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

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    Effect of Cold Deformation and Solid Solution Temperature on σ-phase Precipitation Behavior in HR3C Heat Resistant Steel
    CAO Tieshan, ZHAO Jinyi, CHENG Congqian, MENG Xianming, ZHAO Jie
    Acta Metall Sin, 2020, 56 (5): 673-682.  DOI: 10.11900/0412.1961.2019.00267
    Abstract   HTML   PDF (3791KB) ( 314 )

    HR3C steel, widely applied in ultra-supercritical power plant, suffers an intergranular embrittlement problem during long-term high-temperature ageing or service, which will be enhanced by the precipitation of σ phase. Research has showed that the precipitation behaviors of σ phase are different significantly as the difference of manufacturers, which relates to the preparation process of cold-deformation & solid-solution treatment. In this work, the effects of cold deformation and solution treatment on the precipitation kinetics of σ phase and related mechanical properties for HR3C steel during the ageing process were studied. The results show that cold-deformation and solid solution temperature both have a significant influence on the precipitation of σ phase in the steel. The increase of cold-deformation will promote the precipitation of σ phase, and rising solution temperature helps to inhibit the growth of σ phase but increase the grain size. The precipitation kinetics study of σ phase in HR3C steel with different pre-treatment shows that σ phase growths slowly at first, and then gets into a rapid precipitation period, and finally reaches a steady-state with a value of about 5.7% (volume fraction). The impact toughness analysis shows that the increase of cold-deformation would lower down the impact toughness of HR3C steel during the ageing procedure, while the rise of the solid-solution temperature increases the impact toughness before ageing and reduces it during ageing.

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    Tensile Properties of Selective Laser Melted 316L Stainless Steel
    YU Chenfan, ZHAO Congcong, ZHANG Zhefeng, LIU Wei
    Acta Metall Sin, 2020, 56 (5): 683-692.  DOI: 10.11900/0412.1961.2019.00278
    Abstract   HTML   PDF (3487KB) ( 493 )

    Selective laser melting (SLM), as the most common additive manufacturing (AM) method, is capable of manufacturing metallic components with complex shape layer by layer. Compared with conventional manufacturing technologies such as casting or forging, the SLM technology has the advantages of high degree accuracy, high material utilization rate and environmentally friendly, and has attracted great attention in the fields of aerospace, nuclear power and medicine. The 316L austenitic stainless steel is widely used in the industrial field because of the excellent corrosion resistance and plasticity. It is also one of the commonly used material systems for SLM. In this work, the tensile properties and fracture mechanism of 316L stainless steel fabricated via SLM technology were investigated. The microstructure of the SLMed 316L specimens after tensile fracture was characterized and analyzed. The results show that the SLMed 316L stainless steel has a relatively desirable combination of strength and ductility, and its tensile performance is obviously better than that of 316L stainless steel prepared by traditional methods. The nanometer-scale cell structure inside the grain contributes to the improvement of strength. Deformation twins were observed in the SLMed 316L stainless steel after tensile test. The appearance of twins is oriented-dependent, and it is easy to occur in the grain with the direction near <110>-<111>.

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    Relationship of Inclusions and Rolling Contact Fatigue Life for Ultra-Clean Bearing Steel
    SUN Feilong, GENG Ke, YU Feng, LUO Haiwen
    Acta Metall Sin, 2020, 56 (5): 693-703.  DOI: 10.11900/0412.1961.2019.00337
    Abstract   HTML   PDF (2358KB) ( 340 )

