Strted in 1985 Monthly
ISSN 1005-0302
CN 21-1315/TG
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A review of Fe3O4 thin films: Synthesis, modification and applications
Xiaoyi Wang, Yulong Liao, Dainan Zhang, Tianlong Wen, Zhiyong Zhong
J. Mater. Sci. Technol.    2018, 34 (8): 1259-1272.   DOI: 10.1016/j.jmst.2018.01.011
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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
Lei Li, Peng Guo, Lin-Lin Liu, Xiaowei Li, Peiling Ke, Aiying Wang
J. Mater. Sci. Technol.    2018, 34 (8): 1273-1280.   DOI: 10.1016/j.jmst.2017.12.002
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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
Lijin Dong, Qunjia Peng, En-Hou Han, Wei Ke, Lei Wang
J. Mater. Sci. Technol.    2018, 34 (8): 1281-1292.   DOI: 10.1016/j.jmst.2017.11.051
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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
Wei-Wei Zhang, Guang-Rong Li, Qiang Zhang, Guan-Jun Yang, Guo-Wang Zhang, Hong-Min Mu
J. Mater. Sci. Technol.    2018, 34 (8): 1293-1304.   DOI: 10.1016/j.jmst.2017.11.052
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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
Li-Yin Gao, Hao Zhang, Cai-Fu Li, Jingdong Guo, Zhi-Quan Liu
J. Mater. Sci. Technol.    2018, 34 (8): 1305-1314.   DOI: 10.1016/j.jmst.2017.11.046
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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
Guowei Wang, Jingjing Liang, Yanhong Yang, Yu Shi, Yizhou Zhou, Tao Jin, Xiaofeng Sun
J. Mater. Sci. Technol.    2018, 34 (8): 1315-1324.   DOI: 10.1016/j.jmst.2017.11.027
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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
Dake Xu, Enze Zhou, Ying Zhao, Huabing Li, Zhiyong Liu, Dawei Zhang, Chunguang Yang, Hai Lin, Xiaogang Li, Ke Yang
J. Mater. Sci. Technol.    2018, 34 (8): 1325-1336.   DOI: 10.1016/j.jmst.2017.11.025
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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
Zhishuai Xu, Yuting Dai, Yue Fang, Zhiping Luo, Ke Han, Changjiang Song, Qijie Zhai, Hongxing Zheng
J. Mater. Sci. Technol.    2018, 34 (8): 1337-1343.   DOI: 10.1016/j.jmst.2017.11.023
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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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Atom probe tomographic observation of hydrogen trapping at carbides/ferrite interfaces for a high strength steel
Y.F. Jiang, B. Zhang, Y. Zhou, J.Q. Wang, E.-H. Han, W. Ke
J. Mater. Sci. Technol.    2018, 34 (8): 1344-1348.   DOI: 10.1016/j.jmst.2017.11.008
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A three-dimensional atom probe (3DAP) technique has been used to characterize the hydrogen distribution on carbides for a high strength AISI 4140 steel. Direct evidence of H atoms trapped at the carbide/ferrite interfaces has been revealed by 3DAP mapping. Hydrogen is mainly trapped on carbide/ferrite interfaces along the grain boundaries. Slow strain rate tensile (SSRT) testing shows that the AISI 4140 steel is highly sensitive to hydrogen embrittlement. The corresponding fractographic morphologies of hydrogen charged specimen exhibit brittle fracture feature. Combined with these results, it is proposed that the hydrogen trapping sites present in the grain boundaries are responsible for the hydrogen-induced intergranular fracture of AISI 4140. The direct observation of hydrogen distribution contributes to a better understanding of the mechanism of hydrogen embrittlement.

