Strted in 1985 Monthly
ISSN 1005-0302
CN 21-1315/TG
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Synergistic effect of organic and inorganic nano fillers on the dielectric and mechanical properties of epoxy composites
Khan Muhammad, A. Khurram Aqeel, Li Tiehu, Zhao Tingkai, Subhani T., Gul I.H., Ali Zafar, Patel Vivek
J. Mater. Sci. Technol.    2018, 34 (12): 2424-2430.   DOI: 10.1016/j.jmst.2018.06.014
Abstract   HTML PDF (2111KB)  

Titanium oxide TiO2/epoxy and TiO2 with detonation nano-diamond (DND)/epoxy nanocomposites were prepared by using ultrasonication method. TiO2 and DND particles as reinforcement species and epoxy as matrix were used to produce nanocomposites. The addition of DND particles into TiO2/epoxy composite improved the dielectric and mechanical properties of nanocomposites in significant amount. The dielectric properties of TiO2-DND/epoxy nanocomposite demonstrated increase in permittivity and conductivity after addition of the DND particles. The maximum and minimum reflection losses of TiO2-DND/epoxy nanocomposite for 0.6 and 0.2 wt% DND loading were detected at -14.5 and -1.3 dB, respectively. The flexural and tensile strength of TiO2-DND/epoxy nanocomposites with the addition of 0.4 wt% DNDs were enhanced to 220% and 223%, respectively. Additionally, the energy to break and percent break strain were 3.9 J and 3.86, respectively for 0.4 wt% DND loading in TiO2-DND/epoxy nanocomposite. Therefore, the present work findings claim that DND particles are well suitable to enrich the dispersion of TiO2 nanoparticles in epoxy matrix, which develops a strong load transfer interface between the nanoparticles and epoxy matrix and consequently leads to superior properties.

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Effect of the simultaneous application of a high static magnetic field and a low alternating current on grain structure and grain boundary of pure aluminum
Li Chengshuai, Hu Shaodong, Ren Zhongming, Fautrelle Yves, Li Xi
J. Mater. Sci. Technol.    2018, 34 (12): 2431-2438.   DOI: 10.1016/j.jmst.2018.04.013
Abstract   HTML PDF (4309KB)  

Effect of the simultaneous application of a high static magnetic field and a low alternating electric current on the solidification structure of pure aluminum has been investigated. Results show that the refinement of the solidification structure is enhanced by the electric current under a certain magnetic field. However, when the magnetic field intensity exceeds a certain value, the refinement is impaired under a certain electric current. The observation by electron backscattered diffraction (EBSD) shows the complex fields have led to the increase of the low angle boundaries with the refinement. Moreover, the application of the static gradient magnetic field is capable of modifying the distribution of the refined grains. The above results may be attributed to the formation of the cavities during the electromagnetic vibration process and the high magnetic field.

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Hot deformation characteristics and hot working window of as-cast large-tonnage GH3535 superalloy ingot
Wang Yao, Wang Junsong, Dong Jiasheng, Li Aimin, Li Zhijun, Xie Guang, Loua Langhong
J. Mater. Sci. Technol.    2018, 34 (12): 2439-2446.   DOI: 10.1016/j.jmst.2018.04.001
Abstract   HTML PDF (3166KB)  

Deformation characteristics and range of optimized hot working parameters of a 6.5 tons GH3535 superalloy ingot with an average columnar grain size of over 1?mm in diameter were investigated. Axial compression experiments were performed in temperature range of 900-1240?°C and strain rate range of 0.001-30?s-1 at a total strain of 0.8. The hot deformation activation energy of the experimental GH3535 alloy is calculated to be 483.22?kJ/mol. Furthermore, the deformation constitutive equation is established by the peak stresses obtained from the stress-strain curves under various conditions. The hot working window of the alloy ingot at a strain of 0.8 can be preliminarily discussed based on the deformed microstructures and processing maps. The optimized hot working window was thus determined at the strain of 0.95 for 6.5 tons GH3535 alloy ingot by the supplementary compression tests. A large-size GH3535 superalloy ring with a dimension of Φ3010?mm?×?410?mm was ultimately manufactured.

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Exopolysaccharide produced by Vibrio neocaledonicus sp. as a green corrosion inhibitor: Production and structural characterization
Moradi Masoumeh, Song Zhenlun, Xiao Tao
J. Mater. Sci. Technol.    2018, 34 (12): 2447-2457.   DOI: 10.1016/j.jmst.2018.05.019
Abstract   HTML PDF (3307KB)  

An exopolysaccharide substances produced by Vibrio neocaledonicus sp. was introduced as a novel green inhibitor against the corrosion of carbon steel in artificial seawater and acidic media. The produced extracellular polymeric substance (EPS) is heterogeneous with composition of polysaccharides, nucleic acids and protein and average molecular weight of 29,572 Da. Adsorption of EPS on the metal surfaces and formation of Fe-EPS complexes acted as a barrier to prevent the oxygen penetration and hindered anodic and cathodic reactions. The inhibitory effect increases with increasing EPS concentration and exposure time. The highest corrosion inhibitory effect (95.1%) was observed for 10 g/L of EPS after 5 days of exposure in seawater. This is the highest inhibitory effect ever been reported by EPSs. While, the optimum concentration of EPS with the highest inhibition efficiency in 1 N H2SO4 was 1000 ppm. The influence of different parameters, such as initial pH, growth phase, various nitrogen and carbon sources on the production of EPS and its corrosion inhibitory effect were also investigated. According to results, the optimum culture medium for EPS production is contained artificial seawater including 5% mannitol as carbon source and 0.1% (NH4)2SO4 as nitrogen source at pH = 8. This medium could produce 22.24 g/L EPS during 3 days’ incubation at 30 °C. The corrosion inhibitory efficiency of obtained EPS was 95.97%.