    The cleanliness of bearing steels produced in China has been greatly improved due to the significant progress in the steelmaking technologies in the past decade, leading to their total oxygen (T.O.) contents lowered to no more than 6×10-6. Under such a high cleanliness, it is then expected that the influence of non-metallic inclusions on fatigue property should be different from the previous knowledge, because both the size and quantity of inclusions are reduced greatly. Therefore, both inclusions and fatigue properties for three ultra-clean GCr15 (100Cr6) bearing steels containing T.O. around 6×10-6, which were manufactured via different industrial production processes, were studied for this purpose. First, inclusions were characterized by ASPEX SEM and then statically analyzed by the statistics of extreme values (SEV) and the generalized Pareto distribution (GPD). Next, their rolling contact fatigue lives (RCF) L10 and L50 were measured by flat washer tests. Only the largest inclusion in each sample is required for predicting the characteristic sizes of maximum inclusion (CSMI) for the three steels using the SEV method. The calculated CSMIs, however, are not consistent with the variation of either L10 or L50, indicating they are not relevant. In contrast, the types of inclusions above threshold (u) size can be classified and their number density of inclusions quantified when the GPD method is employed. In particularly, the CSMIs of different types of inclusions can be determined. In this case, it has been found that the CSMI of TiN inclusion, which is the most dangerous for initiating cracking, is in a good agreement with the low probability rolling fatigue life (L10), suggesting that they are very correlated. This, however, cannot explain the variation of high-probability fatigue life (L50). Instead, the density of total inclusions also played an important role on the L50 of ultra-clean bearing steels in addition to the CSMI of TiN inclusions. This is reasonable because cracking shall be initiated at not only the most dangerous TiN inclusion during the early failure but also some other highly dense inclusions particularly during the late failure. Therefore, it is then concluded that the L10 is much more related to the CSMI of most dangerous TiN inclusion; whilst the L50 is strongly affected by the number density of total inclusions.

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    Solidification Structure Refinement in TWIP Steel by Ce Inoculation
    LI Gen, LAN Peng, ZHANG Jiaquan
    Acta Metall Sin, 2020, 56 (5): 704-714.  DOI: 10.11900/0412.1961.2019.00288
    Abstract   HTML   PDF (2643KB) ( 288 )

    Twinning-induced plasticity (TWIP) steel represents a novel grade of advanced high strength and ductility with significant potential for automotive industry. However, high alloying in TWIP steel leads to the inhomogeneous solute distribution and anisotropic local deformation. It is well known that the refinement of solidification structure is an effective solution to the above defects. Much attention has been paid to heterogeneous nucleation by Ce particles, acting as nucleating sites in liquid steel. The present work focuses on how Ce content and casting parameters affect the refinement of solidification structure in Fe-22Mn-0.65C TWIP steel, aiming to provide an effective technology in high alloy steel production. The reaction products of Ce inoculation were predicted by thermodynamics software FactSage 7.0 and their effectiveness of heterogeneous nucleation was estimated by lattice misfit model. The solidification structure refinement by Ce inoculation under different conditions was experimentally studied by OM, SEM, EBSD and EPMA. The results show that, with increasing Ce content the reaction products transferred from Ce2O3 to Ce2O3+a small amount of Ce2O2S, and both kinds of particles can act as heterogeneous nucleation cores theoretically. For as-cast solidification structure, the ratio of equiaxed grain area increased from 25% to 72%, average equiaxed grain size decreased from 480 μm to 130 μm and the segregation ratio of Mn decreased from 1.61 to 1.41. Meanwhile, the tendency of particle agglomeration was weakened by lowering inoculation temperature, resulting in the improvement structure refinement. In this work, the recommended inoculation parameters are concluded as (0.02%~0.04%)Ce with superheat of 20 ℃.

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    Microstructure and Corrosion Behavior of Fe-15Mn-5Si-14Cr-0.2C Amorphous Steel
    ZHAO Yanchun, MAO Xuejing, LI Wensheng, SUN Hao, LI Chunling, ZHAO Pengbiao, KOU Shengzhong, Liaw Peter K.
    Acta Metall Sin, 2020, 56 (5): 715-722.  DOI: 10.11900/0412.1961.2019.00275
    Abstract   HTML   PDF (1970KB) ( 250 )

