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

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    , Volume 43 Issue 4 Previous Issue    Next Issue
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    Research Articles
    Intermediate-temperature transformation behavior of high-nitrogen austenite generated by nitriding thin pure-iron sheets
    Acta Metall Sin, 2007, 43 (4): 337-343 . 
    Abstract   PDF (931KB) ( 1024 )
    Abstract A microstructural study was carried out to clarify the nature and morphology of the microstructure produced in high-nitrogen austenite generated by nitriding thin pure-iron sheets and subjected to an intermediate-temperature isothermal transformation at 225C, using optical microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was found that an upper bainitic transformation, γ-Fe +γ′-Fe4N, occurred at either the grain boundaries or the dislocation lines in the interior of austenite grains, producing a microstructure which, although morphologically looking markedly different, consisted of bainitic colonies composed of parallel bainitic ferrite (-Fe ) laths with γ′-Fe4N laths entrapped between them, and was interspersed with discrete patches of retained austenite(γr). Transformations occurring at the grain boundaries initiated earlier, proceeded faster, and produced a coarser microstructure, than those occurring in the interior of austenite grains did, due to the difference between the two types of nucleation sites in thermodynamics (nucleation energy) and kinetics (diffusivity). The bainitic transformation was diffusional in nature, with γ′-Fe4N serving as the leading phase. The striking similarity of the γ′-Fe4N to the high-nitrogen austenite in crystal structure, and the good coherence of the γ/γ′-Fe4N interface greatly facilitated the precipitation of γ′-Fe4N from austenite.
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    A THEORETICAL ANALYSIS ON EFFECT OF DEFORMATION ABOVE Ae3 TO THE NUCLEATION OF PROEUTECTOID FERRITE TRANSFORMATION
    Zhi-Gang YANG; Chao WANG Qi
    Acta Metall Sin, 2007, 43 (4): 344-348 . 
    Abstract   PDF (449KB) ( 987 )
    A theoretical analysis has been made on the effect of deformation above Ae3 temperature to the nucleation of proeutectioid ferrite transformation in low carbon steel. There are two types of influence differentiated by strain, here mainly focuses on one that ε<0.36. The influence of deformation parameters to deformation energy is discussed. The calculation results show that transformation starting temperature and maximum nucleation temperature raises when adding deformation, nucleation rate increases at the same temperature, incubation time becomes shorter, and with increased nucleation rate, finer ferrite can be obtained if grain growth is controlled.
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    A CALCULATION METHOD OF PLE/NPLE TRANSTION TEMPERATURE IN γ→α TRANSFORMATION OF Fe-C-Xi SYSTEMS
    Zhi-Gang YANG
    Acta Metall Sin, 2007, 43 (4): 349-352 . 
    Abstract   PDF (318KB) ( 937 )
    According to the local equilibrium model, the ferrite growth in Fe-C-Xi system could be divided into the partition local equilibrium (PLE) model and no partition local equilibrium model (NPLE). In this paper, we develop a method to calculate the PLE/NPLE transition temperature in Fe-C-Xi systems according to the thermodynamic models. Using this method, the PLE/NPLE transition temperature in Fe-C-Xi systems were calculated.
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    Multi-stage reversible transformation types and their evolving processes of Ti-Ni base shape memory alloys
    Zhi-rong HE
    Acta Metall Sin, 2007, 43 (4): 353-357 . 
    Abstract   PDF (469KB) ( 993 )
    The multi-stage reversible transformation types and their evolving processes of Ti-Ni base shape memory alloys (SMAs) under various heat treatment processes have been investigated by differential scanning calorimetry (DSC) with partial thermal cycling method. The Ti-Ni base SMAs show many kinds of multi-stage reversible transformation types after various heat treatment processes. If expresses transformation type with peak numbers of cooling transformation / peak numbers of heating transformation on DSC curves, the 2/1, 2/2 and 3/2 type transformations occur upon cooling and heating in 350-550℃ annealed alloys; the 1/1 type transformation occurs when the annealed temperature is high than 600℃; the 3/2 and 3/3 type transformations occur in 300℃ aged alloys; the 2/2 type transformation occurs in 400℃ aged alloys; the 2/1 type transformation occurs in 500℃ aged alloys. The multi-stage reversible transformation is a gradually changing process. When partial thermal cycling was carried out within the temperature range of cooling transformation, the transformation temperature of reverse transformation decreases with decreasing thermal cycling start temperature.
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    INFLUENCE OF RAW Mg POWDER ON BEHAVIOR OF PHASE FORMATION FOR Mg-B SYSTEM
    Shi-Cheng YAN
    Acta Metall Sin, 2007, 43 (4): 358-362 . 