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Introduction of porous structure: A feasible and promising method for improving thermoelectric performance of Bi2Te3 based bulks
Hu Jie, Fan Xi’An, Jiang Chengpeng, Feng Bo, Xiang Qiusheng, Li Guangqiang, He Zhu, Li Yawei
J. Mater. Sci. Technol.    2018, 34 (12): 2458-2463.   DOI: 10.1016/j.jmst.2018.05.010
Abstract   HTML PDF (1841KB)  

The porous p-type Bi0.4Sb1.6Te3 bulks containing irregularly and randomly oriented pores were obtained by artificially controlling the relative density of sintered samples during resistance pressing sintering process. It is demonstrated that the thermoelectric performances are significantly affected by the porous structure, especially for the electrical and thermal conductivity due to the enhanced carrier scattering and phonon scattering. The increasing porosity resulted in the obvious decrease in electrical and thermal conductivity, and little change in Seebeck coefficients. It is encouraging that the reduction of thermal conductivity can compensate for the deterioration of electrical performance, leading to the enhancement in thermoelectric figure of merit (ZT). The maximum ZT value of 1.0 was obtained for the sample with a relative density of 90% at 333?K. Unfortunately, the increase in porosity also brought in obvious degradations in Vickers hardness from 51.71 to 27.74?HV. It is worth mentioning that although the Vickers hardness of the sample with a relative density of 90% decreased to 40.12?HV, it was still about twice as high as that of the zone melting sample (21.25?HV). To summarize, introducing pores structure into bulks properly not only enhances the ZT value of Bi2Te3 based alloys, but also reduces the use of raw materials and saves production cost.

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Corrosion protection of waterborne epoxy coatings containing mussel-inspired adhesive polymers based on polyaspartamide derivatives on carbon steel
Yang Mingliang, Wu Jianhua, Fang Daqing, Li Bo, Yang Yang
J. Mater. Sci. Technol.    2018, 34 (12): 2464-2471.   DOI: 10.1016/j.jmst.2018.05.009
Abstract   HTML PDF (2514KB)  

A novel mussel-inspired adhesive polymer (PHEA-DOPA) containing the 3,4-dihydroxyphenylalanine (DOPA) functional group based on polyaspartamide derivatives was synthesized. The corrosion protection of the waterborne epoxy coatings containing the adhesive polymers was investigated by electrochemical impedance spectroscopy (EIS). The results indicated that the PHEA-DOPA could improve the corrosion resistance of the waterborne epoxy coating. The corrosion products were also analyzed by Raman microspectroscopy (RM), indicating the formation of the insoluble DOPA-Fe complexes on the carbon steel surface. These complexes simultaneously acting as a passivating layer, can inhibit the process of corrosion at the metal-solution interface. The differential scanning calorimeter (DSC) measurement indicated that PHEA-DOPA can increase the crosslinking density of coating. The effect of O2 on the protective mechanism of the PHEA-DOPA coating in a 3.5% NaCl solution was also evaluated by EIS. The results indicated that the barrier effect was significantly improved under aerated conditions because DOPA was oxidized to DOPA-quinone (Dq) by O2, which triggered the reaction with Fe ions that were released from the surface of the carbon steel. This led to more compact coatings.

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Significant effect of as-cast microstructure on texture evolution and magnetic properties of strip cast non-oriented silicon steel
Jiao Haitao, Xu Yunbo, Qiu Wenzheng, Xu Haijie, Misra R.D.K., Du Yifeng, Li Jianping, Wang Guodong
J. Mater. Sci. Technol.    2018, 34 (12): 2472-2479.   DOI: 10.1016/j.jmst.2018.05.007
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In this study, two types of as-cast microstructure produced by strip casting were cold rolled and annealed to investigate the effect of initial microstructure on the textural evolution and magnetic properties of non-oriented silicon steel. The results indicated that the cold-rolled sheets of coarse-grained strip with pronounced {100} components exhibited stronger λ fiber (〈100〉//ND) and weaker γ fiber (〈111〉//ND) texture as composed to the fine-grained strip with strong Goss ({110}〈001〉) texture. After annealing, the former was dominated by η fiber (〈001〉//RD) texture with a peak at {110}〈001〉 orientation, while the latter consisted of strong {111}〈112〉 and relatively weak {110}〈001〉 texture. In addition, a number of precipitates of size ~30-150?nm restricted the grain growth during annealing, resulting in recrystallization of grain size of ~46?μm in the coarse-grained specimen and ~41?μm in the fine-grained specimen. Ultimately, higher magnetic induction (~1.72?T) and lower core loss (~4.04?W/kg) were obtained in the final annealed sheets of coarse-grained strip with strong {100} texture.