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Effect of residual dissolved oxygen on the corrosion behavior of low carbon steel in 0.1 M NaHCO3 solution
Fang Xue, Xin Wei, Junhua Dong, Ini-Ibehe Nabuk Etim, Changgang Wang, Wei Ke
J. Mater. Sci. Technol.    2018, 34 (8): 1349-1358.   DOI: 10.1016/j.jmst.2017.11.004
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The effect of residual dissolved oxygen (DO) on the corrosion behavior of carbon steel in 0.1 M NaHCO3 solution was investigated by electrochemical measurements, corrosion mass loss test, scanning electron microscopy (SEM) and X-ray diffraction (XRD). In the initial immersion stage, the increase of the dissolved oxygen concentration led to the change of from a reductive state of active dissolution to an oxidizing state of pseudo passivation in low carbon steel. While in the final stage, all the steels transformed into the steady state of pseudo passivation. In the anaerobic solution, the formation of α-FeOOH was attributed to the chemical oxidization of the ferrous corrosion products and the final cathodic process only included the reduction of α-FeOOH, while in the aerobic solution, it included the reduction of oxygen and α-FeOOH simultaneously. As the main corrosion products, the content of α-FeOOH was increased while that of Fe6(OH)12CO3 was decreased with increasing concentration of dissolved oxygen. The total corrosion mass loss of the steel was promoted with the increase of dissolved oxygen concentration.

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An intrinsic correlation between driving force and energy barrier upon grain boundary migration
Bo Lin, Kang Wang, Feng Liu, Yaohe Zhou
J. Mater. Sci. Technol.    2018, 34 (8): 1359-1363.   DOI: 10.1016/j.jmst.2017.11.002
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The migration of grain boundary (GB), which plays a key role in the microstructural evolution of polycrystalline materials, remains mysterious due to the unknown relationship between GB mobility associated with specific geometry and external conditions (e.g. temperature, stress, etc., hence the thermodynamic driving force). Combining the rate equation of GB migration with molecular dynamics simulations, an intrinsic correlation between driving force and energy barrier for the migration of various types of GBs (i.e. twist, symmetric tilt, asymmetric tilt, and mixed twist-tilt) is herein explored, showing the decrease of energy barrier with increasing thermodynamic driving force.

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Orientation dependence of deformation twinning in Cu single crystals
S.S. Cai, ,
J. Mater. Sci. Technol.    2018, 34 (8): 1364-1370.   DOI: 10.1016/j.jmst.2017.10.004
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Cu single crystals were subjected to dynamic compression plastic deformation to investigate orientation-dependent twinning. The experimental results showed that twinning is closely related to the ratio of the maximum Schmid factor for twinning partial (mT) to the maximum Schmid factor for perfect dislocation (mS), i.e., mT/mS, rather than mT. The twin volume fraction VT increases with the mT/mS value and the most favorable orientation for twinning has the maximum mT/mS value (1.15). The relationships of mT/mS with both effective stacking fault energy γeff and threshold stress for twinning τT were established for understanding orientation-dependent twinning. Further insights into the orientation-dependent twinning and guidance for developing bulk high density nanotwinned materials are provided.

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Polysaccharide-based magnetically responsive polyelectrolyte hydrogels for tissue engineering applications
Kummara Madhusudana Rao, Anuj Kumar, Sung Soo Han
J. Mater. Sci. Technol.    2018, 34 (8): 1371-1377.   DOI: 10.1016/j.jmst.2017.10.003
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Polysaccharide-based bionanocomposite hydrogels with functional nanomaterials were used in biomedical applications. Self-organization of xanthan gum and chitosan in the presence of iron oxide magnetic nanoparticles (Fe3O4 MNPs) allowed us to form magnetically responsive polyelectrolyte complex hydrogels (MPECHs) via insitu ionic complexation using D-(+)-glucuronic acid δ-lactone as a green acidifying agent. Characterization confirmed the successful formation of (and structural interactions within) the MPECH and good porous structure. The rheological behavior and compressive properties of the PECH and MPECH were measured. The results indicated that the incorporation of Fe3O4 MNPs into the PECH greatly improved mechanical properties and storage modulus (G'). In vitro cell culture of NIH3T3 fibroblasts on MPECHs showed improvements in cell proliferation and adhesion in an external magnetic field relative to the pristine PECH. The results showed that the newly developed MPECH could potentially be used as a magnetically stimulated system in tissue engineering applications.

