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

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    Orginal Article
    Revolutionizing Metallic Biomaterials
    Yufeng ZHENG,Yuanhao WU
    Acta Metall Sin, 2017, 53 (3): 257-297.  DOI: 10.11900/0412.1961.2016.00529
    Abstract   HTML   PDF (6489KB) ( 2280 )

    Entering 21st century, the metallic biomaterials are revolutionizing. New kinds of metallic biomaterials represented by biodegradable metals, nacocrystalline metals and alloys, and bulk metallic glasses, had been explored as implantable biomaterials, and correspondingly the nature of metallic biomaterials are shifting from the bio-inert (with stainless steel, Co-based alloys and Ti alloys) to bio-active and multi-biofunctional (anti-bacterial, anti-proliferation, anti-cancer, etc.). The newly-emerging 3D printing technology and thin film technology had been applied to the advancing manufacture and intelligence of the medical devices made of metallic biomaterials. In this paper, the current research status of the revolutionizing metallic biomaterials had been reviewed, and the future research and development tendencies for newly-developed metallic biomaterials towards bio-functionalization, composite and intelligence are also proposed.

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    Effects of W on Microstructural Stability of the Third Generation Ni-Based Single Crystal Superalloys
    Bo WANG,Jun ZHANG,Xuejiao PAN,Taiwen HUANG,Lin LIU,Hengzhi FU
    Acta Metall Sin, 2017, 53 (3): 298-306.  DOI: 10.11900/0412.1961.2016.00379
    Abstract   HTML   PDF (6712KB) ( 1140 )

    Ni-based single crystal superalloys are widely used in the manufacture of aero engine turbine blades because of the excellent mechanical properties at high temperature. With the development of single crystal superalloys, the content of refractory elements is constantly increased (especially Re) to improve the high temperature capability, which in turn leads to the decrease in microstructural stability of alloys, such as the TCP phase precipitation. It is important to find one element which not only can maintain high temperature performance but also does not evidently promote TCP phase precipitation and is very cheap in price to replace Re partially. W is one of the most important solution strengthening elements in superalloys, its diffusion rate in Ni matrix is close to Re and far below the other alloying elements, meanwhile, the advantage of low price make it to be the most suitable substitute of Re. However, there is little work about the effect of W on microstructural stability in Re contained third generation superalloys. In this work, the effects of W on the elemental segregation, elemental partitioning ratio of γ /γ′, microstructure evolution and TCP phase precipitation during thermal exposure at 950, 1000 and 1050 ℃ have been investigated in a third generation Ni-based single crystal superalloys with varied contents of W (6%~8%, mass fraction). The results show that the addition of W has no obvious effect on segregation of the alloying elements of as-cast alloys as well as the morphology, size and volume fraction of γ′ phase after heat treatment. During the thermal exposure at 950 ℃, the connection and deformation of γ′ phase are accelerated, but its coarsening rate is decreased with increasing W content. The TCP phases precipitated in three alloys during thermal exposure are mainly μ phase and σ phase. The area fraction of TCP phases is increased slightly with the W addition during thermal exposure, which is the largest at 1000 ℃, less at 950 ℃ and the least at 1050 ℃.

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    Effect of Anisotropy and Off-Axis Loading on Fatigue Property of 1050 Wheel Steel
    Qingsong ZHANG,Zhenyu ZHU,Jiewei GAO,Guangze DAI,Lei XU,Jian FENG
    Acta Metall Sin, 2017, 53 (3): 307-315.  DOI: 10.11900/0412.1961.2016.00366
    Abstract   HTML   PDF (12858KB) ( 696 )

    Wheel is one of the key components of a train to transmit power and affect the security operation. With the rapidly development of high-speed railway, rolling contact fatigue of railway wheels has become an important issue with respect to failure. With the increasing of train speeds and axle loads, the wheel-rail dynamic stress and contact stress were increased, resulting in wheel out of round with off-axis wear and potential for derailment. SAE 1050 steel as a typical wheel steel is widely used in high-speed wheel and wagon wheel. Consequently, the wheel rolling contact fatigue performance under service process and the fatigue performance of wheel steel materials have been studied. However, there are less relevant results about the anisotropy of rolling and off-axis loading of wheel steel materials. To investigate the effect of anisotropy and off-axis loading on fatigue property of 1050 wheel steel, uniaxial fatigue tests were conducted at the conditions of 120 Hz and stress ratio R=0.1, and off-axis fatigue tests were conducted at the conditions of 55 Hz and R=0.1 at room temperature in air. All fatigue specimens were cut from bar round with the angles (0°, 30° and 45°) to rolling direction. The fatigue limit of specimens under two kinds of special loading conditions was obtained. Fracture surface of the specimen was observed by SEM. The finite element (FEM) analysis software (Ansys 14.0) was used to analyze static mechanics of specimens under three different off-axis loading angles (0°, 30° and 45°). The results showed that the fatigue limit decreased with increasing angle to rolling direction and the percentage of decline was 9%. The fatigue limit decreased with increasing off-axis loading angle and the percentage of decline was 85%. The shear stress and Von Mises stress were larger and increased with increasing off-axis loading angle when the specimen was subjected to off-axis loading.

