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

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    ADVANCES AND CHALLENGES OF TiAl BASE ALLOYS
    Acta Metall Sin, 2015, 51 (2): 129-147.  DOI: 10.11900/0412.1961.2014.00396
    Abstract   HTML   PDF (5410KB) ( 2989 )

    The history of research and development of γ-TiAl intermetallic alloys was outlined and divided into 4 stages: starting (1974~1985), revolutionary (1986~1995), emerging (1996~2005) and specialty materials (2006~). Major events and landmarks at the different stages were recounted to provide a framework for understanding scientific and technological progress. Key advances in the following 6 areas were reviewed: alloying, microstructure type, primary processing (melting), secondary processing (hot working), properties (including creep, fracture and fatigue, and oxidation), and tertiary processing (forming, covering both investment casting and near-net shape powder metallurgy). Future challenges were identified as follows: improvement of centrifugal casting technology, low-cost wrought process, development of third-generation alloys that meet design specifications, new applications based on new technologies, and viability of new forming routes such as additive manufacturing。

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    SIMULATION OF SOLIDIFICATION MICROSTRUC-TURE OF SPHEROIDAL GRAPHITE CAST IRON USING A CELLULAR AUTOMATON METHOD
    ZHANG Lei, ZHAO Honglei, ZHU Mingfang
    Acta Metall Sin, 2015, 51 (2): 148-158.  DOI: 10.11900/0412.1961.2014.00313
    Abstract   HTML   PDF (2795KB) ( 717 )

    Spheroidal graphite (SG) cast iron is characterized by the presence of spherical graphite nodules distributed in the metallic matrix. The performance of castings is primarily dependent on the solidification microstructures. In this work, a two dimensional (2D) multi-phase cellular automaton (MCA) model previously proposed by the present authors is improved to simulate the microstructure evolution of SG cast iron during divorced eutectic solidification. The present model adopts a local solutal equilibrium approach to calculate the driving force for the growth of both graphite and austenite phases. The density difference between iron and graphite is also taken into account. The diffusion of solute in the simulation domain is calculated using a finite difference method (FDM). The present model is applied to simulate the evolution of microstructure and carbon concentration field during solidification for hypereutectic SG cast irons. The results show that the present model can reasonably describe the typical features of divorced eutectic solidification, involving the independent nucleation and growth of primary graphite and austenite dendrites in liquid, the competitive growth of adjacent graphite nodules, engulfment of graphite nodules by austenite dendrites, the isotropic growth of the austenite shells that envelop the graphite nodules, the austenite to graphite eutectic phase transition controlled by carbon diffusion through the solid austenite shell, and multiple graphite nodules encapsulated in each austenite grain at the end of eutectic solidification. The simulated volume fraction and average diameter for graphite nodules are compared reasonably well with the experimental data and level rule calculation. The interactive and competitive growth behavior between austenite dendrites and graphite nodules is studied in detail. It is found that the growth of a graphite nodule is promoted by the approaching austenite. However, after embedded by an austenite dendrite, the growth velocity of graphite decreases rapidly because of lower carbon diffusivity in austenite than that in liquid. In addition, the effect of cooling rate on the size of graphite nodules is also investigated. The results show that with cooling rate increasing, the size distribution of graphite nodules varies from two peaks to one peak, and the average diameter of nodules decreases. The simulation results compare reasonably well with the experimental data reported in literature, demonstrating the validity of the present model。

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    THREE-DIMENSIONAL IMAGING OF GAS PORES IN FUSION WELDED Al ALLOYS BY SYNCHROTRON RADIATION X-RAY MICROTOMOGRAPHY
    YU Cheng, WU Shengchuan, HU Yanan, ZHANG Weihua, FU Yanan
    Acta Metall Sin, 2015, 51 (2): 159-168.  DOI: 10.11900/0412.1961.2014.00334
    Abstract   HTML   PDF (4056KB) ( 669 )

