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

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    Orginal Article
    The Routes and Mechanism of Plasma Facing Tungsten Materials to Improve Ductility
    Yucheng WU
    Acta Metall Sin, 2019, 55 (2): 171-180.  DOI: 10.11900/0412.1961.2018.00404
    Abstract   HTML   PDF (3521KB) ( 588 )

    As a candidate for plasma facing material (PFM) in nuclear fusion situation, polycrystalline W with a characteristic of bad low temperature ductility shows brittle behaviour at room temperature and possesses a high ductile-to-brittle transition temperature, which limits its engineering application. In this paper, several common methods of grain refinement, addition of alloying elements, second-phase particles and tungsten fibre, and deformation processing for improving ductility of W are illustrated. To in-depth comprehend of how to improving W toughening, these toughening methods are discussed from intrinsic or extrinsic toughening mechanisms. Furthermore, the research status and development prospects for improving ductility of W materials have been presented.

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    The Influence of Rolling Process on the Microstructure, Texture and Magnetic Properties of Low Grades Non-Oriented Electrical Steel After Phase Transformation Annealing
    Chen GU, Ping YANG, Weimin MAO
    Acta Metall Sin, 2019, 55 (2): 181-190.  DOI: 10.11900/0412.1961.2018.00187
    Abstract   HTML   PDF (6361KB) ( 669 )

    Non-oriented electrical steel sheets are important metallic functional materials for the iron cores in transformers and electrical motors, which require the performance characteristics of low iron loss and high magnetic induction. The magnetic properties of electrical steel critically depend on the microstructure and the occurring texture components. In addition, alloy elements can affect the magnetic properties by altering the electrical resistivity, microstructure and texture. At present, the quality of commercial non-oriented electrical steels are mainly optimized by the control of deformation, recrystallization parameters and chemical composition. And the microstructure, texture and magnetic properties are significantly influenced by the rolling process before recrystallization annealing. The favorite {100} texture in such condition takes at maximum only about 20% in volume fraction. In contrast, phase transformation combined with deformation can lead to nearly 80% volume fraction of {100}-oriented grains. In this work, the influence of rolling process on the microstructure, texture and magnetic properties of low grades non-oriented electrical steel after phase transformation annealing was studied by means of EBSD, XRD and magnetism measuring techniques. The starting material is a columnar-grained industrial low grades electrical steel cast slab. Five different initial microstructures are obtained after different rolling processes, the αγα phase transformation annealing of samples is conducted in a tube furnace under H2 atmosphere. The results show that phase transformation annealing can significantly coarsen grains and reduce the iron loss of non-oriented electrical steels compared with traditional recrystallization annealing. And the phase transformation texture is influenced by texture memory. Compared with hot rolling-cold rolling process, more {100}-oriented grains are obtained and the magnetic properties of non-oriented electrical steels are improved significantly after phase transformation in the directly cold rolling process. The proportion of non-{111} oriented grains increases and more initial {100}-oriented grains are retained after phase transformation in the process with lower hot rolling temperature, which improve the magnetic properties of final sample. In addition, the presence of P and Al elements in commercial electrical steels may affect the microstructure, texture and magnetic properties of non-oriented electrical steels due to segregation and oxidation after phase transformation.

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    Microstructure and Mechanical Properties of a Novel Cold Rolled Medium-Mn Steel with Superior Strength and Ductility
    Chengwei SHAO, Weijun HUI, Yongjian ZHANG, Xiaoli ZHAO, Yuqing WENG
    Acta Metall Sin, 2019, 55 (2): 191-201.  DOI: 10.11900/0412.1961.2018.00081
    Abstract   HTML   PDF (7409KB) ( 577 )

