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

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    Research Progress of the Surface Modification of Titanium and Titanium Alloys for Biomedical Application
    CUI Zhenduo, ZHU Jiamin, JIANG Hui, WU Shuilin, ZHU Shengli
    Acta Metall Sin, 2022, 58 (7): 837-856.  DOI: 10.11900/0412.1961.2022.00150
    Abstract   HTML   PDF (2104KB) ( 759 )

    Titanium and titanium alloys have widely been used in biomedical applications as main substitutes for hard human tissues. To better meet the needs of safety, comfort, and durability of titanium and titanium alloys after implantation in the human body, the surface modification treatment of titanium and titanium alloys has become a research hotspot. In this review, based on the basic properties and existing problems of titanium and titanium alloys, the methods of surface modification for titanium and titanium alloys are introduced to improve their mechanical properties, biocompatibility, and bacteriostatic/antibacterial properties. Furthermore, the current challenges and prospects have been presented in this paper.

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    Research paper
    Fabrication of Mg-Based Composites Reinforced by SiC Whisker Scaffolds with Three-Dimensional Interpenetrating-Phase Architecture and Their Mechanical Properties
    GU Ruicheng, ZHANG Jian, ZHANG Mingyang, LIU Yanyan, WANG Shaogang, JIAO Da, LIU Zengqian, ZHANG Zhefeng
    Acta Metall Sin, 2022, 58 (7): 857-867.  DOI: 10.11900/0412.1961.2021.00259
    Abstract   HTML   PDF (3017KB) ( 398 )

    Mg and Mg alloys, as important lightweight metal materials, have attracted great attention due to their excellent properties, such as low density, high specific strength, and good damping properties; however, their extensive applications are strictly limited by their low strength. The strength of Mg and Mg alloys can be effectively increased by introducing reinforcement phases into their matrices, i.e., via fabricating Mg-based composites. Nevertheless, the mechanical properties of Mg-based composites demonstrate a strong dependence on their microstructures. Here, new Mg-based composites reinforced by SiC whisker scaffolds with three-dimensional interpenetrating-phase architecture were fabricated through pressureless infiltration of the melt of pure Mg or AZ91D Mg alloy into the porous scaffolds of SiC whiskers. These whiskers were preferentially stacked in-plane within lamellae in the composites using gravity-assisted sedimentation and subsequent densification during the fabrication process. The microstructures and mechanical properties of the composites, particularly their fracture toughness, were characterized and analyzed. The wettability between the SiC whisker scaffolds and the melt was improved by introducing surface reactions between them which was accomplished by a pre-oxidation treatment of the scaffolds before infiltration. The pre-oxidation temperature was adjusted to ensure an adequate filling of the scaffolds without voids while avoiding the formation of excessive reaction products. The resulting composites exhibited a high flexural strength with a certain extent of fracture toughness as evidenced by stable crack propagation with rising R-curve behavior. In comparison to pure Mg, the composites infiltrated with AZ91D Mg alloy as the matrix contained a larger amount of coarsened precipitates, resulting in apparent brittleness despite increased strength.

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    Interfacial Reaction Between Nickel-Based Superalloy K417G and Oxide Refractories
    SONG Qingzhong, QIAN Kun, SHU Lei, CHEN Bo, MA Yingche, LIU Kui
    Acta Metall Sin, 2022, 58 (7): 868-882.  DOI: 10.11900/0412.1961.2021.00048
    Abstract   HTML   PDF (5547KB) ( 560 )

