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ISSN 1005-0302
CN 21-1315/TG
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      15 March 2014, Volume 30 Issue 3 Previous Issue    Next Issue
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    Modeling and Simulation of Microstructurally Small Crack Formation and Growth in Notched Nickel-base Superalloy Component
    G.M. Owolabi, H.A. Whitworth
    J. Mater. Sci. Technol., 2014, 30 (3): 203-212.  DOI: 10.1016/j.jmst.2013.09.011
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    Studies on microstructurally small fatigue cracks have illustrated that heterogeneous microstructural features such as inclusions, pores, grain size distribution as well as precipitate size distribution and volume fraction create stochasticity in their behavior under cyclic loads. Therefore, to enhance safe-life and damage-tolerance approaches, accurate modeling of the influence of these heterogeneous microstructural features on microstructurally small crack formation and growth from stress raisers is necessary. In this work, computational micromechanics was used to predict the high cycle fatigue of microstructurally small crack formation and growth in notched polycrystalline nickel-base superalloys and to quantify the variability in the driving force for formation and growth of microstructurally small crack from notch root in the matrix with non-metallic inclusions. The framework involves computational modeling to obtain three-dimensional perspectives of microstructural features influencing fatigue crack growth in notched nickel-base superalloys, which accounts for the effects of nonlocal notch root plasticity, loading, microstructural variability, and extrinsic defects on local cyclic plasticity at the microstructure-scale level. This approach can be used to explore sensitivity of minimum fatigue lifetime to microstructures. The simulation results obtained from this framework were calibrated to existing experimental results for polycrystalline nickel-base superalloys.

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    Influence of the Substrate Orientation on the Isothermal Solidification during TLP Bonding Single Crystal Superalloys
    Naicheng Sheng, Bo Li, Jide Liu, Tao Jin, Xiaofeng Sun, Zhuangqi Hu
    J. Mater. Sci. Technol., 2014, 30 (3): 213-216.  DOI: 10.1016/j.jmst.2013.11.013
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    Angle deviations between the two substrates during transient liquid phase (TLP) bonding single crystal superalloys cannot be avoided. In the present work, specimens have been prepared to investigate the influences of the various substrate orientations. It is found that the width of the non-isothermal solidification zone (NSZ) is linear with the square root of the isothermal solidification time. This suggests that the isothermal solidification process is B-diffusion controlled in different substrate orientation deviations. And also the width of the NSZ increases with increasing angle deviation, indicating that the isothermal solidification time needed in the TLP bonding increases with increasing orientation deviation between the two substrates.

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    A Comparative Study of Various Flow Instability Criteria in Processing Map of Superalloy GH4742
    Ge Zhou, Hua Ding, Furong Cao, Beijiang Zhang
    J. Mater. Sci. Technol., 2014, 30 (3): 217-222.  DOI: 10.1016/j.jmst.2013.07.008
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    Hot compression tests were conducted on a Gleeble-1500D thermal simulating tester. Based on the deformation behavior and microstructural evolution of superalloy GH4742, different types of instability criteria of Prasad, Gegel, Malas, Murty and Semiatin were compared, and the physical significance of parameters was analyzed. Meanwhile, the processing maps with different instability criteria were obtained. It was shown that instability did not occur when average power dissipation rate was larger than 50% in the temperature range of 1020–1130 °C, corresponding to the strain rate range of 5 × 10−4–3.2 × 10−3 s−1. The domain is appropriate for the processing deformation of superalloy GH4742.

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    Dendritic Growth Pattern and Dendritic Network Distortion in the Platform of a Ni-based Superalloy
    Xiaoli Zhang, Yizhou Zhou, Yanyun Han, Tao Jin, Xiaofeng Sun
    J. Mater. Sci. Technol., 2014, 30 (3): 223-228.  DOI: 10.1016/j.jmst.2013.09.013
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    The pattern of dendritic growth and distortion of dendritic network in the platform have been investigated by one mold casting with different platform length during directional solidification. As the platform length elongates, the symmetry of dendritic growth along left and right edges gradually worsens in platform base. While the platform length reaches 14 mm, the distortion of dendritic network is first observed in outward platform. It is found that the distortion of dendritic network along platform inside is more serious than that along platform edges. Both [001] deviation and accumulated misorientation along platform inside, up to 9° and 16.3°, respectively, are far greater than those along left–outward–right edges. The deformation of dendritic network in a platform may be caused by the asymmetry of the solidification front at the mush zone.