    Recently, energy conservation, environmental protection and security are the main factors considered by the automotive manufacturers. Medium-Mn steel with excellent combination of specific strength and ductility have been regarded as the potential candidates for automotive applications. The excellent combination of specific strength and ductility depends on the microstructure under different heat treatment processes of the steels. Therefore, the relationship of the combination of specific strength and ductility and microstructure should be studied in detail. A new alloy system of aluminum-containing medium-Mn steel was developed in this study. The addition of aluminum stabilizes α-ferrite, and facilitates the presence of δ-ferrite during solidification. The addition of Mn and C compensates the effect of aluminum on phase stability and ensures austenite formation. In this investigation, the effects of intercritical annealing temperature on the microstructure and tensile properties of a newly designed cold-rolled aluminum-containing medium-Mn steel (0.2C-5Mn-0.6Si-3Al, mass fraction, %) were investigated by SEM, XRD and uniaxial tensile tests. The tensile results show that an excellent combination of ultimate tensile strength (σb) of 1062 MPa, total elongation (δ) of 58.2% and σb×δ of 61.8 GPa% could be obtained after annealing at 730 ℃. The inverted austenite of the cold-rolled steel coarsenes and gradually changes its morphology from mainly lamellar to mainly equiaxed with increasing intercritical annealing temperature, and a duplex microstructure consisting of multi-scale retained austenite could be obtained at 730 ℃, which possesses suitable mechanical stability and thus presents prolonged transformation-induced plasticity (TRIP) effect during tensile deformation. This kind of sustainable TRIP effect and the cooperative deformation of ferrite are responsible for the superior mechanical properties. The investigation of tensile fracture behavior shows that the nucleation and growth of voids occurred mainly at the interfaces between soft ferrite and hard martensite induced by deformation.

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    Microstructures and Growth Orientation of Directionally Solidification Mg-14.61Gd Alloy
    Yan YANG, Guangyu YANG, Shifeng LUO, Lei XIAO, Wanqi JIE
    Acta Metall Sin, 2019, 55 (2): 202-212.  DOI: 10.11900/0412.1961.2018.00053
    Abstract   HTML   PDF (10964KB) ( 464 )

    As one of the most promising heat-resistant magnesium alloys, Mg-Gd series alloy has a wide application prospect in the industrial fields of aerospace, cars, and rail transit. There have been extensive researches on the performance improvement of Mg-Gd series alloys. As known, dendrites are the common solidification microstructures of castings of magnesium alloys, and solidification conditions have a significant effect on dendrite morphologies and growth orientation, which could strongly affect the mechanical properties of castings, thus it is critical to study the grain growth regularity for predicting the performance of magnesium castings. However, there are few studies on numerical simulation of dendrite growth process and growth orientation of magnesium alloys. Solidification behavior of magnesium alloys can be scientifically studied via directional solidification technology, and cellular automaton finite element (CAFE) method should be effective to simulate the dendrite growth process of magnesium alloys. In present work, microstructures and growth orientation of directionally solidified Mg-14.61Gd alloy under the temperature gradient G=30 K/mm and the withdrawal rate v=10~200 μm/s were investigated by EBSD measurement method and CAFE numerical simulation method. It was found that α-Mg primary phase presented unidirectional dendritic morphologies on longitudinal cross-section. The growth interface appearance of α-Mg changed from the protruding forward growth to the flat growth gradually and the dendritic arm spacing decreased gradually with the increasing v. when v increased from 10 μm/s to 100 μm/s, the main growth orientation of α-Mg changed from <1120> and <1010> to <1120>, and the deviation angle (θ) from solidification heat flow direction reduced from 11.0° to 5.7°, the reason for this lied mainly in the change of the heat flux. Further increasing v up to 200 μm/s, the main growth direction of α-Mg was still in <1120>, but the value of θ increased to 10.6°, and the anisotropy of the crystal was the dominant factor then. It was proved that the CAFE numerical simulation model could predict the grain structure and growth orientation reasonably for Mg alloy.

