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

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    TERNARY COMPOUNDS AND RELATIVE PHASE EQUILIBRIA IN THE Mg-RICH SIDE OF THE Mg-Zn-Ca SYSTEM
    LI Hongxiao MA Qianqian REN Yuping JIANG Min QIN Gaowu
    Acta Metall Sin, 2011, 47 (4): 385-390.  DOI: 10.3724/SP.J.1037.2010.00638
    Abstract   PDF (940KB) ( 1209 )
    The structure, composition range and phase equilibria of the ternary compounds in Mg-rich side of the Mg-Zn-Ca system have been investigated by SEM, EPMA, XRD and TEM. It has been shown that there exist two ternary compounds T1 and T2 in equilibrium with the Mg-based solid solution in the Mg-Zn-Ca system. T1 phase is a linear compound with hexagonal structure, whose structure parameters decrease with the Zn content, i.e. a=0.995-0.945 nm, c=1.036-1.003 nm. Its composition region (atomic fraction, %) is Ca about 16, Zn 16.8-49.5 and balanced Mg. The composition region of the T2 phase is Mg 27.1-29.3, Zn 62.1-64.4 and Ca 7.6-9.0. T2 phase also has the hexagonal structure, whose structure parameters are a=1.475 nm and c=0.879 nm. At 335 ℃, the dissolution of Zn has not decreased the solubility of Ca in the α-Mg solid solution, but the solubility of Zn in the α-Mg solid solution increases with the dissolution of Ca, and the maximum solubility of Zn is 4.6. At 335 ℃, there are five three--phase fields consisting of α-Mg+Mg2Ca+T1α-Mg+T1+T2α-Mg+T2+MgZn, MgZn+T2+Mg2Zn3 and α-Mg+Mg7Zn3+MgZn in the Mg-Zn-Ca system, respectively.
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    DENDRITE GROWTH IN SOLIDIFICATION OF UNDERCOOLED Co80Pd20 ALLOY
    ZHOU Shengyin HU Rui JIANG Li LI Jinshan KOU Hongchao CHANG Hui ZHOU Lian
    Acta Metall Sin, 2011, 47 (4): 391-396.  DOI: 10.3724/SP.J.1037.2010.00605
    Abstract   PDF (982KB) ( 1224 )
    Much interest has been focused on the dendrite growth of undercooled melts in the theoretical field of solidification research. The BCT model was widely accepted to interpret dendrite growth behavior in rapid solidification process. In present case, substantial undercooling ΔT up to 415 K was achieved for Co80Pd20 melt applying molten glass denucleation combined with cyclic superheating. The dendritic morphology of the experimental alloy was investigated by OM and the solute concentration of appointed micro-area was analyzed by EDS. Based on the BCT dendrite growth model, the theoretical calculation of the related parameters of the dendrite growth process included tip radius R, dendrite growth velocity V, solute concentration in liquid at dendrite tip CL* and undercooling contributions were completed. It can be found that the dendritic morphology was only formed in the undercooling ranges of 0-72 K and 95-142 K. With the initial undercooling increasing, V rises steeply due to the increase of the growth driving force, but R displays a complicated variation attributed to the combine effects of thermal/solute diffusion. EDS analysis reveals that the experimental data of CL* is in accordance with the theoretical predication by BCT model. The results confirmed that the dendrite growth in undercooled Co80Pd20 melts can be interpreted successfully by BCT model.