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Microbial corrosion resistance of a novel Cu-bearing pipeline steel
Shi Xianbo, Yan Wei, Xu Dake, Yan Maocheng, Yang Chunguang, Shan Yiyin, Yang Ke
J. Mater. Sci. Technol.    2018, 34 (12): 2480-2491.   DOI: 10.1016/j.jmst.2018.05.020
Abstract   HTML PDF (6264KB)  

Microbiologically influenced corrosion (MIC) is becoming a serious problem for buried pipelines. Developing environmentally friendly strategies for MIC control is increasingly urgent in oil/gas pipeline industry. Copper (Cu) in steels can not only provide aging precipitation strengthening, but also kill bacterium, offering a special biofunction to steels. Based on the chemical composition of traditional X80 pipeline steel, two Cu-bearing pipeline steels (1% Cu and 2% Cu) were fabricated in this study. The microstructure, mechanical properties and antibacterial property against sulphate-reducing bacteria (SRB) and Pseudomonas aeruginosa (P. aeruginosa) were studied. It was found that the novel pipeline steel alloyed by 1%Cu exhibited acicular ferrite microstructure with nano-sized Cu-rich precipitates distribution in the matrix, resulting in better mechanical properties than the traditional X80 steel, and showed good MIC resistance as well. The pitting corrosion resistance of 1% Cu steel in as-aged condition was significantly better than that of X80 steel. A possible antibacterial mechanism of the Cu-bearing pipeline steel was proposed.

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6.5 wt% Si high silicon steel sheets prepared by composite electrodeposition in magnetic field
Peng Minghu, Zhong Yunbo, Zheng Tianxiang, Fan Lijun, Zhou Junfeng, Ren Weili, Ren Zhongming
J. Mater. Sci. Technol.    2018, 34 (12): 2492-2497.   DOI: 10.1016/j.jmst.2018.06.004
Abstract   HTML PDF (2447KB)  

A new preparation method of near-net-shape 6.5?wt% Si high silicon steel sheets was proposed by combining composite electrodeposition (CED) and diffusion annealing under magnetic field. The obtained sheets were characterized by scanning electron microscopy, energy dispersive spectrometry, analytical balance and a silicon steel material measurement system. The results show that the surface morphology, the elemental distribution, the cathode current efficiency and the silicon content of coatings were obviously influenced by the micro and macro magnetohydrodynamics (MHD) flows under magnetic field. With the effect of magnetic field, the silicon particles content of coatings showed an increasing trend and the diffusion process showed that an approximately uniform 6.5?wt% silicon steel sheet has been successfully obtained. The magnetism measurement showed that the high silicon steel sheet has the lower iron loss, and the iron loss further decreased under magnetic field. The new method proposed in this article, which is more environmentally friendly and low energy consumption, is feasible to prepare high silicon steel sheets.

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Enhanced localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel in high-concentration hydrochloric acid solutions at room temperature
Wang S.G., Sun M., Xu Y.H., Long K., Zhang Z.D.
J. Mater. Sci. Technol.    2018, 34 (12): 2498-2506.   DOI: 10.1016/j.jmst.2018.06.006
Abstract   HTML PDF (2402KB)  

The localized and uniform corrosion resistances of bulk nanocrystalline 304 stainless steel (NC-304SS) produced by severe rolling technique, and its conventional polycrystalline 304 stainless steel (CC-304SS) counterpart, were investigated in high-concentration hydrochloric acid solutions at room temperature. NC-304SS can scarcely suffer from localized corrosion in 4 mol/L and 5 mol/L HCl solutions during 5-day immersion tests, and in 1-3 mol/L HCl solutions during thirty-five-day immersion tests. The corrosion rate of NC-304SS was also less than that of CC-304SS during these immersion tests. The improved localized and uniform corrosion resistances of NC-304SS were explained in terms of the adsorption and chemical activity of Cl- on NC-304SS and CC-304SS characterized by X-ray photoelectron spectroscopy, and the valence electron configurations of NC-304SS and CC-304SS were characterized by ultra-violet photoelectron spectroscopy rather than conventional electrochemical results.

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Mechanical properties and deformation mechanisms of Ti-3Al-5Mo-4.5 V alloy with varied β phase stability
Xue Q., Ma Y.J., Lei J.F., Yang R., Wang C.
J. Mater. Sci. Technol.    2018, 34 (12): 2507-2514.   DOI: 10.1016/j.jmst.2018.04.004
Abstract   HTML PDF (2366KB)  

Evolution of deformation mechanisms and mechanical properties of Ti-3Al-5Mo-4.5 V alloy with different β phase stability have been systematically investigated. β phase stability alteration is achieved through quenching temperature variation from dual α + β field (700 °C) to single β field (880 °C). Tensile tests at ambient temperature show that apparent yield strength of the alloy experiences an abrupt decrease followed by a significant increase from 700 °C to 880 °C. Work hardening behavior is characterized by transition from the initial two-regime feature to the three-stage outlook. Concurrently, the maximum working hardening rate drops from 14000 MPa to 3000 MPa, which is concurrent with the shrinking volume fraction of primary α phase. Detailed discussion about the relationship between deformation mechanisms and β phase stability has been outlined.

