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

About the Journal

  Current Issue
    , Volume 50 Issue 1 Previous Issue    Next Issue
    For Selected: View Abstracts
    Original Articles
    MICROSTRUCTURES AND PROPERTIES OF 0Cr32Ni7Mo4N DUPLEX STAINLESS STEEL AFTER VARIOUS FORMING PROCESSES
    HE Hong, LI Jingyuan, QIN Liyan, WANG Yide, FANG Fei
    Acta Metall Sin, 2014, 50 (1): 1-10.  DOI: 10.3724/SP.J.1037.2013.00393
    Abstract   HTML   PDF (17483KB) ( 1852 )

    Duplex stainless steels consist of a two phase microstructure involving α-ferrite and γ-austenite. These alloys have a remarkable combination of mechanical properties together with good corrosion resistance under critical working conditions and are suitable for marine and petro-chemical applications. However, the poor hot workability of these materials makes the industrial processing of flat products particularly critical. Many investigations focus on the mechanisms and behaviors of hot deformation on these materials. Several factors are frequently reported give rise to hot cracking: phase proportions, size and morphology of both phases, softening mechanisms in constituting phases, microstructural evolution during hot work, and strain partitioning between α and γ. On the contrary, few studies have been carried on cold rolling performance. Hot cracking should be avoid during forming process of duplex stainless steel, the more effective way of manufacturing in such materials is also needs research. In this work, the formability of 0Cr32Ni7Mo4N duplex stainless steel was studied in the hot rolling and directly cold rolling processes. The deformation mechanism of α and γ phase at room temperature, the microstructure evolution after hot rolling, cold rolling and solution treatment were investigated. Mechanical properties and corrosion resistance of two kinds of cold-rolled sheets were tested. The metallography and corrosion morphology were observed by OM and SEM. The results show that cracks emerged along the edge of hot-rolled plate even it was reheated three times, and it has good cold rolling formability after cutting edge of the plate. On the other hand the as-cast billet solution-treated at 1100 ℃ has good cold rolling performance. Deformation mechanism of α phase at room temperature is that multi-slip system form dislocation cell structure, while single slip model and mechanical twins appear in γ phase. As the temperature of heat-treatment raised, microstructure became more homogeneous and the amount of precipitate particles decreased. The experimental results show that the tensile strength of cold-rolled sheet after heat-treatment reaches 1082.9 MPa and the elongation is 29.3%. Critical pitting potential of the specimen in 3.5%NaCl liquor is 1060 mV; weight loss after intergranular corrosion in 65%HNO3 solution is 0.05 g/(m2·h).

    Figures and Tables | References | Related Articles | Metrics
    EFFECT OF GRAIN BOUNDARY ANGLE ON STRESS RUPTURE PROPERTIES OF A Ni-BASED BICRYSTAL SUPERALLOY
    CAO Liang, ZHOU Yizhou, JIN Tao, SUN Xiaofeng
    Acta Metall Sin, 2014, 50 (1): 11-18.  DOI: 10.3724/SP.J.1037.2013.00342
    Abstract   HTML   PDF (16445KB) ( 3578 )

    Bicrystal slabs with different grain boundary angles were cast to study the effect of varied grain boundary angle on stress rupture properties of a Ni-based bicrystal superalloy. It was found that the stress rupture lives of single crystal specimens were superior to those with grain boundaries. With the increase of grain boundary angle, the stress rupture life was decreased and the fracture type was transferred from trans-granular to inter-granular fracture. The reduced rupture properties was attributed to the inhabitation of grain boundary on slip deformation. With the rise of temperatures, the effect of grain boundaries on rupture properties was enhanced and the critical value of grain boundary angle from trans-granular to inter-granular fracture was decreased. Inter-granular fracture occurred from 12° grain boundary in the rupture test of 871 ℃ and 552 MPa, and it occurred from 4.5° grain boundary in the rupture test of 1100 ℃ and 120 MPa. Since the grain boundary became weaker at higher temperature, the angle of low-angle boundary in single crystal superalloys should be controlled strictly.