    Large numbers of complicatedly distributed gas pores are inevitably formed during the hybrid fusion welding of aluminum alloys because of the sharp reduction of supersaturated hydrogen. However, there is no consistent and explicit view on how these gas pores are distributed and influence the static and fatigue property of welded aluminum joints. In this work, pores in hybrid welded 7020-T651 were characterized by high-resolution synchrotron radiation X-ray computed microtomography. The volume, sphericity, flatness and distance of pores centroid to free surface of samples were statistically measured and fitted. From the 3D characterization, micropores inside hybrid welds are mainly metallurgical pores, which are symmetrically distributed about the seam centerline, giving a mean sphericity larger than 0.65. Moreover, pores inside upper welds appear to be larger in effective diameter and denser in heat affected zone and lower welds. Besides, there are numerous pores with diameter less than 20 μm, with a frequency of 65% and 85% in the upper and lower weld, respectively. It seems that hot cracks with complicated morphology form in the lower weld due to shrinkage and rapid solidification of the molten pool. Furthermore, it is found that the connections of a few pore-pore and pore-hot-crack together with the hot cracks result in the smaller sphericity of gas pores in the lower welds. Finally it can be indicated that the higher welding speed gives rise to the smaller pore volume fraction, but has little influence on the distribution of pore position and sphericity。

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    INFLUENCE OF PARTICLES WITH DIFFERENT SIZES ON MICROSTRUCTURE, TEXTURE AND MECHAN-ICAL PROPERTIES OF Al-Mg-Si-Cu SERIES ALLOYS
    PENG Xiangyang, GUO Mingxing, WANG Xiaofeng, CUI Li, ZHANG Jishan, ZHUANG Linzhong
    Acta Metall Sin, 2015, 51 (2): 169-177.  DOI: 10.11900/0412.1961.2014.00276
    Abstract   HTML   PDF (11081KB) ( 3644 )

    To reduce the weight of car body, Al-Mg-Si-Cu alloys have been used to produce outer body panels of automobiles due to their relatively good formability in the solution treated condition and high strength in the age hardened condition. However, their formability is significantly poor compared to that of steels, which are the major drawbacks to wide-scale application of aluminum in the automotive industry. The microstructural characteristics developed during recrystallization, most notably grain size and crystallographic texture, play a dominant role in controlling the mechanical properties and formability of sheet in the T4 condition. In this work, the effect of particles with different sizes on the mechanical properties, microstructure and texture of Al-Mg-Si-Cu alloys was studied through tensile test, OM, SEM, TEM and EBSD measurement. The results reveal that with increase of solute concentration, the average plastic strain ratio, yield strength and ultimate tensile strength increase, but the elongation decreases and with different extents in the three directions. In addition, the number of observed particles with different sizes in the alloy matrix such as Mg2Si, Al15Mn3Si2 and α-Al(Fe, Mn)Si phases also increases. When the size and concentration of these particles are controlled appropriately, lots of finer recrystallized grains can form during solution treatment due to the particle stimulated nucleation (PSN) effect of coarse particles and pinning effect of finer particles. The main texture components include CubeND18, Goss{011}<100>, P{011}<122> and Cu{112}<111> for the alloy with fine-grained structure. At last, according to the relationship among alloy composition, thermomechanical processing and microstructure, the model of nucleation and growth of recrystallized grains affected by the particles with different sizes was also proposed。

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    NUMERICAL SIMULATION OF HEAT TRANSFER AND FLUID FLOW IN DOUBLE ELECTRODES TIG ARC-WELD POOL
    WANG Xinxin, FAN Ding, HUANG Jiankang, HUANG Yong
    Acta Metall Sin, 2015, 51 (2): 178-190.  DOI: 10.11900/0412.1961.2014.00401
    Abstract   HTML   PDF (7672KB) ( 761 )

    Based on a developed unified three dimension (3D) mathematical model including two tungsten electrodes arc and weld pool for double electrode TIG arc heat source, the temperature, velocity, current density, magnetic flux and Lorentz force of the double electrodes TIG arc and the weld pool are obtained for SUS304 stainless steel. The simulated results are in fair agreement with the experimental results available. Buoyance, Lorentz force, plasma drag force, Marangoni shear stress and turbulent effect are taken into account to formulate the weld pool behavior and the effects of the each force on the flow of the weld pool are studied respectively. The heat flux and shear stress at the weld pool surface are analyzed as well. A dimensionless number Pe is used to compare the relative importance of convective heat and conductive heat in the weld pool. It is shown that non-axisymmetric double electrode arc results in the non-axisymmetric characteristics of the current density, heat flux, plasma drag force and Marangoni shear at the weld pool, and thus produces non-axisymmetric weld pool profiles. The evolution of the weld pool has little effect on the arc behavior. The plasma drag force of the double tungsten electrode TIG arc decreases significantly compared with that of the TIG arc. The Marangoni stress determines the weld pool flow and the heat convected dominates the heat transfer in the weld pool, their combination effect determines the heat transfer in the weld pool, which is the essential reason for the formation of the different weld pool profiles。