    High-performance nickel-based superalloys are highly desired in the aerospace industry. A drawback of vacuum induction melting for processing nickel-based superalloys is that oxide refractories contaminate the molten alloy through crucible-melt interaction. Therefore, crucibles used for producing nickel-based superalloys should be carefully selected to avoid melt contamination. In this study, the interfacial reaction between a molten nickel-based superalloy (K417G) and various oxide refractories, including Al2O3, CaO, MgO, ZrO2 + 12%Y2O3 (mass fraction) (Y-PSZ), ZrO2 + 20%CaO (CSZ), and Y2O3, formed by cold isostatic pressing was investigated at 1600oC by XRD, SEM, and EDS. The effects of the oxide crucibles on the impurity contents of K417G were also evaluated. The results show that physical erosion is the primary mechanism of the interaction between Al2O3 crucibles and alloy melt. The readily detached Al2O3 particles formed inclusions in the alloy. The Ca3Al2O6 liquid phase generated at the melt-crucible interface promoted wettability between the alloy and CaO crucible, resulting in a high adhesion at the interface. The reaction of the MgO crucible with Al in the alloy resulted in the formation of MgAl2O4 at the melt-crucible interface, which subsequently entered the alloy to form inclusions. Al2O3 was generated at the Y-PSZ-crucible-alloy interface. However, there was no corrosion of Al2O3 in the Y-PSZ crucible, indicating the crucible exhibits excellent corrosion resistance to Al2O3 slags. The interaction between the CSZ crucible and alloy melt generated a CaAl2O4 liquid phase, making the crucible unstable to dissolve into the alloy. An Al2Y4O9 reaction layer is mainly formed at the Y2O3-crucible-alloy interface. The dissolution of Y2O3 into the alloy melt was high compared to that of other oxide refractories. The melt-crucible interaction also significantly affected the oxygen content of K417G. The oxygen concentration of the alloy fused by CaO, Y2O3, and Y-PSZ crucibles did not increase, whereas that of the alloy melted in CSZ, MgO, and Al2O3 crucibles increased from 0.0007% to 0.0011%, 0.0034%, and 0.0135%, respectively.

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    Microstructure Evolution at Elevated Temperature and Mechanical Properties of MoNb-Modified FeCrAl Stainless Steel
    WEN Donghui, JIANG Beibei, WANG Qing, LI Xiangwei, ZHANG Peng, ZHANG Shuyan
    Acta Metall Sin, 2022, 58 (7): 883-894.  DOI: 10.11900/0412.1961.2020.00533
    Abstract   HTML   PDF (3883KB) ( 407 )

    MoNb-modified FeCrAl ferritic stainless steel (C35MN: Fe-13Cr-4.5Al-2Mo-1Nb, mass fraction, %) exhibits excellent comprehensive properties, including oxidation and corrosion resistance, as well as moderate mechanical properties, machinability, and neutron irradiation-resistance, making them potential accident-tolerant fuel (ATF) cladding materials for pressurized water reactors. However, the microstructural evolution and corresponding mechanical properties of C35MN alloys at the loss-of-coolant accident temperature have not been systematically studied. Herein, the microstructural evolution and mechanical properties of C35MN alloys during 400 h aging at 800oC and 1 h annealing at 1000-1200oC were systematically investigated. The alloy ingots were prepared by vacuum induction melting and cast into round bars, followed by 1150oC hot-forging, 800oC hot-rolling, and aging at 800oC for 400 h. The samples annealed at 1000-1200oC for 1 h were preaged at 800oC for 24 h. The C35MN alloy exhibited excellent microstructural stability at 800 and 1000oC, which is attributed to the precipitation of the Laves phase. The alloy showed a good combination of strength and ductility. However, when the annealing temperature increased above 1100oC, a large amount of the Laves phase dissolved into the ferritic matrix, resulting in the coarsening of the matrix grains. Annealing above 1200oC for 1 h, the grain size increased to 310 μm, severely degrading the mechanical property of the C35MN alloy below the requirement of ATF cladding materials. The microstructural stability of the C35MN alloy was influenced by the thermal stability of the Laves phase, which depends on the composition of the phase. The thermal stability of the Laves phase depends on the solid solubility of Laves phase forming elements in the ferritic matrix: the lower the solid solubility, the higher thermal stability of the Laves phase. The mechanical properties of C35MN were significantly affected by the grain size. The alloy exhibited ductile fracture when the grain size was less than 50 μm and brittle cleavage fracture when the grain size was above 130 μm.