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    Dynamic Softening Mechanisms of GH4720Li AlloyDuring Hot Deformation
    Zhipeng WAN, Tao WANG, Yu SUN, Lianxi HU, Zhao LI, Peihuan LI, Yong ZHANG
    Acta Metall Sin, 2019, 55 (2): 213-222.  DOI: 10.11900/0412.1961.2018.00179
    Abstract   HTML   PDF (16376KB) ( 413 )

    GH4720Li alloy is a precipitation strengthened Ni-based superalloy and widely applied in high performance applications such as disks and blades of either aircraft engines or land-based gas turbines attributing to its excellent properties including resistance to creep and fatigue, together with corrosion, fracture and microstructural stability for the intended applications. Hot working is an effective way for shaping metals and alloys as well as changing the microstructure and mechanical properties. Lots of typical metallurgical behaviors such as dynamic recovery (DRV), discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) occur, which are related to the hot working parameters, including deformation temperature, strain rate and strain. In order to investigate the effect of deformation parameters on dynamic softening behavior and evolution of twinning for GH4720Li alloy, the hot deformation behavior of as-forged GH4720Li alloy was studied by isothermal compression tests. OM, SEM, EBSD and TEM techniques were employed to investigate systematically the dynamic softening mechanisms, formation of DRX grains and evolution of substructure in grains under different deformation parameters. The results showed that DDRX can take place at all studied deformation conditions. The boundary bulging and nucleation of DDRX grains were restrained as a result of decrease of dislocation substructures and subgrain boundaries density consumed by continuous original boundary migration (COBM) in deformed grains at low strain rates and high temperatures, and then the occurrence of DDRX was suppressed. DDRX was promoted as the strain rate was increased and uniform microstructures composed of fine equiaxed grains can be readily obtained as well. The microstructural changes showed that the pinning effect of fine undissolved γ' precipitates was able to hinder the dislocation movement and promote the formation of high density of dislocation substructures and subgrain boundaries in deformed grains. The increase in sub-boundary misorientation brought about by continuous accumulation of the dislocations was introduced by the deformation, and fine DRX grains formed by particle-induced continuous dynamic recrystallization (PI-CDRX). According to the evolution of twinning under various deformation conditions, the effect of deformation temperature and strain rate on the evolution of twinning was characterized by the occurrence of DRX behavior.

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    Effect of Ru on the Electronic Structure of the [100](010) Edge Dislocation in NiAl
    Liqun CHEN, Zhengchen QIU, Tao YU
    Acta Metall Sin, 2019, 55 (2): 223-228.  DOI: 10.11900/0412.1961.2018.00386
    Abstract   HTML   PDF (978KB) ( 269 )

    NiAl intermetallics have potential application in the aerospace industry as a new high temperature structure material due to its high melting temperature, good thermal conductivity, low density, and good oxidation resistance. However, possible technological applications of NiAl are limited by its poor ductility at low temperatures and brittle grain boundary fracture at elevated temperature. Different methods have been dedicated to manage the brittle behavior of NiAl. Micro-alloying is a effective method. Dislocation is a complicated and widely existing crystal defect. The interaction between dislocation and impurity can greatly influence the mechanical properties of materials. However, the mechanism of interaction between the dislocation and alloying element is not clear. In the work, using the DMol and the discrete variational method within the framework of density functional theory, the site preference and alloying effect of Ru in the [100](010) edge dislocation core (DC) of NiAl are studied. The results of the impurity formation energy show that Ru exhibits a strong Al site preference. The analyses of the interatomic energy, the charge distribution and the partial density of states show that the strong bonding states are formed between the impurity atom and neighboring host atoms. Meanwhile, the bonds keep the atoms in the DC as a whole, which will benefit formation of kink. In addition, in the doped DC system, the interactions between the pair of atoms across the slip plane are weaker, while along the slip direction the interactions are stronger than those in the clean DC system. This bond characters may be in favor of the motion of [100](010) edge dislocation, which will improve the ductility of NiAl.

