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

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    MICROSTRUCTURE AND MECHANICAL PROPER- TIES OF Fe-Mn-Al LIGHT-WEIGHT HIGH STRENGTH STEEL
    YANG Fuqiang, SONG Renbo, SUN Ting, ZHANG Leifeng, ZHAO Chao, LIAO Baoxin
    Acta Metall Sin, 2014, 50 (8): 897-904.  DOI: 10.11900/0412.1961.2013.00850
    Abstract   HTML   PDF (6358KB) ( 2027 )

    The automobile industry pays lots of attention on a new kind of steel with excellent combination of strength and ductility as well as the lower density, aiming at developing more affordable and safe vehicles with less fuel composition and air pollution. Fe-Mn-Al steel, adding more Al and C elements into twinning induced plasticity (TWIP) steel, shows amazing mechanical properties, corrosion resistant and weight reduction than traditional steel. The mechanical properties and microstructure of Fe-27Mn-11.5Al-0.95C-0.59Si steel after hot rolling and solid solution treatment were investigated to analysis the evolution within the range of 950~1100 ℃. Based on the true stress-strain curves and corresponding strain hardening rate, the characteristic of Fe-Mn-Al steel could be obtained. The deformation mechanism was learned by comparing the microstructure and XRD after tensile deformation. The results show that, with the designed composition system, hot rolled steel has the duplex structure of austenite matrix and small amount of banded ferrite with tensile strength of 1315.6 MPa and density of 6.55 g/cm3, which achieves the research targets of high strength and light-weight. Solid solution treatment contributes to austenite growth and banded ferrite crushing. But exorbitant temperature results in coarse and higher volume fraction of ferrite, and the ductility drops as well as the strength. The tensile strength and elongation of the steel solution treated at 1050 ℃ are 925.9 MPa and 50.20%, respectively. Product of tensile strength and elongation is 46.48 GPa·%. Continuous strain hardening behavior provides Fe-Mn-Al steel with perfect combination of strength and ductility. The wider the constant hardening stage, the larger of measured elongation. With the estimated stack fault energy of 86 mJ/m2, the dual phase structure of austenite and ferrite is retained after tensile deformation other than transformation induced plasticity (TRIP) or TWIP effects, and the microstructure of deformed sample, including Taylor lattice, high density dislocation wall and microband, shows the obvious characteristic of planer gliding with obvious slip bands on the surface of deformed austenite. The dislocation gliding observed by TEM is consistent with MBIP theory and should be confirmed by a mount of experiments and contrast in further.

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    EFFECTS OF O, N AND Ni CONTENTS ON HOT PLASTICITY OF 0Cr25Ni7Mo4N DUPLEX STAINLESS STEEL
    CHEN Yulai, ZHANG Tairan, WANG Yide, LI Jingyuan
    Acta Metall Sin, 2014, 50 (8): 905-912.  DOI: 10.11900/0412.1961.2014.00057
    Abstract   HTML   PDF (7887KB) ( 1003 )

    In order to identity the effect of narrow composition control on the hot plasticity of duplex stainless steel, hot rolling test of OCr25Ni7Mo4N steels with various oxygen, nitrogen and nickel contents were performed at 1200 ℃ for 4 steps. The microstructures and inclusions were observed by OM, SEM and EBSD. The steels with the lowest oxygen, nitrogen and nickel contents showed excellent hot plasticity. The inclusions in the steel with 0.0059% oxygen were mainly Al2O3 and MgO·Al2O3, which distributed in the grain interior and did no harm to the hot plasticity of the steel. The steels containing 0.038% and 0.046% oxygen actually cracked at the sheet edge during hot rolling, which resulted from the large inclusion particles of Cr2O3 and MnO2 at the α/γ boundary. Furthermore, the reason for more serious cracking occurred in the steel containing 0.038% oxygen than that containing 0.046% oxygen was its relatively higher contents of nitrogen and nickel, making γ volume fraction of the steel as high as 60% in the hot rolling state. Excessive γ reduced its total strain, so that the inadequate stain did not induce the recrystallization of γ phase, which resulted in hot rolling cracking finally.