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    Relationship Between Retained Austenite Stability and Cryogenic Impact Toughness in 0.12C-3.0Mn Low Carbon Medium Manganese Steel
    Long HUANG,Xiangtao DENG,Jia LIU,Zhaodong WANG
    Acta Metall Sin, 2017, 53 (3): 316-324.  DOI: 10.11900/0412.1961.2016.00373
    Abstract   HTML   PDF (13543KB) ( 1550 )

    Low carbon and low alloy steels require good combination of strength and ductility to ensure safety and stability of structures, and the low temperature toughness has become more significant to low carbon low alloyed high performance steel recently. Retained austenite plays a great role in a multiphase system to improve the toughness of steel as a result of the deformation induced transformation of retained austenite when the steel deformed. In this work, the characterization of multiphase microstructure including retained austenite, tempered martensite and intercritical ferrite which obtained by a three-step intercritical heat treatment in a low carbon medium manganese steel were studied, and the low-temperature impact toughness evolution from -40~-196 ℃ during the process were analyzed. The results showed that C and Mn distributed unevenly after intercritical quenching and were benefit to martensite inverse transformation to austenite, and the enriched C and Mn elements can improve the stability of reverted austenite during the tempering process. The impact energy of the steel is 200 J at -80 ℃ during the processes at intercritical quenching temperature 720 ℃ and tempering temperature 640 ℃, and the energy of impact crack formation and propagation at different temperature were also analyzed.

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    Microstructure and Mechanical Properties of LaserForming Repaired 300M Steel
    Fenggang LIU,Xin LIN,Kan SONG,Menghua SONG,Yifan HAN,Weidong HUANG
    Acta Metall Sin, 2017, 53 (3): 325-334.  DOI: 10.11900/0412.1961.2016.00282
    Abstract   HTML   PDF (8688KB) ( 928 )

    Laser forming repairing (LFR) technology is developed from the laser additive manufacturing, which has a high potential in high strength steel structures' repairing. 300M steel has been widely used in aviation and aerospace vehicles, to provide a high strength for aircraft landing gear and high strength bolts components, which in turn leads to a quick damage due to the severe service environment. If these damaged components can be repaired rapidly, the considerable savings in materials and costs can be achieved. In this work, the microstructure and mechanical properties of the LFRed 300M steel have been investigated. Results showed that the LFRed area can be clearly divided into three areas: the substrate zone (SZ), heat affected zone (HAZ) and repaired zone (RZ). The SZ was consisted of the mixture of martensite, bainite and a small amount of retained austenite. The HAZ presented an uneven martensite. The RZ presented an obvious heterogeneous microstructure, and the bainite, the mixture of martensite and bainite, and tempered martensite from the top to the bottom. After heat treatment, the microstructure became uniform with mixed tempered martensite and bainite. The tensile strength of the as-deposited LFRed 300M steel was far lower than those of the substrate. Its tensile strength and yield strength were 1459 MPa and 1163 MPa, respectively. After heat treatment, tensile strength (1965 MPa), yield strength (1653 MPa), elongation (11.7%) and reduction of area (38.4%) increased significantly and reached the same level of the substrate. Furthermore, compared to the as-deposited sample, the local strain of the RZ increased to 53% after heat treatment, and an obvious necking and breaking up happened as well. The strain hardening exponent of SZ and RZ were 0.1548 and 0.1138, which could be closely related to the compatible deformation capability.