    Abstract   PDF (594KB) ( 737 )
    The MgB2 bulks were prepared using the spherical magnesium powder (denoted as Q-Mg) and scrapping magnesium powder (denoted as X-Mg) as raw materials. The two kinds of magnesium powder were mixed with amorphous boron powder with a nominal stoichiometry of MgB2, then pressed into pellets under a pressure of 10MPa. The pellets were sintered at 650℃,700℃,750℃ and 800℃ respectively. The X-ray diffraction analysis results for the sintered samples show that the phase formation rate of Q-Mg series samples is lower than that of X-Mg series samples. The differential scanning calorimetry (DSC) results indicate that the solid-solid reaction , Mg melting and liqiud-solid reaction during the temperature increasing occur in turn at 527.1℃,650.7℃ and 660.8℃ for the X-Mg series samples, but for the Q-Mg series samples, the Mg melting and liqiud-solid reaction occur in turn at 640.9℃ and 712.3℃.
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    SCREW METHOD FOR MEASURING STRAIN DISTRIBUTION IN METAL PLASTIC DEFORMATION BODY
    Acta Metall Sin, 2007, 43 (4): 363-366 . 
    Abstract   PDF (1561KB) ( 840 )
    A new method for strain measurement was advanced to obtain the strain distribution inside metal plastic deformation body. Through implanting bolts into the specimen and measuring the deformation of the blots, the strain on the screw interface can be calculated quantitatively. Contrast to the traditional mesh grid method, the screw method does not split the specimen and can be used for open forging without changing the stress state.
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    Modeling of Dendrite Growth for Mg Alloy with Compact Hexagonal Crystal Structure
    Zhiyong LIU
    Acta Metall Sin, 2007, 43 (4): 367-373 . 
    Abstract   PDF (778KB) ( 1031 )
    Magnesium alloy is getting more and more worldwide application. Therefore, microstructure simulation of Mg alloy during solidification process not only has important academic value, but also can meet the active demand for development of industry. Based on the crystallographic structure and preferential growth direction of Mg alloy, physical model of grain growth for compact hexagonal structure was founded and a new stochastic simulation method named virtual core growth calculation model was proposed in this paper. Considering dendrite growth kinetics, anisotropy of grain growth and secondary dendrite arm coarsening, the present model adopted dendrite shape functions to reveal the evolution of primary and secondary dendrite arms. A coordinate transformation technique was introduced to calculate the cell capture of growing dendrites with arbitrary orientations rapidly and accurately. Coupled with the calculation of microscopic solute concentration, the simulation can get more accurate growth morphology of dendrites and solute distribution. Finally, applications to the Mg-Al based alloys are presented describing directional as well as equiaxed dendritic growth, which indicated the high theoretic and practical value of proposed models.
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    Quasicrystals in Al-Cu-Ni-Fe Quaternary System
    Acta Metall Sin, 2007, 43 (4): 374-378 . 
    Abstract   PDF (485KB) ( 756 )
    Al-based stable quasicrystals exist only in ternary alloy systems. According to the cluster line rule, these quasicrystals require three constituent elements. For the objective of determining if there is any quaternary quasicrystal, in this paper we have used the electron concentration and atomic size constant criteria to analyze the alloy phase evolution in the Al-Cu-Ni-Fe quaternary system. We have found no evidence of any quaternary quasicrystal. This result confirms the conclusions out of the cluster line rule that only three elements are sufficient to form a stable Al-based quasicrystal.
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    MOLECULAR DYNAMICS STUDY ON THE STRUCTURAL CHANGES OF COPPER NANOCLUSTERS BY HEATING
    Song-Ning XU
    Acta Metall Sin, 2007, 43 (4): 379-384 . 
    Abstract   PDF (1756KB) ( 894 )
    Molecular dynamics simulation were used to study the variations of atom radial density distribution profilesρ(r) and internal energy per atom with temperatures for Cun(n=531,603,683) clusters. The studied cluster could be divided into four parts of surface layer and approximate surface layer, etc. according to the calculations ofρ(r). The simulated results show that parts of Cu603 cluster surface layer have been found in the state of disorder, while the rest of the cluster surface layer remains orderly when the temperature is around 770K. The coexistence of order and disorder has been lasting until the temperature of 1000K. The atomic structure of approximate surface layer and inner layer keeps in order as a whole between the temperature of 770K and 1000K. After variation of internal energy per atom with temperature undergo the shape of the letter N during 1000K-1100K, the atomic structure of individual parts of cluster has changed into disorderly at 1080K, but the radial direction of cluster appears layered distribution. The layered distribution of cluster disappears till the temperature of 1500K.