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Facile synthesis and superior photocatalytic and electrocatalytic performances of porous B-doped g-C3N4 nanosheets
Yan Qian, Huang Gui-Fang, Li Dong-Feng, Zhang Ming, Pan An-Lian, Huang Wei-Qing
J. Mater. Sci. Technol.    2018, 34 (12): 2515-2520.   DOI: 10.1016/j.jmst.2017.06.018
Abstract   HTML PDF (1344KB)  

As a low-cost visible-light-driven metal-free catalyst, graphitic carbon nitride (g-C3N4) has attracted increasing attention due to its wide applications for solar energy conversion, environmental purification, and organic photosynthesis. In particular, the catalytic performance of g-C3N4 can be easily modulated by modifying morphology, doping, and copolymerization. Simultaneous optimization, however, has little been achieved. Herein, a facile one-pot strategy is developed to synthesize porous B-doped g-C3N4 nanosheets by using H3BO3 and urea as the precursor during thermal polymerization. The resultant B-doped g-C3N4 nanosheets retain the original framework of bulk g-C3N4, while induce prominently enhanced visible light harvesting and narrowing band gap by 0.32 eV compared to pure g-C3N4. Moreover, the adsorption capacity and photodegradation kinetics of methylene blue (MB) under visible light irradiation over B-doped g-C3N4 nanosheets can be improved by 20.5 and 17 times, respectively. The synthesized porous B-doped g-C3N4 nanosheets also exhibit higher activities than pure g-C3N4 as bifunctional electrocatalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). The enhanced catalyst performance of porous B-doped g-C3N4 nanosheets stems from the strong synergistic effect originating from the larger exposed active sites generated by the exfoliation of g-C3N4 into nanosheets and the porous structure, as well as the better conductivity owing to B-doping. This work provides a simple, effective, and robust method for the synthesis of g-C3N4-based nanomaterial with superior properties to meet the needs of various applications.

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One-Pot Room-Temperature Synthesis of Mg Containing MCM-41 Mesoporous Silica for Aldol Reactions
Fujita Shin-Ichiro, Segawa Shinji, Kawashima Kazuki, Nie Xuejing, Erata Tomoki, Arai Masahiko
J. Mater. Sci. Technol.    2018, 34 (12): 2521-2528.   DOI: 10.1016/j.jmst.2016.08.025
Abstract   HTML PDF (1681KB)  

One-pot synthesis of Mg containing MCM-41 (Mg-MCM-41) materials was respectively carried out by a room temperature (RT) method and a hydrothermal (HT) method for aldol condensation of 4-nitrobenzaldehyde and acetone and self-condensation of acetone. The RT method can prepare MCM-41 materials containing large amounts of Mg while maintaining the structural characteristics of MCM-41 even at very low Si/Mg ratios (large Mg loadings), but the HT method cannot. The RT method can also give more active catalysts than the HT method, because the catalysts prepared by the RT method are more basic than those prepared by the HT one. The characterization indicates that Mg atoms in the Mg-MCM-41 prepared by the RT method exist as MgO disperses well on the wall surface of pores, while those in Mg-MCM-41 prepared by the HT method are included in the bulk with a smectite-like structure.

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A review of Fe3O4 thin films: Synthesis, modification and applications
Wang Xiaoyi, Liao Yulong, Zhang Dainan, Wen Tianlong, Zhong Zhiyong
J. Mater. Sci. Technol.    2018, 34 (8): 1259-1272.   DOI: 10.1016/j.jmst.2018.01.011
Abstract   HTML PDF (5757KB)  

Magnetite (Fe3O4) has been used for thousands of years as one of the important magnetic materials. The rapid developments of thin film technology in the past few decades attract the attention of material scientists on the fabrication of magnetite thin films. In this article, we present an overview of recent progress on Fe3O4 thin films. The widely used preparation methods are surveyed, and the effect of substrates is discussed. Specifically the modified Fe3O4 thin films exhibit excellent electrical and magnetic properties compared with the pure films. It is noteworthy that modified Fe3O4 thin films can be put into two categories: (1) doped films, where foreign metal ions substitute iron ions at A or B sites; and (2) hybrid films, where magnetite phases are mixed with other materials. Notably, Fe3O4 thin films show great potentials in many applications such as sensors and batteries. It is expected that the investigations of Fe3O4 thin films will give us some breakthroughs in materials science and technology.

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Structural design of Cr/GLC films for high tribological performance in artificial seawater: Cr/GLC ratio and multilayer structure
Li Lei, Guo Peng, Liu Lin-Lin, Li Xiaowei, Ke Peiling, Wang Aiying
J. Mater. Sci. Technol.    2018, 34 (8): 1273-1280.   DOI: 10.1016/j.jmst.2017.12.002
Abstract   HTML PDF (2996KB)  

In this paper, graphite-like carbon (GLC) films with Cr buffer layer were fabricated by DC magnetron sputtering technique with the thickness ratio of Cr to GLC films varying from 1:2 to 1:20. The effect of Cr/GLC modulation ratio on microstructure, mechanical and tribological properties in artificial seawater was mainly investigated by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), nano-indenter and a reciprocating sliding tribo-meter. The propagation of defects plays an important role in the evolution of delamination, which is critical to wear failure of GLC films in artificial seawater. Designing the proper multilayer structure could inhibit the defects propagation and thus protect the basis material. The multilayer Cr/GLC film with optimized ratio of 1:3 demonstrates a low average friction coefficient of 0.08?±?0.006 and wear rate of (2.3?±?0.3)?×?10-8?mm3/(N?m) in artificial seawater, respectively.

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Microstructure and intergranular stress corrosion cracking susceptibility of a SA508-52M-316L dissimilar metal weld joint in primary water
Dong Lijin, Peng Qunjia, Han En-Hou, Ke Wei, Wang Lei
J. Mater. Sci. Technol.    2018, 34 (8): 1281-1292.   DOI: https://doi.org/10.1016/j.jmst.2017.11.051
Abstract   HTML PDF (7804KB)  

Correlation of microstructure and intergranular stress corrosion cracking (IGSCC) susceptibility for the SA508-52M-316L dissimilar metal weld joint in primary water was investigated by the interrupted slow strain rate tension test following a microstructure characterization. The susceptibility to IGSCC in various regions of the dissimilar metal weld joint was observed to follow the order of Alloy 52 Mb> the heat affected zone of 316L> the dilution zone of Alloy 52 Mw> Alloy 52 Mw weld metal. The chromium-depletion at the grain boundary is the dominant factor causing the high IGSCC susceptibility of Alloy 52 Mb. However, IGSCC initiation in the heat affected zone of 316L is attributed to the increase of residual strain adjacent to the grain boundary. In addition, the decrease of chromium content and increase of residual strain adjacent to the grain boundary increase the IGSCC susceptibility of the dilution zone of Alloy 52 Mw.