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    MICROSTRUCTURAL EVOLUTION OF DIRECTIONALLY SOLIDIFIED Ni-BASED SUPERALLOY DZ125 UNDER HIGH TEMPERATURE GRADIENT
    MIN Zhixian SHEN Jun XIONG Yilong WANG Wei DU Yujun LIU Lin FU Hengzhi
    Acta Metall Sin, 2011, 47 (4): 397-402.  DOI: 10.3724/SP.J.1037.2011.00015
    Abstract   PDF (921KB) ( 1693 )
    The Ni-based superalloy DZ125 was prepared by liquid metal cooling (LMC) directional solidification and quenching technology with withdrawal rate ($V$) range of 2-400 μm/s and temperature gradient up to 250 K/cm. The morphologies of solid/liquid (S/L) interface, cellular/dendritic arm spacings and the morphologies of MC carbide were studied systematically. The shallow cellular interface arised at V=2 μm/s. With increasing the withdrawal rate, the S/L interface turns into deep cellular (V=3 μm/s) and dendritic (V≧5 μm/s) interfaces successively. The cellular spacing is increased with increasing the withdrawal rate. However, the primary dendritic arm spacing is decreased with increasing the withdrawal rate. The maximum value of cellular/dendritic spacings appears at transition from cellular to dendritic interfaces (V=5 μm/s). Meanwhile, the morphology of MC carbide changes from octahedron to frame-like, Chinese-script and finally to fine dendrite with increasing the withdrawal rate. Compared with the theoretical models of primary dendrite spacing, the results are good in agreement with Trivedi's and Ma's models. Furthermore, they are also in agreement with Hunt-Lu model only at lower withdrawal rates (V≦50 μm/s). The relationships of primary and secondary dendritic arm spacings with withdrawal rates can be described as λ1=314.6V-0.24±0.02  and λ2=97.76V-0.33±0.01, respectively. MC carbide precipitated from the melt during solidification, and its morphology is dependent both on the withdrawal rate and the morphology of S/L interface.
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    FORMATION AND EVOLUTION OF THE NON-DENDRITIC MORPHOLOGY IN UNDERCOOLING MELT WITH LOWER SHEARING RATE
    ZHAO Lining LIN Xin HUANG Weidong
    Acta Metall Sin, 2011, 47 (4): 403-409.  DOI: 10.3724/SP.J.1037.2010.00519
    Abstract   PDF (964KB) ( 1126 )
    With the development of the semisolid metal processing technology, many efforts have been made to understand the relationship of the microstructural evolution with the shear rate and the melt undercooling. The globular and rosette microstructures can be obtained under the different shearing rates and melt undercooling. Since the microstructure evolves rapidly under the general high shearing rate in the previous researches, it is difficult to reveal the formation process of semisolid microstructure in detail. In this work, the evolutions of globular and rosette crystals were studies by using a transparent organic alloy Succinonitrile-5%H2O (molar fraction) with a small shearing rate. It is found that there is a critical value of the shearing rate in the semisolid process above which the morphology of the globular crystal could be stable and below which it would be destabilized to form equiaxed dendrite. In addition, when the interface lost the stability, the globular crystals will evolve to dendrite under a higher melt undercooling and to rosette under a lower undercooling. The continuous splitting of the tip of the perturbation cells in the globular crystal induces the formation of the rosette morphology.
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    EFFECTS OF Bi ADDITION ON SOLIDIFICATION BEHAVIOR AND MICROSTRUCTURE OF AZ80 MAGNESIUM ALLOY
    WANG Yaxiao FU Junwei WANG Jing LUO Tianjiao DONG Xuguang YANG Yuansheng
    Acta Metall Sin, 2011, 47 (4): 410-416.  DOI: 10.3724/SP.J.1037.2010.00604
    Abstract   PDF (955KB) ( 1390 )
    The solidification behavior and as--cast microstructure in AZ80-Bi magnesium alloy were analysed by OM, SEM, XRD and DSC. Meanwhile, the evolution of the solidification microstructure of AZ80-2%Bi alloy was studied by heating-quenching experiments. The results show that the as-cast microstructure of AZ80-2%Bi consists of primary α-Mg matrix, divorced eutectic β-Mg17Al12 phase and Mg3Bi2 phase. The Mg3Bi2 phase exists in the flake-like and granule-like morphologies. With 2.0%Bi addition, the solidification procedure of AZ80 magnesium alloy is changed. The ternary eutectic transformation L→α-Mg+β-Mg17Al12+Mg3Bi2 (at 435 ℃) takes place during solidification of AZ80-2%Bi alloy instead of the binary eutectic transformation L→α-Mg+β-Mg17Al12 (at 437 ℃) in AZ80 alloy. Comparing with AZ80 alloy, the nucleating temperature of primary $\alpha$--Mg in AZ80--2\%Bi alloy is decreased from 568.8 ℃ to 562.6 ℃, and the eutectic temperature is also decreased from\linebreak 424.2 ℃ to 421.1 ℃.
