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

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Deformation Behavior and Toughening of High-Entropy Alloys
A new alloy design concept, high-entropy alloys (HEAs), has attracted increasing attentions and becomes a new research highlight recently. Different from traditional alloy design strategy which usually blends with one or two elements as the principal constituent and other minor elements for the furt. . .
Acta Metall Sin, 2018 Vol. 54 (11): 1553-1566    DOI: 10.11900/0412.1961.2018.00372
 
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Research progress on fundamentals and applications of metal-induced crystallization PDF (4995KB)
2019-10-15
Study on the Solidification of Ag-Ni Monotectic Alloy PDF (736KB)
2019-10-15
High-resolution X-ray Diffraction Analysis of Epitaxial Films PDF (4911KB)
2019-10-14
Effect of Alloying Elements on Initial Corrosion Behavior of Aluminum Alloy in Bangkok, Thailand PDF (2062KB)
2019-10-14
Seed Preparation And Microstructure Control of PST Crystals of Ti-47Al Alloy PDF (5743KB)
2019-09-29
Current Issue More>>
      11 October 2019, Volume 55 Issue 10 Previous Issue   
    Research Progress in Age-Hardenable Mg-Sn Based Alloys
    Zhangzhi SHI, Min ZHANG, Xuefei HUANG, Xuefeng LIU, Wenzheng ZHANG
    Acta Metall Sin. 2019, 55 (10): 1231-1242.   DOI: 10.11900/0412.1961.2019.00049
    Abstract   HTML   PDF (6682KB)

    Mg-Sn based alloy system is a typical age-hardenable Mg alloy system with Mg2Sn as the major precipitation phase. Eutectic temperature at Mg-rich end of Mg-Sn phase diagram is much higher than those of Mg-Al and Mg-Zn phase diagrams, which is comparable to that of Mg-RE phase diagram. So Mg-Sn based alloys are hopeful candidates of rare-earth free heat resistant Mg alloys with low cost. This paper systematically reviews research progress in age-hardenable Mg-Sn based alloys. The main second phase β-Mg2Sn has a fcc structure with different lattice parameters reported, one of which the most frequently adopted is aβ≈0.676 nm, agreeing well with calculations of interfacial orientations. Twelve orientation relationships (ORs) between Mg2Sn precipitates and Mg matrix have been identified. Those with similar morphologies, i.e., the same long axis direction or the same habit plane, are possibly related to different ORs. Addition of Zn benefits the appearance of β-Mg2Sn precipitates inclined to the Mg basal plane, which are more effective to hinder dislocation movement on the basal plane and result in a greater strengthening effect. Effects of various alloying elements on age-hardening response and mechanical properties of Mg-Sn binary alloys have been summarized. Elements such as Zn, Al, Ag and Na can enhance age-hardening responses. Due to formation of highly thermal stable compounds with Sn, RE, Ca, Sr and Li exhibit negative effects. Consequently, alloy design of Mg-Sn based alloys faces more difficulties, requiring an in-depth investigation of phase transformation processes. Finally, future research directions have been specified.

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    Effect of Pre-Cyclic Stress on Fatigue Crack Propagation Behavior of Key Structural Al Alloy Materials Used in High Speed Trains
    Xiaochen ZHANG, Weiying MENG, Defang ZOU, Peng ZHOU, Huaitao SHI
    Acta Metall Sin. 2019, 55 (10): 1243-1250.   DOI: 10.11900/0412.1961.2018.00497
    Abstract   HTML   PDF (6019KB)

