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

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    Research Progress in Irradiation Damage Behavior of Tungsten and Its Alloys for Nuclear Fusion Reactor
    Yucheng WU
    Acta Metall Sin, 2019, 55 (8): 939-950.  DOI: 10.11900/0412.1961.2018.00405
    Abstract   HTML   PDF (10703KB) ( 402 )

    Controlled thermonuclear fusion energy, regarded as the ultimate and ideal energy source, is considered as the principle way to effectively solve the future energy problem because of its cleaning and abundant raw materials. In the actual fusion reaction process, plasma facing materials (PFMs) will have to face the extremely harsh and severe environment. W and its alloys are the most promising PFMs candidate materials for the present reference design. However, due to its low-temperature brittleness, recrystallization brittleness, radiation-reduced brittleness and other disadvantages, they are still far from all the requirements of PFMs. In this paper, the principles of damage behavior under different irradiation particles were described in detail, and the research progress in related fields in recent years was also reviewed, in order to provide references for the research on the irradiation of W-based materials in the future.

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    Effects of C Content on Microstructure and Properties ofFe-Mn-Al-C Low-Density Steels
    Xingpin CHEN,Wenjia LI,Ping REN,Wenquan CAO,Qing LIU
    Acta Metall Sin, 2019, 55 (8): 951-957.  DOI: 10.11900/0412.1961.2019.00014
    Abstract   HTML   PDF (12111KB) ( 564 )

    The lightweight Fe-Mn-Al-C steels (so-called low-density steels) have received great attentions as promising candidate for automobile structure applications due to their excellent combination of density reduction, mechanical properties and corrosion resistance. In previous studies, most examinations of the Fe-Mn-Al-C alloys focused on the deformation mechanisms and the relationship between the microstructure and mechanical properties. It is well known that chemical composition, especially C content, which enhances strength as the interstitial element and reduces the density of steels, plays an important role in the control of microstructure and performance. However, the influence of C element in the alloy with high Mn content is barely studied. In this work, the effects of C content on microstructure and mechanical properties of four Fe-30Mn-10Al-xC (x=0.53, 0.72, 1.21, 1.68, mass fraction, %) alloys were studied by EBSD, TEM, XRD and universal testing machine. The results show that with the increase of C content, the amount of austenite gradually increases and the ferrite/austenite dual-phase microstructure transforms into single phase austenite. In addition, the strength increases monotonously, while the elongation increases and then decreases ultimately with increasing C content. Statistical analysis reveals that the strain coordination capacity of austenite is higher than that of ferrite. Therefore, with the increase of austenite content, the ductility of the dual-phase steel remarkably increases, while the strength increases slightly. For single austenite steels, the yield strength increases but the elongation and work hardening ability decrease with increasing C content, which is related to the precipitation of κ′ carbides.

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    Correlation Between Ageing Precipitation, Potential and Intergranular Corrosion of 2A97 Al-Li Alloy Sheet
    Chao CAI,Yang LI,Jinfeng LI,Zhao ZHANG,Jianqing ZHANG
    Acta Metall Sin, 2019, 55 (8): 958-966.  DOI: 10.11900/0412.1961.2018.00519
    Abstract   HTML   PDF (21625KB) ( 285 )

    The microstructures and open circuit potential (OCP) of 2A97 Al-Li alloy sheets with different ageing and their corrosion features in intergranular corrosion (IGC) medium were investigated. As the extension of ageing time, T1 (Al2CuLi) phases are precipitated, the alloy potential is decreased, which is accompanied with the following corrosion mode evolution: pitting, IGC (including local IGC and general IGC) and pitting again. Meanwhile, with ageing progress, the IGC depth is increased firstly and then decreased. Compared to T6 ageing, T8 ageing accelerates the precipitation of T1 phases, the potential therefore decreases more quickly. After a certain ageing, the lower the potential, the smaller the IGC degree, and the greater the pitting degree. A correlation between OCP and corrosion mode was proposed, which may be used to compare the IGC sensitivity of Al-Li alloy with different tempers.