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Bimodal TBCs with low thermal conductivity deposited by a powder-suspension co-spray process
Zhang Wei-Wei, Li Guang-Rong, Zhang Qiang, Yang Guan-Jun, Zhang Guo-Wang, Mu Hong-Min
J. Mater. Sci. Technol.    2018, 34 (8): 1293-1304.   DOI: 10.1016/j.jmst.2017.11.052
Abstract   HTML PDF (6716KB)  

Advanced thermal barrier coatings (TBCs) with better thermal barrier performance are required by both advanced gas turbine and air engine. In this work, novel bimodal TBCs with low thermal conductivity were deposited and characterized by a novel co-spray approach with both solid powder and suspension. Experimental and finite element analyses were used to optimize the process parameters to prepare the specific morphology nanostructure features. With a comprehensive understanding on the influence of spraying parameters on the morphology of nano-particles, homogeneous nano-particle heaps with a large aspect ratio were introduced to conventional layered coatings by plasma co-spraying with suspension and solid powder. Co-sprayed bimodal microstructure composite coatings resulted from both wet suspension droplets and molten particle droplets exhibited low thermal conductivity. The thermal conductivity of the composite coating was 1/5 lower than that of the counterpart coatings by conventional plasma spraying with solid powder. This study sheds light to the structural tailoring towards the advanced TBCs with low thermal conductivity.

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Mechanism of improved electromigration reliability using Fe-Ni UBM in wafer level package
Gao Li-Yin, Zhang Hao, Li Cai-Fu, Guo Jingdong, Liu Zhi-Quan
J. Mater. Sci. Technol.    2018, 34 (8): 1305-1314.   DOI: 10.1016/j.jmst.2017.11.046
Abstract   HTML PDF (2488KB)  

Fe-Ni films with compositions of 73 wt% of Ni and 45 wt% of Ni were used as under bump metallization (UBM) in wafer level chip scale package, and their reliability was evaluated through electromigration (EM) test compared with commercial Cu UBM. For Sn3.8Ag0.7Cu(SAC)/Cu solder joints, voids had initiated at Cu cathode after 300 h and typical failures of depletion of Cu cathode and cracks were detected after 1000 h EM. While the SAC/Fe-Ni solder joints kept at a perfect condition without any failures after 1000 h EM. Moreover, the characteristic lifetime calculated by Weibull analysis for Fe-73Ni UBM (2121 h), Fe-45Ni UBM (2340 h) were both over three folds to Cu UBM’s (698 h). The failure modes for Fe-Ni solder joints varied with the different growth behavior of intermetallic compounds (IMCs), which can all be classified as the crack at the cathodic interface between solder and outer IMC layer. The atomic fluxes concerned cathode dissolution and crack initiation were analyzed. When Fe-Ni UBM was added, cathode dissolution was suppressed due to the low diffusivity of IMCs and opposite transferring direction to electron flow of Fe atoms. The smaller EM flux within solder material led a smaller vacancy flux in Fe-Ni solder joints, which can explain the delay of solder voids and cracks as well as the much longer lifetime under EM.

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Effects of scanning speed on microstructure in laser surface-melted single crystal superalloy and theoretical analysis
Wang Guowei, Liang Jingjing, Yang Yanhong, Shi Yu, Zhou Yizhou, Jin Tao, Sun Xiaofeng
J. Mater. Sci. Technol.    2018, 34 (8): 1315-1324.   DOI: 10.1016/j.jmst.2017.11.027
Abstract   HTML PDF (3906KB)  

Scanning speed is a critical parameter for laser process, which can play a key role in the microstructure evolution of laser melting. In the laser melting of single crystal superalloy, the effects of scanning speed were investigated by experimental analysis and computational simulation. The laser was scanning along [71ˉ0] direction on (001) surface in different speeds. Solidification microstructures of dendrites growth direction and the primary dendritic spacing were analyzed by metallograph. Besides, a planar interface during solidification was taken into attention. Experiment results indicated that the primary dendritic spacing and thickness of planar interface decrease with the increase of speed. Through simulation, distribution of dendrites growth velocity and thermal gradient along dendrite growth direction were calculated, and the simulation of dendrites growth direction agreed with the experiment results. Additionally, a constant value was acquired which can be used to predict the primary dendritic spacing. Moreover, according to curve-fitting method and inequality relation, a model was proposed to predict the thickness of planar interface.