    Figures and Tables | References | Related Articles | Metrics
    INFLUENCE OF HEAT TREATMENT ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A HIGH-STRENGTH Zr-Ti ALLOY
    LI Ye, ZHANG Long, ZHU Zhengwang, LI Hong, WANG Aimin, ZHANG Haifeng
    Acta Metall Sin, 2014, 50 (1): 19-24.  DOI: 10.3724/SP.J.1037.2013.00498
    Abstract   HTML   PDF (5772KB) ( 916 )

    Due to the high stress, relative low density and excellent resistance of radiation, Zr-based alloys have become promising structural materials used in the space environment. The relationship between microstructure and mechanical properties is the key issue for designing Zr-based alloy in different alloy systems and has attracted extensive research interests. The microstructures could be adjusted by different processes of heat treatment and thus realizing the optimization of mechanical properties. In this work, the initial microstructure and mechanical properties of a high strength Zr47Ti45Al5V3 (mass fraction, %) alloy was investigated. The XRD results reveal that the initial Zr-based alloy is consisted of α (hcp) and β (bcc) phases. Transmission electron microscopy result shows that the lathy α phase homogenously distributed within the β phase matrix. Mechanical tests of this alloy show very high strength but limited plasticity. The tensile strength is 1648 MPa. However, the tensile elongation is only 0.8%. DSC trace indicates that the transition temperature of α phase to β phase is located between 560~750 ℃ that provides the possibility to adjust the microstructures through different processes of heat treatment. In order to optimize the mechanical properties, several different processes of heat treatment were conducted on this Zr-based alloy, and the relative volume fraction of α and β phase is successfully adjusted. According to the mechanical tests, the plasticity becomes larger as the amount of β phase increases with a slight decrease in strength. When the volume fraction of β phase is about 60%, the alloy exhibits the optimal mechanical performance with a tensile strength of 1398 MPa and an elongation of 3.1%.

    Figures and Tables | References | Related Articles | Metrics
    DIRECTIONAL SOLIDIFICATION OF MONOTECTIC COMPOSITION Al-Bi ALLOY
    YANG Zhizeng, SUN Qian, ZHAO Jiuzhou
    Acta Metall Sin, 2014, 50 (1): 25-31.  DOI: 10.3724/SP.J.1037.2013.00579
    Abstract   HTML   PDF (6603KB) ( 700 )

    Monotectic systems are a kind of extensive alloys. Many of them have great potentials for practical industry application. A lot of work has been carried out to study the solidification of monotectic alloys. But most of them focused on the microstructure formation during cooling a hyper-monotectic alloy through the miscibility gap in the liquid. Little work was done on the solidification behaviors of an alloy of monotectic composition. Directional solidification experiments were carried out with Al-Bi alloy of the monotectic composition (Al-3.4%Bi, mass fraction). The influences of the solidification velocity on the microstructure were investigated. The microstructure evolution during solidification was analyzed. The results indicate that a solute-rich layer forms in front of the solidification interface and the liquid-liquid decomposition occurs there. When the alloy is solidified at such a high velocity so that the minority phase droplets of all sizes in front of the solidification interface are migrating to the solidification interface, the size distribution of the minority phase particles shows only one peak. When the alloy is solidified at a relatively low velocity, the minority phase droplets within a certain size range may move away from the solidification interface under the concurrent actions of the Marangoni migration, Stokes motion of the droplets as well as the movement of the sample. Al-3.4%Bi alloy solidified under such conditions shows a size distribution of the minority phase particles with two peaks. The average radius of the minority phase particles < R > depends on the solidification velocity V 0 exponentially according to < R > V 0 - 1 / 2 . With the decrease of the solidification velocity, the dependence of the average radius of the minority phase particles varies towards to < R > V 0 - 1 / 3 .