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Cobalt(II) coordination polymers as anodes for lithium-ion batteries with enhanced capacity and cycling stability
Yumei Luo, Lixian Sun, Fen Xu, Siyue Wei, Qingyong Wang, Hongliang Peng, Chonglin Chen
J. Mater. Sci. Technol.    2018, 34 (8): 1412-1418.   DOI: 10.1016/j.jmst.2017.11.006
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Coordination polymer Co-btca (H4btca=1,2,4,5-benzenetetracarboxylic acid) was synthesized using a simply hydrothermal method. In particular, the as-prepared Co-btca was applied as an anode material for lithium-ion battery for the first time. Single crystal X-ray diffraction results indicated that the as-prepared Co-btca displayed unique layer structure, which was beneficial to transport Li ions and electrons. Also, owing to the porous structure and appropriate specific surface area, Co-btca electrode delivered a reversible capacity of 801.3mA h/g after 50 cycles at a current density of 200mA/g. The reversible capacity of 773.9mA h/g was maintained after 200 cycles at a current density of 500 mA/g, exhibiting enhanced cycle stability. It also showed improved rate performance, making it a promising anode material and a new choice for lithium-ion batteries.

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Low temperature annealing of metals with electrical wind force effects
Daudi Waryoba, Zahabul Islam, Baoming Wang, Aman Haque
J. Mater. Sci. Technol.    2019, 35 (4): 465-472.   DOI: 10.1016/j.jmst.2018.09.069
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Conventional annealing is a slow, high temperature process that involves heating atoms uniformly, i.e., in both defective and crystalline regions. This study explores an electrical alternative for energy efficiency, where moderate current density is used to generate electron wind force that produces the same outcome as the thermal annealing process. We demonstrate this on a zirconium alloy using in-situ electron back scattered diffraction (EBSD) inside a scanning electron microscope (SEM) and juxtaposing the results with that from thermal annealing. Contrary to common belief that resistive heating is the dominant factor, we show that 5 × 104 A/cm2 current density can anneal the material in less than 15 min at only 135 °C. The resulting microstructure is essentially the same as that obtained with 600 °C processing for 360 min. We propose that unlike temperature, the electron wind force specifically targets the defective regions, which leads to unprecedented time and energy efficiency. This hypothesis was investigated with molecular dynamics simulation that implements mechanical equivalent of electron wind force to provide the atomistic insights on defect annihilation and grain growth.

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Dynamic deformation behavior and microstructural evolution during high-speed rolling of Mg alloy having non-basal texture
Sang-Hoon Kim, Jeong Hun Lee, Chong Soo Lee, Jonghun Yoon, Sung Hyuk Park
J. Mater. Sci. Technol.    2019, 35 (4): 473-482.   DOI: 10.1016/j.jmst.2018.10.010
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The dynamic deformation behaviors and resultant microstructural variations during high-speed rolling (HSR) of a Mg alloy with a non-basal texture are investigated. To this end, AZ31 alloy samples in which the basal poles of most grains are predominantly aligned parallel to the transverse direction (TD) are subjected to hot rolling with different reductions at a rolling speed of 470 m/min. The initial grains with a TD texture are favorable for {10-12} twinning under compression along the normal direction (ND); as a result, {10-12} twins are extensively formed in the material during HSR, and this consequently results in a drastic evolution of texture from the TD texture to the ND texture and a reduction in the grain size. After the initial grains are completely twinned by the {10-12} twinning mechanism, {10-11} contraction twins and {10-11}-{10-12} double twins are formed in the {10-12} twinned grains by further deformation. Since the contraction twins and double twins have crystallographic orientations that are favorable for basal slip during HSR, dislocations easily accumulate in these twins and fine recrystallized grains nucleate in the twins to reduce the increased internal strain energy. Until a rolling reduction of 20%, {10-12} twinning is the main mechanism governing the microstructural change during HSR, and subsequently, the microstructural evolution is dominated by the formation of contraction twins and double twins and the dynamic recrystallization in these twins. With an increase in the rolling reduction, the average grain size and internal strain energy of the high-speed-rolled (HSRed) samples decrease and the basal texture evolves from the TD texture to the ND texture more effectively. As a result, the 80% HSRed sample, which is subjected to a large strain at a high strain rate in a single rolling pass, exhibits a fully recrystallized microstructure consisting of equiaxed fine grains and has an ND basal texture without a TD texture component.

