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

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    THE CURRENT SITUATION OF APPLICATION AND DEVELOPMENT OF SUPERALLOYS IN THE FIELDS OF ENERGY INDUSTRY
    GUO Jianting
    Acta Metall Sin, 2010, 46 (5): 513-527.  DOI: 10.3724/SP.J.1037.2009.00860
    Abstract   PDF (1117KB) ( 3307 )

    Superalloys are extensively applied in the fields of energy industry. In the high parameter ultra--supercritical boiler used for coal--fired generation, superheater/reheater tubes must be made of superalloys which meet the requirement of good creep resistant, good fire--side corrosion resistant and steam--side oxidation resistant properties. In gas turbine engine used for gas power, turbine blades and guide vanes should be made of hot--corrosion resistant superalloys which must meet the requirements with respect to excellent high temperature corrosion resistance and long--term microstructural stability. In the field of nuclear power, heat exchange tubes used for steam generator require superalloys with excellent solution corrosion resistance. In the field of coal gasification and energy conservation and pollution reduction, the superalloys with excellent hot corrosion resistant and high temperature wear resistant properties are widely applied. In petroleum exploitation, especially in deep mining, drilling tools must be made of corrosion resistant and wear resistant superalloys because of the sour environment, the temperature of 4-150 ℃ and the existences of CO2, H2S, sand and so on. This paper makes a brief introduction on the current situation of application and development of the superalloys at home and abroad in these fields.

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    EFFECTS OF RARE EARTH ELEMENT Gd ON THE MICROSTRUCTURE AND MECHANICAL PROPERTIES OF NiAl-Cr(Mo)-Hf EUTECTIC ALLOY
    LIANG Yongchun GUO Jianting; SHENG Liyuan; ZHOU Lanzhang
    Acta Metall Sin, 2010, 46 (5): 528-532.  DOI: 10.3724/SP.J.1037.2009.00747
    Abstract   PDF (691KB) ( 1307 )

    The effects of rare earth element Gd on the microstructure and compressive properties of Ni-33Al-28Cr-5.9Mo-0.1Hf (atomic fraction, %) eutectic alloy at room temperature and 1373 K were studied. Very little amount of Gd dissolved in the NiAl and Cr(Mo) phases, and much more amount of Gd distributed in Heusler phase. Addition of Gd induced the microstructural refinement, including the decrease of the eutectic cell size and the lamellae spacing between the NiAl and Cr(Mo) plates. The proper Gd addition leads to the improvement of the compressive yield strength and ductility of the alloy at room temperature, but Gd has a little effect on the compressive properties at 1373 K. However, the Cr(Mo) phase was coarsened and distributed irregularly when 0.1 Gd (mass fraction, %) was added into the alloy, which resulted in the decrease of compressive properties at the testing temperature.

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    IMPACT FRACTURE BEHAVIOR OF X80 PIPELINE STEEL
    DENG Wei GAO Xiuhua QIN Xiaomei ZHAO Dewen DU Linxiu WANG Guodong
    Acta Metall Sin, 2010, 46 (5): 533-540.  DOI: 10.3724/SP.J.1037.2009.00461
    Abstract   PDF (1001KB) ( 1847 )

