Strted in 1985 Monthly
ISSN 1005-0302
CN 21-1315/TG
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Nano-TiO2 Decorated Radial-Like Mesoporous Silica: Preparation, Characterization, and Adsorption-Photodegradation Behavior
Qian Tingting, Yin Xiaoping, Li Jinhong, Nian Hong’en, Xu Hui, Deng Yong, Wang Xiang
J. Mater. Sci. Technol.    2017, 33 (11): 1314-1322.   DOI: 10.1016/j.jmst.2016.09.013
Abstract   HTML PDF (2875KB)  

Supported nanocrystalline TiO2 with a diameter of 15-30 nm was prepared from previously synthesized radial mesoporous silica (RMS) by a post-synthesis method. In addition, their adsorption-photocatalytic activity toward the degradation of methylene blue (MB) was determined. RMS was tailor-made with the main template of CTAB and the SiO2 precursor of TEOS through a facile self-assembly process. The structural, morphological and textural properties of the well-designed TiO2/RMS samples were characterized. The RMS structure was retained after loading TiO2, but its surface area and pore diameter decreased as a result of partial pore blocking. The removal activity of MB for TiO2/RMS was significantly higher than that of commercial TiO2 nanoparticles. The optimal TiO2 loading (20 wt%) on the support could achieve the complete removal of MB within 70 min. The prepared TiO2/RMS particles can be easily separated and display good durability after six reaction cycles.

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Suppressing Al2O3 nanoparticle coarsening and Cu nanograin growth of milled nanostructured Cu-5vol.%Al2O3 composite powder particles by doping with Ti
Zhou Dengshan, Geng Hongwei, Zeng Wei, Zhang Deliang, Kong Charlie, Munroe Paul
J. Mater. Sci. Technol.    2017, 33 (11): 1323-1328.   DOI: 10.1016/j.jmst.2017.03.010
Abstract   HTML PDF (3045KB)  

Both the coarsening of Al2O3 nanoparticles and the growth of Cu nanograins of mechanically milled nanostructured Cu-5vol.%Al2O3 composites with, and without, trace amounts of Ti during annealing at 973 K for 1 h were investigated. It was found that doping with a small amount of Ti (e.g. 0.2 wt%) in a nanostructured Cu-5vol.%Al2O3 composite effectively suppressed the coarsening of Al2O3 nanoparticles during exposure at this temperature. Further, the Ti addition also prevented the concomitant abnormal growth of the copper grains normally caused by the coarsening of the Al2O3 nanoparticles. Energy dispersive X-ray spectroscopy analysis of the Al2O3 nanoparticles in the annealed Cu-5vol.%Al2O3-0.2wt%Ti sample suggested that the Ti atoms either diffused into the Al2O3 nanoparticles or segregated to the Cu/Al2O3 interfaces to form Ti-doped Al2O3 nanoparticles, which was more stable than Ti-free Al2O3 nanoparticles during annealing at high homologous temperatures.

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Mesoporous silica as micro/nano-carrier: From passive to active cargo delivery, a mini review
Ma Xing, Feng Huanhuan, Liang Chunyan, Liu Xiaojia, Zeng Fanyu, Wang Yong
J. Mater. Sci. Technol.    2017, 33 (10): 1067-1074.   DOI: 10.1016/j.jmst.2017.06.007
Abstract   HTML PDF (437KB)  

Mesoporous silica has been widely explored for biomedical applications due to its unique structure and good biocompatibility. In particular it exhibits superior properties as micro/nano-carriers in the biomedical field. We explore their potentials in controlled drug/gene co-delivery and photodynamic therapy for cancer treatment both in vitro and in vivo. By incorporating mesoporous silica nanoparticles (MSNP) with two-dimensional nanomaterial, graphene oxide nano-sheet, we utilize MSNP in cellular bio-imaging with squaraine dye. Meanwhile, through delicate combination between mesoporous silica micro/nano carriers with catalytic/bio-catalytic reactions, we manage to achieve self-propelled micro/nano-motors based on mesoporous silica that are capable of transporting cargos in an active manner. Especially, enzyme powered mesoporous silica motors can be powered by physiologically available fuels such as glucose and urea, which are advantageous for future biomedical use. Motion control on both velocity and movement direction provides a powerful tool for targeted drug delivery. Therefore, such mesoporous silica based active carriers pave way to the solution of targeted drug delivery for cancer treatment in future nano-medicine field.