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    Corrosion Behavior of Ultrafine Grained Pure Ti Processed by Equal Channel Angular Pressing
    Xin LI,Yuecheng DONG,Zhenhua DAN,Hui CHANG,Zhigang FANG,Yanhua GUO
    Acta Metall Sin, 2019, 55 (8): 967-975.  DOI: 10.11900/0412.1961.2019.00010
    Abstract   HTML   PDF (11271KB) ( 413 )

    Titanium alloy has extensive applications in the field of chemical, biomedical and marine engineering due to high specific strength and excellent corrosion resistance. Ultrafine-grained (UFG) and nanocrystalline (NC) materials with unique properties processed by severe plastic deformation are widely studied in recent decades. In comparison with large number researches on mechanical behavior of UFG/NC materials, corrosion resistance is rarely studied and results indicated inconsistent, even within the same alloy system. In this work, ultrafine-grained pure Ti was fabricated by equal channel angular pressing (ECAP) with 2~4 passes. Grain size, crystallographic texture and grain boundary character distribution of samples were characterized by EBSD. At the same time, dynamic potential polarization and EIS methods were used to study corrosion resistance in simulated seawater. Results showed that grain size and basal texture strength of pure Ti decreased after 2 ECAP passes, but the fraction of low angle grain boundary (LAGB) increased drastically. With increasing of extrusion passes, grain size and the fraction of LAGB decreased for samples, meanwhile, basal texture strength increased at first and then decreased. Electrochemical experiments indicated that all UFG titanium have better corrosion resistance than coarse one. On the other hand, it was founded that corrosion resistance didn't increased monotonously with the development of ECAP passes, and 3 ECAP passes displayed optimum. This could be attributed to the interaction of grain size, basal texture and grain boundary character distribution, and basal texture strength occupied the domination.

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    Microstructure and Texture Evolution of AZ31 Mg Alloy Processed by Multi-Pass Compressing Under Room Temperature
    Liping DENG,Kaixuan CUI,Bingshu WANG,Hongliang XIANG,Qiang LI
    Acta Metall Sin, 2019, 55 (8): 976-986.  DOI: 10.11900/0412.1961.2019.00050
    Abstract   HTML   PDF (15871KB) ( 331 )

    Mg alloy has hexagonal structure and exhibits poor workability at room temperature, which is attributed to the difficulty in activating a sufficient number of independent slips to accommodate the deformation. Twinning plays an important role in plastic deformation of Mg alloys during low and medium temperature to accommodate the imposed strain, especially the strain along the c-axis. Therefore, the microstructure and texture evolutions of AZ31 Mg alloy during multi-pass compressions at room temperature were investigated by EBSD technology. The results show that the microstructure and texture evolutions are mainly controlled by tension twinning during multi-pass compression. And the more the strain passes, the severer the texture transformation. The c-axes of the grains are almost rotated to the compression direction by tension twins. The twins generated during multi-directional compression can separate grains and then refine them. However, the de-twinning can rotate the grains back to the initial orientations, which is against the texture weakening. The Schmid law governs the characteristics of {101ˉ2} twinning, and thus controls the texture evolution. Both the residual matrix and the pre-deformation induced twins intersect with the twins generated during subsequent deformation. And this can separate the grains and weaken the texture strength. The number and morphology of the activated twin behavior during multi-pass compression would be influenced by the pass reductions, consequently affecting the grain refinement.