    Figures and Tables | References | Related Articles | Metrics
    USE OF SO2/AIR/N2 COVER GASES FOR THE PROTECTION ON MOLTEN MAGNESIUM AND AZ91D ALLOY
    WANG Xianfei, XIONG Shoumei
    Acta Metall Sin, 2014, 50 (1): 32-40.  DOI: 10.3724/SP.J.1037.2013.00386
    Abstract   HTML   PDF (762KB) ( 466 )

    Molten magnesium and AZ91D alloy oxidize rapidly during casting process, sulfur dioxide (SO2) mixed with carrier gases can be used to protect the melt by reacting with the melt to form a coherent protective film on the melt surface. In this work, the films formed in SO2/Air/N2 cover gases were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), the formation process and the protective mechanism of the surface film were also discussed. The results show that the protective film is composed of MgO, MgS and MgSO4. MgS increases the pilling and bedworth ratio of the surface film and enhances its protective capability. MgSO4 is the thermodynamically stable phase and its formation is important for the formation of protective film. When SO2/Air/N2 cover gases are used to protect the melt and SO2 content is fixed, air content should be controlled within a certain range.

    Figures and Tables | References | Related Articles | Metrics
    MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Mg-4Zn-2Al-2Sn ALLOYS EXTRUDED AT LOW TEMPERATURES
    ZHAO Dongqing, ZHOU Jixue, LIU Yunteng, DONG Xuguang, WANG Jing, YANG Yuansheng
    Acta Metall Sin, 2014, 50 (1): 41-48.  DOI: 10.3724/SP.J.1037.2013.00352
    Abstract   HTML   PDF (11253KB) ( 13642 )

    Due to the high demand of light-weight alloys in automotive applications, wrought magnesium (Mg) alloys, applied as automotive sheet and extrusions, are attracting great attention. However, some inherent disadvantages of common wrought Mg alloys have limited their application, such as poor corrosion resistance, poor creep resistance and low formability. It is well known that Sn can provide thermally stable Mg2Sn particles in the matrix of magnesium alloys. Our previous study shows that the Mg-4Zn-2Al-2Sn alloy has potential to be developed into a wrought Mg alloy. Currently, the microstructure, texture and mechanical properties of Mg-4Zn-2Al-2Sn alloy extruded at temperatures of 225, 250 and 275 ℃ have been investigated, where complete dynamic recrystallization occurred during extrusion and the average grain size was reduced to 4.4, 7.1 and 10.5 μm, respectively. The amount and morphology of the second phases were directly influenced by the extrusion temperature. Extruded at 225 ℃, irregular Mg2Sn phase in size of 20~60 nm precipitated in the grains. With the extrusion temperature increasing to 275 ℃, Mg2Sn of about 500 nm and micron-size Mg32(Al, Zn)49 precipitates were observed. The {0002} texture was formed at 225 and 250 ℃ during the extrusion. While the temperature increased to 275 ℃, due to the activation of prismatic slip system, { 1 0 1 - 0 } < 0002 > texture of prismatic plane parallel to extrusion direction was also observed. When compressive stress loaded along the extrusion direction, the { 1 0 1 - 0 } < 0002 > texture suppressed the activation of the tensile twinning { 1 0 1 - 2 } < 1 0 1 - 1 > , which leads to a decrease of asymmetry between tension and compression.

    Figures and Tables | References | Related Articles | Metrics
    LOCALIZED CORROSION OF ALUMINUM ALLOY 2024 EXPOSED TO SALT LAKE ATMOSPHERIC ENVIRONMENT IN WESTERN CHINA
    WANG Binbin, WANG Zhenyao, CAO Gongwang, LIU Yanjie, KE Wei
    Acta Metall Sin, 2014, 50 (1): 49-56.  DOI: 10.3724/SP.J.1037.2013.00417
    Abstract   HTML   PDF (10179KB) ( 852 )

    Localized corrosion behavior of aluminum alloy 2024 with/without cladding exposed to salt lakes atmospheric environment in western china for 4 a was investigated. The depth of pitting, corrosion products, morphology of surface and cross-section, and corrosion potential were analyzed by SEM/EDS, OM, XRD and electrochemical analysis system. The results showed that 2024 suffered severe pitting corrosion. The cladding layer of aluminum alloy 2024 exposed for 2 a had been penetrated. Depth of pitting of aluminum alloy 2024 without cladding after 2 a exposure had reached 320 μm; meanwhile, few pitting that penetrated the whole substrate of aluminum alloy 2024 without cladding had been observed. A main corrosion product of aluminum alloy 2024 with/without cladding—[Mg1-xAlx(OH)2]x+ (Cl-, CO2-)x·mH2O (layered double hydroxides, LDH) was determined. Also, the results of electrochemistry indicated that the corrosion potential of aluminum alloy 2024 decreased gradually with the concentration of Cl- increasing. The effects of factors of salt lake atmospheric environments, corrosion product and Cl- concentration on the corrosion behavior of 2024 with/without cladding were discussed.