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Recent progress in fatigue behavior of Mg alloys in air and aqueous media: A review
Wang B.J., Wang S.D., Xu D.K., Han E.H.
J. Mater. Sci. Technol.    2017, 33 (10): 1075-1086.   DOI: 10.1016/j.jmst.2017.07.017
Abstract   HTML PDF (854KB)  

Due to the interactions between mechanics and chemistry, Mg alloys are inevitably subjected to the combined effect of corrosion attack and cyclic loading, which eventually leads to corrosion fatigue failure. In this paper, fundamental aspects regarding the fatigue behavior of Mg alloys have been reviewed, including: (1) fatigue behavior of Mg alloys in air and aqueous media; and (2) the influence of microstructure, anodic dissolution, hydrogen embrittlement (HE), heat treatment and surface protection on fatigue behavior of Mg alloys. Moreover, some remaining unresolved issues and future targets to deeply understand the failure mechanism of corrosion fatigue have been described.

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Research and development of Ce-containing Nd2Fe14B-type alloys and permanent magnetic materials
Jiang Qingzheng, Zhong Zhenchen
J. Mater. Sci. Technol.    2017, 33 (10): 1087-1096.   DOI: 10.1016/j.jmst.2017.06.019
Abstract   HTML PDF (501KB)  

Much demanded and overused are the critical rare-earth elements such as Pr, Nd, Dy, and Tb with increasing need of NdFeB-type rare-earth permanent magnets in the enlarging application areas, developing new high-tech industries, and emerging cutting-age frontiers. The balance and efficient use of rare-earth resources comes into being the national strategy, national defense, and border safety for many major countries and regions in the world. (Nd,Ce)FeB-based permanent magnetic materials, which can not only reduce cost but also offer a feasible way for integrated and effective utilization of rare earth resources, have received much attention in recent years. The existence of CeFe2 and the mixed valence state of Ce in CeFeB compound, the different metallurgy behavior and the particular processing as well as potential various magnetic-hardening mechanisms, however, make it quite different from Nd-based alloys. For instance, the coercivity of Ce-containing magnets in some certain composition range, is even higher than that of the counterpart pure Nd-based magnets though the Ce-containing magnets possess inferior intrinsic properties. Consequently, it is very important to design proper composition and structure, optimize processing, and analyze the mechanisms in depth for this kind of magnet. High performance and cost-effective magnets can be fabricated if we can make full use of the composition’s inhomogeneous and abnormal coercivity variation of the Ce-containing permanent magnets. In this paper, we have summarized the phase structures, magnetic properties and microstructures of (Nd,Ce)FeB-based permanent magnetic materials to shed light on further research and development of this type of so-called “gap magnet”.

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Diamond/β-SiC film as adhesion-enhanced interlayer for top diamond coatings on cemented tungsten carbide substrate
Tian Qingquan, Huang Nan, Yang Bing, Zhuang Hao, Wang Chun, Zhai Zhaofeng, Li Junhao, Jia Xinyi, Liu Lusheng, Jiang Xin
J. Mater. Sci. Technol.    2017, 33 (10): 1097-1106.   DOI: 10.1016/j.jmst.2017.06.005
Abstract   HTML PDF (752KB)  