    Pipeline steels have been widely used in a long-distance transportation of large amounts of crude oil or natural gas under high pressure due to their high transportation efficiency, low energy loss and production cost. For high pressure gas transmission pipelines made from high-strength steels an important problem is to know their fracture behavior in a long running process. In this paper, fracture toughness of X80 pipeline steel was measured by V-notch Charpy impact test at -20 and\linebreak -60 ℃. OM, SEM, EDS and EBSD were used to analyze its fracture mechanism. Experimental results show that the maximum impact load is slightly influenced by temperature, but with the decrease of temperature, crack forming work, crack propagating work and energy absorbed by crack arresting decrease significantly. During fracture process, the intensive tensile stress in the sample would induce the deformation bands formed around the fracture surface and grains elongated along the direction vertical to the main crack, but original austenite grain boundaries are hardly deformed, it would cause stress concentration and then produce intergranular fracture. Generally, brittle second phase particles could act as crack sources under intensive internal stress. In the crack propagation process, grains near the main crack are deformed and elongated tempestuously, resulting in their breaking and new grains with high angle grain boundary (HAGB) formed. Therefore, the grain size decreases and the fraction of HAGB increases in the crack propagation region. Temperature has great influence on the plastic deformation behavior of pipeline steel during facture process. At -20 ℃, the tested steel has good plasticity and the grains are refined during deformation, but at -60 ℃, they are difficult to deform and refine. Consequently, the grain size near crack propagation zones in the sample impacted at -20 ℃ is much smaller than the original grain size, but in -60 ℃ impacted sample the grain sizes has little difference.

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    MICROSTRUCTURE AND TOUGHNESS OF HAZ IN X80 PIPELINE STEEL WITH HIGH Nb CONTENT
    MIAO Chengliang SHANG Chengjia WANG Xuemin ZHANG Longfei Mani Subramanian
    Acta Metall Sin, 2010, 46 (5): 541-546.  DOI: 10.3724/SP.J.1037.2009.00803
    Abstract   PDF (863KB) ( 1994 )

    High Nb-bearing X80 pipeline steel has low cost and excellent combined properties. However, welding will worsen its microstructure and toughness. In this paper, X80 pipeline steel with 0.1%Nb (mass fraction) was chosen, and single welding thermal-cycles with different heat inputs (16, 20, 30, 40, 50, 58 kJ/cm) were simulated by Gleeble-1500 to study the correlation of toughness and microstructure in heat affect zone (HAZ) of actual welding pipe. The evolution characteristics of microstructure of the coarse grain zone in welding heat affect zone (CGHAZ) were investigated by OM, SEM and EBSD. The results indicated heat input in single welding should be less than 30 kJ/cm to ensure good Charpy impact toughness. Although the strong dragging effect of solute Nb can suppress serious coarsening of average grain size in high Nb steel, the uniformity of prior austenite grains is worsened as increasing the heat input. Moreover, the characteristics of high angle boundaries (HABs) and M/A constituents also are influenced by heat input. In the case of low heat put, higher density of HABs, disperse and fine M/A constiuents  were observed, and HABs can form at two sites, one is prior austenite grain boundary, the other is between the lower bainites belong to different Bain groups in the same austenite grain. Otherwise, in the case of high heat input (≥40 kJ/cm), the misorientation between granular bainites in idential austenite grain is small, i.e., the effective grain size is almost the diameter of prior austenite grain, and it will decrease the density of high angle boundary largely, moreover, coarse M/A constituents which are benefit for crack initiation will be generated, consequently, the impact toughness of the coarse grain zone will be worsened obviously in welding heat affect zone.

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    STRESS ORIENTED HYDROGEN INDUCED CRACKING BEHAVIOR OF HEAT AFFECTED ZONE OF L360MCS STEEL IN WET H2S ENVIRONMENT
    ZHOU Chengshuang ZHENG Shuqi CHEN Changfeng
    Acta Metall Sin, 2010, 46 (5): 547-553.  DOI: 10.3724/SP.J.1037.2009.00669
    Abstract   PDF (968KB) ( 1390 )