    The complex cyclic loading is a "potential killer" affecting the service security of high speed trains. It is necessary to investigate the influence of cyclic loading on vehicle structures and explore potential methods to improve the service strength and life of structural materials. In this work, the mechanical property tests for key structural materials (Al alloy) that experienced years of service were described, the fatigue crack propagation (FCP) behavior at different stages were analyzed, and the changing pattern of mechanical behavior of material was demonstrated over time. Since the specimens showed turning characters on FCP behavior, the mechanical property tests for materials that subjected to different levels of pre-cyclic stress (PCS) were further carried out to analyses the "coaxing" effects of PCS and establish a more reasonable life prediction model for materials. It is found that a turning phenomenon or "turning" point is clearly shown in the early stage of the fitted curves for the specimens with service experience, which is mainly due to the delayed extension behavior in the region near the threshold; the curves of crack propagation rates and stress intensity factor (da/dNK) of specimens subjected to PCS show a similar turning phenomenon at the initial stage of steady-state crack growth to that of specimens with service experience; the "coaxing" effect of PCS on material is different for different PCS levels, and there is an optimal PCS for the "coaxing" effect; the model proposed in this study has higher accuracy in FCP life prediction for the da/dNK curves with "turning" character.

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    Effect of Composition Gradient on Microstructure and Properties of Laser Deposition TC4/TC11 Interface
    Bo HE, Meng XING, Guang YANG, Fei XING, Xiangyu LIU
    Acta Metall Sin. 2019, 55 (10): 1251-1259.   DOI: 10.11900/0412.1961.2018.00496
    Abstract   HTML   PDF (25223KB)

    In recent years, gradient composites have been increasingly used in life and industry. The rapid development of laser deposition manufacturing (LDM) technology realizes the manufacturing of dissimilar-metal gradient composite structure used for main bearing component. In this work, laser deposited TC4/TC11 gradient composite structures are taken as the research objects. Since there are few studies on TC4/TC11 titanium alloy, this work focuses on the effect of heat treatment on the microstructures and properties of TC4/TC11 titanium alloy, providing the basis to improve the quality and serving life of laser deposited gradient composite structure. Based on comparative study on the microstructures, residual static performances, tensile fractures, room temperature abrasion results and microhardnesses of laser deposition TC4/TC11 titanium alloy specimens with different composition gradients under different heat treatments, the ways to improve the laser deposition TC4/TC11 titanium alloy microstructure and the comprehensive mechanical properties were explored. Results show that when the temperature of solution and ageing treatment rises to 970 ℃, the length-width ratio of α laths of TC4/TC11 titanium alloy is less than that of the other heat treatment samples. The globular α phase and the short bar α phase are significantly increased. The microstructure of the three-layer transition zone is more uniform and orderly, and the transition interface almost disappears. With the increase of the number of transition layers, the strength and plasticity of solution and ageing samples with different component gradients are increased. The frictional coefficient curve of sample with 1 transition layer is similar to that of the sample with 3 transition layers. The friction coefficient of the sample with the transition layer of 0 is relatively small. The wear mechanism of solution and ageing samples with different component gradients are mainly lamination wear and adhesive wear. From the as-deposited state to the stress relieved and finally to the ageing state of solid solution, the corresponding hardness of the sample with different component gradients increases successively.

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    Microstructure and Properties of a New Third Generation Powder Metallurgy Superalloy FGH100L
    Tian TIAN, Zhibo HAO, Chonglin JIA, Changchun GE
    Acta Metall Sin. 2019, 55 (10): 1260-1272.   DOI: 10.11900/0412.1961.2018.00500
    Abstract   HTML   PDF (25134KB)

