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CN 21-1315/TG
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Current Issue
 15 July 2020, Volume 49 Issue 0 Previous Issue    Next Issue
Research Article
 Select Resistive switching performance improvement of InGaZnO-based memory device by nitrogen plasma treatment Li Zhang, Zhong Xu, Jia Han, Lei Liu, Cong Ye, Yi Zhou, Wen Xiong, Yanxin Liu, Gang He J. Mater. Sci. Technol., 2020, 49 (0): 1-6.  DOI: 10.1016/j.jmst.2020.01.049 With the demand of flat panel display development, utilizing the non-volatile memory devices based on indium-gallium-zinc-oxide (IGZO) film may be integrated with IGZO thin film transistors (TFTs) to accomplish system-on-panel applications. In this work, 1 × 1 μm2 via hole structure IGZO based memory device was fabricated and the resistive switching (RS) behavior was investigated. By inserting a nitrogen doping layer IGZO:N by plasma treatment in Pt/IGZO/TiN device, highly improved RS performance including lower forming voltage, remarkable uniformity, large memory window of 102, retention property of 104 s at 125 °C, excellent pulse endurance of 107 cycles were achieved. The X-ray photoelectron spectroscopy analysis indicates that plasma doping method can evenly dope nitrogen and induce more non-lattice oxygen in the IGZO film. It is deduced that the N atoms of the inserting layer can influence the random formation of oxygen vacancy type conducting filaments, which results in more stable and uniform performance.
 Select Evaluation on the interface characteristics, thermal conductivity, and annealing effect of a hot-forged Cu-Ti/diamond composite Lei Lei, Yu Su, Leandro Bolzoni, Fei Yang J. Mater. Sci. Technol., 2020, 49 (0): 7-14.  DOI: 10.1016/j.jmst.2020.02.023 A Cu-1.5 wt.%Ti/Diamond (55 vol.%) composite was fabricated by hot forging from powder mixture of copper, titanium and diamond powders at 1050 °C. A nano-thick TiC interfacial layer was formed between the diamond particle and copper matrix during forging, and it has an orientation relationship of (111)TiC//(002)Cu&[1 $\ bar {1}$ 0]TiC//[1 $\bar{1}$ 0]Cu with the copper matrix. HRTEM analysis suggests that TiC is semi-coherently bond with copper matrix, which helps reduce phonon scattering at the TiC/Cu interface and facilitates the heat transfer, further leading to the hot-forged copper/diamond composite (referred as to Cu-Ti/Dia-0) has a thermal conductivity of 410 W/mK, and this is about 74 % of theoretical thermal conductivity of hot-forged copper/composite (552 W/mK). However, the formation of thin amorphous carbon layer in diamond particle (next to the interfacial TiC layer) and deformed structure in the copper matrix have adverse effect on the thermal conductivity of Cu-Ti/Dia-0 composite. 800 °C-annealing eliminates the discrepancy in TiC interface morphology between the diamond-{100} and -{111} facets of Cu-Ti/Dia-0 composite, but causes TiC particles coarsening and agglomerating for the Cu-Ti/Dia-2 composite and interfacial layer cracking and spallation for the Cu-Ti/Dia-1 composite. In addition, a large amount of graphite was formed by titanium-induced diamond graphitization in the Cu-Ti/Dia-2 composite. All these factors deteriorate the heat transfer behavior for the annealed Cu-Ti/Dia composites. Appropriate heat treatment needs to be continually investigated to improve the thermal conductivity of hot-forged Cu-Ti/Dia composite by eliminating deformed structure in the copper matrix with limit/without impacts on the formed TiC interfacial layer.
 Select Numerical simulation for dendrite growth in directional solidification using LBM-CA (cellular automata) coupled method Wonjoo Lee, Yuhyeong Jeong, Jae-Wook Lee, Howon Lee, Seong-hoon Kang, Young-Min Kim, Jonghun Yoon J. Mater. Sci. Technol., 2020, 49 (0): 15-24.  DOI: 10.1016/j.jmst.2020.01.047 To predict the dendrite morphology and microstructure evolution in the solidification of molten metal, numerically, lattice Boltzmann method (LBM) - cellular automata (CA) model has been developed by integrating the LBM to solve the mass transport by diffusion and convection during solidification and the CA to determine the phase transformation with respect to the solid fraction based on the local equilibrium theory. It is successfully validated with analytic solutions such as Lipton-Glicksman-Kurz (LGK) model in static melt, and Oseen-Ivantsov solution under the fluid flow conditions in terms of tip radius and velocity of the dendrite growth. The proposed LBM-CA model does not only describe different types of dendrite formations with respect to various solidification conditions such as temperature gradient and growth rate, but also predict the primary dendrite arm spacing (PDAS) and the secondary dendrite arm spacing (SDAS), quantitatively, in directional solidification (DS) experiment with Ni-based superalloy.