    Stress oriented hydrogen induced cracking (SOHIC) behavior of heat affected zone (HAZ) of L360MCS steel in wet H$_{2}$S
    environment was studied by separating crack, SEM and EDS. The cracks are formed by four--point bending test in
    wet H$_{2}$S environment. The microstructure of HAZ is obviously different from
    the base metal, and the hardness of HAZ is lower than those of the base metal and welding joint. The fracture
    surface of the cracks was separated and the hydrogen blisters were torn off. The cross section and fracture surface of
    the cracks are analyzed by SEM and EDS. Results show that the cracks of SOHIC appeared as axial crack and vertical
    crack, and the former is preferential. The appearance of cracks is associated with the low hardness value of
    HAZ. The dimension of hydrogen blasters in tension stress zone of bended specimen is bigger than that in
    unstressed specimen, which is due to hydrogen concentration in bended specimen is higher. Both axial and vertical
    cracks nucleate independently and propagate in the quasi--cleavage manner. Tension stress not only increases the
    supersaturated hydrogen concentration in tension stress zone but directly promotes vertical crack propagation.
    Axial crack nucleates at MnS, CaS and precipitated phase, and propagates under internal hydrogen pressure.
    Vertical crack mainly nucleates on precipitated phase and propagates under both internal hydrogen pressure and
    tensile stress.

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    NUMERICAL SIMULATION OF AIR ENTRAPMENT PHENOMENON DURING MOLD FILLING OF HIGH PRESSURE DIE CASTING PROCESS
    LI Shuaijun XIONG Shoumei Mei Li John Allison
    Acta Metall Sin, 2010, 46 (5): 554-560.  DOI: 10.3724/SP.J.1037.2009.00683
    Abstract   PDF (825KB) ( 1377 )

    The most common defect found in the high pressure die casting (HPDC) process is gas porosity which significantly affects the mechanical properties of the final components. As it is known, the air entrapment of the liquid metal flow during the mold filling stage has a close relationship with the gas porosity distribution in die castings. The generation of the entrapped air is mainly due to the interaction between air and liquid metal in the die cavity. In the past few decades, extensive efforts have been made to develop numerical models for the simulation of mold filling. However, these efforts mainly focused on the single phase flow models which can only predict the liquid metal flow and assume that the effect of air in the die cavity is negligible. As a result, these models could not provide the quantity and location of entrapped air in die castings. Recently, several research results on tracking the entrapped air in the molten metal flow have been reported but some techniques still need to be improved further and much more researches are required. In this study, a liquid-gas coupled model is presented to simulate the air entrapment phenomenon during the HPDC mold filling process. The pressure of the entrapped air bubbles is solved at each time step.  The calculations of the liquid and gas phases are combined together through the pressure transfer. In order to verify the validity and stability of this model, a specially designed water analog experiment was carried out and compared with the numerical simulation results of the liquid-gas coupled model and the single phase flow model, respectively. The comparison shows that the liquid-gas coupled model has better prediction accuracy than the single phase flow model in tracking the entrapped air bubbles.

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    ONE-STEP DEPOSITION AND INTERFACIAL ADHESIVE STRENGTH OF THE MULTILAYER SYSTEM WITH A DIFFUSION BARRIER
    LI Weizhou WANG Qimin GONG Jun SUN Chao JIANG Xin
    Acta Metall Sin, 2010, 46 (5): 561-568.  DOI: 10.3724/SP.J.1037.2009.00472
    Abstract   PDF (1202KB) ( 1173 )

    M-Cr-Al-Y (M=Ni and/or Co) coatings with the good comprehensive property among anti-oxidation, anti-corrosion and mechanical properties have been widely used for the protection for the gas turbine components. However, after a long-term thermal exposure to high temperature atmosphere in service, the coatings are rapidly degraded. The main cause is ascribed to the intensive element interdiffusion between the coating and the substrate. To suppress the interdiffusion, addition of a diffusion barrier (DB) is required at the interface of the overlayer and the substrate. However, M-Cr-Al-Y coating system with a ceramic diffusion barrier prepared by a conventional two-step arc ion plating (AIP) on the superalloy substrate would reduce the interfacial adhesive strength. In this paper, the multilayer system of Ni-Cr-Al-Y-Si overlayer with a DB and a bond coat (BC) was deposited on the DSM11 substrate by one-step AIP. The anti--oxidation property, the anti-diffusion ability of the barrier and the interfacial adhesive strength of the multilayer system were investigated. The results indicate that the multilayer can provide more effective protection for the DSM11 substrate than the single coating at high temperature. After 100 h thermal exposure at 1050 ℃, the surface Al2O3 scales are continuous, dense, and only very little amounts of alloy elements diffused from the substrate is detected in the overlayer. After\linebreak 100 cyc cycles between 1050 ℃ and room temperature (RT), the barrier layer has still well adhesive to the overlayer and the substrate. The tensile adhesion test shows that the interfacial adhesive strength is 63.6 MPa for the annealed multilayer system, which is about 20 MPa higher than that of the coating system with a DB on the DSM11 substrate deposited by the two-step AIP. The one-step AIP method can increase the interfacial adhesive strength and improve the anti-oxidation performance of the multilayer with DB.