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    Isothermal Oxidation Behavior of Dysprosium/S-Doped b-NiAl Alloys at 1200 °C
    Lu Wang, Dongqing Li, Jian Chang, Hongbo Guo, Shengkai Gong, Huibin Xu
    J. Mater. Sci. Technol., 2014, 30 (3): 229-233.  DOI: 10.1016/j.jmst.2013.08.004
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    A β-NiAl alloy with normal purity, a S-doped and a Dy and S co-doped β-NiAl alloys were prepared by arc-melting and their corresponding S contents were less than 20 × 10−6, 33 × 10−6 and 22 × 10−6, respectively. The isothermal oxidation behavior of the alloys at 1200 °C was investigated and the extent of S segregation at the scale–alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from θ- to α-Al2O3, while the addition of Dy retarded this process. For the S-doped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scale–alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.

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    Structural Stability and Half Metallic Features of Zn0.5Cr0.5S under Pressure
    Yuhong Huang, Wanqi Jie, Yan Zhou, Gangqiang Zha
    J. Mater. Sci. Technol., 2014, 30 (3): 234-238.  DOI: 10.1016/j.jmst.2013.08.006
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    Spin-polarized first-principle was performed to study the structural stability and the electronic states of Cr doped ZnS with the Cr component of 50% in zincblende (ZB), wurtzite (W) and rocksalt (RS) structures under pressure. The results show that the zincblende and wurtzite structures become unstable under low pressures of about 4.68 and 9.61 GPa, respectively, but the rocksalt structure can be maintained up to an extremely high pressure of about 32.92 GPa. Both zincblende and wurtzite Zn0.5Cr0.5S display half metallic features under pressure, while rocksalt Zn0.5Cr0.5S exhibits metallic feature. The half metallic features can be ascribed to the stronger interactions between S-3p and Cr-3d states and the metallic feature is due to the higher crystal symmetry of rocksalt Zn0.5Cr0.5S. These results can provide helpful guidance for Cr doped ZnS to be used in spintronic devices.

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    Combined Computational and Experimental Study on the Adsorption and Inhibition Effects of N2O2 Schiff Base on the Corrosion of API 5L Grade B Steel in 1 mol/L HCl
    Hojat Jafari, Iman Danaee, Hadi Eskandari, Mehdi RashvandAvei
    J. Mater. Sci. Technol., 2014, 30 (3): 239-252.  DOI: 10.1016/j.jmst.2014.01.003
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    The electrochemical behavior of low carbon steel (API 5L grade B) in 1 mol/L HCl solution with different concentrations of N,N′-bis(4-formylphenol)-trimethylenediamine Schiff base was studied by electrochemical techniques and density functional theory analysis. The inhibition efficiency was found to increase with increasing inhibitor concentration and decreased with increasing temperature. The high inhibition efficiency was attributed to the blocking of active sites by adsorption of inhibitor molecules on the steel surface. Thermodynamic parameters for the adsorption and activation processes were determined. Galvanostatic polarization data indicated that Schiff base act as a mixed-type inhibitor and the adsorption isotherm obeyed the Langmuir adsorption isotherm. Results obtained from quantum chemical studies show excellent correlations between the quantum chemical parameters and the experimental inhibition efficiencies using density functional theory at the B3LYP/6-31G(d,p) and B3LYP/3-21G basis set levels and ab initio calculations using HF/6-31G(d,p) and HF/3-21G methods.

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    Effect of Cl- on the Properties of the Passive Films Formed on 316L Stainless Steel in Acidic Solution
    Guozhe Meng, Yuan Li, Yawei Shao, Tao Zhang, Yanqiu Wang, Fuhui Wang
    J. Mater. Sci. Technol., 2014, 30 (3): 253-258.  DOI: 10.1016/j.jmst.2013.07.010
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    The corrosion behavior of 316L stainless steel (316L SS) has been investigated in solutions containing various concentrations of chloride ions by using potentiodynamic polarization, capacitance measurement and Mott–Schottky relationship analysis (M–S). The result indicates that passive currents change slightly with the addition of chloride ions. The pitting potential (Epit) decreases linearly with log[Cl]. Correspondingly, the point defect diffusion coefficient (Do) of the passive film increases linearly with increasing log[Cl]. The results also indicate that the pitting corrosion of 316L SS follows the adsorption mechanism in NaCl solution.

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    Effects of Silicon Nanoparticles on the Transient Liquid Phase Bonding of 304 Stainless Steel
    H.M. Hdz-García, A.I. Martinez, R. Mu?oz-Arroyo, J.L. Acevedo-Dávila, F. García-Vázquez,F.A. Reyes-Valdes
    J. Mater. Sci. Technol., 2014, 30 (3): 259-262. 
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    Transient liquid phase (TLP) bonding of 304 stainless steel with nickel based filler metal, BNi-9, was performed to study the influence of silicon nanoparticles (NPs) on the mechanical and structural properties of the bonding area. It was found that silicon NPs act as a melting point depressant in the brazing process; the formation of silicon TLP induces the dissolution of elements of the metal filler and promotes a uniform distribution in the bonding area. Silicon NPs induce the development of smaller eutectic structures in the melting zone; it has been related to microhardness measurements, which are lower when the silicon NPs are used in the brazing process.