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Effects of calcination temperature and Li+ ions doping on structure and upconversion luminescence properties of TiO2:Ho3+-Yb3+ nanocrystals
Kaishun Zou, Guangzong Dong, Juncheng Liu, Boxu Xu, Danping Wang
J. Mater. Sci. Technol.    2019, 35 (4): 483-490.   DOI: 10.1016/j.jmst.2018.10.018
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Ho3+-Yb3+ co-doped and Ho3+-Yb3+-Li+ tri-doped TiO2 nanocrystals were prepared using the sol-gel method. Effects of the calcination temperature and Li+ ions doping on the structure and upconversion luminescence properties of Ho3+-Yb3+ co-doped TiO2 nanocrystals were investigated. The upconversion luminescence of nanocrystals was enhanced with the reduction of the crystal lattice symmetry and the crystallinity improvement of the matrix, which were facilitated by the calcination temperature change and Li+ ions doping. The lowest lattice symmetry and the best crystallinity of the matrix resulted in the maximum luminescence intensity.

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Predicting recrystallized grain size in friction stir processed 304L stainless steel
M.P. Miles, T.W. Nelson, C. Gunter, F.C. Liu, L. Fourment, T. Mathis
J. Mater. Sci. Technol.    2019, 35 (4): 491-498.   DOI: 10.1016/j.jmst.2018.10.021
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A major dilemma faced in the nuclear industry is repair of stainless steel reactor components that have been exposed to neutron irradiation. When conventional fusion welding is used for repair, intergranular cracks develop in the heat-affected zone (HAZ). Friction stir processing (FSP), which operates at much lower peak temperatures than fusion welding, was studied as a crack repair method for irradiated 304L stainless steel. A numerical simulation of the FSP process in 304L was developed to predict temperatures and recrystallized grain size in the stir zone. The model employed an Eulerian finite element approach, where flow stresses for a large range of strain rates and temperatures inherent in FSP were used as input. Temperature predictions in three locations near the stir zone were accurate to within 4%, while prediction of welding power was accurate to within 5% of experimental measurements. The predicted recrystallized grain sizes ranged from 7.6 to 10.6 μm, while the experimentally measured grains sizes in the same locations ranged from 6.0 to 7.6 μm. The maximum error in predicted recrystallized grain size was about 39%, but the associated stir zone hardness from the predicted grain sizes was only different from the experiment by about 10%.

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Hydrogen embrittlement behavior of Inconel 718 alloy at room temperature
Xinfeng Li, Jin Zhang, Eiji Akiyama, Qinqin Fu, Qizhen Li
J. Mater. Sci. Technol.    2019, 35 (4): 499-502.   DOI: 10.1016/j.jmst.2018.10.002
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Hydrogen embrittlement of Inconel 718 alloy was investigated. Multi-scale observation technique were employed, comprising slow strain rate tensile tests, scanning electron microscopy and transmission electron microscopy analysis. The results demonstrate that hydrogen charging deteriorates mechanical properties of the alloy. Inconel 718 alloy shows partial Portevin-Le Chatelier (PLC) effect at room temperature when hydrogen charging current density is 220 mA cm-2 and 590 mA cm-2. Moreover, plastic deformation features with dislocation cells are detected in hydrogen-induced brittle zone. Thus, it is concluded that dragging effect of hydrogen atoms on dislocations contributes to PLC effect.