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    EFFECT OF TEMPERING TEMPERATURE ON MICRO-STRUCTURE AND MECHANICAL PROPERTIES OF HIGH Ti MICROALLOYED DIRECTLY QUENCHED HIGH STRENGTH STEEL
    ZHANG Ke, YONG Qilong, SUN Xinjun, LI Zhaodong, ZHAO Peilin, CHEN Shoudong
    Acta Metall Sin, 2014, 50 (8): 913-920.  DOI: 10.11900/0412.1961.2013.00760
    Abstract   HTML   PDF (4485KB) ( 3489 )

    Over the past years, Ti microalloying technique has not been developed sufficiently compared to Nb and V, due to its special metallurgy characteristics. Higher chemical activity of Ti results in larger inclusions when Ti combines with O, N and S. In addition, higher temperature sensitivity of TiC precipitation leads to the instability of steel strips. Owning to the above reasons, the conventional high strength steels with the microstructure of martensite, bainite or the composite of the two were microalloyed with (0.01%~0.03%)Ti (mass fraction) for austenite grain refinement during soaking. The addition of high Ti (>0.1%) in microalloyed high strength martensitic or bainitic steels were rarely touched upon. The effects of tempering temperature on the microstructure and mechanical properties of high Ti microalloyed directly quenched high strength steel were investigated by TEM, SEM and physical-chemical phase analysis. The results show that with the increase of tempering temperature, the tensile curve has an obvious turning point. The tensile strength gradually decreases first and then increases, while the yield strength increases slowly. At tempering temperature 600 ℃, the experimental steel shows the best mechanical properties with tensile strength at 1043 MPa, yield strength at 1020 MPa and the elongation of 16%, while the Charpy impact energy is 67.7 J at -40 ℃. The main reason is that the amount of nanometer precipitates reaches the maximum, their distributions are also relatively uniform and the size is significantly small. The solid solution strengthening and precipitation strengthening increment of the experiment steel tempering at 600 ℃ were about 149.82 and 171.72 MPa, respectively.

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    EFFECT OF WITHDRAWING RATE ON PORE MORPHOLOGY OF LOTUS-TYPE POROUS COPPER PRODUCED BY SINGLE-MOLD GASAR TECHNIQUE
    ZHUO Weijia, LIU Yuan, LI Yanxiang
    Acta Metall Sin, 2014, 50 (8): 921-929.  DOI: 10.11900/0412.1961.2014.00013
    Abstract   HTML   PDF (7350KB) ( 749 )

    A single mold Gasar process was developed to fabricate lotus-type porous copper with long and straight pores. The effects of withdrawing rate on the solidification front shape, pore morphology and average solidification rate of porous copper ingots were investigated through experimental study and Procast simulation. The results show that the solidification front shape evolves from convex to planar, then to concave with increasing withdrawing rate. In this work, 1.0 mm/s is an appropriate rate for planar solidification front. In this case, all of the gas pores grow along the axial direction (parallel to the withdrawing direction) and the pores′ straightness is the best. The average porosities of copper ingots are constant and independent of the withdrawing rate. But the average pore diameter and penetration ratio of gas pores decreased with increasing withdrawing rate.

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    THERMODYNAMICAL AND KINETIC INVESTIGA-TION OF FORMATION OF PERIODIC LAYERED STRUCTURE IN TiCu/Zn INTERFACE REACTION
    WU Changjun, ZHU Chenlu, SU Xuping, LIU Ya, PENG Haoping, WANG Jianhua
    Acta Metall Sin, 2014, 50 (8): 930-936.  DOI: 10.11900/0412.1961.2013.00771
    Abstract   HTML   PDF (3809KB) ( 895 )

    研究了TiCu/Zn扩散偶在390和450 ℃退火后的扩散层组织, 发现其扩散区域中形成了3类周期层片对, 且γ+TiZn3层片对的厚度随温度升高而减小, 但与退火时间无关. 在TiCu/Zn扩散体系中, 反应扩散主要受Zn原子向TiCu基体端扩散控制, Zn原子扩散至TiCu基体界面附近优先形成TiZn3, 而Ti原子穿过γ层和Cu原子穿过TiZn3层向富Zn端长程扩散均很困难, Cu原子仅能通过短程扩散聚集形成γ相并长大. 周而复始, 扩散通道在γ+TiZn3两相区中来回振荡形成周期层片对, 且其间距与形成的先后顺序无关. 温度的升高加快了原子扩散和TiZn3层的形成, 使层片对变薄. 扩散通道往富Zn方向穿过三相区后, 在经过ε+TiZn3ε+Ti3Zn22两相区时, 同样由于Ti和Cu原子长程扩散困难, 形成ε+TiZn3ε+Ti3Zn22周期层片对.