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    Comparative Study of Hot Corrosion Behavior of theEnamel Based Composite Coatings and the ArcIon Plating NiCrAlY on TiAl Alloy
    Yimin LIAO, Min FENG, Minghui CHEN, Zhe GENG, Yang LIU, Fuhui WANG, Shenglong ZHU
    Acta Metall Sin, 2019, 55 (2): 229-237.  DOI: 10.11900/0412.1961.2018.00293
    Abstract   HTML   PDF (6448KB) ( 414 )

    TiAl intermetallic alloys have attracted great attention for its potential application in preparing low pressure turbine blades in aircraft engine. However, its poor oxidation and corrosion resistance becomes a challenge at temperatures above 800 ℃, which leads to the developing of protective coatings. Enamel coating is considered as one of the candidates that match the TiAl alloy well, meanwhile provide corrosion protection. Enamel coating has many advantages such as high thermochemical stability, adjustable thermal expansion coefficient and simple preparation process. This study comparatively investigates hot corrosion behavior of the Ti-45Al-2Mn-2Nb alloy, the traditional NiCrAlY coating and the enamel based composite coating in (75%Na2SO4+25%NaCl, mass fraction) melted salt. Results indicate that after 80 h of hot corrosion, the bare alloy has completely destroyed. For the NiCrAlY coating, it protects the underlying alloy well by forming a protective Al2O3 scale initially. However, serious interdiffusion between coating and substrate results in the degeneration of the coating as well as the scale. At the same time, the basic dissolution of Al2O3 film accelerates corrosion. So obvious spallation takes place after 60 h corrosion. The enamel based composite coating shows excellent thermal stability and low corrosion rate. During the whole hot corrosion test, it still retains its original blue glazing color and luster. Furthermore, the enamel coating suppresses the inward diffusion of oxygen and corrosive ions into the alloy substrate, and thus, it protects the TiAl alloy well from corrosion of the molten (75%Na2SO4+25%NaCl, mass fraction) salt.

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    Study on Chemical Bonding Between Epoxy Coating and Metal Substrate Using γ-Aminopropyltrimethoxysilaneto Modify Epoxy Resin Molecule
    Fachun CAO, Hang WU, Yange YANG, Jingyi CAO, Tao ZHANG, Fuhui WANG
    Acta Metall Sin, 2019, 55 (2): 238-248.  DOI: 10.11900/0412.1961.2018.00121
    Abstract   HTML   PDF (7978KB) ( 289 )

    Epoxy coatings are widely used to protect metals from corrosion in ocean engineering and process industries. It has been proved that the adhesion between epoxy coating and metal is a key factor that affects their service life of the coating. However, interface between epoxy coating and metal substrate is usually combined by weak van der Waals force or secondary bond, which limits the protective performance of coatings. This work aims to translate the interface state from the physical adsorption to chemical bonding so as to increase the service life of epoxy coating. A kind of reactive resin γ-APS/EP with hydrolysis characteristic was prepared using γ-aminopropyltrimethoxysilane (γ-APS), and used as a coating filler with different contents of 0.5%~10%. Both dry and wet adhesion strength of epoxy coatings with different contents of γ-APS/EP were examined, the resistance to aggressive medium of epoxy varied with the contents of γ-APS/EP was evaluated by water absorption measurement, and the structure and composition of the coating/metal systems were characterized by using SEM, XPS, DSC and FTIR. The results showed that amino groups in γ-APS/EP disappeared and methoxysilyl groups (Si—O—CH3) were remained after the synthesis process. Adhesion strength of the epoxy coating with metal substrate was significantly enhanced by introducing γ-APS/EP. Moreover, the dry adhesion strength of epoxy coating with 3%γ-APS/EP reached the maximum value of 12.4 MPa, which was twice the strength of pure epoxy, and was decreased with the content of γ-APS/EP further increasing. Meanwhile, wet interface adhesion strength of epoxy coating with 3%γ-APS/EP was still kept about 7.4 MPa after 900 h immersion in 3.5%NaCl, more than three times of pure epoxy coating. And also, epoxy coating with 3%γ-APS/EP showed the best performance with lower saturated water absorption. The chemical bonding can be obtained by the generation of oxane on the interface resulting from the reaction between the synthesized reactive resin and the hydroxyl on the metal surface after the reactive resin was added in the epoxy resin. Furthermore, the content of γ-APS/EP affected the number of chemical bonds at the interface, the hydrophilicity and the bulk density of coating. Finally, an interfacial chemical bonding mechanism was proposed.