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    Effect of Inclusions on Pitting Corrosion of C70S6 Non-Quenched and Tempered Steel Doped with Ca and Mg
    SUN Yangting, LI Yiwei, WU Wenbo, JIANG Yiming, LI Jin
    Acta Metall Sin, 2022, 58 (7): 895-904.  DOI: 10.11900/0412.1961.2021.00362
    Abstract   HTML   PDF (3259KB) ( 206 )

    As one of the energy-saving steels, non-quenched and tempered steel commonly requires the addition of alloying elements to improve its properties. The inclusions related to those elements have significant influence on the properties of the steels. In this work, the potentiodynamic polarization curves of C70S6 non-quenched and tempered steel and its Mg-Ca doped samples were measured by solution modification, and the samples before and after the test were characterized by SEM-EDS. The results show that the MnS inclusions in the samples act as active sites for pitting. The doped Ca and Mg elements make the distribution of inclusions more dispersed and the content of MnS in each inclusion lower, leading to the better pitting resistance of the doped specimens.

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    Effects of Ar Ion Irradiation on Microstructure of Fe-Cu Alloys at 290oC
    ZHU Xiaohui, LIU Xiangbing, WANG Runzhong, LI Yuanfei, LIU Wenqing
    Acta Metall Sin, 2022, 58 (7): 905-910.  DOI: 10.11900/0412.1961.2021.00328
    Abstract   HTML   PDF (2242KB) ( 214 )

    Irradiation-enhanced precipitation of Cu clusters is a main factor contributing to the hardening/embrittlement of reactor pressure vessels, and thus, limiting the lifetime of reactors. The Cu clusters are easily formed in ferric alloys under neutron irradiation or ion irradiation, which is used to simulate neutron irradiation. However, the inhibition and even dissolution of Cu clusters in Cu-containing alloys after ion irradiation is also observed in some research. To investigate the reason for ion irradiation-induced dissolution of solute clusters, Fe-1.3%Cu (atomic fraction) alloys were irradiated with Ar ions to the fluence of 4 × 1016 ion/cm2 at 290oC. TEM and atom probe tomography were used to characterize microstructure and solute atom distributions, respectively. Numerous black dot defects and bubbles with average diameters of about 1.3 nm are observed in the irradiated layer. Well-defined Cu-rich clusters are also precipitated in the irradiated layer. The average radius and number density of clusters increase first and then decrease with an increase in distance from the surface. The high displacement damage rate and large cascade size of Ar ions inhibit the irradiation-enhanced diffusion of Cu atoms and bring Cu atoms of the clusters back to matrix, which causes Cu clusters to precipitate weakly near the irradiated surface. With increasing distance from the surface, the Ar ion concentration increases. Ar-vacancy complexes or Ar bubbles form due to the aggregation of Ar ions. Then, the interattraction between Cu atoms and vacancies complexes would enhance the atom diffusion and segregation, which causes an increase in size and number density of the Cu-rich clusters.

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    Strain-Engineered Semiconductor to Semimetallic Transition and Its Mechanism in Bi(111) Film
    REN Shihao, LIU Yongli, MENG Fanshun, QI Yang
    Acta Metall Sin, 2022, 58 (7): 911-920.  DOI: 10.11900/0412.1961.2021.00225
    Abstract   HTML   PDF (2081KB) ( 206 )