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    LASER-IGNITED SELF-PROPAGATING BEHAVIOR OF SELF-SUPPORTING NANO-SCALED Ti/Al MULTILAYER FILMS
    AN Rong, TIAN Yanhong, KONG Lingchao, WANG Chunqing, CHANG Shuai
    Acta Metall Sin, 2014, 50 (8): 937-943.  DOI: 10.11900/0412.1961.2013.00821
    Abstract   HTML   PDF (2149KB) ( 545 )

    通过磁控溅射法并借助有机高分子牺牲层, 制备了具有不同调制结构的自支撑Ti/Al (调制比为1)纳米多层膜. 采用脉冲激光诱发了纳米多层膜的自蔓延反应, 确定了临界诱发能量密度. 利用高速摄影法表征了自蔓延速度, 采用SEM和TEM观察了纳米多层膜结构, 利用差热分析仪和XRD分析了反应过程及产物. 结果表明, 纳米多层膜激光诱发临界能量密度(6~17 J/cm2)高于烧蚀临界能量密度. 调制周期或周期数较小的纳米多层膜激光诱发所需的能量密度较小且自蔓延速度较高. 但当调制周期接近或小于层间原子互溶区厚度时, 临界能量密度和自蔓延速度的变化则有相反趋势. 对于一定厚度的纳米多层膜, 具有大调制周期和小周期数的调制结构对应的放热量大. 随激光脉冲持续时间的延长, Ti/Al纳米多层膜的激光临界诱发能量密度呈现递减趋势, 但最终趋于稳定. 激光诱发Ti/Al纳米多层膜自蔓延反应生成单一的TiAl金属间化合物.

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    FINITE ELEMENT SIMULATION OF WELDING RESIDUAL STRESS FOR BUFFER BEAM OF CRH2A HIGH SPEED TRAIN
    ZHU Ruidong, DONG Wenchao, LIN Huaqiang, LU Shanping, LI Dianzhong
    Acta Metall Sin, 2014, 50 (8): 944-954.  DOI: 10.11900/0412.1961.2013.00832
    Abstract   HTML   PDF (3769KB) ( 1289 )

    A finite element model of the buffer beam is established and the distribution of the welding residual stress is investigated by the finite element method. The results show that the calculated stress agrees well with the measured stress by the indentation strain-gage method. There are large and nonuniform residual stresses in the edge of the bottom flange and the processing hole. The welding of the workpieces hanging has an important effect on the residual stresses of the bottom flange. The replacement of A7N01 aluminum alloy with A6N01 aluminum alloy as the base metal can effectively reduce the residual stresses of the buffer beam. When the reinforcement plate is integrally formed with the buffer beam, the residual tensile stresses near the original weld are reduced remarkably. Two welders operating simultaneously on the opposite welds can significantly reduce the residual tensile stresses of the bottom flange.

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    SUPERPLASTICITY RESEARCH OF Ti-23Al-17Nb ALLOY SHEET
    FU Mingjie, HAN Xiuquan, WU Wei, ZHANG Jianwei
    Acta Metall Sin, 2014, 50 (8): 955-961.  DOI: 10.11900/0412.1961.2014.00055
    Abstract   HTML   PDF (7333KB) ( 553 )