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    EFFECT OF LONGITUDINAL MAGNETIC FIELD ON THE MICROSTRUCTURE OF DIRECTIONALLY SOLIDIFIED Al-40%Cu HYPEREUTECTIC ALLOY
    SHEN Yu REN Zhongming LI Xi, REN Weili
    Acta Metall Sin, 2011, 47 (4): 417-422.  DOI: 10.3724/SP.J.1037.2010.00588
    Abstract   PDF (1016KB) ( 1139 )
    The microstructures of Al-40%Cu (mass fraction) hypereutectic alloy directionally solidified under a longitudinal magnetic field were investigated. The results show that the magnetic field has a great influence on the morphology of the primary Al2Cu phase at the growth rate of R=2 μm/s and a temperature gradient of GL=42.6 K/cm at the solid/liquid interface. The effect of thermoelectromagnetic convection (TEMC) which drives the fluid flow is predominant under low magnetic fields and different at different scales according to the model of TEMC established.
    It is found that TEMC causes severe deformation of the primary Al2Cu phase opposed to the well-aligned faceted
    primary phase in the absence of the field at microscopic scale and the primary phase tends to become a
    faceted-non-faceted transition gradually with the increase of the magnetic field. Moreover, TEMC modifies the
    mushy zone length at macroscopic scale because of the secondary convection from the bulk caused by the microscopic
    TEMC. TEMC also affects the solute distribution in the front of the interface at different scales and the process
    of heat transfer. Under higher magnetic fields, the effect of TEMC is suppressed, however, the considerable
    thermoelectric Lorentz force makes the primary phase become the irregular cellular structure. Meanwhile, the
    primary phases align along the magnetic field closely, which results from the remarkable magnetocrystalline
    anisotropy of the Al2Cu crystal.
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    HYDROGEN ABSORPTION BEHAVIOR OF 1500 MPa--GRADE HIGH STRENGTH STEEL 42CrMoVNb
    LI Yang ZHANG Yongjian HUI Weijun WANG Maoqiu DONG Han
    Acta Metall Sin, 2011, 47 (4): 423-428.  DOI: 10.3724/SP.J.1037.2010.00537
    Abstract   PDF (844KB) ( 971 )
    Hydrogen absorption behaviors of a newly developed 1500 MPa-grade high strength steel 42CrMoVNb at different austenitizing temperatures and tempering temperatures were studied using cathodic charging and hydrogen thermal desorption analysis, which were also compared with commercial structural steel 42CrMo. The results show that the hydrogen escape peak temperatures (θp) in hydrogen evolution curves of hydrogen charged 42CrMoVNb specimens are between 200 ℃ to 300 ℃ both at as-quenched condition and as-tempered condition. The absorbed hydrogen content of 42CrMoVNb specimen increases slowly with increasing tempering temperature up to 500 ℃. When the tempering temperature exceeded 500 ℃, the absorbed hydrogen content increases sharply and reaches its peak, 6.6×10-6, for the specimen tempered at 600 ℃, which is 5 times as much as that of the as-quenched specimen. Thereafter the absorbed hydrogen content declines sharply as the tempering temperature was gone up sequentially. When the specimen was tempered at 400 ℃, the absorbed hydrogen content decreases slightly with austenitizing temperature increasing, and in the microstructure no fine dispersed (V, X)C carbide precipitated, while when the specimen was tempered at 600 ℃, the absorbed hydrogen content increases sharply with austenitizing temperature increasing, and more fine dispersed (V, X)C precipitated. These results indicate that fine dispersed (V, X)C precipitate could  be regarded as a strong hydrogen trap, and the trap activation energy, Ea, is equal to about\linebreak 28.7 kJ/mol, which was obtained by change heating rate.
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    PREPARATION AND BIOCOMPATIBILITY OF ZnHA/TiO2 HYBRID COATING
    ZHANG Jingying QI Min YANG Dayi AI Hongjun
    Acta Metall Sin, 2011, 47 (4): 429-434.  DOI: 10.3724/SP.J.1037.2010.00448
    Abstract   PDF (739KB) ( 1175 )
    A zinc-containing hydroxyapatite (ZnHA)/titania (TiO2) hybrid coating is developed to improve the mechanical character and biocompatibility of titanium (Ti) implants. The ZnHA layer on Ti via sol-gel method after treated by micro-arc oxidation (MAO) to produce an ZnHA/TiO2 porous titania coating on Ti implants. The chemical composition and physical structure of the modified surface layers were characterized by X-ray photoelectron spectroscopy (XPS) as well as scanning electron microscope (SEM). At the same time, in vitro co-culture assays were performed to evaluate the cell morphology, adhesion and proliferation of MG-63 cells to the modified titanium. The cells micro morphology on the ZnHA/TiO2 coatings were more polygonal compared with round than that on HA/TiO2 coatings by SEM. It was confirmed by Fluorescence microscopy observations that the osteoblast-like cells on the hybrid coating layer adhesion and spread favorably. The results in this work suggest that ZnHA/TiO2 hybrid coatings on Ti substrates can function as an implant with good mechanical character and biocompatibility.