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    Investigation of In Situ 1150 High Temperature Deformation Behavior and Fracture Mechanism of a Second Generation Single Crystal Superalloy
    Jinyao MA,Jin WANG,Yunsong ZHAO,Jian ZHANG,Yuefei ZHANG,Jixue LI,Ze ZHANG
    Acta Metall Sin, 2019, 55 (8): 987-996.  DOI: 10.11900/0412.1961.2019.00013
    Abstract   HTML   PDF (26817KB) ( 487 )

    Single-crystal superalloy is the key material of turbine blade and hot end parts in aerospace field. The second generation nickel-based single crystal superalloy has been widely used because of its low cost and excellent high temperature properties. At present, the research on microstructure of superalloys at high temperature mainly depends on SEM and TEM observation after heating and loading experiment. However, such kind of work lacks real-time characterization capabilities. Carrying out in situ experiments has an important significance for understanding the real time deformation behavior and microstructure evolution of superalloys. Therefore, the development of an in situ high temperature (above 1000 ℃) mechanical testing equipment for SEM faces huge challenges. In this work, high temperature tensile experiment at 1150 ℃ of a second generation single crystal nickel-based superalloy were carried out by means of a self-developed in situ heating tensile platform which can used in SEM. A high quality experimental data and serial SEM images were obtained in the course of tensile testing at 1150 ℃. The analysis of force-displacement curve shows that the yield strength and fracture strength of the specimen are 580 and 620 MPa, respectively. The sequential SEM images during this research confirm that there is no obvious shape and size change for γ and γ′ during the elastic deformation, and microstructure changing during plastic stage is mainly due to γ phase widening which is parallel to the stress axis. The results show that the original micro-voids of samples are the weakness in high temperature tensile test at 1150 ℃, the fracture direction is almost perpendicular to the stress axis, the crack propagated by passing the γ′ phase and through in the γ phase, and ultimately, temperature and stress induced adjacent holes connection leading to the sample fracture.

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    Study on the Evolution of Residual Stress During Ageing Treatment in a GH4169 Alloy Disk
    Hailong QIN,Ruiyao ZHANG,Zhongnan BI,Lee Tung Lik,Hongbiao DONG,Jinhui DU,Ji ZHANG
    Acta Metall Sin, 2019, 55 (8): 997-1007.  DOI: 10.11900/0412.1961.2018.00428
    Abstract   HTML   PDF (13805KB) ( 418 )

    GH4169 alloy, a precipitation-strengthened nickel-iron base superalloy, has been widely used in aerospace and energy industries due to its excellent high-temperature strength which derived from the coherent phases (γ″ and γ'). To form these precipitates, the manufacturing process of GH4169 usually involves solid solution heat treatment followed by rapid cooling and double ageing heat treatment. Significant residual stresses are induced during rapid cooling and then partially relieved during the subsequent ageing treatment. However, the reduced residual stress after ageing are still large enough to affect the final machining operations, resulting in the component exceeding the dimensional tolerances if they are not well considered. Furthermore, residual stresses in the final components may lead to further distortion beyond estimation during service, which could deteriorate the engine performances. In the present study, the evolution of residual stresses at heating, isothermal ageing, and air-cooling stages of ageing heat treatment in a GH4169 alloy disk was characterized by in situ neutron diffraction. Considering the effect of residual stresses on the precipitation behavior of γ″, two different types of stress-free samples were used as the basis for the stress analysis. The results show that significant residual stresses were induced during water quenching, which were found to be 340.62 MPa tensile in hoop/radial directions and 33.34 MPa compressive in axial direction in the center of the disk. Subsequently, an in situ ageing heat treatment was undertaken at 720 ℃ for 8 h. During the heating stage, the yield strength of the material decreases with increasing temperature, leading to residual stress relaxation through plastic deformation from 340.62 MPa to 227.67 MPa in hoop/radial direction in the disk center. At the isothermal ageing stage, residual stresses relieved apparently by about 40 MPa during the first 100 min, later on a slower linear relaxation remained for the rest of the ageing heat treatment. The strength of the alloy increased and the creep rate decreased due to the formation of γ″ and γ′ strengthening phases, indicating that most of stress relaxation occurred as a result of creep deformation at the early stage of isothermal ageing. The magnitude of residual stress was almost invariable in the subsequent air-cooling stage.