 Select Deformation twinning in equiaxed-grained Fe-6.5 wt.%Si alloy after rotary swaging Chaoyu Han, Shibo Wen, Feng Ye, Wenjia Wu, Shaowei Xue, Yongfeng Liang, Binbin Liu, Junpin Lin J. Mater. Sci. Technol., 2020, 49 (0): 25-34.  DOI: 10.1016/j.jmst.2020.01.048 Tensile behavior of an equiaxed-grained Fe-6.5 wt.%Si alloy, which was deformed into Φ6 mm bar by hot rotary swaging, was investigated at various temperatures (300-400 °C) and stretching rates (0.42-1 mm/min). The results revealed an enhancement in the intermediate-temperature tensile ductility after heat treatments. Deformation twinning was found in the equiaxed-grained Fe-6.5 wt.%Si bars during the tensile test, and heat treatments can enhance the deformation twinning. More twins can be observed in the necking areas than other regions. The high Schmid factor values above 0.4 after heat treatments demonstrated that deformation twinning can easily occur in the equiaxed-grained Fe-6.5 wt.%Si alloy. Higher deformation temperatures, higher strain rates, and larger degree of order suppressed the formation of deformation twinning, while the grain sizes had little effect on the deformation twinning. The twinning stress of the Fe-6.5 wt.%Si alloy increased with the increasing grain size, which did not agree with the Hall-Petch type relationship. The deformation twinning resulted in the improved ductility of the Fe-6.5 wt.%Si alloy.
 Select Experimental investigation of a Portevin-Le Chatelier band in Ni‒Co-based superalloys in relation to γʹ precipitates at 500 ℃ Yanke Liu, Yulong Cai, Chenggang Tian, Guoliang Zhang, Guoming Han, Shihua Fu, Chuanyong Cui, Qingchuan Zhang J. Mater. Sci. Technol., 2020, 49 (0): 35-41.  DOI: 10.1016/j.jmst.2020.02.001 The macroscopically localized deformation behaviors of Ni-Co-based superalloys with different γ′ precipitate content were investigated at 500 °C and 1 × 10-4 s-1 via an in situ method namely, digital image correlation (DIC). The DIC results showed that the serrated flow of the stress-strain curves was accompanied by localized deformation of the specimens. The fracture morphology was characterized mainly by transgranular fracture with numerous dimples in the low γ′ content alloy, and intergranular fracture with large fracture section in the high γ′ content alloy. The Portevin-Le Chatelier (PLC) effect occurred in the investigated Ni-Co-based superalloys. Furthermore, the localized deformation of the high γ′ content alloy was more severe than that of the low γ′ content alloy, and the band width was slightly larger. Moreover, for the first-time ever, a special propagation feature, namely ±60° zigzag bands characterized by head-to-tail connections, was observed in the high γ′ content alloy.
 Select Au nanospheres modified boron-doped diamond microelectrode grown via hydrogen plasma etching solid doping source for dopamine detection Kaili Yao, Xiaojun Tan, Bing Dai, Jie Bai, Qiaoyang Sun, Wenxin Cao, Jiwen Zhao, Lei Yang, Jiecai Han, Jiaqi Zhu J. Mater. Sci. Technol., 2020, 49 (0): 42-46.  DOI: 10.1016/j.jmst.2020.02.003 Boron doped diamond (BDD) electrode is a promising electrochemical material for detecting dopamine level in the human’s body. In this work, we developed a new doping source - graphite and solid boron oxide powders to synthesize BDD film with microwave plasma chemical vapor deposition, so as to avoid using toxic or corrosive dopants, such as boroethane and trimethylborate. The synthesized BDD film is pinhole free and with high doping density of 8.44 × 1020 cm-3 calculated from the Raman spectroscopy. Subsequently, Au nanospheres were decorated on the surface of BDD film to improve electrochemical performance of the BDD film. The Au nanoparticles modified BDD electrode demonstrates an excellent electrochemical response, a high sensitivity (in the range of 5 μM-1 mM), and a low detection limit (~ 0.8 μM) for detecting dopamine.