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    NUCLEATION AND GROWTH OF INTRAGRANULAR ACICULAR FERRITE AND ITS EFFECT ON GRAIN REFINEMENT OF THE HEAT-AFFECTED-ZONE
    SHU Wei WANG Xuemin LI Shurui HE Xinlai
    Acta Metall Sin, 2011, 47 (4): 435-441.  DOI: 10.3724/SP.J.1037.2010.00578
    Abstract   PDF (1406KB) ( 1512 )
    Nucleation and growth of intragranular acicular ferrites (IAFs) in heat-affected-zone (HAZ) have been investigated by the observation of microstructures quenched at different temperatures during the cooling process of welding thermal cycle. It is proved that IAFs can divide the prior austenite grains and refine the intragranular microstructures. AES show that there is a Mn-depleted-zone near the interface of TiOx-MnS complex inclusion. IAFs prefer to nucleate on the complex inclusion, and a single inclusion can usually induce several IAFs to nucleate. IAFs grow up with lowering of the temperature during the cooling process. Quenched martensite and bainite could collide with the IAFs and make them deform, but the< quenched martensite and bainite can not penetrate through the IAFs. IAFs divide the prior austenite grain and restrain the growth of other intragranular microstructures, and therefore HAZ's microstructure is finally refined effectively.
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    ELECTROCHEMICAL BEHAVIORS OF ULTRA HIGH STRENGTH STEELS WITH CORROSION PRODUCTS
    SUN Min XIAO Kui DONG Chaofang LI Xiaogang
    Acta Metall Sin, 2011, 47 (4): 442-448.  DOI: 10.3724/SP.J.1037.2010.00466
    Abstract   PDF (1200KB) ( 1824 )
    The electrochemical behaviors of ultra high strength steels, 300M and AerMet 100, with corrosion products which were formed during salt spray test were studied using potentiodynamic polarization curve, EIS, SEM, scan Kelvin probe (SKP) and Raman spectroscopy. The results show that the corrosion products on the steel 300M are γ-FeOOH and Fe(OH)3, and those on the steel AerMet 100 are β-FeOOH, Fe3O4 and γ-Fe2O3 after salt spray test. Because of the compact characterization, Fe3O4 and γ-Fe2O3 have a better protection property for substrate by hindering the permeation of O2 and Cl-. The corrosion potentials shift negatively and corrosion current densities become larger with increasing salt spray time, meaning a faster rate of anodic dissolution for these two steels. After salt spray test, the values of Kelvin potential for the two steels are 0.5-0.6 V positive than those before tests, and more uneven. For 300M, the corrosion resistance of rust layer becomes larger/smaller with the corrosion productions gathering/drapping on/from the samples. The electrochemical reaction for AerMet 100 is diffusion--controlled process and the value of Warburg impedence which expresses the diffusion--hindering effect becomes larger. The corrosion resistance and protection ability of corrosion products for steel AerMet 100 are better than those of steel 300M.
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    CORROSION RESISTANCES OF PASSIVE FILMS ON LOW-CARBON REBAR AND FINE-GRAINED REBAR IN ALKALINE MEDIA
    SHI Jinjie SUN Wei GENG Guoqing
    Acta Metall Sin, 2011, 47 (4): 449-454. 
    Abstract   PDF (922KB) ( 959 )
    The passive ranges of low-carbon rebar and fine-grained rebar in simulated concrete pore solution with pH13.0 were determined by means of cyclic voltammetry and potentiodynamic polarization curves. Chronopotentiometry was used to obtain steady state conditions for the formation of passive films on rebar samples at different anodic potentials. Electrochemical impedance spectroscopy and Mott-Schottky curves were employed to compare the passive films formed at different potentials. Additionally, cyclic polarization curves were used to compare the corrosion resistances of passive films formed on the two rebars in alkaline media with or without Cl-. The results show that the passive ranges of the two rebars are all between -0.25 and +0.6 V, and the more stable passive films can be formed on both rebars at the anodic potential of +0.3 V. In the absence of Cl-, the stability and corrosion resistance of the passive film formed on the fine-grained rebar are better than those of low-carbon rebar. However, the pitting corrosion resistance of the former is somehow lower than that of the latter in the presence of Cl-. The amounts of grain boundary and trace elements are responsible for the lower corrosion resistance of fine-grained rebar.