    Amorphous steels exhibit ultra-high strength but room-temperature brittleness and strain-softening behavior as loading, which restricted the application of amorphous steels as high-performance structural material. Developing in situ crystals is an effective way to toughen the amorphous alloys. However, the crystals may sacrifice the corrosion resistance of amorphous steels. In this work, austenite and ferrite duel phases were introduced to the amorphous phase, via transformation induced plasticity (TRIP) of the austenite as loading, to enhance the ductility and improve the work-hardening behavior; and via the synergy of ferrite and amorphous phase to ensure the corrosion resistance. A novel amorphous steel Fe-15Mn-5Si-14Cr-0.2C was fabricated by magnetic suspension melting in a water-cooled copper crucible, and negative pressure suction casting into a copper mold. The microstructure and mechanical properties of the amorphous steel were characterized by XRD, EBSD and the electronic universal testing machine. The corrosion behavior in artificial seawater was studied on an electrochemical work station with a three-electrode system, and the corrosion morphology and corrosion products were characterized by SEM with EDS analysis. The results showed that the as-cast amorphous steel consisted of the amorphous matrix, CFe15.1 super-cooled austenite and Fe-Cr ferrite phases. From surface to inner, amorphous phases mainly exist in the margin, while crystalline phases are abundantly distributed in the center. The amorphous steel exhibited excellent comprehensive mechanical properties at room temperature, and its yield strength, fracture strength and plastic strain were up to 978 MPa, 2645 MPa and 35.8%, respectively. In artificial seawater, compared with 304 stainless steel, the amorphous steel showed high self-corrosion potential, low self-corrosion current density and high polarization resistance, large resistance arc radius, only one high frequency resistance arc and low corrosion kinetic rate. Moreover, the stable and dense passivation film was observed on the corrosion surface. Their excellent corrosion resistance and mechanical properties endow the amorphous steel with the potential to become a novel corrosion-resistant structural material for marine engineering.

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    Deformation Mechanism and Dynamic Recrystallization of Mg-5.6Gd-0.8Zn Alloy During Multi-Directional Forging
    ZHANG Yang, SHAO Jianbo, CHEN Tao, LIU Chuming, CHEN Zhiyong
    Acta Metall Sin, 2020, 56 (5): 723-735.  DOI: 10.11900/0412.1961.2019.00292
    Abstract   HTML   PDF (5277KB) ( 340 )

    Multi-directional forging (MDF) is an effective way to fabricate wrought magnesium alloy with ultrafine grains and random texture. Therefore, microstructure evolution and dynamic recrystallization (DRX) of magnesium alloys during MDF process have been widely investigated. Mg-Zn-RE alloys containing long-period stacking ordered (LPSO) phase have received considerable attention owing to their excellent mechanical properties. In addition, LPSO phase has great effects on the deformation mechanism and DRX behavior. Still, limited comprehensive studies can be found in the literature dealing with the microstructure evolution, deformation mechanism and DRX of magnesium alloys containing LPSO phase in MDF deformation. In this work, MDF was applied to a Mg-5.6Gd-0.8Zn (mass fraction, %) alloy containing LPSO phase. Microstructure characteristics, deformation mechanism and DRX behavior of the material in different passes were examined. Results show that there are several stages of the microstructure evolution. Twinning was activated only in a small part of grains in the early stage of deformation. As the forging direction changes, the number of twinned grains and the volume fraction of DRX grains increased. A mixed structure with coarse deformed grain and DRX grains was sustained till last forging pass, and the average size of DRX grains is about 4 μm with a random orientation. {101ˉ2} tensile twinning is the main deformation mechanism and the selection of twin variants was dominated by the Schmid law. Change in forging direction is beneficial to twinning stimulation in grains of different orientations. Kink and slipping deformation could effectively accommodate the plastic strain where the operation of twinning was hindered. Kink deformation resulted in lattice rotation predominately about the <101ˉ0> axis. DRX grains nucleated at different places during the forging process. Not only the grain boundaries and the twinned region, but also kink boundaries can induce the nucleation of DRX grains. Eventually, the twinned regions were transformed to a strip-like recrystallization structure. Under the combined influence of twinning and kinking, as well as DRX induced by twins, kink bands and grain boundaries, the initial coarse grains were significantly refined.