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Effect of minor content of Gd on the mechanical and degradable properties of as-cast Mg-2Zn-xGd-0.5Zr alloys
Junxiu Chen, Lili Tan, Xiaoming Yu, Ke Yang
J. Mater. Sci. Technol.    2019, 35 (4): 503-511.   DOI: 10.1016/j.jmst.2018.10.022
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RE-containing Mg alloys used as biodegradable medical implants exhibit good promising application due to their good mechanical properties and degradation resistance. In this work, effect of Gd on the microstructure, mechanical properties and biodegradation of as-cast Mg-2Zn-xGd-0.5Zr alloys was investigated. The results showed that there were mainly α-Mg, I-phase, W-phase and MgZn2 phase in Mg-Zn-Gd-Zr alloys. With increase of the Gd content, the strength of the alloys was enhanced due to the second phase strengthening and grain refinement. The degradation resistance of Mg-2Zn-0.5Zr alloy was increased by adding 0.5-1% Gd due to the uniformly distributed second phases which acted as a barrier to prevent the pitting corrosion. However, increasing Gd content to 2% reduced the degradation resistance of the alloy due to the galvanic corrosion between the matrix and the second phases. The good degradation resistance and mechanical properties of as-cast Mg-2Zn-1Gd-0.5Zr alloy makes it outstanding for biomaterial application.

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Microstructure evolution and interface structure of Al-40 wt% Si composites produced by high-energy ball milling
Yuanyuan Chen, Zhangping Hu, Yifei Xu, Jiangyong Wang, Peter Schützendübe, Yuan Huang, Yongchang Liu, Zumin Wang
J. Mater. Sci. Technol.    2019, 35 (4): 512-519.   DOI: 10.1016/j.jmst.2018.10.005
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High silicon content Al-Si composites with a composition of Al-40 wt% Si were fabricated via a high-energy ball milling method. The microstructure evolution of Al-40 wt% Si milled powders and sintered composites has been thoroughly studied by scanning electron microscopy, X-ray diffraction, energy-dispersive spectrometry and high-resolution transmission electron microscopy. The mechanism of ball milling Al-40 wt% Si powders has been disclosed in detail: fracture mechanism dominating in the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. It has been found that the average particle sizes of mixed Al-Si powders can be refined to the nanoscale, and the crystallite sizes of Al and Si have been reduced to 10 nm and 62 nm upon milling for 2 h-50 h, respectively. The finally formed Al-Si interfaces after ball milling for 50 h are well-cohesive. A dense and homogenous Al-40 wt% Si composite have been achieved by solid-state sintering at 550 °C. The results thus provide an effective support for producing bulk nanostructured Al-Si composites.

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Effect of aging treatment on the microstructures and mechanical properties evolution of 25Cr-20Ni austenitic stainless steel weldments with different Nb contents
Xu Zhang, Dianzhong Li, Yiyi Li, Shanping Lu
J. Mater. Sci. Technol.    2019, 35 (4): 520-529.   DOI: 10.1016/j.jmst.2018.10.017
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The microstructure evolutions and the mechanical properties of the 25Cr-20Ni austenitic stainless steel weld metals with different Nb contents were investigated during the long term aging treatment at 700 °C. M23C6, Nb(C, N), α-Cr phase and Nb-nitride phase (Z phase) were observed in the microstructures of the aged weld metals. The results showed that the α-Cr phase precipitated in the interdendritic regions of the weld metals after being exposed to 700 °C for 500 h and the element Nb accelerated the precipitation of the α-Cr phase significantly. The density of the α-Cr phase decreased with the increase of the distance away from the primary Nb(C, N). Additionally, the α-Cr phase showed a crystallographic relationship with the austenitic matrix, [1$\bar{1}$$\bar{1}$]α-Cr // [1$\bar{1}$0]γ and (01$\bar{1}$)α-Cr // ($\bar{1}$$\bar{1}$1)γ. It was observed that the Z phase precipitated in the periphery of the Nb(C, N) and may replace the Nb(C, N) after long term exposure to high temperature. The transformation of the Nb(C, N) into Z phase suggested that the Z phase had a higher stability than the Nb(C, N) particles at 700 °C for long term aging. The tensile strength of the Nb-bearing weld metal showed a continuous decrease at the initial stage of the aging treatment and then went up slightly with the prolonged aging time. However, the elongations and the impact energies of the weld metals decreased monotonously with the increase of the aging time.