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    Influence of Magnetic Shielding on the Power Loss of Induction Heating Power Supply in the Electro-magnetic Induction Controlled Automated Steel Teeming System
    Ming HE, Xianliang LI, Qingwei WANG, Lianyu WANG, Qiang WANG
    Acta Metall Sin, 2019, 55 (2): 249-257.  DOI: 10.11900/0412.1961.2018.00083
    Abstract   HTML   PDF (2298KB) ( 466 )

    In order to reduce the influence of ladle structure on the power loss of power supply in the electromagnetic induction controlled automated steel teeming (EICAST) system, a method of setting magnetic shielding material on the bottom and sides of induction coil is firstly proposed. The influence of the magnetic shielding on the magnetic flux density and the optimal heating position of induction coil are analyzed by numerical simulation, and the correctness of simulation results is verified by laboratory experiments. In addition, the best magnetic shielding sizes and structure for this new technology are determined respectively. The results show that the magnetic shielding method can effectively reduce the power loss of induction coil and improve the optimum heating area of induction coil. When using copper as a magnetic shielding material, the best sizes of magnetic shielding are height of 200 mm, length of 290 mm, width of 290 mm and thickness of 1 mm. At this time, the best heating position of induction coil will move upward, and the moving distance is 20.2 mm, which is beneficial to the installation of induction coil and the improvement of its service life. To improve the strength of nozzle brick and ensure the service life of nozzle brick, a new structure is applied, and its magnetic shielding effect is almost the same as the former. These research works are very important for the wide application of the EICAST technology.

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    Numerical Simulation of Hydrogen Diffusion in X80 Welded Joint Under the Combined Effect of Residual Stress and Microstructure Inhomogeneity
    Timing ZHANG, Weimin ZHAO, Wei JIANG, Yonglin WANG, Min YANG
    Acta Metall Sin, 2019, 55 (2): 258-266.  DOI: 10.11900/0412.1961.2018.00060
    Abstract   HTML   PDF (4999KB) ( 384 )

    Welded joints of hydrogen-containing coal gas transmission pipelines are prone to hydrogen enrichment due to their severe microstructure inhomogeneity and residual stress in them, and thus lead to the decrease of plasticity and toughness. In order to investigate the effect of local hydrogen enrichment on the safety of hydrogen-containing coal gas transport pipelines, a three dimensional numerical simulation model was established to investigate the hydrogen diffusion behaviour considering the combined effect of microstructure inhomogeneity and residual stress in X80 spiral welded pipeline by using ABAQUS software. Results showed that both microstructure inhomogeneity and residual stress could lead to hydrogen diffusion. The distribution of hydrogen concentration in the pipeline was similar to that of hydrostatic stress distribution. That is, the higher the hydrostatic stress value, the higher the corresponding hydrogen concentration, indicating that the influence of residual stress on the hydrogen diffusion behaviour is greater than that of microstructure inhomogeneity. The enriched hydrogen concentration at the center region of the welded joint with the highest residual stress was 2.7 times higher than that without considering residual stress. Equivalent charging hydrogen pressure was put forward to reflect the degree of hydrogen enrichment in weld metal. Slow strain rate tension (SSRT) tests were subsequently performed on weld metal specimen at equivalent charging hydrogen pressure to investigate the effect of hydrogen enrichment on hydrogen embrittlement (HE) susceptibility. The SSRT tests performed in nitrogen gas and simulated coal gas were used for comparison. The HE index increased from 18.56% in simulated coal gas to 32.53% in equivalent charging hydrogen pressure, increasing by 75.27%. Therefore, the residual stress is a non-ignorable factor, because it could lead to hydrogen enrichment and could significantly influence HE susceptibility in welded joint. The determination of hydrogen enrichment in welded joint by using numerical simulation method is the basis to evaluate the safety of coal gas transmission pipeline.