    Figures and Tables | References | Related Articles | Metrics
    ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY MONITORING ON MILD STEEL Q235 IN SIMULATED INDUSTRIAL ATMOSPHERIC CORROSION ENVIORNMENT
    FU Xinxin, DONG Junhua, HAN En-hou, KE Wei
    Acta Metall Sin, 2014, 50 (1): 57-63.  DOI: 10.3724/SP.J.1037.2013.00278
    Abstract   HTML   PDF (5323KB) ( 800 )

    As mild steels are the most widely used structure materials, it is no doubt that the study on their atmospheric corrosion mechanism is of great significance. Traditional study on atmospheric corrosion of mild steels emphasized more on on-site experiments and data collection and physical analysis. Relatively, application of electrochemical researching methods has not been frequently used in this field. Electrochemical impedance spectroscopy (EIS) method has been highly valued by electrochemists due to its multiple advantages. However, it has been less used in study of corrosion process of mild steels after the rust has been generated. As a matter of fact, during the service life of mild steel in atmospheric environments, the rust period is much longer than naked steel period due to the low corrosion resistance of these steels. Therefore, it is more meaningful to study the corrosion behavior of steels with rusts both for development of new weathering steels and for the prediction of the service life of weathering steels. In this work, the corrosion behavior of mild steel Q235 under simulated industrial atmospheric corrosive condition was monitored and studied by EIS method, with a focus on the evolution of cathode reactions. The result showed that there existed a critical condition of electrolyte film for corrosion rate of mild steel Q235 both for the substrate and rusted surface during wet-dry cycles. Comparison and analysis showed that, two parallel reactions, the reduction of oxygen and the reduction of rust, existed at the cathode during the corrosion process. With the increase of the wet-dry cycles, the activity of oxygen reduction tended to decrease, and almost disappeared in the end; while the activity of rust deduction tended to increase and became the main cathode reaction in a short period. In each wet-dry cycle, the corrosion rate first increased then decreased with the decrease of the electrolyte layer thickness, which was caused by the two synchronous and opposite effects on the corrosion reactions.

    Figures and Tables | References | Related Articles | Metrics
    EFFECTS OF TEMPERATURE ON LECTROCHEMICAL CORROSION OF DOMESTIC NUCLEAR-GRADE 316L STAINLESS STEEL IN Zn-INJECTED AQUEOUS ENVIRONMENT
    LIU Xiahe, WU Xinqiang, HAN En-hou
    Acta Metall Sin, 2014, 50 (1): 64-70.  DOI: 10.3724/SP.J.1037.2013.00416
    Abstract   HTML   PDF (6062KB) ( 697 )

    The effects of temperature (T) on oxide films for 316L stainless steel (316L SS) in borated and lithiated water without and with Zn injection were investigated by in situ potentiodynamic polarization curves and electrochemical impedance spectra (EIS). The protective property of oxide films in the Zn-free/Zn-injected solution degraded with increasing temperature. With increasing temperature, the structure of the oxide film varied from a single layer to double layers, the Cr-rich oxide layer played a key role on retarding further oxidation. Compared to the Zn-free case, the corrosion rate decreased significantly in the Zn-injected solution due to the formation of compact Zn-bearing oxide films, but the instinct growth mechanism of the oxide films remained unchangeable. The solubilities and structure model of oxides were proposed to discuss the formation mechanism of oxide films on 316L SS in the hydrothermal solution.