    Spray forming (SF) is a novel rapid solidification technique. Compared with traditional cast & wrought and powder metallurgy technique, it has the advantages of less segregation and shorter process. In this work, a new third generation powder metallurgy (PM) superalloy FGH100L was prepared by SF+hot isostatic pressing (HIP)+isothermal forging (IF)+heat treatment (HT) process. The effects of solution heat treatment temperatures and preparation process on the microstructure and mechanical properties of FGH100L alloy were studied. The results show that the microstructure of SF+HIP+IF state FGH100L alloy is very sensitive to changes of solution temperature. With the increase of the solution temperature (1110~1170 ℃), the grain size of the alloy grew, and the size of the γ' strengthened phase first increased and then decreased. Its hardness, tensile strength and plasticity at room temperature/high temperature all show a trend of increasing followed by decreasing. The quantitative equilibrium of three sizes of γ' phase in the alloy is more reasonable, the microstructure of the alloy is the best, and the hardness and room temperature/high temperature tensile properties of alloy have the highest parameter values at 1130 ℃. At the same temperature, the grain size of FGH100L alloy increased first and then decreased under different processing conditions of SF, SF+HIP+HT and SF+HIP+IF+HT. The morphology of grains changed from subspherical to polygonal to subspherical. Alloy grain size increases, and the grain boundary bending degree decreases in the process of SF+HIP+HT. Due to SF+HIP+IF+HT process, the alloy recrystallizes, refines the grain, and presents chain-like structure, forming curved grain boundary and having higher yield strength. Under SF+HIP+HT and SF+HIP+IF+HT processes, the tensile fracture of the alloy at room temperature changed from intergranular brittle fracture to transgranular and intergranular mixed fracture, and the tensile fracture at high temperature was intergranular fracture.

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    Effect of Pre-Oxidation on High Temperature Oxidation and Corrosion Behavior of Co-Al-W-Based Superalloy
    Bo GAO, Lei WANG, Xiu SONG, Yang LIU, Shuyu YANG, Akihiko CHIBA
    Acta Metall Sin. 2019, 55 (10): 1273-1281.   DOI: 10.11900/0412.1961.2019.00032
    Abstract   HTML   PDF (45668KB)

    In 2006, stable γ' phase was found in Co-Al-W alloy, which provides a new way for developing Co-based superalloys. In order to meet the requirements for applications, the Co-Al-W-based superalloys need to have good oxidation and corrosion resistance. But the oxidation and corrosion resistance of the Co-Al-W-based superalloys is relatively low. In this work, pre-oxidation treatments were used to improve the oxidation and corrosion resistance. Three types of pre-oxidation treatments were carried out at 900 ℃ (in air), 950 ℃ (in air) and 1000 ℃ (in 1%O2+99%Ar), which were marked as 900-PreO, 950-PreO and 1000-LPreO, respectively. High temperature oxidation tests of both the pre-oxidation treated and untreated superalloys were carried out at 1000 ℃. And hot corrosion behaviors were also investigated at both 800 and 850 ℃. XRD, SEM and EDS were used to examine the characteristics of the oxidation and corrosion behaviors. The results show that the pre-oxide layers of the superalloys after different pre-oxidation treatments are compact. During oxidation at 1000 ℃, the Cr2O3 scale in 900-PreO treated superalloy is oxidized to form volatile products, and the diffusion resistance of both oxygen and the metal elements through the oxide layer is poor. In 1000-LPreO treated superalloy, serious spallation of the oxides occurs and leads to poor oxidation resistance. In 950-PreO treated superalloy, since the continuous CoCr2O4 and Al2O3 scales help to reduce the diffusion of oxygen and the metal elements, the mass gain of 950-PreO treated superalloy is consequently decreased. During the hot corrosion process, the pre-oxide layer of 950-PreO treated superalloy can hinder the diffusion of corrosive medium. Therefore, the corrosion resistance can be significantly improved by 950-PreO treatment, and the mass gain is decreased by over 80%.

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    Effect of Surface Roughness by Shot Peening on Stress Corrosion Cracking Behavior of Pure Titanium Welded Joints in HCl Solution
    Conghui ZHANG, Hua RONG, Guodong SONG, Kun HU
    Acta Metall Sin. 2019, 55 (10): 1282-1290.   DOI: 10.11900/0412.1961.2019.00056
    Abstract   HTML   PDF (15731KB)