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Enhanced resistance of 2205 Cu-bearing duplex stainless steel towards microbiologically influenced corrosion by marine aerobic Pseudomonas aeruginosa biofilms
Xu Dake, Zhou Enze, Zhao Ying, Li Huabing, Liu Zhiyong, Zhang Dawei, Yang Chunguang, Lin Hai, Li Xiaogang, Yang Ke
J. Mater. Sci. Technol.    2018, 34 (8): 1325-1336.   DOI: 10.1016/j.jmst.2017.11.025
Abstract   HTML PDF (4146KB)  

An antibacterial 2205-Cu duplex stainless steel (DSS) was shown to inhibit the formation and growth of corrosive marine biofilms by direct contact with copper-rich phases and the release of Cu2+ ions from the 2205-Cu DSS surface. In this work, the microbiologically influenced corrosion (MIC) resistance of 2205-Cu DSS in the presence of the corrosive marine bacterium Pseudomonas aeruginosa was investigated. The addition of copper improved the mechanical properties such as the yield strength, the tensile strength and the hardness of 2205 DSS. Electrochemical test results from linear polarization resistance (LPR), electrochemical impedance spectroscopy (EIS) and critical pitting temperature (CPT) measurements showed that 2205-Cu DSS possessed a larger polarization resistance (Rp), charge transfer resistance (Rct) and CPT values, indicating the excellent MIC resistance of 2205-Cu DSS against the corrosive P. aeruginosa biofilm. The live/dead staining results and the SEM images of biofilm confirmed the strong antibacterial ability of 2205-Cu DSS. The largest pit depth of 2205-Cu DSS was considerably smaller than that of 2205 DSS after 14 d in the presence of P. aeruginosa (2.2 μm vs 12.5 μm). 2205-Cu DSS possessed a superior MIC resistance to regular 2205 DSS in the presence of aerobic P. aeruginosa.

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High-temperature phase transition behavior and magnetocaloric effect in a sub-rapidly solidified La-Fe-Si plate produced by centrifugal casting
Xu Zhishuai, Dai Yuting, Fang Yue, Luo Zhiping, Han Ke, Song Changjiang, Zhai Qijie, Zheng Hongxing
J. Mater. Sci. Technol.    2018, 34 (8): 1337-1343.   DOI: 10.1016/j.jmst.2017.11.023
Abstract   HTML PDF (3444KB)  

A sub-rapidly solidified LaFe11.6Si1.4 plate was fabricated directly from liquid by centrifugal casting method. The phase constitution, microstructure and magnetocaloric effect were investigated using backscatter scanning electron microscopy, X-ray diffraction, differential scanning calorimetry and physical property measurement system. When the plate was annealed at 1373 K, τ1 phase was formed by a solid-state peritectoid reaction. A first-order magnetic phase transition occurred in the vicinity of 188 K, and the effective refrigeration capacities reached 203.5 J/kg and 209.7 J/kg in plates annealed for 1 h and 3 h, respectively, under a magnetic field change of 3 T. It is suggested that centrifugal casting may become a new approach to prepare high-performance La-Fe-Si magnetocaloric plates for practical applications, which could largely accelerate the formation of τ1 phase during high-temperature heat-treatment process due to refined and homogeneous honeycombed microstructure.

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Bimodal microstructure - A feasible strategy for high-strength and ductile metallic materials
Min Zha, Hong-Min Zhang, Zhi-Yuan Yu, Xuan-He Zhang, Xiang-Tao Meng, Hui-Yuan Wang, Qi-Chuan Jiang
J. Mater. Sci. Technol.    2018, 34 (2): 257-264.   DOI: 10.1016/j.jmst.2017.11.018
Abstract   HTML PDF (685KB)  

Introducing a bimodal grain-size distribution has been demonstrated an efficient strategy for fabricating high-strength and ductile metallic materials, where fine grains provide strength, while coarse grains enable strain hardening and hence decent ductility. Over the last decades, research activities in this area have grown enormously, including interesting results on fcc Cu, Ni and Al-Mg alloys as well as steel and Fe alloys via various thermo-mechanical processing approaches. However, investigations on bimodal Mg and other hcp metals are relatively few. A brief overview of the available approaches based on thermo-mechanical processing technology in producing bimodal microstructure for various metallic materials is given, along with a summary of unusual mechanical properties achievable by bimodality, where focus is placed on the microstructure-mechanical properties and relevant mechanisms. In addition, key factors that influencing bimodal strategies, such as compositions of starting materials and processing parameters, together with the challenges this research area facing, are identified and discussed briefly.

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Accelerated precipitation behavior of cast Mg-Al-Zn alloy by grain refinement
Sang-HoonKim, Jong UnLee, Ye JinKim, Jun HoBae, Bong SunYou, Sung HyukPark
J. Mater. Sci. Technol.    2018, 34 (2): 265-276.   DOI: 10.1016/j.jmst.2017.11.019
Abstract   HTML PDF (729KB)  

This study demonstrates that the precipitation behavior of β-Mg17Al12 phase during aging and the resultant variation in hardness and mechanical properties of cast Mg-Al-Zn alloy are strongly dependent on initial grain size. Grain size reduction accelerates discontinuous precipitation at the early stage of aging treatment by increasing the area fraction of grain boundaries that can act as nucleation sites for discontinuous precipitates (DP), but it does not influence DP growth rate. Grain refinement also prematurely terminates continuous precipitation because the formation of a large number of DP reduces the amount of Al dissolved in the matrix, which is required for the formation of continuous precipitates (CP). This promotion of DP formation and early termination of CP formation significantly decrease the peak-aging time to one-third. The enhanced precipitation behavior also leads to an additional hardness improvement in the aged alloy, along with an increase in hardness owing to grain boundary strengthening by grain refinement. The amount of increase in hardness changes with aging time, which is determined by the variation of three variables with aging time: DP fraction difference between refined and nonrefined alloys, hardness difference between DP and matrix, and matrix hardness difference between the two alloys. Grain refinement improves both tensile strength and ductility of the homogenized alloy owing to grain boundary strengthening and suppression of twinning activation, respectively. However, the loss of ductility after peak-aging treatment is greater in the refined alloy because of the larger amount of DP acting as a crack source in this alloy.

