ISSN 0412-1961
CN 21-1139/TG
Started in 1956

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    STRENTHENING MECHANISM OF MODULATED STRUCTURE INITIATED BY SPINODAL DECOMPOSITION
    XU Zuyao (T.Y.HSU)
    Acta Metall Sin, 2011, 47 (1): 1-6.  DOI: 10.3724/SP.J.1037.2010.00231
    Abstract   PDF (1143KB) ( 1901 )
    Through reviewing of a limited number of literatures regarding strengthening mechanism of modulated structure initiated by spinodal decomposition, it is found that the yield strength of aged alloy is mainly dependent on stress field built by the composition different between two precipitate phases which can be characterized by difference between lattice parameter Δa and is independent on modulate wave length and volume fraction of precipitate phase. However, in the ageing courses, the changes in yield stress and Δa did not show a linear relationship. The present author considers that this may be attributed to the local destruction of periodicity of modulated structure, causing change in stress field during ageing and suggests a yield stress equation: σc=MBΔa/a, in which M denotes a sum factor including Taylor (or Schmidt) factor and elastic constants, B, a factor represent the response of local stress field changed the function of Δa/a, Δa, the difference between lattice parameters of two precipitate phases and a, the average lattice parameter. This equation and the B value need to be confirmed and estimated.
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    MODELING AND SIMULATION ON MICROPOROSITY FORMED DURING SQUEEZE CASTING OF ALUMINUM ALLOY
    HAN Zhiqiang LI Jinxi YANG Wen ZHAO Haidong LIU Baicheng
    Acta Metall Sin, 2011, 47 (1): 7-16.  DOI: 10.3724/SP.J.1037.2010.00313
    Abstract   PDF (1384KB) ( 1594 )
    A mathematical model for simulating the microporosity in squeeze casting of aluminum alloy has been developed, in which the heat transfer, solidification shrinkage, feeding flow, pressure transfer, and hydrogen conservation were taken into account. The shrinkage induced flow and the pressure drop in the mushy zone were calculated by solving continuity and momentum equations. A mechanical model was solved for obtaining the pressure transferred into the central area of the casting. By coupling the pressure drop with the pressure transferred into the central area, the pressure distribution in the mushy zone was calculated. Based on the hydrogen conservation equation, the microporosity volume fraction was calculated by referring to the pressure value in the mushy zone. The squeeze casting processes of aluminum alloy under different process conditions were simulated and the simulation results were compared with experimental results. It was shown that the simulation results agree well with the experimental results, and the increases in applied pressure and mould temperature tend to reduce the microporosity in the castings.
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    INFLUENCE OF CARBONATION ON THE CORROSION PERFORMANCE OF STEEL HRB335 IN SIMULATED CONCRETE PORE SOLUTION
    SHI Jinjie SUN Wei GENG Guoqing
    Acta Metall Sin, 2011, 47 (1): 17-24.  DOI: 10.3724/SP.J.1037.2010.00508
    Abstract   PDF (1358KB) ( 1250 )
    Electrochemical impedance spectroscopy, cyclic voltammetry and potentiodynamic polarization were used to investigate the effect of the decrease in pH values of simulated concrete pore (SCP) solutions due to carbonation on the corrosion of steel HRB335. The results indicated that the stability and corrosion inhibition of passive film on the steel surface decrease with decreasing pH value of SCP solutions. In SCP solutions with pH values of 12.5 and 11.5, the stability of passive film is in a competitive balance, the competition results from the dissolution of passive film due to the decreasing pH and the protective effect of calcium-iron containing protective layer CaFe2O4 or deposit CaCO3 formed on the steel surface. When the pH value decreased unceasingly (pH=10.5, 10.0), the stability of passive film decreased gradually,  and the active uniform corrosion occurred on the steel surface.