    Pure titanium is often used in the manufacture of pressure vessels due to its excellent corrosion resistance. Pressure vessels are generally operated in various corrosive media and subjected to varying degrees of corrosion. Stress corrosion cracking is one of the most dangerous forms of damage to pressure vessels used in various fields. Welded joints become the weak link of the pressure vessels because of the uneven microstructure and welding residual stress, which could cause stress corrosion and directly affect the overall performance and service life of pressure vessels. At present, as a method to improve the mechanical and corrosion properties of materials, shot peening has been widely studied. However, shot peening often leads to the increase of surface roughness and even causes defects such as cracks and surface damage, which will affect the effect of improving the corrosion resistance of materials. It remains to be further studied that the specific influence of surface roughness on the stress corrosion resistance of metal materials. In this work, the stress corrosion behavior of the original samples, ultrasonic shot peening (USSP) samples and USSP with surface polished samples of TA2 titanium welded joints in 10%HCl solution were studied by slow strain rate tension (SSRT) experiment. OM, TEM and SEM were used to observe the microstructure and corrosion fracture morphology of the welded joints. The surface roughness and residual stress of different processed samples were measured, and the corrosion mechanisms were analyzed. The results showed that both stress corrosion and hydrogen embrittlement occurred in pure titanium welded joints in this system, and weld metal (WM) was the weakest link in the welded joint. The stress corrosion cracking susceptibility index (ISCC) of the original sample in this system was 25.61%, indicating a tendency of stress corrosion. The ISCC of the USSP sample was reduced by 28.78%, and that of the USSP with surface polished (1500#) sample was reduced by 53.3%; both of them had no obvious tendency of stress corrosion in the system. The roughness of the USSP surface could cause stress concentration to form a crack source, which was similar to the pitting propagation. USSP with surface polished treatment reduced the surface roughness, achieving the homogenization of the stress distribution and increasing the elongation and the plasticity of the samples, which could further improve the stress corrosion cracking resistance.

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    Composition Rule of High Hardness and Electrical Conductivity Cu-Ni-Si Alloys
    Dongmei LI, Beibei JIANG, Xiaona LI, Qing WANG, Chuang DONG
    Acta Metall Sin. 2019, 55 (10): 1291-1301.   DOI: 10.11900/0412.1961.2019.00080
    Abstract   HTML   PDF (12680KB)

    Cu-Ni-Si alloys are among the most widely used electrical conductive (>30%IACS) alloys with quite high strength level (>500 MPa), so they are especially suitable for lead frames and connector joints. However, these two properties are quite composition sensitive, apart from their tight connection with processing. Moreover, their compositions fall within quite broad ranges that poses difficulties for the industries. For instance, typical C7025 alloy has a specified composition (mass fraction, %) range of Ni 2.2~4.2, Si 0.25~1.2, Mg 0.05~0.3, plus less than 0.5 of other impurity elements. Obviously the composition ranges of the elements are far from even their absolute contents. The present work focuses on understanding the composition rule of Cu-Ni-Si via a new structural tool, the cluster-plus-glue-atom model. In this model, any solid solution is described by a nearest neighbor coordination polyhedron plus a one-to-six glue atoms. Specifically for Cu-based alloys, the cluster is cubooctahedron. The composition formula for solute-rich Cu-Ni-Si alloys and pure Cu are established, respectively [(Ni2/3Si1/3)-Cu12]Cu1~6 and [Cu-Cu12]Cu3. A series of Cu-Ni-Si alloys were designed on the basis of the cluster-plus-glue-atom model. In the concentrated solute region with Cu content less than 95%, the alloys were designed using the single cluster model [(Ni2/3Si1/3)-Cu12]Cu1~6. In the dilute solute region where Cu content is larger than or equal to 95%, the alloys were designed using the double cluster model {[(Ni2/3Si1/3)-Cu12]Cu3}A+{[Cu-Cu12]Cu3}B. The alloys were arc-melted into ingots under Ar atmosphere and were subjected to a solution treatment at 950 ℃ for 1 h plus water quenching, and then to an ageing at 450 ℃ for 4 h plus water quenching. The microstructure and properties of the alloys were characterized and tested by XRD, OM, TEM, Vickers hardness tester and digital metal conductivity instrument. The composition rule of the designed Cu-Ni-Si alloy was obtained by experiments.The results shown a special range of Cu content in 95.0%~95.8% as a composition sensitive region, in which, in addition to ageing precipitation strengthening, the alloys also have amplitude modulated decomposition strengthening, resulting in a sudden increase in Vickers hardness and a decrease in electrical conductivity. Vickers hardness and electrical conductivity change with composition variations in an irregular manner. In the concentrated and dilute solute region before and after the composition sensitive region, Vickers hardness (H) is linearly related to the Cu content (CCu) by H=-12.6CCu+1362.7 and H=-26.2CCu+2777.3, and the corresponding electrical conductivity (σ) is also linearly related to the CCu by σ=0.2CCu+28.6 and σ=5.2CCu-466.