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    MICROSTRUCTURE, CORROSION AND WEAR RESISTANCES OF MICROARC OXIDATION COATING ON Al ALLOY 7075
    WANG Yanqiu WANG Yue CHEN Paiming SHAO Yawei WANG Fuhui
    Acta Metall Sin, 2011, 47 (4): 455-461.  DOI: 10.3724/SP.J.1037.2011.00010
    Abstract   PDF (1169KB) ( 1624 )
    Microarc oxidation (MAO), an important surface treatment technology for Al alloys in stead of hard anodization, was applied to prepare coating on Al alloy 7075, of which the microstructure and properties of the anti-corrosion and anti--wear were studied by XRD, SEM, neutral salt spray (NSS) test and ball-on-disc friction and wear test. The results show that the MAO coating formed on Al alloy 7075 mainly consists of γ-Al2O3, α-Al2O3 and some amorphous SiO2. Si element results from electrolyte or from substrate. MAO coating exhibits excellent corrosion resistance, for example, coatings with thickness of 70 μm can endure more than 2000 h in NSS test even without seal treatment. Dense microstructure of MAO coating results in the excellent corrosion resistance. Post seal treatment can greatly enhance the corrosion resistance of the MAO coating, even for thin coating. MAO coating fabricated on Al alloy 7075 possesses similar friction coefficient but much higher wear resistance compared with hard anodized film, for example, the former is as 50 times as the wear resistance of the later. The MAO coating is just slightly worn and its frication coefficient remains unchanged throughout the test.
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    FLOW SOFTENING MECHANSIM OF A Ti ALLOY WITH LAMELLAR STRUCTURE DURING SUBTRANSUS DEFORMATION
    SONG Hongwu ZHANG Shihong CHENG Ming LI Zhenxi CAO Chunxiao
    Acta Metall Sin, 2011, 47 (4): 462-468.  DOI: 10.3724/SP.J.1037.2010.00534
    Abstract   PDF (976KB) ( 1024 )
    The flow stress has a considerable flow softening after a peak strain hardening at very low strains for Ti alloys with lamellar structure during subtransus deformation. In order to study the mechanism of such flow softening behavior, the deformation behavior of TC11 Ti alloy with a lamellar structure was studied using isothermal hot compression tests under a temperature range of 890-995 ℃ and a strain rate range of 0.01-10 s-1. Theoretical calculation shows the Hall-Petch strengthening effects induced by α/β  interface as well as the twin boundary in $\alpha$ lamellar are far more significant than that of the colony boundary. The flow softening can be related to reduction of Hall-Petch strengthening effects due to transfer from the hard slip mode to the soft one.
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    MICROSTRUCTURE, MAGNETIC AND MAGNETOTRANSPORT PROPERTIES OF Co-C NANOCOMPOSITE THIN FILMS
    TANG Ruihe YANG Zhigang ZHANG Chi YANG Bai LIU Xiaofang YU Ronghai
    Acta Metall Sin, 2011, 47 (4): 469-474.  DOI: 10.3724/SP.J.1037.2010.00546
    Abstract   PDF (1031KB) ( 819 )
    Co-C nanocomposite thin films with a Co atomic content of 13.0% were fabricated onto Si (100) substrates by magnetron co-sputtering technique. Post annealing was carried out in vacuum at annealing temperature ranging from 473 K to 773 K for 30 min. TEM images indicate that the Co nanoparticles are dispersed uniformly in an amorphous carbon matrix for the as-deposited samples, and Co particle size is in a range of 1.5-3.0 nm. After annealing at 673 K, the average Co particle size is enlarged distinctly. Magnetization hysteresis loops reveal that the as-deposited thin films show low magnetization. As annealing temperature is increased, both magnetization and coercivity are enhanced significantly. The samples annealed at 673 K and 773 K show ferromagnetic behaviors at low temperature, and superparamagnetic behaviors at room temperature, which are characteristic magnetic features for granular system. A negative magnetoresistance (MR) of 1.33% is observed for the as-deposited Co-C thin films at 4.2 K in the applied magnetic field of 3980 kA/m. The MR value decreases with increasing annealing temperature. Resistance (R) versus temperature (T) curves exhibit a good linear relationship of lnR-T-1/4 at a broad low temperature range, suggesting that the conduction in Co-C nanocomposite thin films follows the variable range hopping transport mechanism.