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    INFLUENCE OF ROLLING DIRECTION ON THE TEXTURE EVOLUTION OF Fe-3\%Si ALLOY
    YAN Mengqi YANG Ping JIANG Qiwu FU Yongjun MAO Weimin
    Acta Metall Sin, 2011, 47 (1): 25-33.  DOI: 10.3724/SP.J.1037.2010.00432
    Abstract   PDF (1174KB) ( 1648 )
    Sharp Goss texture is crucial for superior magnetic properties of grain oriented silicon steel. The strong initial Goss texture in hot rolled plate will markedly favor the final strong Goss texture. In this paper, different initial textures and microstructures in the surface and center layers of hot rolled plates were established by changing cold rolling direction and their influences on the further evolution of textures and microstructures during first cold rolling, intermediate annealing, secondary cold rolling, decarburizing annealing and secondary recrystallization were investigated. The formation of Goss texture in these specially prepared samples is discussed in details. The results show that the strong differences in initial microstructures and textures vanished gradually as increased times of rolling and annealing, and secondary recrystallization progressed smoothly and nearly independent on rolling directions. The discrepancies of the sharpness of Goss texture and magnetic properties between different samples exhibited minor. The insufficient Goss grains can be compensated through the relatively stronger {111}<112> texture formed in all processing stages, although Goss textures in initial samples show different intensities, therefore the rolling direction and initial structure show little influence on secondary recrystallization. Furthermore, results demonstrate the heritage of cube texture and effective elimination of  {112}<110> texture by 90o rotation of sheet around normal direction (ND).
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    HOT DEFORMATION BEHAVIOR OF A HIGH STRENGTH CONTAINER STEEL COMPOUNDED WITH Nb-B
    SONG Renbo ZHANG Yongkun WEN Xinli JIA Yisu
    Acta Metall Sin, 2011, 47 (1): 34-40.  DOI: 10.3724/SP.J.1037.2010.00189
    Abstract   PDF (1159KB) ( 1383 )
    Hot deformation behaviors of high strength container steel compounded with Nb-B have been systematically studied through high temperature compression tests on the Gleeble-1500 thermal-mechanical simulator. In the present deformation conditions, there are different relationships between the strain hardening exponent (n) and the true strain (ε) under different strain rates at the deformation temperature of 1423 K; n-ε curves have single peak and single valley at the strain rates of 0.1 s-1 and 1 s-1, while n-ε curves have double peaks and double valleys at the strain rates of 5 s-1 and 15 s-1. During the heat work-hardening process, dislocation strengthening, twin strengthening and precipitation strengthening are the major work-hardening mechanisms of the tested steel. According to Zener-Hollomon and Ludwik equation, the experimental data have been regressed by using nonlinear method, the apparent deformation activation energy (Q) and stress exponent (n) were obtained to be about (428.188±20.109) kJ/mol and 4.923 in the temperature range of 1123 K-1423 K, respectively. Finally, an expression of Z parameter, hot deformation equation and dynamic recrystallization model diagram of the tested steel are established.
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    DESIGNING Mg-Sn-Mn ALLOY BASED ON CRYSTALLOGRAPHY OF PHASE TRANSFORMATION
    SHI Zhangzhi ZHANG Wenzheng
    Acta Metall Sin, 2011, 47 (1): 41-46.  DOI: 10.3724/SP.J.1037.2010.00323
    Abstract   PDF (813KB) ( 1766 )
    Crystallography of phase transformation is used as the main principal to guide Mg-Sn-X alloy design. Based on a comprehensive literature survey, two criteria of crystallography of phase transformation are given to select the precipitate probably growing along [0001]α direction of Mg matrix. Combined with available data of phase diagram, we deduce that β-Mn in Mg-Sn-Mn system is a hopeful candidate. TEM study on the specimen of Mg-7.5Sn-2.2Mn (mass fraction, %) alloy confirms that rod-like β-Mn precipitates grow along [0001]α, and their orientation relationship (OR) with Mg matrix is [0001]α///[211]β-Mn, [0110]α///[011]β-Mn, [2110]α//[111]β-Mn.