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    Nanoporous Silver via Electrochemical Dealloying and Its Superior Detection Sensitivity to Formaldehyde
    Yulin YANG, Zhangyan MU, Zheng FAN, Zhenhua DAN, Ying WANG, Hui CHANG
    Acta Metall Sin. 2019, 55 (10): 1302-1310.   DOI: 10.11900/0412.1961.2019.00054
    Abstract   HTML   PDF (16041KB)

    Nanoporous silver (NPS) with high specific surface area has a great potential application in efficient formaldehyde detection. In this work, NPS was prepared by potentiostatic or galvanostatic electrochemical dealloying of Ag30Zn70 precursor alloys. The results reveal that applied potential or current has a significant influence on the composition, morphology and nanoporous structure of NPS. A bi-continuous NPS with an average pore size of 80 nm was obtained by electrochemical dealloying in 0.1 mol/L HCl solution at a constant current density of 2.5 mA/cm2 for 6000 s. The cyclic voltammetry experiment results showed that NPS has a superior formaldehyde catalysis and detection abilities in 0.5 mol/L KOH solution due to the optimal combination of nanopores and Ag ligaments in nanoporous structure. The higher formaldehyde catalysis and detection abilities were exhibited at the NPS with smaller nanopores. The detection sensitivity of formaldehyde in NPS with the pore size of 80 nm was 0.22 mA·cm-2·(mmol·L-1)-1 in the concentration range of 10~100 mmol/L, and the peak current density was 25.0 mA/cm2 in 0.5 mol/L KOH solution with 100 mmol/L HCHO.

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    Influence of Cooling Rate on the Contraction of Peritectic Transformation During Solidification of Peritectic Steels
    Junli GUO, Guanghua WEN, Jiaojiao FU, Ping TANG, Zibing HOU, Shaopeng GU
    Acta Metall Sin. 2019, 55 (10): 1311-1318.   DOI: 10.11900/0412.1961.2018.00553
    Abstract   HTML   PDF (11438KB)

    Driven by the demand for the improving mechanical properties of steel products and the cost reduction in alloys, steels falling within the peritectic composition range are designed recently. However, notoriously cast surface defects such as cracks, deep oscillation mark formation and breakouts are found to occur frequently during continuous casting of steels, particularly at high casting speeds. This phenomenon is closely related to the shrinkage of phase transformation caused by the peritectic transformation. In order to understand the effects of cooling rate on the contraction of the peritectic transformation, the initial solidification processes of a peritectic steel (Fe-0.1C-0.21Si-1.2Mn, mass fraction, %) were observed using high-temperature confocal laser scanning microscopy under different cooling rates, and then variations in surface roughness were measured to reflect the degree of peritectic transformation contraction. The results show that the peritectic transformation occurs a massive transformation when the cooling rate exceeds the critical value. The massive transformation results in a sudden peritectic transformation contraction and surface roughness variations, which directly cause the occurrence of surface longitudinal cracks of slabs at high casting speeds. The contraction increases first and then decreases with the cooling rate increasing and the maximum surface roughness at the middle cooling rate (20 ℃/s) is about 2.8 times more extensive than that which occurs at the low cooling rate of 2.5 ℃/s. The phenomenon that the peritectic transformation contraction decreases under the high cooling rate may provide a new strategy to reduce cracks occurring in high speed casting.