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Crystal structure of Cr4AlB4: A new MAB phase compound discovered in Cr-Al-B system
Haiming Zhang, Fu-zhi Dai, Huimin Xiang, Zhili Zhang, Yanchun Zhou
J. Mater. Sci. Technol.    2019, 35 (4): 530-534.   DOI: 10.1016/j.jmst.2018.10.006
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In this communication, the crystal structure of Cr4AlB4, a new MAB phase compound (where M is a transition metal, A is Al or Si, B is boron) discovered in Cr-Al-B system is reported. This new MAB phase was synthesized from a mixture of CrB and Al powders at 1000 °C and its crystal structure was determined by a combination of X-ray diffraction, first-principles calculations and energy dispersive X-ray spectroscopy (EDS). Cr4AlB4 crystallizes in an orthorhombic structure with Immm space group. The lattice constants are a = 2.9343(6) ?, b = 18.8911(0) ?, c = 2.9733(7) ?, and the atomic positions are Cr1 at 4g (0, 0.2936(5), 0), Cr2 at 4h (0.5, 0.5859(7), 0), Al at 2b (0, 0.5, 0.5), B1 at 4h (0, 0.3839(8), 0.5) and B2 at 4g (0.5, 0.6646(2), 0.5).

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Recent advances in biodegradation controls over Mg alloys for bone fracture management: A review
Ming-Shi Song, Rong-Chang Zeng, Yun-Fei Ding, Rachel W. Li, Mark Easton, Ivan Cole, Nick Birbilis, Xiao-Bo Chen
J. Mater. Sci. Technol.    2019, 35 (4): 535-544.   DOI: 10.1016/j.jmst.2018.10.008
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Magnesium (Mg) alloys possess comparable physical and mechanical properties to bone, making them an outstanding candidate of implant materials for bone fracture treatment. In addition to the excellent biocompatibility, and bioactivity, the engagement of Mg alloys is key for a number of biological functionalities in the human body. The unique biodegradation nature of Mg alloy implants implies that it may not require a secondary removal procedure when the expected supporting tasks accomplish, as they may simply and safely “disappear” over time. Nonetheless, the demonstrated drawback of potentially rapid degradation, is an issue that must be addressed appropriately for Mg implants and is consequently given unique attention in this review article. Herein, the critical criteria and the state-of-the-art strategies for controlling the degradation process of Mg alloys are reported. Furthermore, future developments of biodegradable Mg and its alloys systems with satisfactory specifications for clinical trials and deployment, are discussed. This review aims to provide information to materials scientists and clinical practitioners in the context of developing practical biodegradable Mg alloys.