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    DISLOCATION CONFIGURATION IN DZ125 Ni-BASED SUPERALLOY AFTER HIGH TEMPERATURE STRESS RUPTURE
    DING Zhi ZHANG Jun WANG Changshuai SU Haijun LIU Lin FU Hengzhi
    Acta Metall Sin, 2011, 47 (1): 47-52.  DOI: 10.3724/SP.J.1037.2010.00544
    Abstract   PDF (1152KB) ( 1544 )
    The influence of the melt superheating treatment on the dislocation configuration in the as-cast and heat-treated samples of DZ125 Ni-based superalloy after high temperature stress rupture is studied. The results show that with the increase of the melt superheating temperature, the stress rupture life of the as-cast sample is increased and that of the heat-treated sample is first increased and then reduced. When the superheating temperature is 1650℃, the stress rupture life of the heat-treated sample reaches the maximum. With the increase of the melt superheating temperature, the dislocation density is increased and the waved or irregular dislocation networks appear in the as-cast sample, while the regular polygonal dislocation networks appear in the heat-treated sample, which is helpful to elevate the stress rupture property. The Burgers vectors of dislocations in the network are respectively a/2<110> and a<100>. The high temperature stress rupture deformation mechanism is mainly shearing and climbing of dislocation. It is demonstrated that there are few dislocations shearing the γ' phase and there are dislocation arrays or pairs climbing over the γ' phase.
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    CREEP BEHAVIOR OF Al-Cu-Mg-Ag HEAT-RESISTANT ALLOY AT ELEVATED TEMPERATURE
    LIU Xiaoyan PAN Qinglin LU Zhilun CAO Sufang HE Yunbin LI Wenbin
    Acta Metall Sin, 2011, 47 (1): 53-60.  DOI: 10.3724/SP.J.1037.2010.00369
    Abstract   PDF (1275KB) ( 1417 )
    The creep behaviors of heat--resistant alloy Al-5.3Cu-0.8Mg-0.5Ag-0.3Mn-0.15Zr (Al-Cu-Mg-Ag) were studied in a temperature range of 100-210℃ and a load range of 150-300 MPa, and the effect of aging on the properties of Al-Cu-Mg-Ag alloy at elevated temperatures was also investigated. The results show that the steady creep rate of the under-aged alloy is much lower than that of the peak--aged alloy at the same creep conditions. The creep fracture time is 75 h for the under-aged Al-Cu-Mg-Ag alloy at 210℃/200 MPa, while that for the peak-aged alloy is only 21 h. The precipitates grow gradually during the creep process and the growth rate in the peak-aged alloy is higher than that in the under-aged alloy. Dynamic precipitation happened in the under-aged alloy. The fine precipitates inhibite the motion of the dislocations during the creep, which leads to lower creep deformation rate compared to the peak-aged alloy. The steady creep rates of the under-aged Al-Cu-Mg-Ag alloy at 100-150℃ keep a relatively lower level, but increases to a high level when the creep temperature increased to 180℃. The steady creep rate increased with increasing temperature or stress, which can be described by a constitutive equation with an apparent activation energy of 102 kJ/mol.
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    MICROSTRUCTURE EVOLUTION AND FEM ANALYSIS OF [011] ORIENTED SINGLE CRYSTAL OF A Ni-BASED SUPERALLOY DURING TENSILE CREEP
    ZHANG Shu TIAN Sugui YU Huichen SU Yong YU Xingfu YU Lili
    Acta Metall Sin, 2011, 47 (1): 61-68.  DOI: 10.3724/SP.J.1037.2010.00457
    Abstract   PDF (1502KB) ( 1551 )
    By means of the elastic stress-strain finite element method (FEM), the distribution features of the von Mises stress, strain energy density and the influences of the applied stress on the von Mises stress at γ/γ' phases interface and γ' phase directionally coarsening regularity in a [011] oriented single crystal nickel-based superalloy were investigated. Results show that after heat treatment, the microstructure of the superalloy consists of the cubic γ' phases embedded coherently in the γ matrix, and γ' phases arranged regularly along the <100> direction. Compared to the matrix channel near (010)γ' plane, the bigger von Mises stress are produced within the matrix channel near (001)γ' plane when the tensile stress is applied along the [011] direction. Compared to (010)γ' plane, the larger expanding lattice strain occurs on the (001)γ' plane along the [010]γ' direction under the action of the principal stress component, resulting in the Al, Ti atoms with bigger radius to be trapped by the larger strain zone, which is the main reason of promoting the γ' phase grown directionally into the strip-like rafted structure.