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    Effect of Hot Pressing Temperature on Microstructure and Tensile Properties of SiC/Al-Zn-Mg-Cu Composites
    Guonan MA, Dong WANG, Zhenyu LIU, Sheng BI, Yuning ZAN, Bolv XIAO, Zongyi MA
    Acta Metall Sin. 2019, 55 (10): 1319-1328.   DOI: 10.11900/0412.1961.2018.00523
    Abstract   HTML   PDF (20713KB)

    Particulate reinforced aluminum matrix composites have been widely used in industrial fields. In general, high strength aluminium alloys, such as 2024Al are employed to produce stronger composites. However, the composites with high strength Al-Zn-Mg-Cu alloys as the matrices are paid relative attentions. Therefore, the corresponding optimization for fabrication parameters has not been well understood. In the present work, SiC particles with volume fraction of 15% reinforced Al-7.5Zn-2.8Mg-1.7Cu (mass fraction, %) composites were fabricated using powder metallurgy (PM) technique at hot pressing temperatures of 500, 520, 540 and 560 ℃. TEM, EPMA and tensile test were used to study the effect of hot pressing temperature on the microstructure and tensile properties of SiC/Al-Zn-Mg-Cu composites. The measured densities indicated that all the composites were completely condensed, no pores were observed. Undissolved phase containing Mg and Cu segregated in matrix of the composites hot pressed at 500 and 520 ℃, resulting in instable tensile properties. With increasing hot pressing temperature to 540 ℃, Mg and Cu were uniformly distributed in the composites which exhibited the stable tensile properties. With further increasing temperature to 560 ℃, Mg segregated around SiC particles due to interface reaction. In this case, the content of MgZn2 phase was decreased, resulting in the reduction of tensile strength. HAADF-STEM and EDS analyses showed that the interface compounds were oxide of Mg and coarse MgZn2 phase.

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    Optimization and Simulation of Deformation Parameters of SiC/2009Al Composites
    Kai MA, Xingxing ZHANG, Dong WANG, Quanzhao WANG, Zhenyu LIU, Bolv XIAO, Zongyi MA
    Acta Metall Sin. 2019, 55 (10): 1329-1337.   DOI: 10.11900/0412.1961.2019.00020
    Abstract   HTML   PDF (14159KB)

    Particle reinforced aluminum matrix composites (PRAMCs) have the advantages of high specific strength and high specific modulus, and are important engineering materials for aerospace field. However, due to the huge difference in the mechanical properties between the reinforcements and the aluminum matrixes, the plastic forming of PRAMCs is quite difficult, which restricts their wide engineering applications. In order to improve the quality of plastic processing, it is necessary to optimize deformation parameters of PRAMCs. In this study, the hot deformation parameters of a 15%SiC/2009Al composite fabricated by powder metallurgy were optimized using a simulation method. Firstly, true stress-strain curves of the SiC/2009Al composite were obtained through hot compression tests, and then the strain rate sensitivity index (m) map at the ultimate strain was established. Under the deformation parameters corresponding to various m values, the finite element simulation of the hot compression process was carried out. The flow stress, strain and damage coefficient distribution of the hot-compressed samples were analyzed. The results show that it is reliable to use the m value as the basis for optimizing the processing parameters, which were further verified by the microstructural observations. The deformation temperature and strain rate corresponding to the optimum parameters of the composite were determined to be 500 ℃ and 0.01 s-1, respectively.