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    Effects of Artificial Ageing on Mechanical Properties and Precipitation of 2A12 Al Sheet
    LIANG Mengchao, CHEN Liang, ZHAO Guoqun
    Acta Metall Sin, 2020, 56 (5): 736-744.  DOI: 10.11900/0412.1961.2019.00293
    Abstract   HTML   PDF (2909KB) ( 305 )

    2A12 Al alloy has been widely applied in the fields of aviation, aerospace, and vehicles due to its light weight, high specific strength and good corrosion resistance. The solution and ageing treatments are usually performed after the processing on 2A12 Al alloy, and the ageing parameters greatly affect the final mechanical properties. In the present study, the artificial ageing was performed on the cold rolled 2A12 Al sheet under various holding temperatures and holding time. The mechanical properties were evaluated by micro-hardness and tensile tests. Moreover, the evolution of microstructure and precipitations during ageing with different holding time were characterized. The results showed that the 2A12 Al sheet had the sole peak ageing, and the higher the temperature, the shorter time was required for the peak ageing. Both the holding temperature and holding time significantly affected the mechanical properties. The optimal ageing parameters were determined as holding at 185 ℃ for 16 h, and the corresponding yield strength, ultimate tensile strength and elongation along rolling direction were 381 MPa, 476 MPa and 13.6%, respectively. S (Al2CuMg) phase gradually precipitated during ageing process, and the size and distribution of S phase greatly affected the fracture mechanism. At the initial stage of ageing, S phase precipitated near grain boundaries, and the ductility fracture could be observed. With the extension of holding time, the coarsening of S phase took place, and the fracture was gradually transformed to intergranular and transcrystalline modes. Cu-Mg cluster was the main strengthening mechanism at the initial stage of ageing. Both Cu-Mg cluster and GPB zone contributed to the strengthening under the peak ageing, and the precipitations were transformed to stable S phase under the over ageing. Considering the combined effects of homogeneous and inhomogeneous nucleation, the precipitation during ageing of cold rolled 2A12 Al sheet followed the sequence of supersaturated solid solution (SSS)→Cu-Mg cluster+Sinhomo→Cu-Mg cluster+GPB zone+Sinhomo→Cu-Mg cluster +GPB zone+ Shomo+Sinhomo→S.

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    Dimensional Effect on Thermo-Mechanical Evolution of Laser Depositing Thin-Walled Structure
    WANG Xia, WANG Wei, YANG Guang, WANG Chao, REN Yuhang
    Acta Metall Sin, 2020, 56 (5): 745-752.  DOI: 10.11900/0412.1961.2019.00317
    Abstract   HTML   PDF (2076KB) ( 175 )

    To accurately predict and effectively control temperatures, stresses and distortions are key problems existing in laser deposition manufacturing technology. The mechanism of thermo-mechanical evolution during the metal depositing process is not yet clear. In order to study the dimensional effect on thermo-mechanical evolution when TC4 single-pass and thin-walled structures are manufactured by laser deposition, finite element simulations and experiments are combined to explore the influence of the structures' length on temperature, stress and distortion of the substrates. The model reliability is validated by thermocouple temperatures and the residual deformations of substrates. The results show that the temperatures of molten pools increase periodically according to the depositing layers. As soon as the laser is terminated, the maximum temperatures of builds decline at high speed, but the minimum temperatures continue to rise in the form of parabola. When the lengths of thin-walled structures increase, the thermal extremes of molten pools are not affected, but the curvatures of cooling curves diminish, the steady cooling rates accelerate, meanwhile the temperature gradients increase. The initial stresses when depositing the first layer are maximum during manufacturing, the stresses decline progressively with the increasing layer numbers, but recover during cooling. While the lengths expand, stresses of the first layer increase. At the same time both low stress regions during depositing and high stress areas during cooling are enlarged which are around the depositing structures, but the lengths of thin-walled structures appear to have a minimal impact on the stress magnitudes. During deposition, the out-of-plane distortions of the substrates oscillate up and down, after cooling the directions of deformations are fixed towards the light source. The out-of-plane distortions are more obvious as the lengths increase. During cooling the substrates' deformations reach equilibrium earlier than temperatures and stresses.