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    Research on the Collaborative Effect of Plastic Deformation and Solution Treatment in the Intergranular Corrosion Property of Austenite Stainless Steel
    Xiaosong ZHANG,Yong XU,Shihong ZHANG,Ming CHENG,Yonghao ZHAO,Qiaosheng TANG,Yuexia DING
    Acta Metall Sin, 2017, 53 (3): 335-344.  DOI: 10.11900/0412.1961.2016.00284
    Abstract   HTML   PDF (6124KB) ( 1240 )

    AISI 304 austenite stainless steel was applied extensively in the modern industry due to its good properties on mechanics and corrosion resistance. However, there is severe intergranular corrosion when the AISI 304 was working at the temperature 420~850 ℃ called sensitizing temperature. This phenomenon was more obvious with increase of strain. In addition, this effect can not be removed completely even with the heat treatment subsequently. In present work, the influence of solution treatment and plastic deformation on the intergranular corrosion property of AISI 304 was investigated. The specimens subjected to different strain were obtained by the uniaxial tensile tests at room temperature. XRD was used to measure the fraction of martensitic phase which was induced by deformation. Optical metal lographic microscope was applied to observe the evolution of microstructure. The influence of various deformation values, solution temperature and holding time on intergranular corrosion was quantitative analyzed by electrochemical potentiodynamic reactivation (EPR) method. Experimental results showed that the degree of the intergranular corrosion increased with the increase of deformation, and with the decrease of solution temperature and holding time. It is indicated that since the solubility of carbon in martensite and austenite is discrepant, the content of carbon in the grains recrystallized is discrepant too. The more martensite is transformed, the more chromium carbide is formed in the grain boundary after sensitization. This phenomenon causes poor intergranular corrosion resistance due to the lack of chromium. In addition, the carbon segregation which is caused by plastic deformation will relieve with the rise of solution temperature and holding time. It is because that the carbon atom is more active at higher temperature, and the distribution of carbon is more homogeneous with the extended holding time. Then the quantity of chromium carbide will decrease in solution treatment process. Consequently the chromium depletion will be mitigated. From the above, a uniform solution treatment condition is not suitable for austenite stainless steel with the effect of martensitic transformation in cold working. Flexible scheme can be employed to insure better combination property of products.

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    Mechanism Study on Hot Ductility of 2.25Cr1Mo Alloy Based on Non-Equilibrium Grain-Boundary Segregation
    Kai WANG,Liu LIU,Tingdong XU,Xuedong DONG
    Acta Metall Sin, 2017, 53 (3): 345-350.  DOI: 10.11900/0412.1961.2016.00364
    Abstract   HTML   PDF (6096KB) ( 536 )

    Almost all ductile metals and alloys have a ductility minimum in the intermediate temperature range at about from 0.5 to 0.8 melt point, with an intergranular fracture mode l (intermediate temperature brittleness, ITB, or intermediate temperature ductility minimum, ITDM). That was found in Ni-based alloys, Fe-based alloys, Co-based alloys, Ti-based alloys, intermetallic compounds and Al-Mg alloys. One of the problems specific to the continuous casting of steels is transverse cracking, which is induced by the ITB of steel, called as hot ductility. The mechanisms suggested are mostly related to the especial properties such as ferrite mechanism for steels and precipitates mechanism at grain-boundaries. It is clear that the ferrite mechanism cannot clarify the ITB of austenitic steels and the precipitates mechanism cannot clarify that of metals and alloys which have no precipitates at grain-boundaries. In this work, based on the prior works for single-phase and phase transition alloys, the mechanism of hot-ductility for 2.25Cr1Mo alloy was analyzed by using Gleeble machine and Auger spectroscopy (AES). The results show the ductility minimum near 850 ℃ corresponds to the maximum concentration of the impurity sulfur at grain boundaries. And the hot ductility of 2.25Cr1Mo alloy can be explained reasonably by non-equilibrium grain-boundary segregation of sulfur.

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    Effect of Sb-Rich Intermetallic Phase on the CorrosionResistance of Zn Alloy in Near-Neutral and Acidic Solutions
    Xiuling SHANG,Bo ZHANG,Wei KE
    Acta Metall Sin, 2017, 53 (3): 351-357.  DOI: 10.11900/0412.1961.2016.00419
    Abstract   HTML   PDF (6518KB) ( 689 )