    Superplastic forming is one of effective method to solve the forming difficulty of Ti3Al based alloy. In this work, the superplasticity of Ti-23Al-17Nb alloy sheet under the conditions of 940~1000 ℃ and 1.7×10-3~5.5×10-5 s-1 are studied. The results show the elongation changes as a parabola with the deformation temperature increasing, and the maximum elongation obtained at 960 ℃ and 5.5×10-5 s-1 is 1447.5%. Deformation hardening period increases much more than soften period due to the increasing of element Nb under low strain rate. Compared with primary microstructure, the superplastic deformation could eliminate the texture, the lath-like α2 grains gradually disappeared, the α2 grains became more equiaxed, and the content and size of α2 grains are decreasing with increasing of deformation temperature, the volume fraction of α2 and B2 phase could reach the optimum deformation at 50∶50. A constitutive relationship based on the Zener-Hollomn parameter and Arrhenius equation was defined for the TAC-1B alloy, and the deformation activation energy Q=390.76 kJ/mol. The results could provide a theory basis for the design and control of TAC-1B alloy superplastic forming process.

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    MICROSTRUCTURE EVOLUTION AND ORIENTATION ANALYSIS OF HYPEREUTECTIC Al-Al2Cu ALLOY UNDER DIRECTIONAL SOLIDIFICATION
    GAO Ka, LI Shuangming, FU Hengzhi
    Acta Metall Sin, 2014, 50 (8): 962-970.  DOI: 10.11900/0412.1961.2013.00766
    Abstract   HTML   PDF (6341KB) ( 1389 )

    Dendrite is a fundamental growth pattern in alloy solidification. Normally, dendrites with a specific growth orientation which can remarkably influence casting properties have attracted many great interests. The previous investigations mainly focus on the growth of simple monophase dendrites solid solution. For complex intermetallics in solidification, the correlation between processing parameters and microstructure morphologies with the preferred growth directions has not been shed a light. In this work, considering intermetallic Al2Cu phase has crystalline anisotropy and can exhibit colorfully complicated growth morphologies with specific growth direction in different solidification conditions, the primary Al2Cu phase growth behavior of Al-40%Cu (mass fraction) hypereutectic alloy was investigated by using a high thermal gradient directional solidification apparatus. The Al2Cu phase growth behavior in the experiments included its change in growth morphology and orientation transition. With solidification distance increasing, due to the alloy liquid composition ahead of the solid/liquid interface approaching the eutectic point, the primary Al2Cu dendrite transited from regular faceted V-shaped morphology to the entirely coupled eutectic at 10 μm/s. Its growth direction changed from [110] direction to the normal direction of (121) plane. The EBSD result indicated that the [001] direction of Al2Cu phase was along the direction of heat flux. As the growth rate was changed abruptly from 10 to 2 μm/s, the alloy liquid composition ahead of the solid/liquid interface increased firstly and then decreased to the eutectic point. It caused that the primary Al2Cu dendrite transited from regular faceted V-shaped morphology to long smooth lath morphology, and finally disappeared to form the entirely coupled eutectic. Moreover, the growth direction of Al2Cu phase changed from [110] direction to [001] direction. The experimental results show that the directional solidification process parameter is the dominant factor affecting the final morphology and growth direction of dendrites.

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    MECHANICAL BEHAVIOR OF Al-20Mg ALLOY SOLIDIFIED UNDER HIGH PRESSURE
    JIE Jinchuan, ZOU Chunming, WANG Hongwei, WEI Zunjie
    Acta Metall Sin, 2014, 50 (8): 971-978.  DOI: 10.11900/0412.1961.2013.00767
    Abstract   HTML   PDF (2559KB) ( 770 )