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    The Lattice Instability Induced by Ti-Site Ni in B2 Austenite in TiNi Alloy
    Jiangang NIU, Wei XIAO
    Acta Metall Sin, 2019, 55 (2): 267-273.  DOI: 10.11900/0412.1961.2018.00299
    Abstract   HTML   PDF (1874KB) ( 275 )

    The shape memory effect exists in the temperature range between martensitic phase transformation temperature and reverse martensitic phase transformation temperature, thus the control of martensitic phase transformation temperature is a key issue for the application of shape memory alloys. Valence electrons have been thought to dominate phase stability and phase transformation temperature in TiNi alloy. Inconsistent with the valence electron theory, Ti-site Ni could lead to a significant decrease of phase transformation temperature in TiNi alloy. To deeply understand the effect of Ti-site Ni, a point-defect-perturbation strategy was proposed to prove that Ti-site Ni indeed induced a local lattice instability in B2 austenite. It is the structural feature of instability final phase that one-dimensional <100>B2 atomic column compression and <111>B2 column expansion from the perturbation site. The final phase is energetic lower than B2 structure, and the lowest energy of final phase is 20 meV/atom lower than B2 structure, when the perturbing Ti-site Ni content reaches 2%~4%. In contrast to the case in austenite, Ti-site Ni did not induce the lattice instability in B19′ martensite. The difference between austenite and martensite is to some extent the origin of the significant decrease of phase transformation temperature brought by Ti-site Ni in TiNi alloy.

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    Effect of Different Temperatures on He Atoms Behavior inα-Fe with and without Dislocations
    Jin WANG, Liming YU, Chong LI, Yuan HUANG, Huijun LI, Yongchang LIU
    Acta Metall Sin, 2019, 55 (2): 274-280.  DOI: 10.11900/0412.1961.2018.00190
    Abstract   HTML   PDF (5267KB) ( 328 )

    The requirement of meeting rapidly growing demand for energy while maintaining environmentally friendly has been motivating the hot research on thermonuclear fusion. One of the key issues in future fusion reactors is that structural materials, especially fusion device first wall material, will suffer from He cumulative effects and atomic displacements from radiation cascades. Such harsh service conditions lead to the formation of He bubbles, which are responsible for severe degradation of the structural materials (e.g., swelling, embrittlement, loss of ductility etc.). It is thus essential to further understand the formation of He bubbles and hardening characteristics for the development of future nuclear materials. In this work, the behaviors of He segregation and tensile deformation have been investigated by molecular dynamics (MD) simulations in α-Fe with and without dislocations (dislocation densities are 0 and 3.36×1011 cm-2, respectively ) and at the annealing temperatures of 300 and 600 K with 0.1%He (atomic fraction) injection. The results show that during the process of 300 K annealing, the effect of dislocation is rather weak, and He atoms are easier to form small He clusters by self-trapping. The size of He clusters and the number of dislocation loops are lower. Furthermore, higher temperature can notably intensify He diffusion, and the size of He clusters and the number of dislocation loops both increase at 600 K. In the process of tensile deformation, dislocations can notably accelerate small He clusters to develop into larger He bubbles, which leads to lower yield stress and strain. In addition, at 300 K, the model mainly occurs to brittle fracture and the dislocations density is lower. At 600 K, larger He bubble can promote dislocation multiply and enhance the deformability. Therefore, there exhibits a better plasticity in the model.