In present work, diamond/β-SiC composite interlayers were deposited on cemented tungsten carbide (WC-6%Co) substrates by microwave plasma enhanced chemical vapor deposition (MPCVD) using H2, CH4 and tetramethylsilane (TMS) gas mixtures. The microstructure, chemical bonding, element distribution and crystalline quality of the composite interlayers were systematically characterized by means of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), electron probe microanalysis (EPMA), Raman spectroscopy and transmission electron microscropy (TEM). The influences of varying TMS flow rates on the diamond/β-SiC composite interlayers were investigated. Through changing the TMS flow rates in the reaction gas, the volume fraction of β-SiC in the composite interlayers were tunable in the range of 12.0%-68.1%. XPS and EPMA analysis reveal that the composite interlayers are composed of C, Si element with little cobalt distribution. The better crystallinity of the diamond in the composite is characterized based on the Raman spectroscopy, which are helpful to deposit top diamond coatings with high quality. Then, the adhesion of top diamond coatings were estimated using Rockwell C indentation analysis, revealing that the adhesion of top diamond coatings on the WC-6%Co substrates can be improved by the interlayers with the diamond/β-SiC composite structures. Comprehensive TEM interfacial analysis exhibits that the cobalt diffusion is weak from WC-6%Co substrate to the composite interlayer. The homogeneous microcrystalline diamond coatings with the most excellent adhesion can be fabricated on the substrates with the composite interlayer with the β-SiC/diamond ratio of about 45%. The composite structures are appropriate for the application in high-efficiency mechanical tool as a buffer layer for the deposition of the diamond coating.

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Electron-beam irradiation induced optical transmittance enhancement for Au/ITO and ITO/Au/ITO multilayer thin films
Wei Wenzuo, Hong Ruijin, Wang Jinxia, Tao Chunxian, Zhang Dawei
J. Mater. Sci. Technol.    2017, 33 (10): 1107-1112.   DOI: 10.1016/j.jmst.2017.07.006
Abstract   HTML PDF (2217KB)  

Electron beam (EB) irradiation experiments on Au/ITO and ITO/Au/ITO multilayer thin films are reported. The structure and the optical-electrical properties of the samples were investigated by X-ray diffraction, atomic force microscopy, four-point probe resistivity measurement system, and UV-vis-NIR double beam spectrometer, respectively. Those results show that the EB irradiation has the effects of improving the crystalline of samples, widening the optical band gap of both thin films, reducing the sheet resistance, and improving the transmittance of samples.

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Flexible carbon nanotube-enriched silver electrode films with high electrical conductivity and reliability prepared by facile screen printing
Hu Dan, Zhu Wei, Peng Yuncheng, Shen Shengfei, Deng Yuan
J. Mater. Sci. Technol.    2017, 33 (10): 1113-1119.   DOI: 10.1016/j.jmst.2017.06.008
Abstract   HTML PDF (2637KB)  

Flexible electrode films play critical and fundamental roles in the successful development of flexible electronic devices. In this study, carbon nanotubes (CNTs) were implanted into silver (Ag) ink to enhance the electrical conductivity and the reliability of the printed Ag electrode films. The fabricated carbon nanotubes-enriched silver (Ag-CNTs) electrode films were printed on the polyimide substrates by a facile screen printing method and sintered at a relatively low temperature. The resistivity of Ag-CNTs films was decreased by 62.27% compared with the pure Ag film. Additionally, the Ag-CNTs films exhibited excellent flexibility under a bending radius of 4 mm (strain ε = 2.09%) over 1000 cycles. Furthermore, the Ag-CNTs film displayed unchangeable electrical conductivity together with a strong adhesion after an accelerated aging test with 500 thermal shock cycles. These improvements were attributed to the Ag-CNTs interconnected network structure, which can provide electronic transmission channels and prevent cracks from initiating and propagating.

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Loose-fit graphitic encapsulation of silicon nanowire for one-dimensional Si anode design
Lim Seh-Yoon, Chae Sudong, Jung Su-Ho, Hyeon Yuhwan, Jang Wonseok, Yoon Won-Sub, Choi Jae-Young, Whang Dongmok
J. Mater. Sci. Technol.    2017, 33 (10): 1120-1127.   DOI: 10.1016/j.jmst.2017.07.003
Abstract   HTML PDF (435KB)  

Silicon nanowires (SiNWs) encapsulated with graphene-like carbon sheath (GS) having a void space in between (SiNW@V@GS) are demonstrated for the improved electrochemical performance of Si anode in lithium ion battery. The SiNW@V@GS structure was synthesized by a scalable fabrication method including four successive reactions: metal-catalyzed CVD growth of SiNWs, controlled thermal oxidation, and deposition of the graphitic layer, to form SiNW@SiO2@GS and additional chemical etching of sacrificial SiO2 layer between SiNWs and carbon sheath. During the synthetic process, the thickness of the void spacing was controlled by adjusting the oxidation-dependent process. The well-controlled void space and crystalline graphitic carbon sheath of the SiNW@V@GS structure enable good reversible capacity of 1444 mAh g-1 and cycling stability of 85% over 150 cycles.