 Select Improving the fretting biocorrosion of Ti6Al4V alloy bone screw by decorating structure optimised TiO2 nanotubes layer Jiajun Luo, Maryam Tamaddon, Changyou Yan, Shuanhong Ma, Xiaolong Wang, Feng Zhou, Chaozong Liu J. Mater. Sci. Technol., 2020, 49 (0): 47-55.  DOI: 10.1016/j.jmst.2020.02.027 TiO2 nanotubes (NT) has been demonstrated its potential in orthopaedic applications due to its enhanced surface wettability and bio-osteointegration. However, the fretting biocorrosion is the main concern that limited its successfully application in orthopaedic application. In this study, a structure optimised thin TiO2 nanotube (SONT) layer was successfully created on Ti6Al4V bone screw, and its fretting corrosion performance was investigated and compared to the pristine Ti6Al4V bone screws and NT decorated screw in a bone-screw fretting simulation rig. The results have shown that the debonding TiO2 nanotube from the bone screw reduced significantly, as a result of structure optimisation. The SONT layer also exhibited enhanced bio-corrosion resistance compared pristine bone screw and conventionally NT modified bone screw. It is postulated that interfacial layer between TiO2 nanotube and Ti6Al4V substrate, generated during structure optimisation process, enhanced bonding of TiO2 nanotube layer to the Ti6Al4V bone screws that leading to the improvement in fretting corrosion resistance. The results highlighted the potential SONT in orthopaedic application as bone fracture fixation devices.
 Select Microstructural evolution and FCC twinning behavior during hot deformation of high temperature titanium alloy Ti65 Zhixin Zhang, Jiangkun Fan, Bin Tang, Hongchao Kou, Jian Wang, Xin Wang, Shiying Wang, Qingjiang Wang, Zhiyong Chen, Jinshan Li J. Mater. Sci. Technol., 2020, 49 (0): 56-69.  DOI: 10.1016/j.jmst.2020.02.026 Although the development of titanium alloys with working temperatures above 600 ℃ faces enormous difficulties and challenges, the related research has not stopped. In the present work, detailed analyses on microstructure evolution and hot deformation behavior of a new temperature resistant 650 ℃ titanium alloy Ti65 were investigated from micrometer scale to nanometer scale. The results revealed that lamellar α grains gradually fragmentized and spheroidized during the α + β phase region compression and the orientation of the c-axis of α grains gradually aligned to radial directions, forming two high Schmid factors (SFs) value texture eventually with the increase of strain to 0.7. Moreover, there were some strengthening characters in the α + β phase region such as lenticular αs and nano silicide (TiZr)6Si3. In the β phase region, fine equiaxed dynamic recrystallized (DRX) β grains were formed. Besides, the variant selection of α′ martensite followed Burgers orientation relationship during the compression process. The main deformation mechanisms of the α + β phase region were dislocation slip and orientation dependent spheroidization. Whereas, the deformation process in the β phase region was controlled by β grain DRX. Interestingly, many nano scale FCC twins were generated at the interface of α′ lath during deforming in the β phase region, which was firstly observed in Ti65 alloy.
 Select Kinetic transitions and Mn partitioning during austenite growth from a mixture of partitioned cementite and ferrite: Role of heating rate Geng Liu, Zongbiao Dai, Zhigang Yang, Chi Zhang, Jun Li, Hao Chen J. Mater. Sci. Technol., 2020, 49 (0): 70-80.  DOI: 10.1016/j.jmst.2020.01.051 Austenite formation from a ferrite-cementite mixture is a crucial step during the processing of advanced high strength steels (AHSS). The ferrite-cementite mixture is usually inhomogeneous in both structure and composition, which makes the mechanism of austenite formation very complex. In this contribution, austenite formation upon continuous heating from a designed spheroidized cementite structure in a model Fe-C-Mn alloy was investigated with an emphasis on the role of heating rate in kinetic transitions and element partitioning during austenite formation. Based on partition/non-partition local equilibrium (PLE/NPLE) assumption, austenite growth was found alternately contribute by PLE, NPLE and PLE controlled interfaces migration during slow-heating, while NPLE mode predominately controlled the austenitization by a synchronous dissolution of ferrite and cementite upon fast-heating. It was both experimentally and theoretically found that there is a long-distance diffusion of Mn within austenite of the slow-heated sample, while a sharp Mn gradient was retained within austenite of the fast-heated sample. Such a strong heterogeneous distribution of Mn within austenite cause a large difference in driving force for ferrite or martensite formation during subsequent cooling process, which could lead to various final microstructures. The current study indicates that fast-heating could lead to unique microstructures which could hardly be obtained via the conventional annealing process.
