Showing papers by "H.F. Zhang published in 2007"

Dynamic compressive deformation and failure behavior of Zr-based metallic glass reinforced porous tungsten composite

Abstract: The dynamic compressive deformation and fracture behavior of the Zr-based metallic glass reinforced porous tungsten composite were investigated at room temperature by means of the Split Hopkinson Pressure Bar (SHPB). Both fracture stress and fracture strain increased significantly compared to the pure metallic glass phase. The deformation behavior of the composite was found to be dominated by the ductile W phase and the 3D net structure of the W phase. It was found that the composite appeared to exhibit some work hardening during the dynamic compressive deformation. The failure mode of the specimen is a mixture of one major shear band and axial splitting, and the shear plane inclined similar to 56 degrees with respect to the loading axis. Scanning election microscope (SEM) was used to evaluate damage initiation and propagation. It was found that the increase of fracture stress and fracture strain is due to the interaction between localized shear banding and axial splitting, promoting additional fracture surface area, and large volume fraction of ductile W phase. The dynamic compressive deformation and fracture behavior of the composite are discussed by taking the effect of the complex stress state within the composite into account. (c) 2006 Elsevier B.V. All rights reserved.

New criteria of glass forming ability, thermal stability and characteristic temperatures for various bulk metallic glass systems

Abstract: Six mathematical criteria used for quantitatively measuring their glass forming ability, thermal stability and characteristic temperatures (temperature of glass transition T-g, crystallization onset T-x and liquidus T-l) of various bulk metallic glasses (BMGs) have been proposed in this article. It is found that the criteria are suitable for evaluating these quantities for BMGs. The estimated results are better than those calculated by Fang et al.'s models and Lu et al.'s gamma criterion, but our analyses indicate that these criteria, defined by the data (Pauling electronegativity xi, atomic radius ri, electron concentration ni and melting temperature T-mi) easily found in literatures, still need to be further refined in future research for shortcomings of the parameters. (C) 2007 Elsevier B.V. All rights reserved.

Mechanical properties and ion irradiation of bulk amorphous Zr55Cu30Al10Ni5 alloy

Abstract: The bulk amorphous Zr55Cu30Al10Ni5 alloy is one of the widely studied Zr-based alloys due to very attractive thermal and mechanical properties. Alloy ribbons and bulk samples were synthesized by Cu mould casting and characterized by SEM/EDS, DSC and XRD. Mechanical properties like Vicker's hardness, nanohardness and elastic modulus etc. were measured. Ion irradiation of the samples was carried out to enhance the surface properties without altering the amorphous nature of the bulk material. Ion irradiation by singly charged Ar+ enhanced the hardness as well as elastic modulus considerably. (C) 2007 Elsevier B.V. All rights reserved.

Influence of rapid solidification on the mechanical properties of Mg-Zn-Ce-Ag magnesium alloy

Abstract: This paper presents the differences in microstructure and mechanical properties between the conventional casting and rapidly solidified Mg-Zn-Ce-Ag alloy. The experimental results showed that the mechanical properties of rapidly solidified alloy are enhanced, which can be attributed to the changes of the microstructure significantly. The grain was refined and homogeneously distributed β-Mg12Ce phase was obtained. High cooling rate refined the microstructure and changed the morphology of divorce eutectic phase. The mechanical properties of rapidly solidified alloy are high and variable. Microporosity appeared to degrade affect the mechanical properties of magnesium alloys.

Prior Electrodeposition of Nanocrystalline Ni – CeO2 Film Fabricating an Oxidation-Resistant Chromized Coating on Carbon Steels

Abstract: With the prior electrodeposition of nanocrystalline Ni film without or with the dispersions of CeO2 nanoparticles, a carbon steel was chromized using a conventional pack-cementation method but at a greatly decreased temperature (700 degrees C). The chromized coating on the Ni-CeO2 film had a considerable thickness, throughout which chromium was continuously distributed, and an extremely low scaling rate during oxidation at 700 degrees C in air. The study offers a novel approach for fabricating a low- temperature chromized coating with a desired oxidation performance on conventional steels. (c) 2006 The Electrochemical Society.

Effect of additional elements on mechanical properties of a specially constituted Zr-based alloy

Abstract: Bulk metallic glasses (BMGs), especially ZrCuAlNi alloys, are important materials due to their very attractive physical and mechanical properties. However, their applications are restricted due to processing limitations and cost effectiveness. Materials scientists are trying to design and synthesize economical BMGs using inexpensive materials with improved properties. In the present study, six alloys having compositions (Zr0.65Cu0.18Ni0.09Al0.08)(100-x)M-x (where M = Y, Ti, Nb, Er and W and x = 0 and 2 at.%) were synthesized by Cu mould casting using 2-3N pure elements. The base alloy Zr65CU18Ni9Al8 was designed following the Inoue's rules and also adopting the criterion of average valance electrons/atom (e/a ratio = 1.3950) and average atomic size R. = 0.1498 nm. Characterization of alloys was done by XRD, differential scanning calorimetry (DSC) and SEWEDS. Maximum AT, was found to be 129 K for the base alloy. Mechanical properties like Vicker's microhardness, nanohardness, elastic modulus, density, fracture strength and shear angles were measured. Enhancement in ductility was achieved by adding Ti and Nb. Microstructure of as-cast and heat-treated compression tested samples was evaluated. (c) 2006 Elsevier B.V. All rights reserved.

Effect of Zr addition on the glass-forming ability and mechanical properties of Ni–Nb alloy

Abstract: The effect of zirconium (Zr) addition on the glass-forming ability (GFA) and mechanical properties of the Ni61.5Nb38.1 alloy has been studied. The addition of Zr improves the GFA. When x = 5 for N61.5Nb38.1-xZrx (in at.%) alloys, the alloy exhibits the best GFA and can be cast into 3-mm-diameter amorphous samples by using the copper mold injection-casting method. Differential scanning calorimetry measurements indicated that the thermal parameters, such as T-rg and gamma, have not a good correlation with the GFA in the Ni-Nb-Zr alloys. Compression tests reveal that the addition of Zr just decreases the fracture strength slightly from 3.4 to 3 GPa and that all of the tested samples exhibit a little compressive plasticity of about 2%. When x = 9, the feature of the fracture surface Indicates that the alloy has a tendency for transition from the ductile to the brittle. And delicate "dimple" and microscale vein pattern Structures have been observed on it.

Influence of moving tape speed on continuous deposition of buffer layers for long-length YBCO coated conductors

Abstract: This paper reports our activity for development of Y 2 O 3 buffer layer on rolled NiW substrates using continuous electron beam evaporation and magnetron sputtering technique. X-ray diffraction of θ –2 θ scan and ϕ -scan were employed to characterize the in-plane alignment and cube texture. The surface morphology of buffer layers was evaluated in SEM. We study the effect of moving speed of NiW substrates on continuous preparation of buffer layer and two deposition techniques were compared in detail. Results show that textured, crack-free buffer layers were obtained and two techniques are promising for developing long-length YBCO tape.