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Potential application of electron work function in analyzing fracture toughness of materials
Lu Hao, Ouyang Chenxin, Yan Xianguo, Wang Jian, Hua Guomin, Chung Reinaldo, Li D.Y.
J. Mater. Sci. Technol.    2017, 33 (10): 1128-1133.   DOI: 10.1016/j.jmst.2017.05.001
Abstract   HTML PDF (1252KB)  

Fracture toughness determines materials’ resistance to fracture, which is measured often using impact or bending tests. However, it is difficult to evaluate fracture toughness of coatings and small samples. In this article, using white irons as sample materials, we explore a possible approach of using electron work function (EWF) as an indicator in evaluating fracture toughness of hard metallic materials. This parameter is promising for being utilized to analyze toughness of protective coatings and small objects as well as bulk materials. Through comparison with results obtained from impact tests and elastic modulus measurement, effectiveness of this EWF approach is demonstrated.

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Grain nucleation and growth behavior of a Sn-Pb alloy affected by direct current: An in situ investigation
Yang Fenfen, Chen Zongning, Cao Fei, Fan Rong, Kang Huijun, Huang Wanxia, Yuan Qingxi, Xiao Tiqiao, Fu Yanan, Wang Tongmin
J. Mater. Sci. Technol.    2017, 33 (10): 1134-1140.   DOI: 10.1016/j.jmst.2017.05.011
Abstract   HTML PDF (1484KB)  

In situ synchrotron X-ray radiography was used to study the effect of direct current (DC) on the grain nucleation and growth of Sn-50 wt.%Pb alloy. The results showed that applying DC adequately during solidification could effectively enhance the grain nucleation and inhibit its growth. Imaging of comparative experiments with varying DC intensity indicated that the final grain size, determined by the competition between grain nucleation and growth, was sensitively dependent on the DC intensity. It was found that the average grain size was decreased from 1632 to 567 μm with DC density of 1.5 A/mm2 compared to the case without DC. Beyond this value, raising the current density may cause a significant decrease in the nucleation rate, and thus lead to a coarsening of the grain structure.

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Fabrication of cellular Zn-Mg alloy foam by gas release reaction via powder metallurgical approach
Yang Donghui, Chen Jianqing, Chen Weiping, Wang Lei, Wang Hui, Jiang Jinghua, Ma Aibin
J. Mater. Sci. Technol.    2017, 33 (10): 1141-1146.   DOI: 10.1016/j.jmst.2017.03.019
Abstract   HTML PDF (564KB)  

By using CaCO3 as the “blowing agent”, Zn-(10-50) wt% Mg alloy foams with close-pore structure were fabricated by the powder metallurgical route. The key of successful foaming is Mg addition and the proper sintering treatment, which lead to the formation of intermetallic compounds and can make the gas release reaction between Mg melt and CaCO3 happen the during foaming process.

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Mechanism and kinetics of treatment of acid orange II by aged Fe-Si-B metallic glass powders
Qin Xindong, Li Zhengkun, Zhu Zhengwang, Fu Huameng, Li Hong, Wang Aimin, Zhang Hongwei, Zhang Haifeng
J. Mater. Sci. Technol.    2017, 33 (10): 1147-1152.   DOI: 10.1016/j.jmst.2017.01.024
Abstract   HTML PDF (335KB)  

The mechanism and kinetics of acid orange II (AOII) treated by aged gas-atomized Fe-Si-B metallic glass (MG) powders were investigated in this study. The decolorization reaction is shown to obey the pseudo-first-order kinetic model, and the treatment processes could be divided into two stages: a slow step followed by a rapid one. This observation is in accordance with the following results, the azo dye is simply adsorbed onto the Fe-based MG powders in the initial stage, because the oxide layer coated on the powder surface depresses the degradation reaction by covering the activity sites, and then the degradation occurs with the desquamation of the powders. The AOII could be degraded with a rapid reaction rate when the Fe-based MG powders are applied to the treatment process again, because of the consumption of the oxide layer and the unchanged core of the Fe-based MGs. These findings will promote the practical application of MGs in degrading azo dyes.