 Select Design of binder jet additive manufactured co-continuous ceramic-reinforced metal matrix composites Pablo D. Enrique, Ehsan Marzbanrad, Yahya Mahmoodkhani, Ali Keshavarzkermani, Hashem Al Momani, Ehsan Toyserkani, Norman Y. Zhou J. Mater. Sci. Technol., 2020, 49 (0): 81-90.  DOI: 10.1016/j.jmst.2020.01.053 Ceramic-reinforced metal matrix composites (MMCs) display beneficial properties owing to their combination of ceramic and metal phases. However, the properties are highly dependent on the reinforcing phase composition, volume fraction and morphology. Continuous fiber or network reinforcement morphologies are difficult and expensive to manufacture, and the often-used discontinuous particle or whisker reinforcement morphologies result in less effective properties. Here, we demonstrate the formation of a co-continuous ceramic-reinforced metal matrix composite using solid-state processing. Binder jet additive manufacturing (BJAM) was used to print a nickel superalloy part followed by post-processing via reactive sintering to form a continuous carbide reinforcing phase at the particle boundaries. The kinetics of reinforcement formation are investigated in order to develop a relationship between reactive sintering time, temperature and powder composition on the reinforcing phase thickness and volume fraction. To evaluate performance, the wear resistance of the reinforced BJAM alloy 625 MMC was compared to unreinforced BJAM alloy 625, demonstrating a 64 % decrease in the specific wear rate under abrasive wear conditions.
 Select Predicting gas and shrinkage porosity in solidification microstructure: A coupled three-dimensional cellular automaton model Cheng Gu, Colin D. Ridgeway, Emre Cinkilic, Yan Lu, Alan A. Luo J. Mater. Sci. Technol., 2020, 49 (0): 91-105.  DOI: 10.1016/j.jmst.2020.02.028 Porosity formation during solidification of aluminum-based alloys, due to hydrogen gas and alloy shrinkage, has been a major issue adversely affecting the performance of solidification products such as castings, welds or additively manufactured components. A three-dimensional cellular automaton (CA) model has been developed, for the first time, to couple the predictions of hydrogen-induced gas porosity and shrinkage porosity during solidification microstructure evolution of a binary Al-Si alloy. The CA simulation results are validated under various cooling rates by porosity measurements in an experimental wedge die casting using X-ray micro computed tomography (XMCT) technique. This validated porosity moel provides a critical link in integrated computation materials engineering (ICME) design and manufacturing of solidification products.
 Select Superior anti-icing strategy by combined sustainable liquid repellence and electro/photo-responsive thermogenesis of oil/MWNT composite Aeree Kim, Seonghyeon Kim, Myoung Huh, Hyungmo Kim, Chan Lee J. Mater. Sci. Technol., 2020, 49 (0): 106-116.  DOI: 10.1016/j.jmst.2020.02.022 This paper introduces an effective anti-icing strategy that uses passive anti-icing property and active de-icing functions concurrently. These dual capabilities can alleviate the icing problem more effectively than either a passive or active function alone. The developed material is a slippery liquid-repellent elastic conductor (SLEC); it is an organogel that is composed of multi-walled carbon nanotubes, oil, and polydimethylsiloxane. The SLEC maintains passive water-droplet sliding ability even on wet surfaces that frequently occur in cold conditions (e.g., during condensation and defrosting), suppresses ice nucleation, and shows ice adhesion strength as low as ~ 20 kPa. The SLEC releases heat when it is subject to electrical or photonic stimulation, and can therefore it can prevent ice formation and melt ice that has already formed on a surface. This material has sustainable liquid repellence by syneresis and replenishment; this ability ensures long-lasting anti-icing property, and results in exceptional durability. This durability is stable against mechanical damage. The superior dual anti-icing capabilities together with the sustainable and stable liquid repellence should generate synergistic effects, and yield a powerful anti-icing tool that can broaden the range of icing applications.