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    Fabrication and Properties of Anodic Oxide Nanotubular Arrays on Zr-17Nb Alloy
    Ling LI,Shenglian YAO,Xiaoli ZHAO,Jiajia YANG,Yexi WANG,Luning WANG
    Acta Metall Sin, 2019, 55 (8): 1008-1018.  DOI: 10.11900/0412.1961.2018.00469
    Abstract   HTML   PDF (18154KB) ( 217 )

    Zr-17Nb alloy has been introduced as a candidate for spinal ?xation rods because of its excellent mechanical properties and biocompatibility, low magnetic susceptibility, appropriate initial Young's modulus, remarkable deformation-induced variation of the Young's modulus, good ductility and relatively small springback. It has been recognized that nanotubular surface modification via anodic oxidation on metals is an efficient approach to highly improve biocompatibility of metallic implant. It is thus necessary to understand the formation of nanotubular arrays on Zr-17Nb alloy and carry out the evaluation on the nanotubular arrays. Electrochemical anodization was applied to modify the Zr-17Nb alloy surface to promote the bonding of alloy to human bone. Nanotubular arrays were formed on the surface of Zr-17Nb alloy by applying a 70 V constant potential in a glycerol electrolyte containing 0.35 mol/L NH4F and 5%H2O (volume fraction). XRD, SEM, HRTEM, EDS and XPS were used for the structural, morphological and compositional analyses of the nanotubular arrays. Results showed that during anodic oxidation process, the oxidation and dissolution rate of Zr were almost consistent with those of Nb. By extending the anodization duration from 10 min to 120 min, the diameter of nanotubes increased from about 20 nm to about 67 nm, and the length of nanotubes increased from about 2.4 μm to about 6.8 μm. After annealing at 450 ℃ for 60 min, the nanotube films were converted from amorphous to crystalline, mainly composed of orthogonal phase zirconia (ZrO2) and orthogonal phase zirconium niobium oxide (Nb2Zr6O17). The elastic modulus of the nanotube films decreased and the hardness increased. At the same time, the contact angle was reduced and the hydrophilicity was improved after annealing. Results demonstrate that highly ordered nanotubular arrays could be fabricate on the Zr-17Nb alloy. It is promising that nanotubular surface modification could be an efficient approach for enhancement of the biocompatibility of the alloy.

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    Effect of Cross Rolling Cycle on the Deformed and Recrystallized Gradient in High-Purity Tantalum Plate
    Jialin ZHU,Shifeng LIU,Yu CAO,Yahui LIU,Chao DENG,Qing LIU
    Acta Metall Sin, 2019, 55 (8): 1019-1033.  DOI: 10.11900/0412.1961.2018.00470
    Abstract   HTML   PDF (28078KB) ( 255 )

    Cross rolling plays an important role in the production of high-quality tantalum (Ta) sputtering targets, which are crucial in achieving thin films for micro-electronic components. However, the effect of the cross rolling cycle on the microstructure homogeneity is always ignored. Therefore, 1 and 2 cycle samples were obtained by a new approach named a 135° cross rolling. The deformation and recrystallization behavior of high-purity Ta plate then was systematically compared between 1 and 2 cross rolling cycles, aiming to elucidate why the increase of cross rolling cycles can effectively ameliorate the microstructure gradient along the thickness direction. XRD results showed that the 2 cycle sample through the thickness consisted of a relatively homogenous {111}<uvw> ([111]//normal direction (ND)) and {100}<uvw> ([100]//ND) fibers while texture distribution was extremely uneven for the 1 cycle sample. The stored energy was quantitatively analyzed by X-ray line profile analysis (XLPA) and it was found that the stored energy across the thickness distributed more homogeneously for the 2 cycle sample. Misorientation characteristics of deformed grains with different rolling cycles were analyzed in detail by visualizing the misorientation angle based on an electron backscatter diffraction dataset. Many well-defined microbands and microshear bands occurred in the {111} grain at the center layer for the 1 cycle sample, while it can be effectively destroyed with the increase of the cross rolling cycle and few peaks occurred in the "point to point" plot. Kernel average misorientation (KAM) and grain reference orientation deviation-hyper (GROD-Hyper) further confirmed their differences. Then, micorband and microshear bands were detailedly characterized by TEM, and the analysis based on relative Schmid factor suggested that the primary slip system activated in the {111} grains led to the formation of microbands in the 1 cycle sample, while multiple slip systems appeared to be activated in the 2 cycle sample and deformation was more uniform. Upon annealing, the remarkably reduced stored energy gap between the {111} and {100} grain as well as the relatively homogeneous deformation microstructure between the surface and center layer for the 2 cycle sample was conductive to synchronous recrystallization together, while the high stored energy as driving force and preferential nucleation sites at the center region led to faster recrystallization for the 1 cycle sample. The recrystallization microstructure was relatively uniform and smaller variation in grain size for the 2 cycle sample through the thickness, which was beneficial to the application of Ta sputtering target. Therefore, the increase of cross rolling cycle can ameliorate the recrystallized kinetics and microstructure of high purity Ta plate.