    In the process of hot-dip galvanizing, some beneficial alloying elements are deliberately added to the molten Zn bath, in order to improve the coating properties, such as formability and corrosion resistance. Sb is one of the interesting alloying additions to the Zn bath, as it can decrease the viscosity and the surface tension of the molten Zn, contributing to producing a uniform Zn coating. Due to the low solid solubility of Sb in molten Zn at galvanising temperature, Sb-rich intermetallic particles were always found in the galvanized layers. The presence of Sb-rich phases may affect the structural properties and corrosion performance of galvanized coating. In the literature, it was reported that small addition of Sb has no significant effect on the structure and growth of galvanized layers, but a higher amount (>1%, mass fraction) of Sb can promote the dendritic solidification of Zn. In order to understand the mechanism of Sb addition on the structure and growth of galvanized coating, it is essential to identify the crystal structure of Sb-rich phases. It was reported that the Sb-rich phases found in the η layer of a galvanized coating corresponds to the electron diffraction patterns of Sb2Zn3. However, some researchers hold that the Sb2Zn3 compound does not exist at room temperature, since it can transform to Sb3Zn4 and Zn at some elevated temperature. Consequently, in this work, the structure of Sb-rich intermetallic phase in the Zn-1.2Sb (1.2%Sb) alloy has been investigated by SEM and TEM. SEM/EDS showed that Sb is present in the form of Sb-rich intermatallic phase and there is no detectable Sb in the Zn solid solution. Transmission electron diffractions analysis and EDS results indicated that the composition of Sb-rich intermatallic phases is close to that of Sb2Zn3, whereas the structure is totally different from the latter. The corrosion resistance of Zn-1.2Sb alloy has been analysed by electrochemcial polarization measurements in the different solutions. The analysed results showed that the Sb-rich phase has no obvious effect on the oxygen reduction reaction, in the aerated 0.1 mol/L NaCl (pH=6.5) solution. However, the Sb-rich phase can promote the hydrogen evolution reaction, in the deaerated acidic solution (0.1 mol/L NaCl, pH=3). Corrosion pits were found in the Zn matrix around the Sb-rich phases by SEM observations, which indicate that Zn has higher activity than Zn-Sb phase.

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    Local Liquation Phenomenon and Its Effect on Mechanical Properties of Joint in Friction Stir Welded 2219 Al Alloy
    Ju KANG,Suying LIANG,Aiping WU,Quan LI,Guoqing WANG
    Acta Metall Sin, 2017, 53 (3): 358-368.  DOI: 10.11900/0412.1961.2016.00311
    Abstract   HTML   PDF (13969KB) ( 564 )

    Al alloy 2219 (AA2219) exhibits excellent mechanical properties in a wide temperature range from -250 ℃ to 250 °C, indicating great potential for application in aerospace structures. Compared to fusion welding, friction stir welding (FSW) could significantly improve mechanical properties of the AA2219 joints. Since invented by the welding institute (TWI) of UK in 1991, FSW has been treated as a solid-state joining technique by the commercial companies, which has been in an agreement in most scientific researchers. However, recently a controversy that has been raised over the viewpoint that FSW is a strict solid-state process, and some observations of liquation have been reported, especially in the stir zone of friction stir spot welding (FSSW) joint. However, the phenomenon of liquation in FSW AA2219 joints has not been reported previously. Therefore, the aim of this work is to reveal the evidence of local liquation during FSW AA2219-T8 and its effect on mechanical properties of the joints. In this work, AA2219-T8 plates (8 mm thick) were friction stir welded at a welding speed of 180 mm/min and a rotation speed of 800 r/min using a welding tool with threaded pin. Heat treatment and thermal simulation experiments were carried out to contrast the characteristics of the local liquation regions. A Vickers microhardness testing machine and an in situ SEM imaging tensile test facility were employed to study the effect of local liquation on mechanical properties of the joints. The results showed that the microstructures in the local liquation regions were divorced eutectic, and its formation was related to the coupled thermal-mechanical interaction during the FSW process. In the FSW process, the local high temperature led to constitutional liquation. During the cooling period, the semisolid mixtures decomposed into α(Al) matrices and θ (Al2Cu) particles under stir and material flow actions. The liquation regions had a lower value of hardness than the normal regions in the nugget zone (NZ), making the liquidation region susceptible to cracks initiation and decreasing the ultimate tensile strength and elongation for a local liquation region contained NZ sample. However, the negative effect of local liquation regions on the mechanical properties of the FSW AA2219-T8 joint was less than that of the thermo-mechanically affected zone (TMAZ), since the local liquation regions were only localized and tiny fractions being in the NZ, whereas the TMAZ was whole softened.