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    EARLY INTERFACIAL REACTION AND UNDERCOOLING SOLIDIFICATION BEHAVIOR  OF Sn-3.5Ag/Cu SYSTEM
    ZHOU Minbo LI Xunping MA Xiao ZHANG Xinping
    Acta Metall Sin, 2010, 46 (5): 569-574.  DOI: 10.3724/SP.J.1037.2009.00566
    Abstract   PDF (749KB) ( 1471 )

    For electronic packaging technologies using lead-free solders, one of the major problems related to reliability for the solder interconnects is the existence of the interfacial intermetallic compound (IMC). The interfacial failures between IMC and solder alloy often lead to loss of function in interconnects and result in product failure. Therefore, considerable attention has been focused on study of formation, growth and control of IMC during solder process. In this paper, the early interfacial reaction in Sn-3.5Ag/Cu (UBM) system and the system's melting and solidification characteristics were investigated using differential scanning calorimeter incorporating with reflow process. The results show that during heating the diffusion of Cu atom into Sn-3.5Ag solder results in the formation of Sn-Ag-Cu ternary alloy at the interface before melting of Sn-3.5Ag solder and the ternary eutectic system melts at a temperature nearly 4 ℃ lower than Sn-3.5Ag solder's melting temperature. The early interfacial reaction also leads to earlier wetting of the liquid solder alloy at the interface, and consequently brings about formation of scallop-type Cu-Sn intermetallics layer with a certain thickness as well as makes the initial Sn-3.5Ag/Cu system changed into Sn-Ag-Cu/Cu system, which makes the undercooling of the solder alloy decrease obviously.

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    PRECIPITATION BEHAVIOR OF GP ZONES DURING AGEING PROCESS OF Mg-Zn ALLOY
    WANG Xiaoliang LI Changrong GUO Cuiping DU Zhenmin HE Wei
    Acta Metall Sin, 2010, 46 (5): 575-580.  DOI: 10.3724/SP.J.1037.2009.00708
    Abstract   PDF (822KB) ( 1583 )

    The age--hardening behavior of the Mg-1.9Zn (atomic fraction, %) alloy, morphologies of GP zones and temperature range of GP zone precipitation in the alloy were investigated by micro-hardness, XRD and TEM. The results show that the Zn atoms segregation occurs in the super-saturated solid solution, forming GP zones with different shapes during ageing process at 343 and 383 K; while at 423 K the age-hardening peak occurs earlier but no typical GP zone appeared. Using the thermodynamic parameters of the Mg-Zn system, the Gibbs free energy relations of the Mg-based solid solution phase were calculated, indicating the existences of the metastable miscibility gap and the solute atoms segregation in the super-saturated solid solution. With the reported data and the present experimental results, the ranges of composition and aging temperature for GP zone precipitation in the Mg-Zn alloy were determined.