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Bending behavior of as-cast and annealed ZrCuNiAl bulk metallic glass
Huang Yongjiang, Ning Zhiliang, Shen Zhe, Liang Weizhong, Sun Haicao, Sun Jianfei
J. Mater. Sci. Technol.    2017, 33 (10): 1153-1158.   DOI: 10.1016/j.jmst.2017.07.002
Abstract   HTML PDF (370KB)  

Here ZrCuNiAl bulk metallic glass samples were annealed below its glass transition temperature. The bending behaviors and thermal properties of the as-cast and the annealed samples were studied. The increase of annealing time leads to the transition from ductile to more brittle behavior during bending tests. Meanwhile, prolonging the annealing causes a gradual decrease in the free volume content. Based on free volume theory, the change in the microstructure and mechanical properties induced by annealing treatment has been interpreted in detail.

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Atomic-scale mechanism of the θ″ → θ′ phase transformation in Al-Cu alloys
Shen Zhenju, Ding Qingqing, Liu Chunhui, Wang Jiangwei, Tian He, Li Jixue, Zhang Ze
J. Mater. Sci. Technol.    2017, 33 (10): 1159-1164.   DOI: 10.1016/j.jmst.2016.08.031
Abstract   HTML PDF (1468KB)  

The phase transformation of θ″ → θ′ in an Al-5.7Cu alloy was investigated by aberration-corrected scanning transmission electron microscopy, and the tranformation mode of θ″ → θ′ during aging treatment was clarified. In the presence of the θ″ phases, θ′ was found to be formed by in-situ transformation from θ″ with the same plate shape, size and broad faces. The transformation starts from multiple sites within the θ″ precipitate and the whole θ′ phase finally forms as the preferential θ′ sections grow and connect with each other. Antiphase domain boundaries are also found in some θ′ precipitates when the disregistry exists between different θ′ sections.

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Rapid in-situ reaction synthesis of novel TiC and carbon nanotubes reinforced titanium matrix composites
Sun Xianglong, Han Yuanfei, Cao Sanchen, Qiu Peikun, Lu Weijie
J. Mater. Sci. Technol.    2017, 33 (10): 1165-1171.   DOI: 10.1016/j.jmst.2017.07.005
Abstract   HTML PDF (432KB)  

In-situ TiC and remained multi-walled carbon nanotubes (MWCNTs) reinforced Ti composites were synthesized using vacuum hot-press sintering and hot rolling. The effect of weight fraction of MWCNTs on microstructural evolution and mechanical properties of the Ti composites was investigated. The results indicated that both proportion and particle size of TiC increased in proportion to MWCNTs content, which resulted in different matrix microstructure, and the grains were obviously refined after rolling deformation. The hardness tests indicated that MWCNTs addition could make the composites harden, and 18.4% improvement in hardness was obtained after hot rolling. The significant improvement in both strength and hardness could be attributed to grain refinement, solid solution strengthening of carbon and dispersion strengthening of TiC particles and remained MWCNTs. A good combination of strength and ductility were achieved in Ti-1 wt% MWCNTs composites, which were in accordance with the uniform distribution of smaller-sized TiC particles in Ti matrix.