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    EFFECT OF pH VALUE ON THE CORROSION EVOLUTION OF Q235B STEEL IN SIMULATED COASTAL-INDUSTRIAL ATMOSPHERES
    CHEN Wenjuan, HAO Long, DONG Junhua, KE Wei, WEN Huailiang
    Acta Metall Sin, 2015, 51 (2): 191-200.  DOI: 10.11900/0412.1961.2014.00407
    Abstract   HTML   PDF (1109KB) ( 634 )

    The atmosphere in many cities along the coastal lines such as Qingdao in China has been polluted with SO2 due to the development of industry, and the atmosphere therefore has been changed to coastal-industrial atmosphere. The corrosion behavior and mechanism of steels in coastal-industrial atmosphere with the co-existence of SO2 and Cl- are different from that in the coastal atmosphere containing only Cl- or the industrial atmosphere containing only SO2. In addition, pH value is diverse in different coastal-industrial atmosphere. However, there are only few researches on the effect of pH value on the corrosion evolution of steels in the coastal-industrial atmosphere. Almost all the atmospheric corrosion data of steels were obtained by the field exposure test, which could not reflect the dependence of the atmospheric corrosion evolution of steels on pH value due to the difficulties in controlling the field conditions. In this work, the effect of pH value on the corrosion evolution of Q235B steel in the simulated coastal-industrial atmospheres has been investigated by the dry/wet cyclic corrosion test (CCT), XRD and EIS. The results indicate that, when the content of SO2 is lower, changing pH value has no effect on the corrosion of the steel. When the content of SO2 is higher, the corrosion rate of Q235B steel influenced by changing pH value shows an extreme phenomenon, that is, when the pH value being a certain value between the "higher" and the "lower", the corrosion rate of Q235B steel reaches the maximum value. When the SO2 content is certain, changing pH value almost has no effect on the rust composition. To some extent, the existence of SO2 inhibits the formation of β-FeOOH. With the increasing of SO2 content, the relative contents of β-FeOOH and ϒ-FeOOH are decreasing, and ϒ-FeOOH maybe reduced back to Fe3O4 or transform to α-FeOOH. With the corrosion process prolongs, the rust evolution shows almost the same trend. In addition, when the content of SO2 in the simulated coastal-industrial atmosphere is lower, the Q235B steel mainly follows Cl- corrosion mechanism, and the influence of pH value on corrosion behavior of the steel is not obvious. When the content of SO2 is higher, the Q235B steel also follows Cl- corrosion mechanism in the early stage; with prolonging the dry/wet cyclic corrosion test number, H2SO4 regeneration mechanism accelerates corrosion of the steel as the effect of SO2 on corrosion increasing significantly。

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    EFFECT MECHANISM OF Mn CONTENTS ON SHAPE MEMORY OF Fe-Mn-Si-Cr-Ni ALLOYS
    ZHANG Chengyan, SONG Fan, WANG Shanling, PENG Huabei, WEN Yuhua
    Acta Metall Sin, 2015, 51 (2): 201-208.  DOI: 10.11900/0412.1961.2014.00394
    Abstract   HTML   PDF (4868KB) ( 985 )

    Fe-Mn-Si base shape memory alloys (SMAs), as compared with Ni-Ti and Cu base SMAs, have attracted much attention since the 1980s due to their promising advantages, such as low cost, good workability and weldability. However, the recovery strain of polycrystalline Fe-Mn-Si base SMAs is only about 2%~3% except single crystals and ribbons ones. At the present time, in order to enhance the recovery strain of this kind of alloys, some methods such as thermo-mechanical training, ausforming and thermo-mechanical treatment are used. In recent years, the research group had prepared training-free cast Fe-Mn-Si base alloys showing an excellent shape memory effect (SME). Unfortunately, the grains of cast Fe-Mn-Si base alloys are coarse, certainly leading to low yield strength and recovery stress. Many factors affecting the shape memory effect, such as alloy elements, the amount of pre-strain, deformation temperatures, annealing treatments and the training, have been studied. However, there is a debate on the effect of Mn contents on the shape memory effect of Fe-Mn-Si base alloys. The aim of this work is to clarify the debate, shape memory effect and microstructures of solution treated Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni alloys were investigated by OM, EBSD, XRD, TEM and SQUID before and after deformation at 10 K higher than their start temperature of martensitic transformation (Ms+10 K). The result showed that the shape memory effect of solution treated Fe-(14~21)Mn-5.5Si-8.5Cr-5Ni alloys increased with the Mn contents. There are two reasons for this result. One is that the difference value between austenitic yield strength and critical stress of stress-induced e martensite increased with the Mn contents. In other word, the ability resisting plastic deformation was improved by increasing the Mn contents. The other is that the reversibility of e martensite reverse transformation was enhanced by increasing the Mn contents because the width of stress-induced e martensite decreased while the α' martensite was difficult to be introduced with increasing the Mn contents。