 Select A simultaneous improvement of both strength and ductility by Sn addition in as-extruded Mg-6Al-4Zn alloy Xiao-Yuan Wang, Yu-Fei Wang, Cheng Wang, Shun Xu, Jian Rong, Zhi-Zheng Yang, Jin-Guo Wang, Hui-Yuan Wang J. Mater. Sci. Technol., 2020, 49 (0): 117-125.  DOI: 10.1016/j.jmst.2019.04.048 Commercial wrought Mg alloys normally contain low alloying contents to ensure good formability. In the present work, high-alloyed Mg-6Al-4Zn-xSn (x = 1, 2 and 3 wt.%, respectively) alloys were fabricated by extrusion. Hereinto, Sn was proven to play an effective contribution to simultaneous improvement in strength and ductility that are traditional trade-off features of synthetic materials. It was found that the average grain size of those alloys decreases significantly from ~11 to ~4 μm as a function of Sn contents increasing from 0 to 3 wt.%, while the amounts of Mg2Sn and Mg17Al12 particles continuously increase. More importantly, the addition of Sn leads to the transformation of dominated deformation modes from {10$\bar{1}$2} extension twinning (1 wt.%) to pyramidal slip (3 wt.%) during tensile tests along the extrusion direction at room temperature. The advantageous combination of ultimate tensile strength (~366 MPa) and elongation (~19 %) in Mg-6Al-4Zn-3Sn alloy is mainly attributed to the strong strain hardening ability induced by the enhanced activity of non-basal slip. This work could provide new opportunities for the development of high-alloyed wrought Mg alloys with promising mechanical properties.
 Select Twinned substructure in lath martensite of water quenched Fe-0.2 %C and Fe-0.8 %C steels Haidong Sun, Yuhui Wang, Zuohua Wang, Ning Liu, Yan Peng, Xiujuan Zhao, Ruiming Ren, Hongwang Zhang J. Mater. Sci. Technol., 2020, 49 (0): 126-132.  DOI: 10.1016/j.jmst.2019.12.025 In the present investigation, twinned substructures within lath martensite of two water quenched steels (0.2 wt. %C and 0.8 wt. %C) were studied. The lath martensite has typical hierarchical packet-block-lath with dislocation substructure. Besides, laths that are misoriented by <011>/70.5° or <111>/60° and bordered by {011} plane, namely twinned laths, are observed, of which the density increases and the scale decreases as more carbons were presented. Such twinned laths have body centered cubic (bcc) crystal structure, belonging to twinned variants following the classical Kurdjumov-Sachs (K-S) orientation relationship with respect to the parent austenite. Unlike bcc {112}<111> twins, twinned variants produce strong double diffraction and in turn the extra diffraction spots that are commonly observed in the martensite in steels with wide range of carbon contents.
 Select Highly efficient visible photocatalytic disinfection and degradation performances of microtubular nanoporous g-C3N4 via hierarchical construction and defects engineering Jing Xu, Zhouping Wang, Yongfa Zhu J. Mater. Sci. Technol., 2020, 49 (0): 133-143.  DOI: 10.1016/j.jmst.2020.02.024 Herein, microtubular nanoporous g-C3N4 (TPCN) with hierarchical structure and nitrogen defects was prepared via a facile self-templating approach. On one hand, the hexagonal tubular structure can facilitate the light reflection/scattering, provide internal/external active sites, and endow the electron with oriented transfer channels. The well-developed nanoporosity can result in large specific surface area and abundant accessible channels for charge migration. On the other hand, the existence of nitrogen vacancies can improve the light harvesting (λ > 450 nm) and prompt charge separation by acting as the shallow charge traps. More NHx groups in g-C3N4 framework can promote the interlayer charge transport by generating hydrogen-bonding interaction between C3N4 layers. Therefore, TPCN possessed highly efficient visible photocatalytic performances to effectively inactivate Escherichia coli (E. coli) cells and thoroughly mineralize organic pollutants. TPCN with the optimum bactericidal efficiency can completely inactivated 5 × 106 cfu mL-1 of E. coli cells after 4 h of irradiation treatment, while about 74.4 % of E. coli cells were killed by bulk g-C3N4 (BCN). Meanwhile, the photodegradation rate of TPCN towards methylene blue, amaranth, and bisphenol A were almost 3.1, 2.5 and 1.6 times as fast as those of BCN. Furthermore, h+ and ?O2- were the reactive species in the photocatalytic process of TPCN system.