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Multi-scale study of ductility-dip cracking in nickel-based alloy dissimilar metal weld
Yifeng Li, Jianqiu Wang, En-Hou Han, Wenbo Wu, Hannu H?nninen
J. Mater. Sci. Technol.    2019, 35 (4): 545-559.   DOI: 10.1016/j.jmst.2018.10.023
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A ductility-dip-cracking (DDC)-concentrated zone (DCZ) in a width of about 3 mm was observed adjacent to the AISI 316 L/52 Mw fusion boundary (FB) in 52 Mw. The morphology, microstructure, mechanical and thermal properties and corrosion behavior in simulated primary water of DDC/DCZ were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), 3D X-ray tomography (XRT), 3D atom probe (3DAP), slow strain rate tensile (SSRT) testing and thermal dilatometry. The results indicate that DDCs are random-shaped and disc-like cavities with corrugated structure of inner surface and are parallel in groups along straight high-angle boundaries of columnar grains, ranging from micrometers to millimeters in size. Large-size M23C6 carbides dominate on the grain boundaries rather than MC (M=Nb, Ti), and thus the bonding effect of carbides is absent for the straight grain boundaries. The impurity segregation of O is confirmed for the inner surfaces of DDC. The oxide film formed on the inner surface of DDC (about 50 nm) is approximately twice as thick as that on the matrix (about 25 nm) in simulated primary water. The yield strength, tensile strength and elongation to fracture of 52 Mw-DCZ (400 MPa, 450 MPa and 20 %, respectively) are lower than those of 52 Mw-MZ (460 MPa, 550 MPa and 28 %, respectively). The intrinsic high-restraint weld structure, the additional stress/strain caused by the thermal expansion difference between AISI 316 L and 52 Mw as well as the detrimental carbide precipitation and the resulting grain boundary structure all add up to cause the occurrence of DCZ in the dissimilar metal weld.

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A novel direct reduction method to synthesize ordered Fe-Pt alloy nanoparticles
Q. Zheng, Z.R. Zhang, J. Du, L.L. Lin, W.X. Xia, J. Zhang, B.R. Bian, J.P. Liu
J. Mater. Sci. Technol.    2019, 35 (4): 560-567.   DOI: 10.1016/j.jmst.2018.09.036
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In this work, a direct green solid-phase reduction method for the fabrication of large yield of ordered phase Fe-Pt alloy nanoparticles was reported, in which inorganic salts were used as metal precursors and H2-containing atmosphere was used as reducer. Utilizing this method, the composition and chemical ordered phase, such as L12-Fe3Pt, L12-FePt3, and L10-FePt phases can be easily achieved by one step reaction. The synthesized nanoparticles have clean surface because no organic precursors, no organic solutions or organic surfactants/ligands were used. Their magnetic performance and the formation mechanism of Fe-Pt alloy nanoparticles were also investigated. This strategy can be applied to synthesize many other types of alloy nanoparticles with desired composition and necessary crystal structure, which can be used for a variety of practical applications, such as in magnetism and catalyst research fields.

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Evolution of the microstructure and solute distribution of Sn-10wt% Bi alloys during electromagnetic field-assisted directional solidification
Zhe Shen, Minghu Peng, Dongsheng Zhu, Tianxiang Zheng, Yunbo Zhong, Weili Ren, Chuanjun Li, Weidong Xuan, Zhongming Ren
J. Mater. Sci. Technol.    2019, 35 (4): 568-577.   DOI: 10.1016/j.jmst.2018.09.037
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The effects of forced flows at different velocities on microstructure and solute distribution during the directional solidification of Sn-10 wt% Bi alloys under a simultaneous imposition of a transverse static magnetic field (TSMF) and an external direct current (DC) have been investigated experimentally and numerically. The experimental results show that the solid-liquid interface will gradually become sloping with the increase of the forced flow velocity when the thermoelectric magnetic convection (TEMC) dominates the forced flow at solidification front. However, the interface will gradually become planar as the flow velocity further increases when the electromagnetic convection (EMC) dominates the forced flow. Moreover, when the flow velocity gradually increases, the primary dendrite spacing decreases from 384 to 105 μm accordingly. The simulation results show that the solute distribution at the two sides of the sample can be significantly changed by the forced flow at solidification front. The rejected solute will be unidirectionally transported to one side of the sample along the TEMC (a low-velocity forced flow), thereby causing the formation of a sloping interface. However, the rejected solute will be returned back along the EMC (a higher-velocity force flow), which results in a planar interface. Furthermore, the solute content at the two sides of the sample under the forced flows at different velocities was measured. The results are in good agreement with the simulation results, which shows that the solute content difference between the two sides of the sample reaches the maximum when a 0.5 T TSMF is applied, while the solute content difference decreases to zero with a simultaneous application of a 0.5 T TSMF and a 1.6 × 105 A/m2 external DC.