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    THREE--DIMENSIONAL RECONSTRUCTION OF GRAINS IN PURE IRON SPECIMEN
    LUAN Junhua LIU Guoquan WANG Hao
    Acta Metall Sin, 2011, 47 (1): 69-73.  DOI: 10.3724/SP.J.1037.2010.00233
    Abstract   PDF (1130KB) ( 1217 )
    The informations of hree dimensional (3D) grain in real materials were rarely obtained directly, especially when the grain size, shape, topology and orientation were all required. By combining the classical serial sectioning and electron backscatter diffraction (EBSD) technique, a 3D digital visible model of a group of grains in a real pure iron specimen was constructed based on 400 parallel serial section images (about 150 grains appearing in each section image) with an average inter-section distance of (1.69±0.3) μm. The model presented enables the stereoscopic observation in a 3D space. Besides, this model can provide not only the quantitative geometric information including grain sizes, shapes and topological characteristics, but also the real orientation information of both the grains and their boundaries in 3D polycrystal space, which offers new insights into the digitalization and visualization of real material microstructures.
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    PREPARATION OF MICROARC OXIDATION COATING ON (Al2O3-SiO2)sf/AZ91D MAGNESIUM MATRIX COMPOSITE AND ITS ELECTROCHEMICAL IMPEDANCE SPECTROSCOPIC ANALYSIS\par
    ZHU Qingzhen XUE Wenbin LU Liang DU Jiancheng LIU Guanjun LI Wenfang
    Acta Metall Sin, 2011, 47 (1): 74-80.  DOI: 10.3724/SP.J.1037.2010.00330
    Abstract   PDF (1380KB) ( 1806 )
    A thick protective ceramic coating on 33% (Al2O3-SiO2)sf/AZ91D (volume fraction) magnesium matrix composite was prepared by the microarc oxidation (MAO) technique in silicate electrolyte. SEM, EDS and XRD were employed to analyze the surface morphology, composition and phase constituent of the coating, furthermore, the microhardness profile of the coating was also measured. The electrochemical corrosion properties of magnesium matrix composite before and after the MAO surface treatment were evaluated by electrochemical impedance spectroscopy (EIS), and the equivalent circuits corresponding to different immersion times were suggested. The results show that the fiber-reinforced composite surface is completely covered by the MAO coating. The ceramic coating mainly consists of MgO and Mg2SiO4 phases. The maximum microhardness of coating is up to 1017 HV. The electrochemical impedance modulus, |Z|, of the coated magnesium matrix composite increases significantly compared with bare composite, thus the magnesium matrix composite coated by MAO displays a good corrosion resistance. The occurrence of inductive loop in EIS of coated composite after 96 h immersion in 3.5% NaCl solution implies the pitting deterioration in the coating. The corrosion resistance of coated magnesium matrix composite is determined by the properties of inner compact layer of MAO coating.
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    SOLIDIFICATION OF Al-Pb MONOTECTIC ALLOY UNDER A STATIC MAGNETIC FIELD
    LI Haili ZHAO Jiuzhou
    Acta Metall Sin, 2011, 47 (1): 81-87.  DOI: 10.3724/SP.J.1037.2010.00470
    Abstract   PDF (1232KB) ( 1565 )
    A static magnetic field has great effect on the solidification structure of monotectic alloys, so the rapid directional solidification in a static magnetic field has great potentials in the manufacturing of monotectic alloys. But up to date little is known about the details of the effect of the magnetic field on the microstructure development during liquid-liquid decomposition. Directional solidification experiments with Al-Pb monotectic alloys in a static magnetic field were carried out, and the effects of the field intensity and the solidification velocity on the solidification microstructure were investigated. Samples with well-dispersed microstructure were obtained. A model was proposed to describe the microstructure evolution in a monotectic alloy solidified in a static magnetic field, which was verified by comparing with experimental results and then applied to investigate the microstructure formation in the unidirectionally solidified Al-Pb alloys. The numerical results indicate that the convective flow of the melt is very strong during the liquid-liquid phase transformation, and leads to a nonuniform distributions of the nucleation rate, number density, average radius and volume fraction of the minority phase droplets along the radial direction of the sample, resulting in serious phase segregation in solidified structure. A static magnetic field can effectively suppress the convective flow and causes a more uniform distributions of the nucleation rate, number density, average radius and volume fraction of the minority phase droplets. The application of a static magnetic field is favorable for the formation of a well dispersed microstructure. The lower the Pb content of the alloy and the higher the solidification velocity, the lower the intensity of the magnetic field needed for obtaining a sample with homogeneous distribution of the minority phase particles.