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    INVESTIGATION OF POST-COLD ROLLING AGING PROCESSES ON SOLUTIONIZED 7050 ALUMINUM ALLOY
    WANG Dong MA Zongyi
    Acta Metall Sin, 2010, 46 (5): 581-588.  DOI: 10.3724/SP.J.1037.2009.00723
    Abstract   PDF (849KB) ( 1339 )

    7050 aluminum alloy samples were subjected to 67% cold rolling (CR) deformation after solution treatment, and then were aged at 120℃. The dislocations introduced by the CR increased the strength of the samples. The strength of the sample aged at 120℃ for 4 h (CR4) increased by 12.6% compared to that of T6 sample. The strength of the 7050 samples decreased with increasing the aging time due to the coarsening of heterogeneously--nucleated precipitates. However, the strength of the sample aged at 120 ℃ for 32 h is still higher than that of the T6 sample. Furthermore, the size and particle interval of the grain boundary precipitates increased as the aging time increased. The CR4 sample was aged at 165℃ for different times. The strength of the samples decreased with increasing the aging time due to the annihilation of dislocations and the growth of the precipitates. The strength of the sample aged at 165 ℃ for 6 h is similar to that of T76 sample. In the CR4 sample aged at 135-180℃ for 1 h, the number of dislocations reduced and the size of precipitates increased with increasing the temperature, which results in a decrease in the strength of the samples.

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    Mg/Al REACTION AND MECHANICAL PROPERTIES OF Al ALLOY/Mg ALLOY FRICTION STIR WELDING JOINTS
    WANG Dong LIU Jie XIAO Bolv MA Zongyi
    Acta Metall Sin, 2010, 46 (5): 589-594.  DOI: 10.3724/SP.J.1037.2009.00802
    Abstract   PDF (742KB) ( 1466 )

    Mg alloys are increasingly used in aerospace, aircraft and automotives structures due to the low density and good damping properties, especially, the welding of Mg alloy to Al alloys is of practical importance for widening the application of Mg alloys. Although friction stir welding (FSW) has been used to join Mg and Al alloys, defect free joints are achieved only in the thin plate (less than 4 mm). In this paper, three ways of FSW of 6 mm thick 6061--T651 Al alloy and AZ31 Mg alloy plates, offsetting the pin to the seam between the two plates (M4A4), to the Mg alloy side 2 mm (M6A2) and to the Al alloy side 2 mm (A6M2), were studied. The aim is to examine the effects of the relative position between tool and plate on the microstructure and mechanical properties of FSW Mg/Al alloys joint. SEM and XRD analyses revealed the formations of intermetallics Mg17Al12 and voids in the interface between Mg and Al alloy plates in the three FSW samples. The voids are resulted from the melting and subsequent solidification of eutectic. In the M4A4 and M6A2 samples, some Al are stirred into the Mg alloy side during FSW, forming the Mg17Al12,  whereas in the A6M2 sample, some Mg stirred into the Al alloy side are also transformed to the Mg17Al12. Some fine pores are observed around the Mg17Al12. The hardness of the nugget zone exhibits a slight increase due to the formation of a small amount of Mg17Al12. The intermetallics and pores at the jointed interface decrease the strength of the joints significantly.

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    INFLUENCE OF MARTENSITE ON MECHANICAL PROPERTIES OF HOT-DIP GALVANIZED TRIP STEEL
    DING Wei TANG Di JIANG Haitao HUANG Wei
    Acta Metall Sin, 2010, 46 (5): 595-599.  DOI: 10.3724/SP.J.1037.2009.00773
    Abstract   PDF (699KB) ( 1628 )