    Figures and Tables | References | Related Articles | Metrics
    MICROSTRUCTURE AND HYDROGEN PERMEATION CHARACTERISTIC OF NEAR EUTECTIC Nb-Ti-Co HYDROGEN SEPARATION ALLOY
    YAN Erhu, LI Xinzhong, TANG Ping, SU Yanqing, GUO Jingjie, FU Hengzhi
    Acta Metall Sin, 2014, 50 (1): 71-78.  DOI: 10.3724/SP.J.1037.2013.00474
    Abstract   HTML   PDF (9786KB) ( 800 )

    Because of the high hydrogen permeability and high resistance to hydrogen embrittlement of Pd-based alloys, Pd-Ag alloys have been used as hydrogen permeation membranes for separation and purification of hydrogen gas. However, Pd is too expensive for large-scale industrial applications as hydrogen permeation membranes. The development of alternative membrane materials with higher hydrogen purification efficiency and lower cost is therefore strongly desired. From the viewpoint of the hydrogen permeability, some bcc metals such as Nb, V and Ta are promising candidates since their predicted hydrogen permeability are larger than that of Pd. Nb-Ti-Co ternary alloy has been considered as the best candidate because of lower cost, good thermal stability, the high hydrogen permeability and high resistance to hydrogen embrittlement. In this work, the eutectic composition in Nb-Ti-Co alloy was probed and verified through Bridgman directional solidification experiment. Microstructures, hydrogen permeation properties and hydrogen embrittlement of near eutectic Nb-Ti-Co alloy were investigated and compared with those of pure Pd. The results indicate that the eutectic composition in Nb-Ti-Co alloy is Nb31Ti35Co34, and its solidification microstructures contain only the Nb(Ti, Co) and TiCo phase, which shows regular coupled growth by Bridgman directional solidification at the rate of 5 μm/s. The eutectic alloy shows the higher hydrogen permeability of 2.7×10-8 mol/(m·s·Pa0.5) at 673.5 K, which is 1.72 times higher than that of Pd alloy. The hydrogen permeability decreases with the decrease of Ti/Co ratio at the same Nb content. A slight crack first appears in the TiCo phase, which is the source of cracks in the membrane, and then the cracks propagate along the edge of the membrane. When the volume fraction of TiCo phase is less than 5%, the eutectic Nb(Ti, Co)+TiCo phases may offset the crack in the TiCo phase, thus the membrane exhibits large resistance to the hydrogen embrittlement.

    Figures and Tables | References | Related Articles | Metrics
    HOT CORROSION RESISTANCE OF FILLER ALLOY BCo46
    JING Yanhong, LIU Enze, ZHENG Zhi, TONG Jian, Ning Likui, HE Ping
    Acta Metall Sin, 2014, 50 (1): 79-87.  DOI: 10.3724/SP.J.1037.2013.00216
    Abstract   HTML   PDF (10964KB) ( 3073 )

    DZ468 alloy is a promising candidate in turbine blade serving in marine atmosphere because of its superior mechanical properties and good hot corrosion resistance. And brazing technology is indispensable to produce turbine blade because of its complicated hollow structure. Therefore, for accelerating the application of DZ468 superalloy, a new type Co-based filler named BCo46 was developed. Due to serving in marine atmosphere, the attack of hot corrosion can be inevitable. Frequently, the quality of turbine blade depends on the joining region, and the joining region has a lot to do with the filler used to braze the base alloy. Therefore, in this work, the hot corrosion behavior and mechanism of BCo46 alloy in the mixture of 75%Na2SO4 + 25%NaCl (mass fraction) at 900 ℃ was investigated, and compared with a common Ni-based filler BNi-2, and the base alloy DZ468. Moreover, the hot corrosion resistance of the joint bonded with BCo46 was evaluated. XRD, SEM, EDS and ICP spectrograph were employed to study the corrosion products of the tested alloys. The results show that the hot corrosion processes of BCo46, BNi-2 and DZ468 alloys are all accompanied with the dissolution of oxide scale and the formation of sulfide, which support the model of sulfidation-(acid-based) melting model. For filler alloy BCo46, Cr2O3, Co3BO5 and (Ni, Co)Cr2O4 mainly exist in the outer corrosion layer and some CrS is formed in the inner corrosion layer; the external corrosion products of BNi-2 are NiO, (Ni, Co)Cr2O4, Ni2FeBO5 and Cr2O3, and the internal precipitation is Ni2S3. The hot corrosion resistance of filler alloy BCo46 is superior to DZ468 superalloy and BNi-2 filler, it is because (1) BCo46 contains 22% Cr which can form dense and continuous oxide scale Cr2O3; (2) the diffusion rates of O and S are slower in Co- than Ni-based alloy; (3) Co can increase the adhesion of the oxide scale-base metal; (4) collaboration dissolution doesn't occur in BCo46. Furthermore, the formation of boride can deteriorate the hot corrosion resistance of alloy by forming oxides of boron which can dissolve oxide scale, consume Cr and increase phase interfacial area to accelerate the diffusion of S and O. The joint after heat treatment can reach the level of the hot corrosion resistance of the base metal DZ468.