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    OXIDATION RESISTANCE OF COPPER PARTICLES MODIFIED WITH MANNICH BASES
    Acta Metall Sin, 2007, 43 (4): 388-392 . 
    Abstract   PDF (463KB) ( 691 )
    Oxidation resistance of copper particles modified with one king of mannich base was studied. Anti-corrosion properties were tested by etching copper particles in acid medium, and the results showed that the corrosion of copper particles was effectively inhabited by modification with the mannich base. On the basis of TG-DTA thermal analysis, we found the original copper particles were oxidized at 200 degrees centigrade, while the treated copper particles were oxidized at 300 degrees, 100 degrees higher than the original ones. XPS analysis showed the mannich base improved the oxidation resistance of copper particles by coordinating with Cu2+ to form protective film on the surface of copper particles. To discover the reaction between the manncih base and copper particles, we tried to obtain the reaction product of the mannich base and copper particles, and furthmore prepared the complex of the manncih base and Cu2+. IR and UV-vis spectrum of the complexes showed that the N atom in the manncih base molecular, instead of O atom was the coordinating atom bonded to Cu2+.
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    EXPERIMENTAL RESEARCH ON THE SURFACE MODIFICATION OF 316L STAINLESS STEEL BY HIGH-INTENSITY PULSED ION BEAMS
    Xu Wang
    Acta Metall Sin, 2007, 43 (4): 393-398 . 
    Abstract   PDF (689KB) ( 933 )
    The surface of 316L stainless steel was treated by high-intensity pulsed ion beams (HIPIB) with ion energy (70% H+, 30% C+) E = 300 keV, current density J = 200 A/cm2, shot number N = 1, 5, 10, pulse duration τ = 75ns. The surface morphology and the phase structure in the near surface region of original and treated specimens were analyzed with scanning electron microscopy (SEM) and X-ray diffraction (XRD). Electron probe microanalysis (EPMA) was used to study the distribution of elements on the irradiated specimens. It is found that the HIPIB irradiation can smooth the surface of the targets, and the preferred orientation was present in the surface layer of the treated specimens. Otherwise, selective ablation of impurities occurred during the interaction between HIPIB and the targets. The microhardness was increased in a depth range of up to 100 μm due to extremely high stresses and shock waves induced by the bombardment, so as to the friction coefficient of the irradiated surfaces was reduced and the wear resistance of them was improved significantly. Under the cooperation of the smooth surface and the grain refinement with the selective ablation of impurities, the electrochemical corrosion resistance of 316L was enhanced markedly. HIPIB irradiation prolongs the fatigue limit and creep rupture life of 316L, simultaneity reduces the steady creep rate with increasing the shot number.
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    Gigacycle Fatigue Life Distribution of Aluminum Alloy LC4CS
    Wei-Xing YAO
    Acta Metall Sin, 2007, 43 (4): 399-403 . 
    Abstract   PDF (473KB) ( 820 )
    Very high cycle fatigue (VHCF) test of 66 aluminum alloy LC4CS specimens was done by piezo-electric fatigue testing machine and fatigue life data were obtained. It is found that the fatigue life distribution of LC4CS under very high cycle fatigue has the duplex peak property and this property is related with the locations of fatigue crack initiation. For the specimens with shorter fatigue life the fatigue cracks initiate at the defects such as inclusions and caves and for the longer the cracks initiate at the surfaces of the specimens. This property makes it inconsequential that the staircase method is used to measure the fatigue limit, and the fatigue life deviation of the VHCF is far larger than those of low cycle fatigue (LCF) and high cycle fatigue (HCF).
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    STUDY ON THE FORMATION OF POLYANILINE COATINGS AND ITS CORROSION BEHAVIOR FROM SILANE SOLUTIONS
    Acta Metall Sin, 2007, 43 (4): 404-408 . 
    Abstract   PDF (544KB) ( 826 )
    The effects of silane on the formation of polyaniline coatings electropolymerized on zinc-electroplated steel have been investigated by Chronopotentiometry technique. The morphology and thickness of polyaniline coatings are investigated by SEM. Corrosion behavior of chromating films and polyaniline coatings in 3.5% NaCl solution is studied by salt spray test and electrochemical impedance spectroscopy (EIS) method. Experimental results show that the anticorrosion properties of polyaniline coatings are close to that of chromating film because of its good shielding and inhibiting properties. From the FTIR and XPS values, conclusions can be as follows: (1) The doping level for the Pani films modified by γ-APS is increased and the oxidation level is reduced comparing with Pani films without modification, which are 11% and 64% respectively;(2)There are four chemical environment : C-Si-O-Si, C-Si-OH, C-Si-O-C, C-Si-O-Zn.