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    EBSD Characterization of the Laser Remelted Surface Layers in a Commercially Pure Mg
    Kemin Zhang, Jianxin Zou, Jun Li, Zhishui Yu
    J. Mater. Sci. Technol., 2014, 30 (3): 263-267.  DOI: 10.1016/j.jmst.2013.10.002
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    Laser surface melting has been applied on a commercially pure Mg. The microstructure and texture modifications encountered in the surface layers were carefully investigated by using electron backscattered diffraction (EBSD) technique. Due to the melting followed by rapid solidification and cooling, a layer having graded microstructures and texture formed. At the bottom of the melted layer, the solidified Mg grains have an elongated shape with a <0001> basal fibre texture nearly parallel to sample normal direction, while equiaxed grains were observed in the top melted layer having a much weaker basal fibre texture. Solidification twinning and deformation twinning were found in the vicinity of the melt/substrate interface where the Mg grains grow larger due to the heating. In addition, no epitaxial type grain growth was observed at the melt/substrate interface.

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    Oxidation Resistance Coatings of Ir–Zr and Ir by Double Glow Plasma
    Zhaofeng Chen, Wangping Wu, Xiangna Cong
    J. Mater. Sci. Technol., 2014, 30 (3): 268-274.  DOI: 10.1016/j.jmst.2013.06.002
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    Oxidation resistance coatings of Ir–40 at.% Zr and Ir were produced onto Mo substrates by double glow plasma technology. The oxidation resistances of the coatings were evaluated at high temperature. Ir–Zr coating consisted of two layers: the primary layer close to the substrate was composed of dense columnar grains and the second layer was composed of dense grains of nanometric size. The mass gain of Ir coating above 800 °C was about 1.35% due to the formation of solid IrO2. The mass loss of Ir coating was about 5.3% due to the formation of gaseous oxide IrO3 when being held at 1227 °C for 30 min. The substrate was protected more effectively by multilayer than monolayer coating of Ir in oxidizing environment. The Ir–Zr coating was well bonded to the substrate after oxidation at 800 °C. After oxidation at 1000 °C, the Ir–Zr coating was poorly bonded to the substrate. The oxidation resistance of Ir–Zr coating was poor due to high content of Zr.

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    Room Temperature Ferromagnetism in Dual Doped (Mn2+, Ni2+) ZnO Codoped with Li1+ Prepared Using EDTA Sintered at Low Temperature
    R. Pugaze, A. Sivagamasundari, D. Vanidha, S. Chandrasekar, A. Arunkumar
    J. Mater. Sci. Technol., 2014, 30 (3): 275-279.  DOI: 10.1016/j.jmst.2013.10.013
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    Nanopowders of Zn1−xyzMnxNiyLizO [(x = 0.04, y = 0, z = 0), (x = 0.04, y = 0.03, z = 0) and (x = 0.04, y = 0.03, z = 0.03)] have been synthesized by sol–gel precursor route using ethylene diamine tetraacetic acid (EDTA) as a metal chelating agent. X-ray diffraction analysis confirms the formation of wurtzite hexagonal structure for all the three compositions. Mn2+ doped ZnO exhibits room temperature ferromagnetism (RTFM), and it is found that further Ni2+ doping has decreased Ms because of limit of solid solubility of transition metal in ZnO. But codoping of monovalent Li1+, further increases the ferromagnetism (FM) value, due to introduction of free carriers compared to the dual doped samples. Photoluminescence (PL) spectra of the system, exhibit near band edge (NBE) emission peak at ∼464 nm due to the electron transition from interstitials to the valence band. Recombination of conduction electron with hole trapped at oxygen vacancy, leads to prominent defect emission peaks at ∼482 nm and 532 nm. The evidence of the formation of metal–EDTA complexes are found from the Fourier transform infrared spectra at 2800–3800 cm−1 with shifting, splitting of the peak and also drastic variations in the intensity.