    The hot--dip galvanized transformation induced plasticity (TRIP) steel is an advanced automobile steel with excellent mechanical proprieties, which meets the requirements of energy preservation and environment protection. The microstructure and mechanical properties of hot-dip galvanized TRIP steel are different from conventional TRIP steel treated by continuous annealing processing. Three hot-dip galvanizing processes (main difference is isothermal bainitic transformation (IBT) time) are designed according to the characteristics of hot--dip galvanized TRIP steel manufacturing process to study the influence of microstructure on mechanical properties. By means of SEM, TEM, XRD, dilatometry and tensile test, the microstructure characteristic, phase transformation and mechanical properties were investigated. Combined these experimental results and the carbon diffusion balance theory, the content of martensite and its effect on mechanical properties were analyzed. The results show that the IBT time has a significant impact on the content of martensite. The volume fractions of martensite are 7.08%, 4.17% and 1.18%, when IBT times are 20, 30 and 60 s, respectively. Both the transformation induced plasticity of retained austenite and the martensite hardening are effective but the latter plays a dominant role, when the content of martensite is 7.08\% the strength is similar as dual-phase steel, but a better elongation. When the volume fraction of martensite decrease to 1.18%, the mechanical properties are similar to the conventional TRIP steel, as so small amount of martensite has no obvious effect on the mechanical properties. By changing the hot-dip galvanizing process, the amount of martensite and retained austenite can be controlled, and hot-dip galvanized TRIP steel with different mechanical properties can be obtained.

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    SALT SPRAY CORROSION BEHAVIOUR OF CrN COATINGS DEPOSITED BY ARC ION PLATING
    WAN Xiansong SHI Yuying MA Jun LI Haiqing GONG Jun SUN Chao
    Acta Metall Sin, 2010, 46 (5): 600-606.  DOI: 10.3724/SP.J.1037.2009.00759
    Abstract   PDF (895KB) ( 1317 )

    CrN coatings were deposited onto 38CrA substrate using arc ion plating (AIP) method. The microstructures of CrN coatings were investigated by XRD and SEM. The corrosion behaviour affected by deposition parameters was studied by salt spray corrosion test in a neutral mist of NaCl solution at (35±2) ℃ for 300 h. The results show that all of the CrN coatings contain primarily fcc-CrN along with hcp-Cr2N and bcc-Cr phases. CrN phase in coating deposited under lower N2 pressure exhibited {100} preferred orientation, while {110} preferred orientation under higher N2 pressure. Under the deposition condition of higher bias voltage and lower N2 pressure, the CrN coating achieves dense microstructure with less residual stress and porosity, which leads to better corrosion resistance in salt spray test. The corrosion product of salt spray test was investigated by SEM and EDS, and the corrosion mechanism was discussed.

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    PREPARATION OF SUBMICRO AND NANOSIZED MAGNESIUM ALLOYS BY MULTIPLY COMPRESSED DEFORMATION
    YANG Xuyue SUN Zhengyan ZHANG Lei
    Acta Metall Sin, 2010, 46 (5): 607-612.  DOI: 10.3724/SP.J.1037.2009.00785
    Abstract   PDF (788KB) ( 1244 )

    Twining--induced grain refinement in magnesium alloy AZ31 has been studied by using multiple compression, i.e., changing the loading direction after each pass. The tests were carried out to 50 passes at room temperature with pass strain of 0.05 and 0.1 under a strain rate of 3×10-3 s-1. The structure evolution is characterized by the formations of c-axis extension twins and c-axis compression twins, and their intersections in various directions, followed by the appearance of fragmented structure. The gradual formation of very fine grains along the c-axis compression twins with increasing cumulative strain finally leads to a ultra-fine grained structure with an average grain size of about 80-150 nm. Low strain may promote the rapid formation of more amounts of mutually crossing twins due to orientation change from pass to pass. The ultra-fine grain evolution can be accelerated by increasing pass strain. The grain refinement mechanisms under cold multiple deformation were discussed in some details.