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Influence of size and distribution of W phase on strength and ductility of high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca alloy processed by indirect extrusion
Hansi Jiang, Xiaoguang Qiao, Chao Xu, Shigeharu Kamado, Kun Wu, Mingyi Zheng
J. Mater. Sci. Technol.    2018, 34 (2): 277-283.   DOI: 10.1016/j.jmst.2017.11.022
Abstract   HTML PDF (951KB)  

A high strength Mg-5.1Zn-3.2Y-0.4Zr-0.4Ca (wt%) alloy containing W phase (Mg3Y2Zn3) prepared by permanent mold direct-chill casting is indirectly extruded at 350 °C and 400 °C, respectively. The extruded alloys show bimodal grain structure consisting of fine dynamic recrystallized (DRXed) grains and unrecrystallized coarse regions containing fine W phase and β2? precipitates. The fragmented W phase particles induced by extrusion stimulate nucleation of DRXed grains, leading to the formation of fine DRXed grains, which are mainly distributed near the W particle bands along the extrusion direction. The alloy extruded at 350 °C exhibits yield strength of 373 MPa, ultimate tensile strength of 403 MPa and elongation to failure of 5.1%. While the alloy extruded at 400 °C shows lower yield strength of 332 MPa, ultimate tensile strength of 352 MPa and higher elongation to failure of 12%. The mechanical properties of the as-extruded alloys vary with the distribution and size of W phase. A higher fraction of DRXed grains is obtained due to the homogeneous distribution of micron-scale broken W phase particles in the alloy extruded at 400 °C, which can lead to higher ductility. In addition, the nano-scale dynamic W phase precipitates distributed in the unDRXed regions are refined at lower extrusion temperature. The smaller size of nano-scale W phase precipitates leads to a higher fraction of unDRXed regions which contributes to higher strength of the alloy extruded at 350 °C.

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Heat-treatable Mg-9Al-6Sn-3Zn extrusion alloy
Chaoqiang Liu, Chenglong Liu, Houwen Chen, Jian-Feng Nie
J. Mater. Sci. Technol.    2018, 34 (2): 284-290.   DOI: 10.1016/j.jmst.2017.11.012
Abstract   HTML PDF (462KB)  

Mg-9Al-6Sn-3Zn (wt%) alloy was extruded and heat treated in T5 and T6 conditions, and its mechanical properties and microstructures were investigated. The extruded product can be slightly strengthened by the T5 treatment as a result of sparse and heterogeneous precipitation. Significant increase in strength is achieved by the T6 treatment, and this is mostly attributed to the formation of lamellar discontinuous Mg17Al12 precipitates. The segregation of Al and Zn at grain boundaries is responsible for the discontinuous Mg17Al12 nucleation. The T6-treated alloy exhibits a tensile yield strength of 341 MPa and an ultimate tensile strength of 409 MPa, together with an elongation to fracture of 4%.

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Effect of trace HA on microstructure, mechanical properties and corrosion behavior of Mg-2Zn-0.5Sr alloy
Jian-Xing Li, Yuan Zhang, Jing-Yuan Li, Jian-Xin Xie
J. Mater. Sci. Technol.    2018, 34 (2): 299-310.   DOI: 10.1016/j.jmst.2017.06.013
Abstract   HTML PDF (898KB)  

Effect of the addition of trace HA particles into Mg-2Zn-0.5Sr on microstructure, mechanical properties, and bio-corrosion behavior was investigated in comparison with pure Mg. Microstructures of the Mg-2Zn-0.5Sr-xHA composites (x = 0, 0.1 and 0.3 wt%) were characterized by optical microscopy (OM), scanning electron microscopy (SEM) equipped with energy dispersion spectroscopy (EDS) and X-ray diffraction (XRD). Results of tensile tests at room temperature show that yield strength (YS) of Mg-2Zn-0.5Sr/HA composites increases significantly, but the ultimate tensile strength (UTS) and elongation decrease with the addition of HA particles from 0 up to 0.3 wt%. Bio-corrosion behavior was investigated by immersion tests and electrochemical tests. Electrochemical tests show that corrosion potential (Ecorr) of Mg-2Zn-0.5Sr/HA composites significantly shifts toward nobler direction from -1724 to -1660 mVSCE and the corrosion current density decreases from 479.8 to 280.8 μA cm-2 with the addition of HA particles. Immersion tests show that average corrosion rate of Mg-2Zn-0.5Sr/HA composites decreases from 11.7 to 9.1 mm/year with the addition of HA particles from 0 wt% up to 0.3 wt%. Both microstructure and mechanical properties can be attributed to grain refinement and mechanical bonding of HA particles with second phases and α-Mg matrix. Bio-corrosion behavior can be attributed to grain refinement and the formation of a stable and dense CaHPO4 protective film due to the adsorption of Ca2+ on HA particles. Our analysis shows that the Mg-2Zn-0.5Sr/0.3HA with good strength and corrosion resistance can be a good material candidate for biomedical applications.