 Select Performance of Ni-Cu bimetallic co-catalyst g-C3N4 nanosheets for improving hydrogen evolution Zhiliang Jin, Lijun Zhang J. Mater. Sci. Technol., 2020, 49 (0): 144-156.  DOI: 10.1016/j.jmst.2020.02.025 The Ni-Cu bimetallic nanoparticles were successfully anchorred on the surface of g-C3N4 nanosheets by a simple heat treatment process which was applied to the photocatalytic hydrogen evolution reaction. In-situ introduction of Ni-Cu could significantly improve the photocatalytic hydrogen evolution performance compared with pure g-C3N4 in the system sensitized by eosin Y under a visible irradiation condition. The hydrogen production activity of the composite reached 104.4 μmol (2088.28 μmol g-1 h-1) after using the Ni—Cu double promoter strategy, which was 24.3 times higher than g-C3N4. The excellent electrical conductivity of the bimetallic Ni-Cu and the close interfacial contact between Ni—Cu and g-C3N4 played an important role for increasing the charge transfer rate. They were also the reasons of more efficient charge separation, which ultimately led to a significant promotion on the photocatalytic hydrogen production reaction. Ni-Cu/g-C3N4 coupling with a close Schottky interface between metal and semiconductor which enhanced H2-evolution performance and TEOA oxidation kinetics. This work provided a new way to load Ni—Cu bimetallic nanoparticles in situ onto g-C3N4 and a reference on relative semiconductor materials.
 Select Multi-length scale modeling of carburization, martensitic microstructure evolution and fatigue properties of steel gears Edward Charles Henry Crawford O’ Brien, Hemantha Kumar Yeddu J. Mater. Sci. Technol., 2020, 49 (0): 157-165.  DOI: 10.1016/j.jmst.2019.10.044 Multi-length scale modeling is performed to (i) predict the carburized case depth of SAE8620 steel gears by solving the Fick’s second law of diffusion, (ii) model the martensitic microstructure evolution in a grain inside the carburized case as well as to study the effect of stress cycling on retained austenite (RA) and martensite using a 3D phase-field model, (iii) simulate the effect of carburization and different RA contents on macroscale fatigue behavior of SAE8620 steel spur gear using the finite element method. The diffusion model predicts that the case depth increases with increasing heat treatment time and temperature. The phase-field simulations show that RA can transform to martensite during fatigue loading, where the extent of the transformation will depend on the type of stresses applied, i.e. stresses in a high stress regime or low stress regime of fatigue loading. Reverse transformation of martensite to austenite is also observed in low RA sample under high stress regime. The macroscale simulations show that the carburized case with high RA gives rise to better fatigue life compared to that with low RA.
 Select Near-neutral pH corrosion of mill-scaled X-65 pipeline steel with paint primer Shidong Wang, Lyndon Lamborn, Karina Chevil, Erwin Gamboa, Weixing Chen J. Mater. Sci. Technol., 2020, 49 (0): 166-178.  DOI: 10.1016/j.jmst.2020.01.016 The corrosion behaviour of mill-scaled X65 pipeline steel with and without a primer layer was studied in a simulated near-neutral pH soil solution. Results revealed a three-stage corrosion process of the mill-scaled pipeline steel surface. The first stage included an initial preferential dissolution of goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) in mill scale. The second stage was marked by enhanced localized corrosion and pit-formation because of either galvanic corrosion or acidic dissolution in areas enclosed by mill scale. The final stage was general corrosion after the mill scale flaked off the steel surface. When the primer layer was applied, localized corrosion was significantly enhanced on the steel surface and persisted for an extended period as compared to the mill-scaled condition. The precipitation of siderite (FeCO3) was observed at flawed locations of mill scale, although the bulk chemistry is not favorable for its formation on the steel surface free of mill scale. The local precipitation of siderite formed a capped mill scale enclosure where localized corrosion can be further enhanced.