    Pressure is, like temperature, a basic thermodynamic variable which can be used to alter the matter state. The atom volume, free energy of matter and other physical and chemical properties can be changed due to the application of high pressure. Many interesting materials including superconducting, super-hard, amorphous, nano-materials can be prepared under high pressures. Meanwhile, the application of high pressure during solidification of metallic materials has also attracted much attention of researchers in recent years. However, the understanding of high pressure on alloy solidification behavior is still lacked, and needs more experimental and theoretical investigation. In the present work, the effect of high pressure on solidification microstructure, phase constitution and mechanical properties of Al-20Mg alloy was investigated by OM, XRD and tensile test. Influence of solute distribution on mechanical properties of solid solution was analyzed and the corresponding mechanism was discussed based on the solute strengthening theory. The results showed that the amount of intermetallic compound b-Al3Mg2 decreases and the amount of Al(Mg) solid solution increases in the Al-20Mg alloy solidified under high pressure, resulting in the remarkable enhancement of the mechanical properties. The Al-20Mg alloy is fragile under 1.0×105 Pa. However, it can transform to be a ductile material with elongation of 11% when solidified under 2 and 3 GPa. Meanwhile, its strength can be also greatly improved. The ultimate tensile strength of Al-20Mg alloy solidified under 2 GPa is 8.9 times of that solidified under 1.0×105 Pa. The yield strength of Al-20Mg alloy solidified under 2 GPa is higher than that under 3 GPa. This phenomenon was explained by solute strengthening theory, and proved that the inhomogeneous distribution of Mg solute in the solid solution can enhance the mechanical properties. The fracture characteristic is essentially altered under the condition of high pressure solidification. The Al-20Mg alloy is cleavage fracture under 105 Pa, however, it transforms to the dimple fracture when solidified under 2 and 3 GPa. The present work provides a potential route to improve the mechanical properties of solid solution through the control of solute distribution in the solid solution.

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    MICROSTRUCTURE, MECHANICAL AND CORROSION PROPERTIES OF Mg-(4-x)Nd-xGd-Sr-Zn-Zr BIOMAGNESIUM ALLOYS
    ZHANG Xiaobo, XUE Yajun, WANG Zhangzhong, HE Xiancong, WANG Qiang
    Acta Metall Sin, 2014, 50 (8): 979-988. 
    Abstract   HTML   PDF (4836KB) ( 738 )

    Magnesium and its alloys have been widely studied as biomaterials for over a decade due to their good biocompatibility, good bio-mechanical properties and biodegradation in human body. However, most of them are commercial magnesium alloys, which are not taken biocompatibility into account. Even though some novel magnesium alloys were developed recently, there are still no biodegradable magnesium alloys available for clinical application because of the rapid corrosion rate and localized corrosion mechanism. In order to develop new kinds of biodegradable magnesium alloys with excellent mechanical properties and corrosion resistance in simulated body fluid, four alloys with nominal composition Mg-(4-x)Nd-xGd-0.3Sr-0.2Zn-0.4Zr (mass fraction, %, x=0, 1, 2, 3) were prepared by gravity casting on the basis of previous studied Mg-Nd-Zn-Zr alloys, and solution treatment + artificial aging treatment (T6) was conducted on the as-cast alloys. The phases were identified using XRD, the microstructure was observed with SEM, the tensile properties and microhardness were carried out using tensile test machine and microhardness tester, the corrosion rate of the alloys was evaluated in simulated body fluid by mass loss method, and corrosion morphology was observed by SEM. It was found that Mg41Nd5 phase was formed in grain boundaries when Gd addition was less than Nd, while Mg3Gd was formed when Gd addition was more than Nd. The microstructure was refined firstly but was coarsen finally, and the volume fraction of the second phase decreased with increasing Gd addition due to relatively large solubility of Gd in Mg matrix than Nd. The mechanical properties at room temperature and corrosion resistance of the as-cast alloys at 37.5 ℃ were improved with Gd addition. As for the T6 state alloys, the strength and microhardness of the alloys with Gd addition were lower than those of the alloy without Gd, which indicates that the precipitation strengthening effect of Gd is weaker than that of Nd. Nevertheless, the corrosion resistance of the alloys with Gd addition was better than the alloy without Gd under T6 condition. The four alloys both under as-cast and T6 conditions exhibit relatively uniform corrosion mode, which is a desired corrosion characterization for degradable biomaterial.

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    STUDY ON PREPARATION OF Al-Li-Gd ALLOYS BY ELECTROCHEMICAL CODEPOSITION FROM CHLORIDE MELTS
    YAN Yongde, YANG Xiaonan, ZHANG Milin, WANG Li, XUE Yun, ZHANG Zhijian
    Acta Metall Sin, 2014, 50 (8): 989-994.  DOI: 10.11900/0412.1961.2014.00026
    Abstract   HTML   PDF (3439KB) ( 782 )