    Bi is a key semimetallic element with strong spin-orbit coupling characteristics, long Fermi wavelengths, quantum size effects, and competitive structural phases. Its spin-orbit coupling can induce the metal surface state of Bi thin film, which is completely different from its bulk properties, indicating that thin Bi film has important research significance in the control of the transmission performance of semiconductor sensors. The biaxial strain deformation and film thickness can induce the transition from semiconductors to semimetals and changes in topological properties. However, the current critical transition thickness obtained using different methods is contentious, and the inherent transition mechanism remains unclear. In this work, the effect and affecting mechanism of biaxial strain on the geometric and band structures of Bi thin films with different thicknesses of Bi thin films were systematically studied and discussed using a first-principles method based on density functional theories. The results show that the band and geometric structures of Bi(111) films are strongly correlated to the thickness. With the increase in the number of atomic layers, the lattice constant increases, the buckling height decreases, the surface energy increases, and the energy bandgap decreases, where a transition of the films from semiconductor to semimetal occurs at the critical thickness of three bilayers (BLs). The application of tensile strain to the one-BL Bi film can induce the transition of energy bandgap from indirect to direct semiconductor accompanied with a band inversion, whereas the compressive strain can induce the transition from semiconductor to semimetal. The analysis of the bond nature of the near-band-edge electronic orbitals revealed that the transition of the semiconductor to the semimetallic state originates from the transition of the conduction band minimum induced by the different response rates of the bonding and antibonding states of the band edge electrons to the strain. A similar transition can be observed for 2-5 Bi BL films under biaxial deformation. The strain deformation can also improve the transport property of Bi films by changing the effective mass of electrons and holes. These findings provide a theoretical insight to regulating the electronic properties of Bi film integrated electronic devices using the strain field.

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    Effect of Printing Parameters of 3DP Sand Mold on the Casting Performance of ZL205A Alloy
    WANG Chunhui, YANG Guangyu, ALIMASI Aredake, LI Xiaogang, JIE Wanqi
    Acta Metall Sin, 2022, 58 (7): 921-931.  DOI: 10.11900/0412.1961.2021.00293
    Abstract   HTML   PDF (2514KB) ( 302 )

    Sand inkjet three-dimensional printing (3DP) technology is ideal for rapidly producing sand mold and sand core for complex thin-walled castings without using traditional casting flasks and patterns, as it offers high printing speed, high dimensional accuracy, good collapsibility, high productivity, and low cost. The constrained rod casting and single spiral fluidity methods were used to investigate the hot tearing susceptibility (HTS) and fluidity of ZL205A casting alloy under various printing parameters of a 3DP sand mold (furan resin content 1.5%-3.0% (mass fraction), printing layer 0.28-0.32 mm). The HTS of the ZL205A alloy first increased and then decreased with increasing resin content, whereas steadily decreased as the printing layer thickness increased. The HTS of the ZL205A alloy was mainly related to the strength of the 3DP sand mold. The fluidity of the ZL205A alloy decreased with increasing resin content and printing layer thickness. Finally, using the theoretical regression and normalization method, the regression equations between the 3DP sand mold's printing parameters and ZL205A alloy's castability were established. The optimized 3DP-printing parameters suitable for ZL205A alloy using 3DP sand mold casting were determined. The resin content was 1.5%, and the printing layer thickness was 0.28 mm.

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    Microstructure Evolution and Recrystallization Behavior During Hot Deformation of Spray Formed AlSiCuMg Alloy
    WU Caihong, FENG Di, ZANG Qianhao, FAN Shichun, ZHANG Hao, LEE Yunsoo
    Acta Metall Sin, 2022, 58 (7): 932-942.  DOI: 10.11900/0412.1961.2021.00329
    Abstract   HTML   PDF (5069KB) ( 294 )

    Wrought Al-Si alloy has partially replaced the traditional wear-resistant alloy for structural weight reduction owing to the excellent comprehensive properties, such as wear resistance, low coefficient of thermal expansion, and high specific strength. The deformation aluminum alloy based on Al-Si binary alloy is widely used in aerospace and automotive industries. The hot compression test, SEM, TEM, and EBSD technologies were used to investigate the microstructure evolution and dynamic recrystallization nucleation mechanism of spray formed Al25Si4Cu1Mg (mass fraction, %) alloy. The results show that the as-sprayed microstructure consists of equiaxed α-Al, coarse Si phase, AlSiCuMg phase, and Al2Cu phase with different scales. Under 623-723 K and 0.001-5 s-1, the fine Al2Cu phases gradually dissolve with the increase in deformation temperature. During high strain rate (5 s-1) compression, dislocation accumulation causes a high degree of stress concentration in front of the coarse and insoluble primary phases, resulting in the cracking of some brittle primary phases. Local cracks also appear at the interfaces between α-Al and primary phases. The α-Al phase undergoes complete dynamic recrystallization. The recrystallized grain size decreases with the increase and decrease in strain rate and deformation temperature, respectively. The residual dislocation and deformation substructure in the grain decrease with the increase in deformation temperature. The random texture demonstrates that the dynamic recrystallization mechanism of spray formed Al25Si4Cu1Mg alloy is “particle stimulated nucleation (PSN)”.