 Select An effective strategy towards construction of CVD SiC fiber-reinforced superalloy matrix composite Haoqiang Zhang, Lin Liu, Zhiliang Pei, Nanlin Shi, Jun Gong, Chao Sun J. Mater. Sci. Technol., 2020, 49 (0): 179-185.  DOI: 10.1016/j.jmst.2020.01.050 In this work, a modified approach for preparing CVD SiC fiber-reinforced superalloy matrix composites was rationally developed. The composites were fabricated by vacuum hot pressing (VHP) process using precursor wires coated with (Al + Al2O3) diffusion barrier layers and GH4169 superalloy coatings. BNi-7 brazing filler metals were introduced on the surface of precursor wires in order to decrease the temperature of the VHP process. It was found that the VHP temperature was reduced by about 100 °C, and the melting, diffusion, nucleation and growth processes of BNi-7 fillers at 900 °C motivated the recrystallization and plastic flow of the matrix under the increasing pressure, thereby a compact composite composed of intact SiC fibers and fine equiaxial grain structure superalloy matrix was achieved. Meanwhile, the elements were distributed homogeneously among the fibers in the composite and no interfacial reactions occurred. This method provides a new insight for designing and manufacturing high-quality composites in practical engineering.
 Select Development mechanism of internal local corrosion of X80 pipeline steel Zhuowei Tan, Liuyang Yang, Dalei Zhang, Zhenbo Wang, Frank Cheng, Mingyang Zhang, Youhai Jin J. Mater. Sci. Technol., 2020, 49 (0): 186-201.  DOI: 10.1016/j.jmst.2019.10.023 The occurrence and development mechanism of internal local corrosion has always been a controversial topic, and especially under flow conditions. In this paper, an improved high shear force loop was experimentally used, and local flow field is induced by simulating corrosion defects on the surface of X80 pipeline steel specimens. The characteristics of corrosion products deposited on the surface of specimens in CO2-saturated NACE solution were investigated by means of electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). The 3D micromorphology of the corrosion test surface after remove the corrosion scale used to measure the size of localized corrosion pit. Under the influence of local defects, the wall shear stress (WSS) and turbulent kinetic energy of local flow fields enhanced significantly, and pressure fluctuations in local flow field were induced. The results showed that the characteristics of surface corrosion products varied with flow velocity. The corrosion scales formed in various regions of specimens with defects exhibited different surface micro-morphologies and chemical compositions. Overall, these data offer new perspectives for better understanding the mechanisms behind local corrosion.
 Select An improved deep forest model for forecast the outdoor atmospheric corrosion rate of low-alloy steels Yuanjie Zhi, Tao Yang, Dongmei Fu J. Mater. Sci. Technol., 2020, 49 (0): 202-210.  DOI: 10.1016/j.jmst.2020.01.044 The paper proposes a new deep structure model, called Densely Connected Cascade Forest-Weighted K Nearest Neighbors (DCCF-WKNNs), to implement the corrosion data modelling and corrosion knowledge-mining. Firstly, we collect 409 outdoor atmospheric corrosion samples of low-alloy steels as experiment datasets. Then, we give the proposed methods process, including random forests-K nearest neighbors (RF-WKNNs) and DCCF-WKNNs. Finally, we use the collected datasets to verify the performance of the proposed method. The results show that compared with commonly used and advanced machine-learning algorithms such as artificial neural network (ANN), support vector regression (SVR), random forests (RF), and cascade forests (cForest), the proposed method can obtain the best prediction results. In addition, the method can predict the corrosion rates with variations of any one single environmental variable, like pH, temperature, relative humidity, SO2, rainfall or Cl-. By this way, the threshold of each variable, upon which the corrosion rate may have a large change, can be further obtained.