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Nanoscale deformation of multiaxially forged ultrafine-grained Mg-2Zn-2Gd alloy with high strength-high ductility combination and comparison with the coarse-grained counterpart
counterpartK. Li, V.S.Y. Injeti, P. Trivedi, L.E. Murr, R.D.K. Misra
J. Mater. Sci. Technol.    2018, 34 (2): 311-316.   DOI: 10.1016/j.jmst.2017.07.023
Abstract   HTML PDF (269KB)  

Cold processing of magnesium (Mg) alloys is a challenge because Mg has a hexagonal close-packed (HCP) lattice with limited slip systems, which makes it difficult to plastically deform at low temperature. To address this challenge, a combination of annealing of as-cast alloy and multi-axial forging was adopted to obtain isotropic ultrafine-grained (UFG) structure in a lean Mg-2Zn-2Gd alloy with high strength (yield strength: ~227 MPa)-high ductility (% elongation: ~30%) combination. This combination of strength and ductility is excellent for the lean alloy, enabling an understanding of deformation processes in a formable high strength Mg-rare earth alloy. The nanoscale deformation behavior was studied via nanoindentation and electron microscopy, and the behavior was compared with its low strength (yield strength: ~46 MPa) - low ductility (% elongation: ~7%) coarse-grained (CG) counterpart. In the UFG alloy, extensive dislocation slip was an active deformation mechanism, while in the CG alloy, mechanical twinning occurred. The differences in the deformation mechanisms of UFG and CG alloys were reflected in the discrete burst in the load-displacement plots. The deformation of Mg-2Zn-2Gd alloys was significantly influenced by the grain structure, such that there was change in the deformation mechanism from dislocation slip (non-basal slip) to nanoscale twins in the CG structure. The high plasticity of UFG Mg alloy involved high dislocation activity and change in activation volume.

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Microstructure and mechanical properties of Mg-5Li-1Al sheets prepared by accumulative roll bonding
bondingLegan Hou, Tianzi Wang, Ruizhi Wu, Jinghuai Zhang, Milin Zhang, Anping Dong, Baode Sun, Sergey Betsofen, Boris Krit
J. Mater. Sci. Technol.    2018, 34 (2): 317-323.   DOI: 10.1016/j.jmst.2017.02.005
Abstract   HTML PDF (756KB)  

Ultrafine-grain and high-strength Mg-5Li-1Al sheets were prepared by accumulative roll bonding (ARB) process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated.Results show that, during ARB process, the evolution of deformation mechanism of t Mg-5Li-1Al alloy is as follows: twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization (DRX). The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.

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Grain Size Distribution and Interfacial Heat Transfer Coefficient during Solidification of Magnesium Alloys Using High Pressure Die Casting Process
P. Sharifi, J. Jamali, K. Sadayappan, J.T. Wood
J. Mater. Sci. Technol.    2018, 34 (2): 324-334.   DOI: 10.1016/j.jmst.2016.09.004
Abstract   HTML PDF (495KB)  

The objective of this study is to predict grain size and heat transfer coefficient at the metal-die interface during high pressure die casting process and solidification of the magnesium alloy AM60. Multiple runs of the commercial casting simulation package, ProCAST?, were used to model the mold filling and solidification events employing a range of interfacial heat transfer coefficient values. The simulation results were used to estimate the centerline cooling curve at various locations through the casting. The centerline cooling curves, together with the die temperature and the thermodynamic properties of the alloy, were then used as inputs to compute the solution to the Stefan problem of a moving phase boundary, thereby providing the through-thickness cooling curves at each chosen location of the casting. Finally, the local cooling rate was used to calculate the resulting grain size via previously established relationships. The effects of die temperature, filling time and heat transfer coefficient on the grain structure in skin region and core region were quantitatively characterized. It was observed that the grain size of skin region strongly depends on above three factors whereas the grain size of core region shows dependence on the interfacial heat transfer coefficient and thickness of the samples. The grain size distribution from surface to center was estimated from the relationship between grain size and the predicted cooling rate. The prediction of grain size matches well with experimental results. A comparison of the predicted and experimentally determined grain size profiles enables the determination of the apparent interfacial heat transfer coefficient for different locations.

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Influence of electric field on the quenched-in vacancy and solute clustering during early stage ageing of Al-Cu alloy
Shang Fu, Ying Zhang, Huiqun Liu, Danqing Yi, Bin Wang, Yong Jiang, Zhiquan Chen, Ning Qi
J. Mater. Sci. Technol.    2018, 34 (2): 335-343.   DOI: 10.1016/j.jmst.2017.07.020
Abstract   HTML PDF (456KB)  

The effects of electric field on the evolution of excess quenched-in vacancy as well as solute clustering in Al-4wt%Cu alloy, and on the vacancy migration and formation enthalpy of pure aluminum were investigated, using positron annihilation lifetime spectroscopy, high-angle annular dark-field scanning transmission electron microscopy, transmission electron microscopy, hardness measurement and four-probe electrical resistivity measurement. The results showed that the electric field improved age hardening response obviously and postponed the decay of excess vacancies for 30 min during the early stage ageing of Al-4wt%Cu alloy. A large number of 2-4 nm GP zones with dense distribution were observed after 1 min ageing with an electric field applied. The electric field-assisted-aged sample owned a lower coarsening rate of GP zone, which was about three fifths of that in the aged sample without an electric field, from 1 min to 120 min ageing. The electric field contributed 8% increase of the vacancy migration enthalpy (0.663 ± 0.021 eV) of pure Al, comparing with that (0.611 ± 0.023 eV) of pure Al without an electric field. The increase of vacancy migration enthalpy, induced by the electric field, was responsible for the difference on evolution of quenched-in vacancy, rapid solute clustering and age hardening improvement during the early stage ageing of Al-4wt%Cu alloy.

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CN: 21-1315/TG
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