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    MAGNETIC STRUCTURE OF RAPIDLY QUENCHED FeCo-BASED RIBBON ANNEALED UNDER TENSILE STRESS IN FLOWING ATMOSPHERE
    FANG Yunzhang XU Qiming YE Huiqun FAN Xiaozhen QIU Jianfeng
    Acta Metall Sin, 2011, 47 (4): 475-481.  DOI: 10.3724/SP.J.1037.2010.00597
    Abstract   PDF (847KB) ( 1193 )
    The FeCo-based ribbons (Fe36Co36Nb4Si4.8B19.2) with dirrerent magnetic structures were prepared by single roller quenched method and then annealed with direct current under tensile stress in flowing atmosphere. The longitudinally driven giant magneto-impedance (LDGMI) effect in the stress-Joule-heated FeCo-based ribbon was measured with HP4294A impedance analyzer. The dependences between the characteristic parameters of the LDGMI profiles, ratio of giant magneto-impedance and half-height width of the applied magnetic field at the bottom, and driving current frequency were analyzed. The difference of the LDGMI profiles of the annealed FeCo-based ribbons with various remained thicknesses obtained by etching with 16.7% HCl solution was compared. The mechanism and the character of the stress-induced magnetic structure in FeCo-based ribbons were exposured by means of the principle of the skin effect and the theory of the dependence of giant magneto-impedance on the magnetic anisotropy in the magnetic materials.
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    STUDY OF DYNAMIC RECRYSTALLIZATION OF A Cu-BASED ALLOY BFe10-1-1 WITH CONTINUOUS COLUMNAR GRAINS
    YU Junwu LIU Xuefeng XIE Jianxin
    Acta Metall Sin, 2011, 47 (4): 482-488.  DOI: 10.3724/SP.J.1037.2010.00568
    Abstract   PDF (1227KB) ( 1100 )
    Dynamic recrystallization behavior of a Cu-based alloy BFe10-1-1 with continuous columnar grains was investigated by hot compression test. Specimen was compressed in the temperature range of 750 to 900℃ and the strain rate range of 0.01 to 10 s-1. The results indicate that the dynamic recrystallization temperature of the tested alloy is about 850 ℃ and the thermal activated energy Q is 427.937 kJ/mol, higher than those of the alloy with equiaxial grains. When ln Z<43, dynamic recrystallization always happens in the alloys. When\linebreak ln Z>51, dynamic recrystallization can not occur. When 43≦ln Z≦51, dynamic recrystallization may happen at 850 or 900 ℃, may not happen at 750 or 800 ℃, which can serve as the critical regions of the alloy for dynamic recrystallization. Such effect is probably ascribe to the difference in the dynamic recrystallization mechanisms of the continuous columnar grained materials and ordinary polycrystalline materials. It is observed that the dynamically recrystallized area in the sample has expanded when the strain rate increases. Dynamic recrystallization preferentially nucleates at grain boundary in the form of grain-boundary bulging. Twins form in the recrystallized grains and are evolved into grain belt by “twinning dynamic recrystallization”.