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    EFFECT OF INTERLAYERS ON THE MICROSTRUC-TURE AND SHEAR STRENGTH OF ALUMINA CERAMIC AND 1Cr18Ni9Ti STAINLESS STEEL BRAZED BONDING
    LIU Yi, JIANG Guofeng, XU Kun, LUO Ximing, CHEN Dengquan, LI Wei
    Acta Metall Sin, 2015, 51 (2): 209-215.  DOI: 10.11900/0412.1961.2014.00343
    Abstract   HTML   PDF (4599KB) ( 1023 )

    In recent years, there have been great efforts focused on joining ceramics to metals to establish processes for a wide range of industrial uses. Several important problems, however, still remain unsolved. Among them, how to produce atomic bonds at ceramic/metal interfaces and how to minimize the residual stress due to large thermal expansion mismatch between two constituents are the most critical. The thermal expansion mismatch effect is a serious problem because, even if a strong interface could be achieved, joints with large residual stress are easily broken. Therefore, it is desirable to reduce the magnitude of the residual stress. Some researchers have succeeded in achieving a strong joint between alumina and stainless steel by using a soft metallic interlayer. In this study, the effects of interlayers of nickel, copper and copper coated with nickel on the microstructure and shear strength of alumina ceramic and 1Cr18Ni9Ti stainless steel bonding with Ag-Cu-Ti filler metal were investigated. The results indicated that, when using copper as an interlayer, sufficient interfacial reaction between the ceramic and the filler metal could obtain. However, when using nickel as an interlayer, resulting in an insufficient reaction between the ceramic and the filler metal and the formation of large amount Ni3Ti intermetallic compounds, and thus, the strength of the joint decreased heavily. It is very interesting that when using copper coated with Ni, the existence of the small amount of nickel didn't affect the activity of titanium in the filler metal, meanwhile, it decreased the effect of the filler metal on the solubility of copper. Compared with copper and Ni interlayer, this interlayer could reduce interfacial residual stress more effectively. And the shear strength of 109 MPa was obtained when the thickness of Cu was 0.2 mm coated with 30 μm thick nickel。

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    OPTIMIZATION OF GRADING ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF Al13Fe4/Al COM- POSITES IN SITU SYNTHESIZED BY MECHANICAL ALLOYING AND SPARK PLASMA SINTERING
    HU Na, XUE Lihong, GU Jian, LI Heping, YAN Youwei
    Acta Metall Sin, 2015, 51 (2): 216-222.  DOI: 10.11900/0412.1961.2014.00283
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    Al-Fe alloys are widely applied in automobile, aerospace, military industry and other fields owing to their high specific strength, high specific stiffness and good stability of the microstructure originating from the low diffusivity of Fe in Al. However, conventional casting method leads to inferior mechanical properties of Al-Fe alloys due to the coarse grain microstructure, which cannot meet application requirements. In this work, fully densed Al13Fe4/Al composites were fabricated by combination of mechanical alloying and spark plasma sintering (MA-SPS) approaches. Effect of gradation of grinding balls on microstructure and properties of composites was investigated by means of XRD, SEM, TEM, hardness and compressive test. The results showed that the size of powders became more uniform by ball gradation in MA treatment, and solid solubility was greatly enhanded as well. Furthermore, the Al-Fe powder after MA using a single grinding ball size showed the microstructure of tiny white Fe particles on the surface of each particle, while no white Fe particles were observed for the one with ball gradation, which confirmed that ball gradation was more beneficial to the mixture and solid solution of Al and Fe, resulting in more homogeneously distributed powders with smaller particle sizes of 10 μm. The composites after SPS contained α-Al phase and intermetallic compound Al13Fe4. Three types of Al13Fe4 were observed: large particles (1~2 μm), ultrafine particles (0.1~1.0 μm) and nano-particles (about 20 nm). The large particles and ultrafine Al13Fe4 formed by the reaction between undissolved Fe particles and the Al melt while nano-particles of Al13Fe4 originated from the precipitation of supersaturated Al(Fe) solid solutions. The sintered sample with ball gradation after SPS showed optimized microstructure with coarser α-Al particles and ultrafine Al13Fe4 particles, resulting in good comprehensive properties with 227 HV in microhardness, 845.8 MPa in compressive strength and 13.6% in plastic deformation. The combination of large quantities of coarse α-Al particles and ultrafine Al13Fe4 particles were considered as the reason for high strength and high toughness of Al-Fe alloy。