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    Influence of Hydrostatic Pressure on the Thermodynamics and Kinetics of Metal Corrosion
    Rongyao MA, Lin ZHAO, Changgang WANG, Xin MU, Xin WEI, Junhua DONG, Wei KE
    Acta Metall Sin, 2019, 55 (2): 281-290.  DOI: 10.11900/0412.1961.2018.00215
    Abstract   HTML   PDF (965KB) ( 367 )

    In recent years, researches on deep sea corrosion have attracted much attention of many researchers. The high hydrostatic pressure is a distinctive feature of deep-sea environment. The hydrostatic pressure affects the corrosive behavior of metallic materials by modifying the composition, structure and compactness of corrosion products, changing the polarization processes of cathode electrode and anode electrode, altering pitting nucleation rate and growth rate, impacting on chemical reaction rate and equilibrium constant, and varying hydrogen diffusion rate and coverage. However, in essence, the influence of hydrostatic pressure on the corrosion behavior of different metal materials is the manifestation of the thermodynamic and kinetic parameters of the corrosion electrode process caused by hydrostatic pressure. At present, the mechanism of effect of hydrostatic pressure on the thermodynamics and kinetics of corroding electrode processes is unclear yet. In addition, the concerns about the effects of hydrostatic pressure on the chemical properties of materials and seawater are comparatively low. Based on thermodynamics and kinetics, the effects of hydrostatic pressure on the activities of electrode material and ions in environment, including on the solubility, fugacity or activity of gases in environment are analyzed. The influence of hydrostatic pressure on pH value and chemical equilibrium is also discussed. The relationships between hydrostatic pressure and equilibrium electrode potential, as well as the exchange current density, are analyzed. The theoretical model of the effect of hydrostatic pressure on the corrosion behavior of active metals is established. The studies have shown that hydrostatic pressure would increase the activities of materials, ions and dissolved gas in environments, and this is closely related to their partial molar volume. The hydrostatic pressure would magnify the difference in the activity of heterogeneous materials. The larger the partial molar volume difference of the heterogeneous materials, the more obvious the difference in activity. Increasing hydrostatic pressure reduces the equilibrium electrode potential of iron and aluminum anode dissolution reaction while reducing its exchange current density. Increasing hydrostatic pressure increases the equilibrium electrode potential of oxygen reaction and decreases its exchange current density. Increasing hydrostatic pressure reduces the equilibrium electrode potential of hydrogen evolution reaction and increases its exchange current density.

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    Molecular Dynamics Simulation of the Structure and Deformation Behavior of γ/α2 Interface in TiAl Alloys
    Aidong TU, Chunyu TENG, Hao WANG, Dongsheng XU, Yun FU, Zhanyong REN, Rui YANG
    Acta Metall Sin, 2019, 55 (2): 291-298.  DOI: 10.11900/0412.1961.2018.00182
    Abstract   HTML   PDF (9199KB) ( 494 )

    TiAl alloys with γ-TiAl and α2-Ti3Al dual-phase lamellar structure possess not only excellent high temperature performance but also density only about half of traditional superalloys. Such lamellar structure largely determines the mechanical properties of TiAl alloys. However, there is still a lack of understanding on the atomic structure of lamella, as well as their influence on the mechanical behaviors. For this reason, molecular dynamics with an embedded-atom potential is employed to investigate the energies of both the coherent and semi-coherent γ/α2 interfaces. The interface coherency is found to depend on the thickness ratio of γ lamellae to α2 lamellae, and there exists a critical lamella thickness, below/above which the interface is coherent/semi-coherent. Tensile loading perpendicular to the lamella interface indicates that the yield strength of coherent interface is higher than that of semi-coherent interface and the crack nucleation behavior varies with the thickness ratio of γ lamellae to α2 lamellae. The plastic deformation occurs first in the γ region, forming Shockley partial dislocations and then crosses the γ/α2 interface via slip transfer, activating stacking faults on the pyramidal plane in the α2 region. In this process, the γ/α2 interface provides nucleation sites for subsequent dislocations and cracks.

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