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    EFFECTS OF NOVEL Q-P-T AND TRADITIONAL Q-T  PROCESSES ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF MARTENSITIC STEELS WITH DIFFERENT CARBON CONTENT
    ZHANG Ke XU Weizong GUO Zhenghong RONG Yonghua WANG Maoqiu DONG Han
    Acta Metall Sin, 2011, 47 (4): 489-496.  DOI: 10.3724/SP.J.1037.2010.00547
    Abstract   PDF (1492KB) ( 1854 )
    Compared with traditional quenching and tempering (Q-T) treatment, the product of strength and elongation of the carbon steel can be enhanced significantly by novel quenching-partitioning-tempering (Q-P-T) treatment, especially for the medium carbon steel. Based on the tensile results, the product of strength and elongation of the Fe-0.42C-1.46Mn-1.58Si-0.028Nb specimen treated by Q-P-T, is up to 31627 MPa?% with elongation 20.3\%, which not only is higher than the specimen treated by Q-T process, but also meets the mechanical properties predicted of next generation advanced high strength steel. Microstructural analysis indicates the differences in Q-T and Q-P-T process lie on the amount of retained austenite and its size distribution as well as the size range of lath martensite. The former results in the low amount (<3%) of thin film-like austenite in addition to nonuniform martensite size, while the later results in the high amount of thick flake-like austenite accompanying uniform martensite size. Therefore, the higher barrier for micro-crack propagation and the better plastic deformation ability of advanced high strength steel (AHSS) can be obtained by Q-P-T treatment.
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    PREPARATION OF COMPOSITE COATING (Al+Al2O3) ON SiC LONG FIBER
    ZHANG Lu SHI Nanlin GONG Jun PEI Zhiliang GAO Lijun SUN Chao
    Acta Metall Sin, 2011, 47 (4): 497-501.  DOI: 10.3724/SP.J.1037.2010.00714
    Abstract   PDF (717KB) ( 1042 )
    Reactive magnetron sputtering was used to prepare (Al+Al2O3) diffusion barrier layer on SiC fiber surface. The relationships between deposition process parameters with composition and deposition rate of the coating, and the influence of the coating on mechanical property of SiC fiber were measured. Results show that with increasing sputtering power, the deposition rate increases rapidly at first and then slowly. With increasing of working pressure, the deposition rate of the coating deceases slowly at first, and then sharply at a typical value of working pressure, finally drops gradually. (Al+Al2O3) protected C-rich layer of SiC fiber, and improved the adherence between fiber and diffusion barrier layer. Results of laser Raman spectrum show that the coating has little influence on surface residual stress of SiC fiber. The measured tensile strength of the composite fibers is 97.69% of the calculated tensile strength according to meaning rule, and is 98.77% of the calculated one for the fiber after vacuum treatment at 850 ℃ for 10 h, meaning that (Al+Al$_{2}$O$_{3}$) coating has not much influence on mechanical property of SiC fiber.
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    EFFECTS OF PREANNEALING UNDER PRESSURE ON THE CRYSTALLIZATION BEHAVIOR AND THERMAL STABILITY OF Gd36La20Al24Co20 BULK
    METALLIC GLASS
    LIU Tong ZHU Yarong ZHANG Tongwen ZHANG Tao
    Acta Metall Sin, 2011, 47 (4): 502-506.  DOI: 10.3724/SP.J.1037.2011.00001
    Abstract   PDF (777KB) ( 1223 )
    Gd36La20Al24Co20 bulk metallic glass (BMG) was prepared by copper-mold casting. The crystallization behavior and thermal stability of Gd36La20Al24Co20 during annealing under two temperatures in supercooled liquid region and the pressures ranging from ambient pressure to\linebreak 725 MPa were investigated by XRD and DSC. High pressure was found to retard the crystallization of Gd36La20Al24Co20 BMGs. The apparent activation energy of the crystallization, E, determined by Kissinger equation increases with increasing applied pressure. The relative mechanisms were analyzed appropriately.
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    CONSTITUTIVE RELATIONSHIPS OF Nb MICROALLOYED STEEL DURING HIGH TEMPERATURE DEFORMATION
    JIA Bin PENG Yan
    Acta Metall Sin, 2011, 47 (4): 507-512.  DOI: 10.3724/SP.J.1037.2011.00031
    Abstract   PDF (823KB) ( 1118 )
    The flow stress curves of Nb microalloyed steel Q345B during hot compression deformation were obtained on Gleeble-3500 thermo-simulation machine. Based on the experimental results, the constitutive model of Nb microalloyed steel during high temperature deformation was established to describe the stress-strain relationship during dynamic softening (dynamic recovery and dynamic recrystallization) and in the steady flow state, in which the influences of the thermal deformation parameters (strain rate and deformation temperature) and dynamic softening mechanism (dynamic recovery and dynamic recrystallization) on the flow stress were considered. A method was provided to solve constitutive equation and establish the mathematic expressions of the correlation coefficients. It is shown that the predicted results by the model are in good agreement with the experimental ones.
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