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    Numerical Simulation of Nanohardness in Hastelloy N Alloy After Xenon Ion Irradiation
    LIU Jizhao, HUANG Hefei, ZHU Zhenbo, LIU Awen, LI Yan
    Acta Metall Sin, 2020, 56 (5): 753-759.  DOI: 10.11900/0412.1961.2019.00324
    Abstract   HTML   PDF (2120KB) ( 207 )

    Ion irradiation experiments are of importance for investigating irradiation damage of reactor structural materials. However, estimating the irradiation hardening of ion-irradiated materials is difficult due to the limitation of ion penetration depth. In recent years, nanoindentation test has been widely used to study the irradiation hardening of materials, because the continuous stiffness measurement (CSM) mode can obtain the relationship between nanohardness and indentation depth at a very small penetration depth. In this work, the average nanohardness of Hastelloy N alloy irradiated by xenon ion at room temperature was tested by this mode. The results showed that the nanohardness in the irradiated samples was larger than that in the unirradiated sample and this value of irradiated samples is saturated when the irradiation dose is in the range of 0.5~3.0 dpa. Based on the Nix-Gao model, the indentation size effects (ISE) of unirradiated and irradiated samples were separated from nanohardness measured by nanoindentation. The volume law of mixture model (VLM) was subsequently applied to simulate the measured nanohardness. As the depth of indentation increases, the plasticity affected region (PAR) includes both irradiation damage layer and matrix. Interface parameter was introduced to correct the volume of matrix deformation. The results indicated that the improved VLM model leads to a characteristic relation for the depth dependence of nanohardness that is in excellent agreement with nanoindentation experiments.

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    Fabrication and Performance Characterization of Cu-10Sn-xNi Alloy for Diamond Tools
    LIU Zhenpeng, YAN Zhiqiao, CHEN Feng, WANG Shuncheng, LONG Ying, WU Yixiong
    Acta Metall Sin, 2020, 56 (5): 760-768.  DOI: 10.11900/0412.1961.2019.00282
    Abstract   HTML   PDF (5476KB) ( 171 )

    Diamond tools are widely used in industry. Co is considered as the best matrix for the diamond tools due to its excellent retention of diamond grits and flexible control of wear resistance. But its application is suppressed because of its high price. The rapidly increasing contribution of matrices to tool production costs continues to encourage researchers to find and implement cheaper alternatives. Cu-based alloys are ideal materials to replace Co used as diamond tool matrices because of their low sintering temperature, good formability and low price. However, Cu-based matrices can not effectively hold the diamonds due to their low mechanical strength and small elastic modulus, so the service life and processing efficiency of Cu-based diamond tools are difficult to be satisfied. In this work, four kinds of Cu-10Sn-xNi pre-alloyed powders with different Ni contents (x=15, 30, 45 and 60, mass fraction, %) were prepared by ball milling. Bulk samples were fabricated from the pre-alloyed powders by hot pressing sintering at 820, 850 and 880 ℃, respectively. The microstructures and mechanical properties of pre-alloyed powders and bulks were characterized and tested. The results show that Cu3.8Ni phase is detected in the pre-alloyed powders prepared by ball milling. For the powder with 60%Ni, Ni3Sn phase and amorphous phase are detected. With increasing the Ni content as well as the sintering temperature, the segregation of Sn element in sintered alloys is effectively suppressed and the microstructure becomes homogeneous significantly, and the density, flexural strength and flexural modulus of the alloys are correspondingly improved. However, increasing the Ni content has little effect on the hardness of the alloys. The Cu-10Sn-60Ni alloy prepared by hot pressing at 880 ℃ has the best comprehensive performance. Its hardness, flexural strength and flexural modulus are 100 HRB, 1308 MPa and 75.6 GPa, respectively.