    Figures and Tables | References | Related Articles | Metrics
    UPCONVERSION WHITE PHOTOLUMINESCENCE AND FERROELECTRIC PROPERTY FOR Er3+-Tm3+- Yb3+ TRI-CODOPED Bi4Ti3O12 THIN FILM
    SUN Lina, TAN Jun, BA Dechun, YUAN Peixin
    Acta Metall Sin, 2014, 50 (1): 88-94.  DOI: 10.3724/SP.J.1037.2013.00503
    Abstract   HTML   PDF (6686KB) ( 692 )

    The Er3+-Tm3+-Yb3+ tri-codoped Bi4Ti3O12 thin films were prepared by chemical solution deposition method and its upconversion (UC) photoluminescence and ferroelectric properties were studied. There are four emission bands in the visible UC luminescence spectra excited by 980 nm infrared light at room temperature. The 478 nm blue emission band corresponds to 1G43H6 transition of Tm3+, and the 527, 548 nm green emission bands correspond to 2H11/2 4I15/2 and 4S3/24I15/2 transitions of Er3+, and the 657 nm red emission band corresponds to 4F9/24I15/2 transition of Er3+ and 1G43F4 transition of Tm3+. The fluorescent color can be tuned by adjusting Er3+, Tm3+ and Yb3+ concentrations. For Bi3.59-xErxTm0.01Yb0.4Ti3O12 (BErxTYT) thin films with fixed Tm3+ and Yb3+ concentrations, the intensity ratio of green and red emissions to blue one gradually increased with the increase of Er3+ concentrations, and the quenching concentration of Er3+ is only about 1.75‰ (mole fraction). For Bi3.593-yEr0.007TmyYb0.4Ti3O12 (BETmyYT) thin films with fixed Er3+ and Yb3+ concentrations, the intensity ratio of green and red emissions to blue one decreased with the increase of Tm3+ concentrations, and Tm3+ quenching concentration is about 2.5‰. For Bi3.98-zEr0.01Tm0.01YbzTi3O12 (BETYbzT) thin films with fixed Er3+ and Tm3+ concentrations, the intensity ratio of blue or red emission to green one increase with increase of Yb3+ concentrations, and Yb3+ quenching concentration is less than 5 mol% for the luminescence from Er3+ and lager than 18 mol% for the luminescence from Tm3+. The optimal color coordinate in these films is (0.31, 0.34), close to standard white-light coordinate of (0.33, 0.33), which appears in Bi3.5815Er0.0085Tm0.01Yb0.4Ti3O12 thin film. The color coordinate has only a little change with increasing pumping power, which suggests that luminescence from the thin films has good color stability. There exist significant energy transfers from Er3+ to Tm3+, which will affect the relative intensities of blue, green and red emissions and their quenching concentrations by analyzing the UC emission mechanism of the thin films. The remnant polarization value of the film prepared on Pt/Ti/SiO2/Si substrate reaches the maximum and is equal to 27.8 μC/cm2 when the total codoping concentration of Er3+, Tm3+ and Yb3+ is about 10% (Bi3.5815Er0.0085Tm0.01Yb0.4Ti3O12 film).