    The electrochemical co-reduction process of Gd(III) and Al(III) and the preparation of Al-Li-Gd alloys were studied in LiCl-KCl-AlCl3-GdCl3 molten salt at 773 K by cyclic voltammetry, square wave voltammetry and chronopotentiometry. XRD, SEM-EDS were employed to characterize Al-Li-Gd alloys. The results suggested that the underpotential deposition (UPD) of Gd(III) on pre-deposited Al forms two Al-Gd intermetallic compounds. When current densities was higher than -279.5 mA/cm2, the co-reduction of Al, Li and Gd occurred. Different phases Al-Gd alloys can be obtained by adjusting the concentration of AlCl3. XRD indicated that the Al-Li-Gd alloys contain Al2Gd and Al2Gd3 phases. The analysis of SEM and EDS demonstrated that the element Gd distributes unevenly while Al is relatively uniform distribution.

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    RESEARCH ON THE CORRELATION BETWEEN THE STATUS OF THREE-DIMENSIONAL WELD POOL SURFACE AND WELD PENETRATION IN TIG WELDING
    ZHANG Gang, SHI Yu, LI Chunkai, HUANG Jiankang, FAN Ding
    Acta Metall Sin, 2014, 50 (8): 995-1002.  DOI: 10.11900/0412.1961.2013.00819
    Abstract   HTML   PDF (5479KB) ( 778 )

    Measurement of the weld pool surface is a difficult but urgent task in the welding community. It plays an important role in developing the next generation intelligent welding machines, in particular, controlling the weld joint penetration in automatic welding. In this work, the images of front-side free surface and back-side width of the weld pool are synchronously captured with two CCD cameras in tungsten inert gas (TIG) arc welding process based on laser vision, and the three dimensional weld pool surface is reconstructed using designed algorithm. Then, the correlation between the weld pool surface under different weld joint penetration and its back-side width is analyzed qualitatively. The variation of reflected laser dots shape is reversely simulated under different depths of weld pool surface, which represents the different weld joint penetration, after established the standard model of weld pool, incident, reflected ray and imaging plan's mathematical model. It is found that the change of weld pool surface obtained by this method has an intimate immanent correlation with the weld joint penetration. When the weld joint penetration changes from partial penetration to complete joint penetration, the weld pool surface's shape changes from convexity to concave, and its depth is increasing with the increased back-side width. The row curvature of reflected laser dots is diminishing. When the penetration achieves excessive penetration, the depth of the weld pool surface is more rapidly increased, and the row curvature is also increased. The gathered laser dots is drawn back again at parallel direction. The simulated results associate with the measurement very well. The variations of reflected laser dots shape can represent the degree of weld joint penetration. This research lays a good foundation for the control of weld joint penetration using the characteristics of weld pool surface.

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    MICROSTRUCTURE EVOLUTION OF PARTIALLY MELTED ZONE OF TIG WELDING JOINT OF Ni-BASED INCONEL-718 SUPERALLOY
    YE Xin, HUA Xueming, WANG Min, LOU Songnian
    Acta Metall Sin, 2014, 50 (8): 1003-1010.  DOI: 10.11900/0412.1961.2013.00753
    Abstract   HTML   PDF (8773KB) ( 1345 )

    Element segregation, such as Nb in Ni-based Inconel-718 superalloy, causes the precipitation of low melting point phase during solidification. The actual base metal can melt in a lower temperature and the structural continuity is damaged during welding thermo cycle curve. The liquid film easily generates between austenite grains and leads to stress concentration before solidifying into the low melting point phase. Microstructure evolution of Inconel-718 welding joint increases the hot crack sensitivity and changes mechanical property of the joint. The partially melted zone (PMZ) is close to the molten metal in the fusion zone, which is the most liquation crack sensitive region of welding joint heat affected zone (HAZ). Different microstructures exists among wrought, as-cast and homogenization Inconel-718 superalloy inducing weldability differences of these material. Especially, the solidus-liquidus curve differences of low melting point phase in PMZ notably affect the high temperature mechanical property of welding joint. The wrought, as-cast and homogenization Inconel-718 superalloy sheets were respectively welded by tungsten inert gas arc welding (TIG) with different heat inputs. The microstructure of PMZ was observed by OM and SEM. Alloy element content of intradendritic austenite, interdendritic segregated region and Laves phase was investigated by EDS. The theoretical solidus-liquidus temperature of these phases was calculated by Thermo-Calc software. The melting and solidification temperature of austenite and Laves in PMZ of different base metal was investigated to analyze the temperature range for the formulation of liquid film. The results show that the microstructure heredity phenomenon obviously exists in the PMZ of Inconel-718 welding joint. The equiaxed grains remain in the PMZ of wrought joint, and the dendritic structure is still kept in the PMZ of as-cast and homogenization joint. The slender Laves and particle MC phase precipitate along the boundary of the austenite in PMZ of welding joint. But the segregated region originally existed in base metal disperses. The calculating results show that the maximum solidus-liquidus temperature range is in as-cast base metal, secondary in homogenization, minimum in wrought. The width of PMZ is increased with the increasing heat input and PMZ of as-cast is larger than PMZ of wrought and homogenization Inconel-718 superalloy.