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    MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Nb-16Si-22Ti--2Hf--2Cr--2Al INGOT PREPARED BY VACUUM INDUCTION MELTING
    JIA Lina GAO Ming GE Jingru ZHENG Lijing SHA Jiangbo ZHANG Hu
    Acta Metall Sin, 2011, 47 (1): 88-94.  DOI: 10.3724/SP.J.1037.2010.00434
    Abstract   PDF (1464KB) ( 1532 )
    The melt with a nominal composition of Nb-16Si-22Ti-2Hf-2Cr-2Al was poured in a ceramic shell mould with a temperature gradient of about 4℃/mm, and the ingot with the dimension of 60 mm×170 mm was obtained. The relationship between the microstructure and mechanical properties was measured, and the effects of the silicide on fracture toughness at ambient temperature and compression strength at high temperature were analyzed. It is revealed that the microstructure of the alloy consists of Nb solid solution and silicides, and the cooling rate can obviously change primary phase and constituent phases. The volume fraction of Nb3Si formed at rapid cooling rate is significantly increased, and Nb5Si3 phase is formed with decreasing in cooling rate, whereas the volume fraction of the eutectic colonies and NbSS dendrites increase evidently, especially the second dendrite arm. Fine and uniform eutectic colonies are contributed to the ambient tensile strength, while the coarse primary Nb3Si decreases the tensile strength but improves the compression strength of the alloy. When the microstructure is mainly composed of fine (NbSS+Nb5Si3) eutectic colonies, the tensile strength and elongation of the alloy reach 449 MPa and 0.3%, respectively. When lath-like Nb3Si phase has 80 $\mu$m in width and 50% in volume fraction as well as its long axis is parallel to compression direction, the compression strength of the alloy at 1250℃ is about 650 MPa.
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    INFLUENCES OF PREPARATION PARAMETERS ON MORPHOLOGY AND PHOTOLUMINESCENCE PROPERTY OF BaZrO3:Ce NANO-POWDERS
    LI Yuling MA Weimin WEN Lei WEN Qiang YUAN Xiaoyu
    Acta Metall Sin, 2011, 47 (1): 95-101.  DOI: 10.3724/SP.J.1037.2010.00398
    Abstract   PDF (1280KB) ( 1392 )
    BaZrO3:Ce nano-materials were synthesized by coprecipitation reaction under different conditions. XRD, SEM and TG-DTA were applied to analyze the changes of phase and characteristic of the powders during calcing process. The luminescence spectra of samples were analyzed by the fluorescence photometer. It is shown that BaZrO3:Ce nano-materials calcined at 1000℃ for 3 h has the best luminescence property, especially the samples doped 0.7%Ce3+ (molar fraction) is optimal, and its excited spectrum is at 247 nm and emitted spectrum is from 475 nm to 505 nm. The best liquid conditions are that the initial concentration of mother liquor is 0.04 mol/L, containing 2%-3% (mass fraction) of DBS, the titration rate is 2 mL/min and the temperature is 0℃. The as-prepared powders are of well dispersed property and small average size of 20 nm.
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    GROWTH BEHAVIOR OF FATIGUE CRACK IN SPRAY-FORMED SiCp/Al-7Si COMPOSITE
    LI Wei CHEN Zhenhua CHEN Ding TENG Jie
    Acta Metall Sin, 2011, 47 (1): 102-108.  DOI: 10.3724/SP.J.1037.2010.00315
    Abstract   PDF (1406KB) ( 1468 )
    In order to investigate the fatigue crack growth behaviors of SiCp/Al-7Si composite and the unreinforced alloy prepared by spray deposition, compact tension (CT) specimens were prepared and tension-tension fatigue tests were carried out under constant-amplitude load and load shedding technique (ΔK-decreasing) control to obtain the fatigue threshold. The experimental data demonstrate that the addition of SiC particles results in superior fatigue crack propagation properties for a given ΔK, i.e. lower crack growth rate and higher intrinsic threshold stress intensity factor. The SiC particles play a significant role in dictating the rate of fatigue crack growth. OM and SEM observations show that crack deflections around SiC particles and particle cracking are the principle mechanisms of interaction between SiC particles and crack tip. Moreover, detailed quantitative analysis indicates that the extent of particle cracking induces a high level of fatigue crack closure, which effectively reduces the driving force of crack growth and so slows down fatigue crack growth. However, when the closure-corrected effective stress intensity factor range (ΔKeff) acts as the crack driving force, the composite shows a higher crack growth behavior than the unreinforced alloy.