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    Precipitation σ Phase Evoluation and Mechanical Properties of (CoCrFeMnNi)97.02Mo2.98 High Entropy Alloy
    YAO Xiaofei, WEI Jingpeng, LV Yukun, LI Tianye
    Acta Metall Sin, 2020, 56 (5): 769-775.  DOI: 10.11900/0412.1961.2019.00330
    Abstract   HTML   PDF (2496KB) ( 333 )

    Mo in the form of solid solution atom or compound phase is distributed in CoCrFeMnNi high entropy alloy, which has the effect of solution strengthening or second phase strengthening. The method of annealing was used to heat treated (CoCrFeMnNi)97.02Mo2.98 high entropy alloy to investigate effects of σ phase on mechanical properties of (CoCrFeMnNi)97.02Mo2.98 high entropy alloy. SEM, EDS and XRD were used to analyze effects of annealing temperature on precipitation σ phase (CrMo phase) in (CoCrFeMnNi)97.02Mo2.98 high entropy alloy. The mechanical properties were tested by microhardness and tensile test, and the influencing mechanism of σ phase on the mechanical properties was investigated. The results show that with increase of the annealing temperature, the quantity of precipitation σ phase increases in (CoCrFeMnNi)97.02Mo2.98 high entropy alloy, and the σ phase is first precipitated at the grain boundary, and is after precipitated in intracrystalline. The morphologies of σ phase at the grain boundary are changed gradually from tiny strips of discontinuous distribution to thick strip of continuous distribution. With the annealing temperature increases further, the morphologies of σ phase are changed from strip of continuous distribution to granular of continuous distribution. The precipitation σ phases in (CoCrFeMnNi)97.02Mo2.98 high entropy alloy by annealing have the effect of second phase reinforcement, with the annealing temperature increase, the numbers of precipitation σ phase increase, and the hardness and strength both increase, which is obviously at temperature higher than 900 ℃. The σ phase precipitation in intracrystalline, and its refinement, can improve the strength and plasticity of (CoCrFeMnNi)97.02Mo2.98 high entropy alloy synchronously.

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    Effect of Nanopores on Tensile Properties of Single Crystal/Polycrystalline Nickel Composites
    LI Yuancai, JIANG Wugui, ZHOU Yu
    Acta Metall Sin, 2020, 56 (5): 776-784.  DOI: 10.11900/0412.1961.2019.00277
    Abstract   HTML   PDF (2964KB) ( 208 )

    The performance of the new generation aero-engine is strongly dependent on the application of integral blisk technologies, while the high-risk failure of integral disk joints severely restricts the promotion of those technologies. Therefore, the molecular dynamics method is used to investigate the influence of nanopores on the tensile properties of single crystal/polycrystalline Ni composites. The results show that the addition of single crystal nickel can increase the tensile strength of single crystal/polycrystalline Ni compared with polycrystalline nickel. The influence of pore position distribution on the tensile properties of single crystal/polycrystalline Ni is investigated. The simulation results show that nanopore defects in a single crystal region significantly aggravate the fracture at the single crystal/polycrystalline Ni interface. Pores not only penetrate the interface of composites but also rapidly expand inside the single crystal and the polycrystalline crystal, in which the interface of composites is further reduced resulting in the failure acceleration of single crystal/polycrystalline Ni composites. On the contrary, when the pores are in a polycrystalline region, the interface of single crystal/polycrystalline Ni hinders the amorphization of the polycrystalline nickel side and inhibits the pores from spreading toward the interface. When the pores are in the interface region, the pores do not continue to expand into the single crystal, but propagate inside the polycrystalline crystal. The effect of the porosity of interface pores on the tensile properties of single crystal/polycrystalline Ni is also discussed. It is found that the tensile strengthof single crystal/polycrystalline Ni decreases rapidly when the void porosity exceeds 0.8%. Finally, the influence of the number of voids on the tensile properties while maintaining the porosity of the interface pores is analyzed. When the porosity of the prefabricated pores of the interface is kept constant at 0.8%, the larger the number of pores (i.e., the smaller the pores), the larger the elastic modulus. In the plastic deformation stage, due to the large number of dispersed small pore structures at the interface of the single crystal/polycrystalline Ni composites, the dislocation motion is hindered, which plays a certain strengthening role and improves the tensile strength of the single crystal/polycrystalline Ni composites. It can be concluded that single crystal/polycrystalline Ni with dispersed small pores has better tensile properties than those with large pores.