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    Electromaganic Wave Absorbing Property of Polyaniline / Polystylene Blends
    Acta Metall Sin, 2007, 43 (4): 409-412 . 
    Abstract   PDF (687KB) ( 813 )
    The electromaganic wave absorbing property of Polyaniline (PAni) / Polystylene (PS) blends were studied. The results indicated that The conductivity and electromagnetic wave absorbing property of PAni/PS blends increased with the increasing content of the doped PAni. Doped PAni with fibrous morphology had better electromagnetic wave absorbing property than that of PAni with nonfibrous morphology. The frequency breadth of the reflectivity below -10dB was 6GHz(11.6~17.6 GHz)by optimization of the electromaganic parameters of the PAni/ PS micro/nano-blend.
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    ELECTROMECHANICAL COUPLING COEFFICIENT (K33) of A Fe-Ga MAGNETOSTRICTIVE ALLOY
    BAI Xia-Bing
    Acta Metall Sin, 2007, 43 (4): 413-416 . 
    Abstract   PDF (426KB) ( 967 )
    Fe81Ga19 magnetostrictive oriented crystalline have been prepared by zone melting unidirectional solidification. Vacuum annealing at 900°C for 3h has been carried out followed by oil quenching. The electromechanical coupling coefficient (k33) is determined by the impedance resonance frequency tested using AC impedance instrument. With the increase of DC magnetic field, K33 is increased appreciably with the value of 0.126 for 327Oe, 0.129 for 481Oe and 0.133 for 636Oe. Respectively with the increase of stress from 0MPa to 15MPa, K33 remains unchanged in 327Oe, but in 636Oe K33 is increased obviously. Heat treatment at 900°C for 3h followed by oil quenching, K33 is improved with the value of 0.157 in 636Oe magnetic field and 15Mpa stress. Surface quality of sample affects the AC impedance curve and it is hard to measure the K33 of defective sample.
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    The preferred orientation and microstructure changes in directionally solidified Co-Ni-Ga ferromagnetic shape memory alloys
    Hua Xie
    Acta Metall Sin, 2007, 43 (4): 417-421 . 
    Abstract   PDF (838KB) ( 1011 )
    The directionally solidified Co-Ni-Ga ferromagnetic shape memory alloys were prepared by liquid metal cooling method. The preferred orientation and microstructure evolution of crystals under different growth velocity were investigated. The results indicate that keeping the temperature gradient GL=250K/cm, when the growth velocity was 0.9mm/min, a preferred orientation <110> was obtained and the worm-like second phase γ′ precipitated in the martensite matrix which was found to be coarsening along the solidification direction; While the growth velocity was increased to 9mm/min, a <110>+ <001>+<211> mixed orientation was obtained, and the single martensite phase was observed in this case. No obvious macro-segregation was detected based on the results of energy dispersive spectrometer. The paper proposes a new method to fabricate the ferromagnetic shape memory polycrystals with preferred orientation.
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    DEVELOPMENT OF A NEW HIGH STRENGTH AND GOOD HOT CORROSION RESISTANCE FOR LOW SEGREGATION SUPERALLOY DZ68
    Acta Metall Sin, 2007, 43 (4): 422-426 . 
    Abstract   PDF (457KB) ( 853 )
    A more homogeneous microstructure and more alloying of alloys can be obtained by controlling segregation during solidification, so properties of alloys can be improved. For directional solidification (DZ) of turbine blades,a new nickel-base superalloy DZ68, which makes use of low-segregation, is developed. This superalloy can meet the need of engine operation under offshore condition. Besides the hot corrosion resistance, DZ68 possesses an outstanding property of the high-strength aero engine blade material. This paper mainly studies properties of mechanic and hot corrosion resistance. It is shown that DZ68 possesses an excellent performance of hot corrosion resistance similar to DZ38G(In738)and shows mechanical properties equivalent to DZ125.
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    NUMERICAL SIMULATION OF ELECTROMAGNETISM PARAMETERS AND STRUCTURE PARAMETERS IN TWO-STAGE SLIT-LESS MOLD
    Bai-Gang JIN
    Acta Metall Sin, 2007, 43 (4): 427-432 . 