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    PREPARATION OF Na1.4Co2O4 BASED THERMOELECTRIC MATERIALS BY SOL-GEL METHOD AND CHARACTERIZATION
    LI Ying MA Beiyue WANG Zhenming JIANG Maofa
    Acta Metall Sin, 2011, 47 (1): 109-114.  DOI: 10.3724/SP.J.1037.2010.00370
    Abstract   PDF (1112KB) ( 1189 )
    Sr, Li and Cu-doped Na1.4Co2O4 based thermoelectric materials were prepared by sol-gel process. The phase constitution of Na1.4Co2O4 based thermoelectric materials was analyzed by XRD. According to DTA-TG curves, the pre-sintering and sintering temperatures of the materials were obtained to be 450 ℃ and 850 ℃, respectively. The influences of doping amount on the electrical resistivity, Seebeck coefficient and power factor of Na1.4Co2O4 based materials were investigated. The results showed that doping Li could decrease the electrical resistivity of Na1.4Co2O4, doping Sr and Cu could increase the electrical resistivity. Doping Li and Cu could improve the Seebeck coefficient and power factor of Na1.4Co2O4. The improving effect on Na1.4Co2O4 by doping Sr is not remarkable but by doping Li is the best. When 0.40 Li was doped, the power factor of Na1.0Li0.4Co2O4 at 15 ℃ reaches maximum value of 7444.73 μW?m-1?K-2.
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    INFLUENCE OF PROCESS PARAMETERS ON THE PERFORMANCE UNIFORMITY OF DETONATION GUN SPRAYED WC-Co COATINGS
    WANG Tiegang SONG Binghong HUA Weigang GONG Jun SUN Chao
    Acta Metall Sin, 2011, 47 (1): 115-122.  DOI: 10.3724/SP.J.1037.2010.00351
    Abstract   PDF (1488KB) ( 1377 )
    Based on the orthogonal experiment, the effects of oxygen-fuel ratio and spraying distance on physical and mechanical properties of D-gun sprayed WC-Co coatings were investigated. An ideal coating with the uniform dense microstructures, high hardness and elastic modulus, and excellent wear resistance was obtained by technology optimization. The phase identifications and microstructure observation of the optimized WC-Co coating were conducted by XRD and SEM, respectively. The coating showed near-isotropic behaviors, which has been verified by the comparisons of mechanical and wear properties between cross section and surface. The mechanisms how the spraying parameters affected near--isotropic characters of the D-gun sprayed WC-Co coating were analyzed and discussed.
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    ELECTROPLATING MECHANISM OF NANOSTRUCTURED BLACK Ni FILMS
    SONG Lixiao ZHANG Zhao ZHANG Jianqing CAO Chunan
    Acta Metall Sin, 2011, 47 (1): 123-128.  DOI: 10.3724/SP.J.1037.2010.00268
    Abstract   PDF (974KB) ( 1709 )
    Nanocrystalline black nickel film has been obtained from a modified Watt bath by using DC (direct current) electroplating method, and characterized by using SEM and XRD. Meanwhile, the initial electroplating behavior of the nanocrystalline black Ni film was investigated using cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The results showed that the black Ni film is substantially smooth and bright, and consists of particles with the mean size 51.4 nm. The deposition of black Ni film followed the mechanism of three-dimensional (3D) nucleation and subsequent grain growth. With the increase of the negative potential bias, the main deposition process of black Ni film onto brass changed from the under-potential deposition (UPD) through heterogeneous finally to homogeneous nucleation/growth, which consequently resulted in the initial increase and subsequently decrease of charge-transfer-resistance (Rt). At the high negative bias, the occurrence of the low and the ultra-low frequency inductive loops on EIS plots, can be attributed to the adsorptions of hydrogen atoms and the nickel hydroxyl compound onto cathode surface, which retarded the nucleation/growth process of nickel.
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