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Strengthening FCC-CoCrFeMnNi high entropy alloys by Mo addition
Gang Qin, Ruirun Chen, Huiting Zheng, Hongze Fang, Liang Wang, Yanqing Su, Jingjie Guo, Hengzhi Fu
J. Mater. Sci. Technol.    2019, 35 (4): 578-583.   DOI: 10.1016/j.jmst.2018.10.009
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In order to strengthen the face-centered-cubic (FCC) type CoCrFeMnNi high entropy alloys (HEAs), different contents of Mo (0-16 at.%, similarly hereinafter) were alloyed. Phase evolution, microstructure, mechanical properties and related mechanism of these HEAs were systematically studied. The results show that sigma phase is appeared with addition of Mo, and the volume fraction of it increases gradually from 0 to 66% with increasing Mo content. It is found that Mo is enriched in sigma phase, which indicates that Mo element is beneficial to form sigma phase. Compressive testing shows that the yield strength of the alloys increases gradually from 216 to 765 MPa, while the fracture strain decreases from 50% (no fracture) to 19% with increasing of Mo. The alloy exhibits the best compressive performance when Mo content reaches 11%, the yield strength, fracture strength and fracture strain are 547 MPa, 2672 MPa and 44% respectively. The increased volume fraction of sigma phase plays an important role in improving the compressive strength of (CoCrFeMnNi)100-xMox HEAs.

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General trends in surface stability and oxygen adsorption behavior of transition metal diborides (TMB2)
Wei Sun, Fuzhi Dai, Huimin Xiang, Jiachen Liu, Yanchun Zhou
J. Mater. Sci. Technol.    2019, 35 (4): 584-590.   DOI: 10.1016/j.jmst.2018.10.012
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The potential applications of transition metal diborides (TMB2) in extreme environments are particularly attractive but still blocked by some intrinsic properties such as poor resistances to thermal shock and oxidation. Since surface plays a key role during grain growth and oxygen adsorption, an insight into the surface properties of TMB2 is essential for understanding the materials performance and accelerating the development of ultra-high temperature ceramics. By employing two-region modeling method, the stability and oxygen adsorption behavior of TMB2 surfaces were investigated by first-principles calculations based on density functional theory. The effects of valance electron concentration on the surface stability and oxygen adsorption were studied and the general trends were summarized. After analyzing the anisotropy in surface stability and oxygen adsorption, the observed grain morphology of TMB2 were well explained, and it was also predicted that YB2, HfB2 and TaB2 may have better initial oxidation resistance than ZrB2.

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Analysis of local crystallographic orientation in an annealed Ti60 billet
Z.B. Zhao, Z. Liu, Q.J. Wang, J.R. Liu, R. Yang
J. Mater. Sci. Technol.    2019, 35 (4): 591-595.   DOI: 10.1016/j.jmst.2018.10.014
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A heterogeneous microstructure in terms of local orientation distribution is often found in near-α titanium alloys. The presence of large regions with similar crystallographic orientation, called ‘macrozones’, could drastically decrease the fatigue performance of titanium alloys. The present work reports on the crystallographic orientation of a near-α titanium alloy, Ti60, billet after annealing in an α+β phase field. The texture was found to be weak, and no obvious macrozone was found in our measured zone where the variant selection is suppressed. Meanwhile, in-depth electron backscattered diffraction (EBSD) analysis was applied to evaluate the final microstructure, and the mechanisms by which they formed were analyzed.

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CN: 21-1315/TG
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