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    MICROSTRUCTURES AND PROPERTIES OF LEAD-FREE FREE-CUTTING GRAPHITE-BRASS PREPARED BY GRAPHITIZATION OF CEMENTITE
    XUE Yingyu, TANG Jiancheng, ZHUO Haiou, YE Nan, WU Tong, ZHOU Xusheng
    Acta Metall Sin, 2015, 51 (2): 223-229.  DOI: 10.11900/0412.1961.2014.00380
    Abstract   HTML   PDF (5282KB) ( 797 )

    Graphite is believed to be an attractive candidate substituting for lead to produce free-cutting brasses, because of its lubricating property and the role in chip breaking. The major hindrances of developing graphite-brass are the large density difference and nonwetting characteristic between graphite and copper. In this work, eutectic cast iron (ECI) was added into brasses instead of other form of carbon source. Cementite particles were in situ formed during casting, then annealing treatment was conducted to facilitate the graphitization of cementite particles, and finally uniformly dispersed graphite particles with the size of 3~6 mm were obtained in brass alloys. SEM and EDS observation indicate that the microstructures of the graphite-brass are refined with the cast iron content increased from 1% to 7%. The tensile strength and microhardness are increased, and the chip morphologies are improved gradually with the cast iron content increased from 1% to 7%. However, the graphite brass with 7% addition shows suboptimal chip morphologies because of the segregation of graphite particles. The chips of graphite brasses with 5% addition are desired, which are short and discontinuous. Its tensile strength, elongation and Vickers hardness are 502.00 MPa, 22.6% and 148.9 HV, respectively. The graphite brass shows comparable machinability to conventional lead brass HPb59-1。

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    EFFECT OF Nb CONTENT ON MICROSTRUCTURE, WELDING DEFECTS AND MECHANICAL PROPERTIES OF NiCrFe-7 WELD METAL
    MO Wenlin, ZHANG Xu, LU Shanping, LI Dianzhong, LI Yiyi
    Acta Metall Sin, 2015, 51 (2): 230-238.  DOI: 10.11900/0412.1961.2014.00288
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    Ni-based filler metal is one of the most important filler metals in building the key components of nuclear power plants, however, ductility-dip-cracking (DDC) and inclusion defects form easily in the weldment and need to be repaired afterward. The precipitation of M23C6 (M=Cr, Fe) at grain boundaries will promote the nucleation and propagation of DDC. Adding Ti can form Ti(C, N) and reduce M23C6 precipitate at grain boundaries, which reduces DDC in the weld metal. However, the increase of Ti content in filler metal will cause the inclusion defects. Nb replacing part of Ti in Ni-based filler metal is proposed in this work. The reduction of Ti in filler metal is to reduce the sensitivity of inclusion defects in the weld metal. Nb can form MX (M=Nb, Ti, X=C, N) precipitates to reduce the M23C6 and DDC in weld metal. The effect of Nb on the size, number, and location of MX and M23C6 in Ni-based weldment has been investigated systematically in this work. Phase diagram calculations show that Nb is an element forming high temperature MX precipitate, and its affinity with oxygen is poor and not easy to form oxide. According to the phase diagram calculations, five different filler metals are designed and made with 0, 0.4%, 0.7%, 0.85%, 1.1%Nb content. The results show that the intragranular precipitates are distributed along sub grain boundaries. The intragranular precipitate for the Nb-free weld metal is Ti(C, N), whereas the intragranular precipitate in the Nb-bearing weld metals is MX. For the increased Nb in weld metals, more MX is produced, and more C is fixed within the grain. As the Nb content increased in weld metals, the initial precipitation temperature of M23C6 decreases, the intergranular M23C6 precipitate decreases and M23C6 turns discreted at grain boundaries. As Nb content increases in weld metals, the total crack length of DDC decreases. When the Nb content is over 0.85%, little DDC is found in the weld metals. The addition of Nb can improve the tensile strength, plasticity and bending property of the weld metals。