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    Effect of Temperature on Mechanical Propertiesof Carbon Nanotubes-Reinforced Nickel Nano-Honeycombs
    LI Yuancai, JIANG Wugui, ZHOU Yu
    Acta Metall Sin, 2020, 56 (5): 785-794.  DOI: 10.11900/0412.1961.2019.00299
    Abstract   HTML   PDF (3638KB) ( 150 )

    Nickel nano-honeycombs (NNHC) would be expected to an ideal anode material for solid oxide fuel cells (SOFC) because of its high surface area and highly ordered pore network. But, the anode material requires excellent mechanical properties to withstand stresses that arise during processing and service at different temperatures. The influence of temperature on the mechanical behaviors under radial (y axis) tension, radial compression, axial (z axis) tension and axial compression, is investigated by molecular dynamics (MD) by taking the carbon nanotubes (CNT)-reinforced NNHC (CRNNHC) composites with the mass fractions of CNT (ωCNT) of 5.22‰ and its corresponding NNHC as the example. The results show that the mechanical properties including elastic modulus(E) and ultimate stress (σu)in NNHC and CRNNHC both decrease approximately linearly with the increase of temperature. Compared to NNHC, the addition of CNT has no obvious effect on the enhancement of radial mechanical properties of CRNNHC under different temperatures, but it results in a good reinforced effect on axial mechanical properties. While the axial tensile and compressive elastic moduli can be increased by 6.4%~10% and 9%~12% respectively, and the ultimate stress can be increased by 1.5%~5.3% and 10%~14% respectively. The study indicates that axial mechanical properties of the CRNNHC are generally superior to their radial mechanical properties, and the energy absorption before the axial deformation is relatively larger due to the existence of CNT.

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    Motion Characteristics of <c+a> Edge Dislocation on the Second-Order Pyramidal Plane in Magnesium Simulated by Molecular Dynamics
    LI Meilin, LI Saiyi
    Acta Metall Sin, 2020, 56 (5): 795-800.  DOI: 10.11900/0412.1961.2019.00305
    Abstract   HTML   PDF (1661KB) ( 174 )

    Magnesium has a hcp lattice structure, in which insufficient independent slip systems are available to accommodate applied plastic deformation at room temperature. The ductility of Mg is intimately related to the fundamental behaviors of pyramidal <c+a> dislocations, which are the major contributor to c-axis strain. In this study, the motion of <c+a> edge dislocation on the second-order pyramidal plane in Mg under external shear stress of different magnitudes and directions are simulated by molecular dynamics at 300 K, and the motion and structural evolution of dislocations are studied. The results show that the effective shear stress causing dislocation motion is lower than the external applied one and the dislocation velocity increases linearly with increasing applied shear stress. Under the same level of external shear stress, the dislocation velocity in shearing leading to c-axis tension deformation is higher than that for shearing leading to c-axis compression, and in both cases the corresponding viscous drag coefficients are significantly higher than those for basal and prismatic edge dislocations at the same temperature. The tension-compression asymmetry of dislocation motion is essentially related to the effect of applied shear stress on the extended dislocation width.

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