 Select Phase transformation and structural evolution in a Ti-5at.% Al alloy induced by cold-rolling Bingqiang Wei, Song Ni, Yong Liu, Xiaozhou Liao, Min Song J. Mater. Sci. Technol., 2020, 49 (0): 211-223.  DOI: 10.1016/j.jmst.2020.02.032 The phase transformation, deformation mechanism and their correlation in a cold-rolled Ti-5at.%Al alloy were investigated. Two types of phase transformations from a hexagonal close-packed (HCP) structure to a face-centered cubic (FCC) structure were observed: the basal-type (B-type) with an orientation relationship of $<1\bar{2}\text{10}{{\text{}}_{\text{HCP}}}<1\bar{1}\text{0}{{\text{}}_{\text{FCC}}}$ and {0001}HCP//{111}FCC, and the prismatic-type (P-type) with an orientation relationship of $<1\bar{2}\text{10}{{\text{}}_{\text{HCP}}}<1\bar{1}\text{0}{{\text{}}_{\text{FCC}}}$ and ${{\text{ }\!\!\{\!\!\text{ 10}\bar{1}\text{0 }\!\!\}\!\!\text{ }}_{\text{HCP}}}\text{// }\!\!\{\!\!\text{ 110}{{\text{ }\!\!\}\!\!\text{ }}_{\text{FCC}}}$. The two types of transformations both accommodate the strain along the < c> axis of the HCP matrix. With the proceeding of deformation, different deformation mechanisms were activated in the FCC and the HCP structures, respectively, which led to a faster grain refinement rate in the FCC structure than in the HCP matrix. Deformation twins with zero macroscopic strain were prevalent in the FCC domains produced by the B-type transformation, while deformation twins with macroscopic strain were normally observed in the FCC domains produced by the P-type transformation. This is in accordance with the lattice mismatches produced during phase transformation. The easy occurrence of deformation twinning in the FCC structure contributed significantly to the grain refinement process. In addition, the interaction between neighboring FCC domains produced by the two types of phase transformations also accelerated the grain refinement process.
 Select Corrosion resistance of an amino acid-bioinspired calcium phosphate coating on magnesium alloy AZ31 Xiao-Li Fan, Chang-Yang Li, Yu-Bo Wang, Yuan-Fang Huo, Shuo-Qi Li, Rong-Chang Zeng J. Mater. Sci. Technol., 2020, 49 (0): 224-235.  DOI: 10.1016/j.jmst.2020.01.046 An l-cysteine-bioinspired calcium phosphate (Ca-P) coating is prepared upon magnesium alloy AZ31 in a water bath at 60 °C. FE-SEM, FTIR, XRD, electrochemical characterization, hydrogen evolution tests and XPS were used to evaluate the microstructure, chemistry and corrosion performance of the samples. Results indicate that l-cysteine promotes the nucleation process of the coating and significantly increases its thickness. This can be attributed to the complexation of the carboxyl group and mercapto group of l-cysteine with calcium ions. Indeed, the obtained Ca-P coating possesses higher corrosion resistance than that prepared in l-cysteine-free bath.
 Select Modes of grain growth and mechanism of dislocation reaction under applied biaxial strain: Atomistic and continuum modeling Ying-Jun Gao, Qian-Qian Deng, Zhe-yuan Liu, Zong-Ji Huang, Yi-Xuan Li, Zhi-Rong Luo J. Mater. Sci. Technol., 2020, 49 (0): 236-250.  DOI: 10.1016/j.jmst.2020.01.030 The phase field crystal method and Continuum Modeling are applied to study the cooperative dislocation motion of the grain boundary (GB) migration, the manner of the nucleation of the grain and of the grain growth in two dimensions (2D) under the deviatoric deformation at high temperature. Three types of the nucleation modes of new finding are observed by the phase field crystal simulation: The first mode of the nucleation is generated by the GB splitting into two sub-GBs; the second mode is of the reaction of the sub-GB dislocations, such as, the generation and annihilation of a pair of partial Frank sessile dislocation in 2D. The process can be considered as the nucleation of dynamic recrystallization; the third mode is caused by two oncoming rows of the dislocations of these sub-GBs, crossing and passing each other to form new gap which is the nucleation place of the new deformed grain. The research is shown that due to the nucleation of different modes the mechanism of the grain growth by means of the sub-GB migration is different, and therefore, the grain growth rates are also different. Under the deviatoric deformation of the applied biaxial strain, the grain growth is faster than that of the grain growth without external applied stress. It is observed that the cooperative dislocation motion of the GB migration under the deviatoric deformation accompanies with local plastic flow and the state of the stress of the system changes sharply. When the system is in the process of recrystallized grain growth, the system energy is in an unstable state due to the release of the strain energy to cause that the reverse movement of the plastic flow occurs. The area growth of the deformed grain is approximately proportional to the strain square and also to the time square. The rule of the time square of the deformed grain growth can also be deduced by establishing the continuum dynamic equation of the biaxial strain-driven migration of the GB. The copper metal is taken as an example of the calculation, and the obtained result is a good agreement with that of the experiment.
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