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    EFFECT OF W AND Re ON DEFORMATION AND RECRYSTALLIZATION OF SOLUTION HEAT TREATED Ni-BASED SINGLE CRYSTAL SUPERALLOYS
    PU Sheng, XIE Guang, ZHENG Wei, WANG Dong, LU Yuzhang, LOU Langhong, FENG Qiang
    Acta Metall Sin, 2015, 51 (2): 239-248.  DOI: 10.11900/0412.1961.2014.00292
    Abstract   HTML   PDF (7711KB) ( 883 )

    Ni-based single crystal superalloys have been widely used for blades and vanes in gas turbine. However, recrystallization (RX) induced by residual strain has been a serious problem for the application of single crystal superalloys. In previous work, effect of microstructure, such as ϒ', g/g' eutectics and carbides, as well as heat treatment parameters, on the RX behavior have been studied. However, the effect of alloy elements on the RX behavior has rarely been reported. Therefore, in this work, the effect of the important solution strengthening elements, W and Re, on the deformation and RX of solution heat treated Ni-based single crystal superalloys was investigated. At first, two single crystal superalloys were prepared, and W and Re were added into one alloy among them. After solution heat treatment, these two single crystal superalloys were deformed by shot-peening or Brinell indentation. Then these deformed samples were heat treated to observe the microstructure of RX. It indicated that RX depth decreased with the addition of W and Re irrespective of deformation mode and heat treatment temperature. Short time heat treatment experiment of indented and shot-peened samples both indicated that incubation period of RX was prolonged and nucleation of RX was slowed with the addition of W and Re, which verified that RX was suppressed by W and Re. After shot-peening, micro-hardness of the alloy with W and Re increased, but the depth of deformation zone was obviously reduced. Higher density of dislocation was found in the single crystal superalloy with W and Re, and also lots of dislocation tangles were observed. So, in this alloy, dislocation annihilated slowly, that is, recovery was slowed down, which prolonged the incubation period of RX. During the process of RX grain growth, the maximum RX grain boundary migration velocity was reduced with the addition of W and Re. Moreover, the change of mean RX grain boundary migration velocity showed the same trend with the micro-hardness along the direction of RX depth。

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    MICROSTRUCTURE AND MECHANICAL PROPERTIES OF A NEW CORROSION-RESISTING NICKEL-BASED ALLOY AND 625 ALLOY DISSIMILAR METAL WELDING JOINT
    ZHAO Xia, ZHA Xiangdong, LIU Yang, ZHANG Long, LIANG Tian, MA Yingche, CHENG Leming
    Acta Metall Sin, 2015, 51 (2): 249-256.  DOI: 10.11900/0412.1961.2014.00285
    Abstract   HTML   PDF (5875KB) ( 591 )

    With the fast development of industry, pollution becomes a very serious problem. The industrial and life wastewater are discharged and cause the environment pollution. Supercritical water oxidation (SCWO) becomes the most effective method to treat the wastewater. But the material used in the equipment plays a key role in restricting the application of the SCWO process. Currently, during the SCWO wastewater treatment process, 304 austenitic stainless steel, Alloy 625, P91 and P92 steels are the main preheater and reactor materials. In order to reduce the serious corrosion and improve economic efficiency of the materials for this process, a new corrosion resistant Ni-based alloy X-2# alloy has been developed with an aim of replacing the previous ones. In particular, it is highly important to the related behavior of this new alloy welding with the original SCWO. Therefore, the microstructure and mechanical properties of the welding joint of the new alloy and alloy 625 with manual argon arc welding were investigated. The microstructure and fracture morphologies of the welding joint were analyzed by OM, SEM and EDX. The micro-hardness, tensile strength and other mechanical properties were tested and analyzed. The results indicated that more isometric crystals in remelting zone to improve the welding seam strength and the microstructure in fusion zone of X-2# side did not show welding defects. However, some NbC and Laves phases formed near the fusion zone of 625 alloy sides, which affected the mechanical properties of material. Due to the influence of two thermal cycles near the remelting zone, the grains of heat affected zone (HAZ) were easy to grow. But the thermal stability of X-2# side HAZ could reach excellent level. Fine grains of 625 parent material led to grain growth seriously in HAZ, which reduced its Vickers hardness. Because of the tensile strength of welding joints of room temperature and 500 ℃ was lower than the parent materials, the welding seam could be the weakest link. The tesile fracture of X-2#/625 dissimilar metal welding joint was dimple morphology。

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