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    EFFECT OF HEAT TREATMENTS ON THE MICROSTRUCTURE AND PROPERTY OF A NEW NICKEL BASE SINGLE CRYSTAL SUPERALLOY
    NING Likui, ZHENG Zhi, JIN Tao, TANG Song, LIU Enze, TONG Jian, YU Yongsi, SUN Xiaofeng
    Acta Metall Sin, 2014, 50 (8): 1011-1018.  DOI: 10.11900/0412.1961.2013.00846
    Abstract   HTML   PDF (9681KB) ( 1417 )

    Nickel base single crystal superalloys are widely used to fabricate turbine blade materials, since they have high temperature capability, excellent mechanical and environmental properties. Re is known as a very efficient solid-solution element that increases high temperature strength, so novel single crystal superalloys contain a high level of Re content. Whereas enhancement of Re in the dendrite arms facilitates inhomogeneous distribution of other alloy elements, it become difficult and important to determine the heat treatment in Re-containing single crystal superalloys. Effects of heat treatments on microstructure and properties in a new Re-containing single crystal superalloy have been investigated in this work. The solidus and liquidus temperature measured by differential thermal analysis (DTA) is 1339 and 1371 ℃, respectively. The incipient melting temperature determined by metallographic testing method is in the range between 1305 and 1310 ℃. The results show that Ti resides preferentially followed by B and S in the incipient melting regions. γ' precipitates all display cubic after 4 h aged at 1080, 1100 and 1120 ℃ followed by air cooling (A.C.). The optimum heat treatment is 1290 ℃, 2 h+1320 ℃, 4 h, A.C.+1100 ℃, 4 h, A.C.+900 ℃, 24 h, A.C.. Microsegregation of alloy elements reduces significantly after this heat treatment. The rupture property performs well and the rupture life is up to 78.2 h under the condition of 1070 ℃ and 140 MPa.

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    EFFECT OF Hf ON THE INTERFACIAL REACTION BETWEEN A NICKEL BASE SUPERALLOY AND A CERAMIC MATERIAL
    CHEN Xiaoyan, ZHOU Yizhou, ZHANG Chaowei, JIN Tao, SUN Xiaofeng
    Acta Metall Sin, 2014, 50 (8): 1019-1024.  DOI: 10.11900/0412.1961.2014.00033
    Abstract   HTML   PDF (4633KB) ( 1329 )

    The influence of Hf content on the wettability and interfacial reaction between a nickel base superalloy and a ceramic material was investigated by using a sessile drop method. The wetting angle was measured through the geometric parameters of the metal drop. The interfacial morphology and elements distribution were studied by SEM and EPMA, respectively. XPS was employed to study the phase formation at the metal-ceramic interface. The relationship between wettability and interfacial reaction was discussed. It was found that the wetting angle of the metal drop on the ceramic substrate was decreased with increasing Hf content in the alloy and the wettability of the studied superalloy on the ceramic material was enhanced with increasing Hf content in the alloy. When the content of Hf increased from 0.1% to 2.0% (mass fraction), the wetting angle decreased from 132° to 112°. The interfacial reaction led to a sharp decrease in wetting angle as Hf content was 1.5%. The product of interfacial reaction was HfO2 and the thermodynamic analysis indicated that Hf was able to substitute Si in SiO2 in the ceramic material.

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