    Figures and Tables | References | Related Articles | Metrics
    EFFECT OF Ce-Cu CODOPING ON OPTOELECTRONIC PROPERTY OF SnO2 FILM
    SHAN Linting, BA Dechun, CAO Qing, HOU Xueyan, LI Jianchang
    Acta Metall Sin, 2014, 50 (1): 95-102.  DOI: 10.3724/SP.J.1037.2013.00210
    Abstract   HTML   PDF (9054KB) ( 581 )

    Tin dioxide (SnO2) is a wide band gap semiconductor. SnO2 has recently received a large interest because of its multiple technological applications, including solar cells, optoelectronic devices, flat panel displays, gas sensors, architectural windows and catalysts, owing to its good optical and electrical properties and excellent chemical and thermal stability. Compared to traditional materials which based on sulfur compound, rare earth elements doped oxides possess obvious advantages, such as good chemical stability, high transparency in the range of visible light, and nontoxic. In this work, the Ce-Cu codoping of SnO2 thin films were prepared by sol-gel method. The influence of Ce-Cu codoping on the microstructural and optoelectrical properties has been investigated. Both Cu and Ce dopants are incorporated at substitutional sites (C u S n 2 + , C e S n 3 + ), acting as the acceptors. With increasing the Ce content, the film grain size and optical band gap decrease, while the resistivity decreases at first and then increases due to the change of spatial trap distribution. The ultraviolet peak of the films can be attributed to the oxygen vacancies, while the blue emission at 470 nm belongs to the electron transition between 5d excited state and 4f state of Ce3+ ion. Besides, the intensity of the visible emission peak is influenced by the Ce content. The band structure, density of states of SnO2, intrinsic and doped separately with Cu and Ce were investigated by first-principles full potential linearized augmented plane wave method. The Ce-Cu co-dopants make the conduction band shift down and induce a fully occupied impurity band above the valance band, and 4f orbital of Ce inserts into the conduction band, which leads the shift of the bottom of the conduction band to lower energy zone and narrowing of band gap, thus the band gap is decreased and the conductivity is improved.

    Figures and Tables | References | Related Articles | Metrics
    EFFECTIVE PAIR INTERACTION POTENTIAL OF INTERSTITIAL ATOMS IN METAL
    ZHANG Zhipeng, LEI Mingkai
    Acta Metall Sin, 2014, 50 (1): 103-109.  DOI: 10.3724/SP.J.1037.2013.00255
    Abstract   HTML   PDF (5000KB) ( 720 )

    利用Hillert亚点阵理论和点阵静力学分析方法, 建立了简谐近似下包含弹性效应即应变诱发相互作用的间隙合金总能量模型, 获得了间隙原子间有效相互作用势. 分别将描述基体亚点阵和间隙亚点阵的能量及其相互作用的点阵静力学方程, 在标准态附近作简谐近似, 给出了包括化学相互作用势、Kanzaki力和动力学矩阵等系数的间隙合金总能量公式, 再依据点阵静力学方程的平衡条件, 确定了包含应变诱发相互作用的间隙原子间有效相互作用势. 合金间隙原子间的有效相互作用势取决于化学相互作用势以及Kanzaki力与动力学矩阵耦合的应变诱发相互作用势, 与原子种类、 点阵参数及合金浓度相关. 利用间隙合金的总能量模型计算了δ-Pu中He原子的有效相互作用势, 结果表明, 随着He原子浓度增加, 间隙亚点阵常数增大, 化学相互作用势和应变诱发相互作用势均减小, 造成有效相互作用势降低. 有效相互作用主要受应变诱发相互作用的影响.

    References | Related Articles | Metrics
    PHASE FIELD CRYSTAL SIMULATION OF DISLOCA- TION MOVEMENT AND REACTION
    GAO Yingjun, LU Chengjian, HUANG Lilin, LUO Zhirong, HUANG Chuanggao
    Acta Metall Sin, 2014, 50 (1): 110-120.  DOI: 10.3724/SP.J.1037.2013.00308
    Abstract   HTML   PDF (13829KB) ( 1652 )