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    Corrosion Behavior of Al(Y)-30%Al2O3 Coating Fabricated by Low Pressure Cold Spray Technology
    Yang BAI, Zhenhua WANG, Xiangbo LI, Yan LI
    Acta Metall Sin. 2019, 55 (10): 1338-1348.   DOI: 10.11900/0412.1961.2019.00047
    Abstract   HTML   PDF (22314KB)

    Low-pressure cold spray technology (LPCS) is a new type of surface treatment technology. Compared with the conventional thermal sprayed aluminum coating, the LPCS aluminum coating has the advantages of a low degree of oxidation, high density and good resistance to uniform corrosion. However, the inert aluminum coating is not stable in marine environment, it is prone to localized corrosion, which leads to coating failure. Therefore, in order to solve the key common problems of corrosion, which are common in offshore oil and gas equipments, such as deep-sea drilling rigs, platforms and on-line storage and offloading devices, the corrosion resistance performance of the low pressure cold sprayed Al(Y)-30%Al2O3 (volume fraction) composite coatings were carried out. In this work, Al(Y)-30%Al2O3 composite coating with different rare earth elements (Y) was prepared on the Q235 carbon steel substrate by low pressure cold spray technology, aiming to improve the local corrosion resistance performance of aluminum coating in marine environment. The effects of Y addition on the corrosion behavior of Al(Y)-30%Al2O3 coating with different Y contents (mass fraction: 0.05%, 0.1%, 0.2%, 0.5%) were studied by electrochemical measurements and microstructural analysis. The corrosion mechanism of the composite coating was elucidated. The results show that the addition of an appropriate amount of Y element is very important to improve the corrosion resistance of the coating; whether the addition amount of Y is too low or too high, the improvement can be negligible or even negative; the optimal amount of Y is 0.2% (mass fraction), by which the corrosion resistance of the coating is one order of magnitude higher than that of Al-30%Al2O3 coating; the corrosion process of Al(Y)-30%Al2O3 coating includes four stages: the surface uniform corrosion, the interfacial erosion-infiltration diffusion, the localized corrosion and the corrosion inhibition.

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    Effect of Nd Content on the Structure and Magnetic Properties of Si(111)/Cr/Nd-Co/Cr Thin Films Prepared by Magnetron Sputtering
    Xianmei HE, Liuniu TONG, Cheng GAO, Yichao WANG
    Acta Metall Sin. 2019, 55 (10): 1349-1358.   DOI: 10.11900/0412.1961.2018.00490
    Abstract   HTML   PDF (19580KB)

    A series of Si(111)/Cr(10 nm)/NdCox(400 nm)/Cr(10 nm) thin films with the atomic ratio of Co/Nd (x) varying from 2.5 to 7.2 were prepared by radio frequency magnetron sputtering. The influence of Nd content on the structure and magnetic properties of the as-prepared and post annealed films were investigated by XRD, SEM, VSM and AFM/MFM. Magnetic measurements at room temperature show that the compositional variation of the perpendicular anisotropy energy (Ku) exhibits a broad peak around x=5.2 with maximum of Ku=(80±5) kJ/m3 for the as-prepared Nd-Co amorphous films. MFM characterization shows that the root mean square deviation of phase shift in MFM images (Δ?rms) also have a compositional dependence which is similar to that of Ku-x. The experimental results show that the stress induced magneto-elastic anisotropy is the primary origin of the perpendicular magnetic anisotropy (PMA) in the as-prepared Nd-Co amorphous film. After rapid thermal annealing (RTA) process in a vacuum atmosphere at 600 °C, intermetallic compounds such as Nd2Co17, Nd4Co3 and NdCo2 are precipitated in all the studdied films, while NdCox nanocrystals accompanied by the precipitation of Nd2Co7 symbiotic phase were observed only in the films with x=2.5 and 3.8 (the atomic fraction of Nd excesses at least 4%). The in-plane coercivity of the films with x=2.5 and 3.8 was significantly enhanced (Hc-in=54, 51 kA/m) due to the precipitation of NdCox and Nd2Co7 nanocrystals, while that of the samples with x>4.4 remained low value (Hc-in=4~8 kA/m).

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