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    STUDY ON THE STRAIN HARDENING BEHAVIOR OF Al-Mg-Si-Cu ALLOY SHEET FOR AUTOMOTIVE BODY
    TIAN Ni ZHAO Gang ZUO Liang LIU Chunming
    Acta Metall Sin, 2010, 46 (5): 613-617.  DOI: 10.3724/SP.J.1037.2009.00799
    Abstract   PDF (712KB) ( 1436 )

    Al-Mg-Si-Cu series alloy sheet, which can be strengthened by heat treatment, is a perfect material for automotive body since it can be substituted from the conventional steel sheet for automotive body to reduce the vehicle weight and respond to the demands of energy saving and emissions reduction. However, because the crystal structure of aluminum alloy sheet is different from that of the steel sheet and especially there are a great deal of second-phases in aluminum alloy matrix, the forming characteristics of aluminum alloy sheet such as strain hardening behavior is different from that of steel sheet. Therefore the experiences obtained during forming steel sheet are not applicable to forming aluminum alloy sheet. It is urgent to clarify the relationship between microstructure especially second-phases and forming behavior of aluminum alloy sheet, from which a reasonable evaluation system of formability for aluminum alloy sheet can be established. In the present study, the variation of strain hardening exponent $n$ during plastic deformation and the strain hardening behaviors of Al-0.9Mg-1.0Si-0.7Cu-0.6Mn alloy sheet subjected to solid solution, T4 and annealing treatment were investigated by tensile test and TEM/EDS. The results show that the relationship between true strain and true stress of alloy sheet during tensile test does not fully meet the Hollomon formula, and the $n$ value of alloy sheet varies as the strain range to calculate the n value changes. The annealed alloy sheet has the most significant  strain hardening effect at the initial stage of plastic deformation, but the alloy sheet subjected to solid solution treatment shows the most distinct strain hardening effect at the latter stage of plastic deformation. The n values of alloy sheet subjected to solid solution treatment are larger than those of T4 alloy sheet at each given strain range during tensile test, which is attributed to the much lower shear stress for dislocation slip in the former sheet than in the latter sheet.

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    ULTRASONIC BONDABILITY AND ANTIOXIDATION PROPERTY OF TiN/Ag METALLIZATION ON Cu PAD
    TIAN Yanhong WANG Chunqing ZHAO Shaowei
    Acta Metall Sin, 2010, 46 (5): 618-622.  DOI: 10.3724/SP.J.1037.2009.00807
    Abstract   PDF (843KB) ( 1392 )

    Copper interconnect has become the only one option for the semiconductor manufacturing under 110 nm. However, there are some problems to be solved in the copper interconnect, especially the bad bondability due to the oxidation of the copper. In this paper, TiN/Ag metallization was fabricated as the protective layer of copper pad by magnetron sputtering. The amorphous TiN film as the barrier layer to prevent copper atoms diffusing from the copper pad to the surface, and the crystalline Ag film as the bonding layer to enhance the bond abilities. The TiN/Ag metallization was characterized by AFM, XPS, XRD and SEM, respectively, and then the ultrasonic bondability of Au wire and antioxidation property of the metallization were measured. The shear test of the Au ball bond was performed by micro-force tester. Ultrasonic bondability test shows that TiN/Ag metallization as the copper chip protective layer has good bonding performance. The bondability and shear strength of the Au ball bond on the metallization increased with the temperature increase from the room temperature to 180 ℃. The TiN/Ag metallization has 100% bondability at 180 ℃, and the shear failure occurred at the interface of Ag film and Au ball bond. High temperate storage test shows that TiN/Ag metallization has better antioxidation property than the Ag film, since the amorphous TiN layer plays an excellent role of diffusion barrier.

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    FIRST-PRINCIPLES STUDY OF THE PHASE STRACTURES OF Al-Sc ALLOYS
    SU Zhenxing WANG Yuchen WANG Shaoqing
    Acta Metall Sin, 2010, 46 (5): 623-628.  DOI: 10.3724/SP.J.1037.2009.00827
    Abstract   PDF (709KB) ( 1302 )

    The formation enthalpies of the Al-Sc compounds and the Al-rich solid solution phase have been studied from first-principles based on plane--wave pseudopotential method. To calculate the electronic structure of the disordered Al-Sc alloys, the small-size special quasirandom structures (SQS), which exhibited similar structure environments as that of the disordered Al-Sc alloys, are employed. It is shown that the Sc atoms in supersaturated solid solution tend to segregation forming ordered Al3Sc< (L12) and AlSc (L10) precipitations. The nucleation mechanism of Al3Sc precipitation phase in the supersaturated Al(Sc) solid solution is analyzed in terms of the calculated densities of states and distributions of electron densities.