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    Stress Relaxation and Elastic Recovery of Monocrystalline Cu Under Water Environment
    Junqin SHI,Kun SUN,Liang FANG,Shaofeng XU
    Acta Metall Sin, 2019, 55 (8): 1034-1040.  DOI: 10.11900/0412.1961.2019.00041
    Abstract   HTML   PDF (8286KB) ( 181 )

    The stress relaxation and elastic recovery have an important effect on the mechanical and electrical properties of metallic crystal materials, which restricts the range of application and working life of materials. However, during plastic deformation of materials, the relaxation and elastic recovery behaviors are still not very clear at the nanoscale. In this work, the stress relaxation and elastic recovery of monocrystalline Cu under water environment is studied by molecular dynamics simulation. The results indicate the stress acting on Cu surface decreases at constant strain, meaning the occurrence of stress relaxation phenomenon. The stress relaxation increases with water film thickening compared with no-water environment. The separation between Cu atoms dramatically decreases with the increasing indentation depth at indenting stage, and there is no clear change in the nearest interatomic separation at stress relaxation stage, but the separation increases rapidly due to the release of elastic energy and dislocation energy at the unloading stage. The nucleated dislocations within Cu coated by water film are obviously more than that without water, which suggests the water film increases the unrecovered deformation in the total nanoindentation process. During unloading, partial dislocations disappear because of the deformation energy release, while the water film impedes the elastic recovery and plastic release.

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    Study on Vaporizing Foil Actuator Welding Process of 5A06/0Cr18Ni10Ti with Interlayer
    Shan SU
    Acta Metall Sin, 2019, 55 (8): 1041-1048.  DOI: 10.11900/0412.1961.2018.00432
    Abstract   HTML   PDF (8480KB) ( 273 )

    Aluminum alloy and stainless steel composite structure have been widely used in the chemical industry. Aluminum alloy and stainless steel are difficult to weld by fusion weld method because of differences in physical and chemical properties. Joints of aluminum alloy 5A06 and 0Cr18Ni10Ti stainless steel with good mechanical properties were created using vaporizing foil actuator welding with an interlayer. The interlayer was welded to both the target and the flyer on a ring-shaped welded area. The influences of the input energy on the time of the occurrence of vaporization and mechanical properties of the joints were analyzed. Single collection system and photonic Doppler velocimetry system were used to analyze the burst time, discharge current and voltage changes with energy input increased, and microstructure and element distribution were analyzed by OM and SEM with EDS. The results show that as the input energy increases, the vaporization of the foil occurred earlier and achieved higher impact velocity, resulting in a larger diameter of the welded area. The peak tensile load and shear load were increased with energy input increased, the peak tensile load is 44.0 kN and peak shear load is 2.1 kN with 9 kJ energy input. The Al3003 was joint to 5A06 in symmetric wavy pattern and joint with 0Cr18Ni10Ti stainless steel by intermetallic compounds. The joining areas were not aligned.