    Transformations of grain boundaries often strongly influence both the structure and the properties of polycrystalline and nanocrystalline materials. Thus, plastic deformation processes in fine-grained polycrystals and nanocrystalline solids are associated with transformations of grain boundaries, which crucially affect the structure and mechanical characteristics of such solids. Motion of grain boundary dislocations in plastically deformed materials is commonly considered to be the absorption of lattice dislocations by grain boundaries. In order to reveal the mechanism of motion of a low-angle symmetric tilt grain boundary (STGB) associated with the emission and absorption of lattice dislocation, the emission and evolution of a STGB under strain were simulated by phase-field crystal (PFC) model. The decay of STGB and dislocation reactions of separation, annihilation and mergence and their mechanisms were analyzed from the energy point of view, furthermore, the active energy of the dislocation separation was calculated. The research results show that the low-angle STGB is composed of pair dislocations in a line arrangement in two dimensions of triangular atomic lattice, in which there are two sets of basic Burgers vectors. The evolution process of STGB decay can be divided into six typical stages which includes the detail features as: dislocation climbs firstly along the STGB under strain, then the dislocation occurs to break up into two new dislocations after it gets enough energy to overcome the active potential barrier of dislocation, at this time the STGB emits pair dislocations to move in gliding in grain instead of climbing along STGB; gliding for while, the dislocation crosses the grain until it is annihilated by another dislocation at the STGB right in the front, i.e. the Grain boundary absorbs or merges the gliding dislocation. The remain of dislocation in the STGB can still climb along the grain boundary in which splits off again into two dislocations when it gets enough energy, at the same time it looks as if STGB emits the dislocations and changes the dislocation movement from climbing to gliding again. The dislocation continues gliding until it meets another gliding dislocation in grain to be annihilated, finally the total dislocations are annihilated and the STGB disappears. The two grain systems with STGB become one grain system. The two sets of basic Burgers vectors of lattice dislocation in triangular lattice can validly be used to express the dislocation reaction of emission, separation, mergence, absorption, annihilation, and also can reveal the creation of new Burgers vector and the annihilation of old Burgers vectors and mechanism of the directional change of Burgers vectors during the dislocation reaction.

    Figures and Tables | References | Related Articles | Metrics
    RESIDUAL STRESS IN THE WHEEL OF 42CrMo STEEL DURING QUENCHING
    LI Yongkui, CHEN Jundan, LU Shanping
    Acta Metall Sin, 2014, 50 (1): 121-128.  DOI: 10.3724/SP.J.1037.2013.00476
    Abstract   HTML   PDF (9175KB) ( 804 )

    42CrMo steel, a typical low alloy medium carbon structural steel, is widely used in important structural components that require high strength, plasticity and toughness, such as crane weight-on-wheel, automobile crank shaft, locomotive gear hub, oil drill pipe joints of deep well, fishing tools and so on, for its good harden ability, high temperature strength, good creep resistance and little quenching deformation. The wheels of the polar crane that used in the Chinese third generation nuclear power plant are made of steel 42CrMo. However, cracks and surface peeling normally occur after heat treatment at quenching process of wheel forgings. There is important application background and practical significance to research the effect of the heat treatment process on the microstructures and mechanical properties and the influence of porosity defects inside the forging wheel on the heat treatment process. Large numbers of research work had been focused on segregation and heat treatment process for solving this matter in passing days. This work aims to study the effects of thermal residual stress on porosity defect in a wheel, and explain the reason for cracking and surface feeling in the way of mechanical behavior during quenching. A wheel with surface peeling was analyzed by measuring chemical compositions, macro- and micro-crack observation. Random testing position for mechanical compositions showed that the effects of segregation was small in the wheel. A set of tests and measurements for thermal mechanical properties of 42CrMo steel were conducted from room temperature to 850 oC. FEM models containing porosity defects in different sizes and without defects were constructed by Abaqus for studying the residual stresses during quenching in fully coupled temperature-displacement analysis. Simulation results indicate that the porosity defects in wheel cause stress concentration within themselves. The maximum residual stress is not affected by the length of porosity region. The hoop residual stress in porosity region in the wheel due to quenching process is in the highest level and believed to be the driving force of cracks. According to the stress distribution in the wheel, the cracks caused by the hoop residual stress can not propagate out of the defects region too far. While the assumptions of surface peeling of wheel are concluded due to combined influence of the residual stress and external loads when the defects region emerges near the wheel surface border in view of the current simulation.

    Figures and Tables | References | Related Articles | Metrics