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    THERMAL STABILITY AND DEUTERIUM ABSORPTION AT ROOM TEMPERATURE OF Ti36Zr40Ni20Pd4 QUASICRYSTAL
    HUANG Huogen CHEN Liang LI Rong LUO Deli
    Acta Metall Sin, 2010, 46 (5): 629-633.  DOI: 10.3724/SP.J.1037.2009.00821
    Abstract   PDF (754KB) ( 1080 )

    Ti-Zr-Ni quasicrystals can absorb a large amount of hydrogen, so have strong application potential in the hydrogen energy field and international thermonuclear experimental reactor (ITER) program. However, the hydrogenation of the quasicrystals is often hindered and even poisoned due to their surface oxidation. To inhibit the oxidation, Pd has been selected, because of its catalysis to hydrogen absorption, as a minor alloying element in Ti-Zr-Ni quasicrystals. In this paper, the Ti36Zr40Ni20Pd4 alloy was designed and its thermal stability and room--temperature deuteration were studied with XRD, DSC, OM, XPS and gas--solid reaction measurement apparatus. The XRD result shows that a single icosahedral quasicrystal (IQC) phase with a quasilattice constant aR=0.5174 nm was formed in the alloy by suction-casting method, which is metastable and transforms to conventional crystals tI-Zr2Ni and C14-TiZrNiPd (MgZn2 type) phase at about 400℃. The deuteration test below the transformed temperature indicates that the alloy can absorb deuterium up to a large concentration of 11.0 mmol/g (corresponding to 2.2%H, mass fraction) at room temperature after vacuuming and heating activation without any surface treatment. Once fully activated, the IQC can load deuterium rapidly with an absorption rate of\linebreak 0.030 s-1 at ambient temperature, and has the quasilattice constant with about 5.5% expansion after two absorption cycles. The Ti36Zr40Ni20Pd4 IQC has better activation property and hydrogen capacity than the Ti40Zr40Ni20 IQC, which shows the catalyzing function of Pd.

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    EFFICIENCY AND INFLUENCING FACTORS OF ELECTROMAGNETIC STEEL-TEEMING TECHNOLOGY
    GAO Ao WANG Qiang LI Dejun JIN Baigang WANG Kai HE Jicheng
    Acta Metall Sin, 2010, 46 (5): 634-640.  DOI: 10.3724/SP.J.1037.2009.00848
    Abstract   PDF (803KB) ( 958 )

    A new method (electromagnetic steel-teeming method) using electromagnetic induction heating in slide-gate was proposed to overcome the disadvantage of the pollution of the traditional nozzle sand on the molten steel. The basic idea of this new process is to melt part of or the whole of the new ladle well-packing materials (i.e. Fe-C alloy with similar composition of the molten steel), which became the substitute of the traditional nozzle sand, and achieved smoothly molten steel-teeming. Experimental and numerical simulation methods were employed to investigate the surface temperature of the upper nozzle where the Fe-C alloy was used to replace the traditional nozzle sand. The calculated temperature is consistent with the experimental results. In addition, the effects of the induction parameters such as current intensity, frequency and diameter of the coil on teeming time were investigated. The results showed that the teeming time was decreased with the increases of current intensity and frequency, but with the decrease of coil diameter. The order of the factors affecting the teeming time is current intensity, frequency and diameter of the coil. The best parameters were found under the conditions of this research. The experimental results indicated that automatically teeming of the ladle would be achieved by using the electromagnetic steel-teeming technology.

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