    Abstract   PDF (1801KB) ( 1152 )
    Numerical simulation and orthogonal experiment had been conducted to study the magnetic field distribution in the two-stage soft contact EMCC (electromagnetic continuous casting) mold of round billets. The effects of some factors such as the thickness of mold wall, the resistivity of mold upside part, electrical frequency and coil current intensity to the penetration of magnetic field in two-stage mold were investigated. The magnetic flux density is decreased with the electrical frequency and thickness of mold increasing, but increased with the resistivity of upside mold and coil current intensity increasing. The order of factors affecting the penetration of magnetic field in two-stage mold is electrical frequency>mold upside resistivity>coil current intensity>mold wall thickness. By dimensionless analysis, the relation equation between magnetic flux density and four parameters was given: B/(μ0I/d)= 4.36×109(ρ/If)0.89. Finally, the perfect parameters of two-stage mold used in EMCC are obtained: the thickness of mold wall is 5 mm,the resistivity of mold upside part is 8.8×10-7 Ω•m,coil current intensity is 2000 A, the supply frequency is above 2000 Hz.
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    STUDY OF BRAZING ALLOY USED IN BRAZING COMPOSITE ALLOY CLADDING REINFORCED WITH HARD PARTICLES
    Acta Metall Sin, 2007, 43 (4): 433-438 . 
    Abstract   PDF (831KB) ( 856 )
    ABSTRACT A new type of brazing alloy used in brazing composite alloy cladding reinforced with hard particles on steel substrate was developed in this paper. Using the brazing alloy, stable composite alloy cladding on surface of common steel castings was made by optimum brazed hardfacing process. The composite alloy cladding is superior to other claddings obviously in design and regulation of cladding composition, microstructure and performance as well as thickness (maximum up to 30mm) according to practical demands. Besides, it is possessed of good combination property. SEM observation, energy spectrum and XRD analysis have shown that the composite alloy cladding is in strong combination with steel parent metal, and metallurgical bonding is formed between copper brazing alloy matrix and WC grains in the cladding wherein volume fraction of granular WC phase can be up to 54%. The composite alloy was composed of copper alloy solid solution as base-alloy, Cr-phase and MnNi type of compound dispersion phases as well as WC hard phase. WC particles with different grain sizes and volume fractions were close and well distributed in dispersion strengthened copper alloy. Impingement erosion wear tests have proved that the composite alloy is far superior to 30MnSiTi low-alloy steel in wear resistance.
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    The stability of Cr3C2/Ni3Al Composite at elevated temperature
    Acta Metall Sin, 2007, 43 (4): 439-443 . 
    Abstract   PDF (770KB) ( 907 )
    The phase stability and chemical stability of Cr3C2/Ni3Al composite at 1000℃ have been investigated through long-term aging and oxidation experiment. After long-term aging at 1000℃,chromium carbides kept stable, a few gamma phases separated out and strengthened the Ni3Al matrix, which resulted in the harness of Cr3C2/Ni3Al composite increase. On the other hand, Cr3C2/Ni3Al composite possessed good oxidation resistance. The protective oxides that mainly consisted of α-Al2O3 were formed and the chromium carbides exhibited good anti-oxidation stability and oxidation synergism with Ni3Al matrix. The analyse shows that the chromium carbides are dissolved during welding and some dissolved Cr enter into Ni3Al matrix. The existence of Cr promotesα-Al2O3 formation, which improves the oxidation resistance of the composite obviously. The oxidation rate of the Ni3Al alloy is two times greater than that of the composite in air. Good phase stability and chemical stability make Cr3C2/Ni3Al composite be suitable for long-term service at 1000℃.
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    Study of Interfaces in SiC Fiber Reinforced Nickel-Based Composites
    Acta Metall Sin, 2007, 43 (4): 444-448 . 
    Abstract   PDF (456KB) ( 813 )
    Interface reaction between SiC fiber and matrix is a major problem which directly influences the mechanical properties. In this article, the SiO2-Al2O3,C-Al2O3 layers have been coated on the surface of the SiC fibers as the barrier layer to inhibit the SiCf/Ni element mutual diffusion. The SiCf/Ni composites have been prepared by vacuum heat press. The coatings can effectively block the SiCf/Ni element mutual diffusion and protect fiber’s integration well after heat treatment in vacuum at 850-950℃ for150 hours. The SEM observation indicated that a compact Al2O3 layer is well coated on the surface of the fiber. In contrast, the SiO2 coating is weakness and brittleness combine with fiber, and some cracks in the interface can be seen clearly. The C layer in the C-Al2O3 coating disappeared and dissolved after heat treatment at 850-950℃ for 100 hours.
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