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    Fabrication of (Ti,Hf)-rich NiTiHf Alloy Using Graphitic Mold and Crucible
    Mahdi Moshref-Javadi, Majid Belbasi, Seyed Hossein Seyedein, Mohammad Taghi Salehi
    J. Mater. Sci. Technol., 2014, 30 (3): 280-284.  DOI: 10.1016/j.jmst.2013.10.001
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    In this research, fabrication of a (Ti,Hf)-rich NiTiHf alloy by using vacuum induction melting (VIM) process and a graphitic crucible was investigated. For this purpose, casts with the nominal composition of Ni49Ti36Hf15 were prepared in graphitic crucible and mold. Optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC) tests were employed to characterize the samples. Results demonstrated that microstructure of the first cast was composted of a B2 austenite phase as well as a great amount of two differently formed (Ti,Hf)C carbides. Moreover, no austenite ↔ martensite transformation peak was detected in the DSC curve of this sample, indicating a drastic decline in the transformation temperatures. In the succeeding cast, however, owing to the formation of carbide layers on the inner surfaces of the graphitic crucible and mold during the initial casting process, the amounts of carbides decreased remarkably. This cast exhibited transformation temperatures above 100 °C, while XRD pattern denoted the presence of B19′ monoclinic martensite phase at room temperature. All in all, results confirmed that VIM process using graphitic mold and crucible can be considered as an appropriate method for the fabrication of (Ti,Hf)-rich NiTiHf high temperature shape memory alloys.

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    Effect of Y2O3–MgO Addition on Heterogeneous Precipitation-Thermal Reduction Synthesis and Sintering of Fe–Mo/Si3N4 Powders
    Ruiming Yin, Fubao Ji, Qinglin Hou, Fusheng Liu, Jing Li, Linzhang Chen
    J. Mater. Sci. Technol., 2014, 30 (3): 285-289.  DOI: 10.1016/j.jmst.2013.05.010
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    Effect of Y2O3–MgO addition on heterogeneous precipitation-thermal reduction synthesis and the sintering of Fe–Mo/Si3N4 powders has been investigated. It was found that the whiskers-like β-Si3N4, good wettability phases on Si3N4 surface, and high toughness Fe phase appeared in Fe–Mo/Si3N4 cermets with Y2O3–MgO additives. The results show that Y2O3–MgO additives can effectively optimize the microstructures of Fe–Mo/Si3N4 cermets, and improve the material mechanical properties. Therefore, it indicated that Y2O3–MgO additives can be used for strengthening of sintered cermets, and the dual function of whiskers self-toughening and different metal-composition toughening can be achieved in Fe–Mo/Si3N4 cermets with Y2O3–MgO additives.

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    Temperature-Dependent Luminescence Characteristic of SrSi2O2N2:Eu2+ Phosphor and Its Thermal Quenching Behavior
    Jinlan Qin, Chaofan Hu, Bingfu Lei, Jinfang Li, Yingliang Liu, Shuiping Ye, Miaozhu Pan
    J. Mater. Sci. Technol., 2014, 30 (3): 290-294.  DOI: 10.1016/j.jmst.2013.08.009
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    The yellow SrSi2O2N2:Eu2+ phosphor has been synthesized by using a simple solid-state reaction method with Sr2SiO4:Eu2+ as the precursor. It shows a broad excitation band extending from 250 to 520 nm and an asymmetric emission band with a main peak at about 550 nm. The emission intensity of the SrSi2O2N2:Eu2+ is about 1.2 times higher than the commercial yellow phosphor YAG:Ce3+ (P46-Y3). The temperature-dependent luminescence characteristic of SrSi2O2N2:Eu2+ has been investigated in this paper. With increasing temperature, the emission band of SrSi2O2N2:Eu2+ shows anomalous blue-shift along with decreasing emission intensity and the broadening full width at half maximum (FWHM). Particularly, compared with YAG:Ce3+ (P46-Y3), the yellow SrSi2O2N2:Eu2+ phosphors exhibit higher thermal stability due to their weaker electron-phonon coupling strength (1.1), lower stokes shift (0.0576 eV) and larger activation energy (0.288 eV). All these results indicate that SrSi2O2N2:Eu2+ yellow phosphors have potential application for white light-emitting diodes (LEDs). What's more, an energy level scheme is constructed to explain the anomalous blue-shift phenomenon.

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    La Doping Effect on the Dielectric Property of Barium Strontium Titanate Glass–Ceramics
    Jichun Chen
    J. Mater. Sci. Technol., 2014, 30 (3): 295-298.  DOI: 10.1016/j.jmst.2013.07.007
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    Ferroelectric barium strontium titanate (BST) glass–ceramics doped with different content of La2O3 were prepared via the melt-quenching technique followed by controlled crystallization. The microstructures of crystallized samples were examined by X-ray diffraction and scanning electron microscopy. Dielectric properties were also investigated. The aliovalent substitution of Ba by La induced dispersion of semiconducting BaxSr1−xTiO3 crystallites sealed in a glassy silicate matrix, which increased the εr and loss tangent values of the BST glass–ceramic. The experimental results indicate that aliovalent substitution is an effective method to process glass–ceramics with better dielectric properties.

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ISSN: 1005-0302
CN: 21-1315/TG
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