, within the supercooled liquid region, at ambient pressure and a range of strain rates. The constitutive model is incorporated into a finite element program (ABAQUS/Explicit) via a user-defined material subroutine. Numerical predictions are compared with compression test results on BMG composites cast in-house. The comparison shows that the model is able to describe the material behavior observed.     

Microstructure Evolution of Zr50Cu18Ni17Al10Ti5 Bulk Metallic Glass during Cold-rolling

Zr50Cu18Ni17Al10Ti5 bulk metallic glass has been rolled at room temperature up to 95% in thickness reduction, and the dependence of microstructure on the strain was investigated. With increasing thickness reduction, the full width at half maximum (FWHM) and crystallization enthalpy decrease gradually till 80%, and then increase evidently at 95%. It is revealed that the reversible transition between the ordered and disordered atomic configurations was found in the metallic glass as the deformation proceeds, which is further verified by the high-resolution transmission electron microscopy images. The final microstructure in metallic glass during cold-rolling is the net result of two competing processes between shear-induced disordering and diffusion controlled reordering.     

Characterization,Removal and Evaluation of Oxide Film in the Diffusion Bonding of Zr55Cu30Ni5Al10 Bulk Metallic Glass

The composition of oxide film of ZrssCu3oNi5Al10 bulk metallic glass was identified by X-ray photoelectron spectroscopy. In addition, the relatively sound joints of bulk metallic glass without macroscopic deformation were obtained by removing the oxide film before diffusion bonding. The joint interfaces were observed by scanning electron microscopy and atomic force microscopy. The hardness of joints near the interface was higher than that far away from the interface, which is attributed to the difference of structural relaxation. According to the result of micro-focused X-ray diffractometry and transmission electron microscopy, the joints retained the amorphous structure when the holding time is less than 20 min. The surface area fraction of oxide film on the interface of joints was detected by ultrasonic inspection. Moreover, the surface area fraction of oxide film is in excellent agreement with the theoretical value calculated by shear strength. The result indicated that surface oxide film is the dominant barrier on the diffusion bonding of bulk metallic glass rather than low atomic diffusion coefficient.     

Quasistatic and Dynamic Tensile Behavior of Zr52.5Al10Ni10CU15Be12.5 Bulk Metallic Glass

Quasistatic and dynamic tensile behavior of Zr52.5Al10Ni10Cu15Be12.5 bulk amorphous alloy was investigated at the strain rates of 10^-4--10^3s^-1 by using a Shimadzu AG-100KNA autograph and a pneumatic tensile impact tester. It was shown that the tensile fracture strength and the fracture morphology were sensitive to the strain rate. With the increase of the strain rate,the tensile fracture strength decreased and the fracture morphology changed from cleavage into quasi-cleavage, and then into a mixture of microvoid-coalescence dimples and quasi-cleavage veins.