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    Structure-Property Correlation of High Fe-ContentFe-B-Si-Hf Bulk Glassy Alloys
    Yaoxiang GENG,Zhijie ZHANG,Yingmin WANG,Jianbing QIANG,Chuang DONG,Haibin WANG,Ojied TEGUS
    Acta Metall Sin, 2017, 53 (3): 369-375.  DOI: 10.11900/0412.1961.2016.00281
    Abstract   HTML   PDF (2006KB) ( 486 )

    Fe-based amorphous alloys are well known for their good magnetic properties. But these alloys were only prepared into ribbon form in early times due to their insufficient glass-forming abilities (GFAs). After first synthesized of Fe-(Al, Ga)-P-C-B bulk glassy alloy, many Fe-based bulk metallic glasses (BMGs) were synthesized. Compared with amorphous alloy ribbons, the GFA of these alloys was significantly improved, but the saturation magnetization (Bs) was less than 1.5 T. To achieve higher Bs in Fe-based amorphous alloys, the Fe content should be maximized and the metalloid and alloying elements contents should be minimized, but it makes glass formation difficult. It is difficult to reveal the effect mechanism of Fe atoms in high Fe-content amorphous alloys, due to the complexity of the amorphous structure. The present work focuses on explores the structure-property correlations of high Fe-content Fe-B-Si-Hf multi-component glassy alloys with an amorphous structure model. A series of high Fe-content alloys with the composition of [Si-B2Fe7.7Hf0.3]Fe+Fex (x=0, 1.5, 2, 2.5 and 3) was produced by adding Fe atoms to the ideal cluster formula, which is based on the composition with the best glass-forming ability of [Si-B2Fe7.7Hf0.3]Fe (Fe72.5B16.7Si8.3Hf2.5) for Fe-B-Si-Hf quaternary alloys. Liquid quench, thermal analysis and magnetic measurement results show that the critical rod size for glassy alloys gradually decreases from 2.5 mm to 1 mm as the number of Fe atoms increases from 0 to 2. The [Si-B2Fe7.7Hf0.3]Fe+Fe2 (Fe76.4B14.3Si7.1Hf2.2) bulk glassy alloy has a high saturation magnetization of 1.58 T and a low coercive force of 2.8 A/m. The decreasing of the glass transition temperature, the thermal stability, the glass-forming ability and the Curie temperature with increasing Fe content in Fe-B-Si-Hf glassy alloys was evaluated using a “dual-cluster” ({[Si-B2Fe7.7Hf0.3]+[Fe-Fe14]x/15}Fe) amorphous structure model. The result shows that the [Fe-Fe14] cluster from the α-Fe phase plays an important role in determining the properties change for this series high Fe-content Fe-B-Si-Hf glassy alloys.

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    Growth Mechanism and Photocatalytic Activity of NaNbO3 with Controllable Morphology
    Tingting ZHANG,Yang QI,Gang LIU,Minghua LIU
    Acta Metall Sin, 2017, 53 (3): 376-384.  DOI: 10.11900/0412.1961.2016.00216
    Abstract   HTML   PDF (5739KB) ( 881 )

    Semiconductor photocatalysis for harvasting and utilizaing solar energy to solve worldwide environmental pollution and energy shortage is attracted flourishing interest. A complete understanding of structure-function relationships in well-defined model catalysts is essential to better understanding “real world” photocatalysis as well as rationally design photocatalysts. Well-defined NaNbO3 crystals are successful synthesized via facile hydrothermal method. Systematically characterzation is performed by XRD, Raman, SEM, BET specific surface area analyzer and DRUV-Vis. The results of XRD and Raman show that the as-prepared samples are pure orthorhombic NaNbO3 and NaNbO3 with different morphology possess various mainly exposed facets. On the basis of statistical SEM measurements, it presents that the shape evolution of NaNbO3 is shown to be dependent on the reaction time, from nanowires to a mixture of nanowires and microcubes, and finally to microcubes, and realized the morphology control systhesis of NaNbO3. The possible growth mechanism is proposed combined with previous study, highlighting the crucial role of P123. The photocatalytic performance of the as-prepared NaNbO3 crystals is assessed towards aqueous methyl bule under UV illumination, and compared with that of commercial NaNbO3 powders. DRUV-Vis evidenced that the absorption edge of NaNbO3 nanowires is blue shifted due to quantum size effect. The results show that the photoreactivity is morphology-dependent, with the BET specific surface area normalized reaction rate constants follow the order NaNbO3 nanowires> NaNbO3 microcubes > commercial NaNbO3. The exposed facets play a crucial role in determining the observed photocatalytic activity.

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