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    Calculation of Critical Nucleus Size and Minimum Energy Path of Cu-Riched Precipitates During Radiation in Fe-Cu Alloy Using String Method
    LIU Xuxi, LIU Wenbo, LI Boyan, HE Xinfu, YANG Zhaoxi, YUN Di
    Acta Metall Sin, 2022, 58 (7): 943-955.  DOI: 10.11900/0412.1961.2020.00531
    Abstract   HTML   PDF (2593KB) ( 272 )

    As a pressure containment shell that supports all components in the nuclear reactor, reactor pressure vessel (RPV) is an irreplaceable core component during the whole life of nuclear power plant. Cu-riched particles precipitated in the early stage of radiation have significant effects on the mechanical property (such as radiation hardening and embrittlement) changes during the application of RPV steel. However, the Cu-riched precipitate with extremely small size (smaller than 2 nm) cannot be detected by the conventional experimental method, such as scanning electron microscope and transmission electron microscope. Hence, it is essential to calculate the critical nucleus size of Cu-riched precipitate under radiation in RPV steel. In this study, based on the constrained string method and phase-field theory, the critical nucleus size and minimum energy path of Cu-riched precipitate in Fe-Cu alloy under irradiation were calculated, and the minimum energy path, critical nucleus radius, and vacancy concentration distribution were also studied. The calculated results showed that both temperature and Cu concentration have a great influence on the energy path and critical nucleus cluster size of Cu-riched particles in Fe-Cu binary alloy. Temperature is the main factor influencing the energy path direction of the nucleus, while Cu concentration is the main factor influencing the growth rate of the nucleus radius. With the increase of temperature, the Cu concentration in the nucleus increases, while the time needed for the Cu-riched particles to reach its critical nucleus size decreases, and the energy barrier needed to be crossed also decreases. The distribution of Cu concentration also has a great influence on the distribution of vacancy during radiation. The vacancy concentration in the Cu-riched cluster is lower than that in the Fe-Cu matrix. The vacancy concentration decreased as the Cu concentration increased. The calculated results are consistent with the experimental results.

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    Fracture Behavior of DMWJ Under Different Constraints Considering Residual Stress
    WU Jin, YANG Jie, CHEN Haofeng
    Acta Metall Sin, 2022, 58 (7): 956-964.  DOI: 10.11900/0412.1961.2021.00253
    Abstract   HTML   PDF (2078KB) ( 188 )

    In nuclear power pressure vessels, dissimilar metal welded joints (DMWJs) are the weak link owing to their highly heterogeneous microstructure, mechanical, thermal, and fracture properties; and some defects that occur at different positions within the DMWJs. To ensure the safety of nuclear power pressure vessels, it is important to examine the fracture behavior of DMWJ in detail. In addition to residual stress, constraint is an important factor affecting the fracture behavior of DMWJ. To understand this behavior, both constraint and residual stress must be considered. In this work, taking nuclear safety and DMWJ as the research objects, three-point bending (SENB) specimens with a central crack were selected. Different loads were applied to different sides of the specimen to produce different stresses at the crack tip, such as left and right, up and down, front and back, and both six sides, and the stresses were introduced into the SENB specimen as the residual stress by restart method. The fracture behavior of DMWJ was then systematically studied under various constraints considering residual stresses and the interaction between residual stress and constraint. The results showed that the change in residual stress significantly influenced the fracture behavior of DMWJ under different constraints. In contrast to the DMWJ with low constraint, the J-R curve of the DMWJ with high constraint was more sensitive to the change in residual stress. The main cause was the Mises stress at the crack tip and the triaxial stress. The direction of residual stress also influenced the J-R curve.

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