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    Effect of TiC Contents on Mechanical Properties and Wear Resistance of Iron-Based Composites
    Hulin DONG,Haiping BAO,Jianhong PENG
    Acta Metall Sin, 2019, 55 (8): 1049-1057.  DOI: 10.11900/0412.1961.2018.00373
    Abstract   HTML   PDF (12255KB) ( 379 )

    The TiC particle reinforced iron-based composite materials were prepared by mechanical alloying (MA) and vacuum hot-pressing (HPing) using titanium (99.9%, 75 μm), graphite (>99.9%, 10 μm) and grey cast iron (>99.5%, 25 μm) powders as starting materials. And TiC particles were also in situ synthesized during HPing. The phase composition, microstructures and distribution of TiC of as-fabricated composite materials were investigated using XRD and FESEM equipped with EDS. The density, hardness, compressive stress-strain and two-body abrasive wear behavior of as-fabricated composite materials were tested using densitometer, rockwell hardness tester, electro-mechanical universal testing machines and pin-on-disk type two body abrasive wear tester, respectively. The results confirm that the in situ synthesized TiC particulate reinforced iron-based composite materials only have TiC and α-Fe phases when sintered at 1200 ℃ for 60 min at the pressure of 70 MPa. The TiC particles were dispersed homogeneously in the iron matrix. The composite with TiC content of 40% (TiC40/Fe) possesses the best comprehensive performance among all as-produced TiC/Fe composites. Its relative density and hardness are 94% and 34 HRC (without heat treatment), respectively. And the compressive property of the TiC40/Fe composite is the best too. Its elastic modulus, yield strength, maximum compressive strength and fracture strain are 19.6 GPa, 420 MPa, 605 MPa and 6.1%, respectively. The TiC40/Fe composite has the best wear resistance, especially at 1.5 kg load, its relative wear resistance is 2.67 times higher than that of pure grey casting iron.

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    Influence of Size Factor on Calculation Accuracy of Welding Residual Stress of Stainless Steel Pipe by 2D Axisymmetric Model
    Peiyuan DAI,Xing HU,Shijie LU,Yifeng WANG,Dean DENG
    Acta Metall Sin, 2019, 55 (8): 1058-1066.  DOI: 10.11900/0412.1961.2018.00567
    Abstract   HTML   PDF (7704KB) ( 324 )

    Austenitic stainless steel, owing to its good mechanical properties and excellent corrosion resistance, is widely used in petroleum, chemical, nuclear power and other fields. Welding is an extremely important manufacturing method in industrial production. When the thermal elastic-plastic finite element method (TEP-FEM) is used to simulate welding residual stress, especially in thick welded joints, a long calculation time is generally needed. Therefore, it has become an urgent problem to develop an efficient and high-precision computational approach to simulate welding residual stress. In this work, numerical simulation and experimental methods were combined to explore the effect of size on the calculation precision of welding residual stress of SUS316 stainless steel by the 2D axisymmetric model, in order to clarify the applicability of 2D axisymmetric model in the prediction of welding residual stress in pipe butt joints. This research can provide theoretical support for the development of computational methods suitable for engineering applications. Based on the finite element software MSC. Marc, the temperature field and welding residual stress distribution of three different sizes of pipes were calculated by 2D axisymmetric model and 3D model. The calculated residual stress distributions in the thin pipe model are compared with the experimental measurements. The results show that calculated residual stress by the 2D axisymmetric model agrees well with the 3D model. However, in the weld seam near the inner surface and the areas near the weld seam, a deviation on the residual stress distribution between in the 2D axisymmetric model and in the 3D model was observed, which is significant as the pipe size increases. For practical engineering applications, with the regardless of the stress problems at the beginning and end positions, the 2D axisymmetric model can be used instead of the 3D model to calculate the residual stress of the girth weld, which is very beneficial to calculation time saving.

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