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Fabrication of laminated TiB2-B4C/Cu-Ni composites by electroplating and spark plasma sintering
Wu Ziyi, Zhang Jinyong, Shi Taojie, Zhang Fan, Lei Liwen, Xiao Han, Fu Zhengyi
J. Mater. Sci. Technol.    2017, 33 (10): 1172-1176.   DOI: 10.1016/j.jmst.2017.05.012
Abstract   HTML PDF (1305KB)  

We proposed a new method, electroplating followed by spark plasma sintering (SPS), to fabricate laminated TiB2-B4C/Cu-Ni composites with high strength and high toughness. It is found that a thin intermediate Cu layer can effectively enhance the strength of the interface between the ceramics and the metals, resulting in a high flexural strength and toughness of the laminated TiB2-B4C composites simultaneously. A flexural strength and fracture toughness of 651 MPa and 11.6 MPa m1/2 respectively, are achieved, an approximately 90% improvement over TiB2-B4C bulk.

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In-situ synthesis of Al76.8Fe24 complex metallic alloy phase in Al-based hybrid composite
Zhao Ke, Cao Baobao, Liu Jinling, Wang Yiguang, An Linan
J. Mater. Sci. Technol.    2017, 33 (10): 1177-1181.   DOI: 10.1016/j.jmst.2017.05.009
Abstract   HTML PDF (1744KB)  

The complex metallic alloy (CMA), Al76.8Fe24, was in-situ synthesized in the Al-based hybrid composite by powder metallurgy technique. The structural analysis by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy indicated that the Al76.8Fe24 CMA phase was formed by diffusion of Fe atoms into the Al matrix during the sintering stage. The formation of the CMA phase was mainly determined by the sintering temperature which was just above the eutectic temperature of Al-Fe. Moreover, the fully dense Al-based hybrid composite was obtained and exhibited ultrahigh strength ~1100 MPa, indicating that this method is expected to be effective in producing CMA particle reinforced Al-based hybrid composite.

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Mechanical, tribological and heat resistant properties of fluorinated multi-walled carbon nanotube/bismaleimide/cyanate resin nanocomposites
Li Pengbo, Li Tiehu, Yan Hongxia
J. Mater. Sci. Technol.    2017, 33 (10): 1181-1186.   DOI: 10.1016/j.jmst.2017.04.001
Abstract   HTML PDF (2019KB)  

Bismaleimide containing cyanate resin (BMI/CE) pre-ploymer was used as resin matrix. Fluorinated multi-walled carbon nanotubes (F-MWCNTs) were used as fillers to prepare F-MWCNT/BMI/CE nanocomposites via a solution intercalation method. The influence of F-MWCNT content on the mechanical, tribological and heat resistant properties of the nanocomposites was investigated. The morphology of the fracture surface and the wear surface of nanocomposites were characterized by scanning electron microscopy. Results show that the addition of F-MWCNTs is beneficial to improving the mechanical and tribological properties of the nanocomposites. It’s worth noting that when the content of F-MWNTs was 0.6 wt%, the performances of nanocomposite are optimized (i.e., highest impact strength, lowest frictional coefficient and wear rate). In addition, the nanocomposites exhibit good thermal stability in comparison with BMI/CE.

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Structure, mechanical and thermal properties of BMI/E-44/CNTs ternary composites via amination method
Cheng Youliang, Xia Bingbing, Fang Changqing, Yang Lu
J. Mater. Sci. Technol.    2017, 33 (10): 1187-1194.   DOI: 10.1016/j.jmst.2017.04.013
Abstract   HTML PDF (563KB)  

Multi-walled carbon nanotubes (CNTs) were modified by an amination treatment with hexamethylenediamine (HMD), and then bismaleimide (BMI)/epoxy (E-44)/CNTs ternary composites were prepared using modified CNTs as the reinforcement via a simple mixing and curing molding method. The results show that the surfaces of CNTs are grafted polymer with the thickness of 3 nm and the dispersity of surface grafted carbon nanotubes (SG-CNTs) in the resin composites can be improved. The prepared composites contain C─C, C─N, C═O and -COOH groups and can keep a smooth surface. In addition, the composites have the flexural strength of 152 MPa, the tensile strength of 73 MPa and the impact strength of 87 kJ m-2, respectively, when the weight ratio of BMI to E-44 is 1:8 and the content of SG-CNTs is 2 wt%. However, the thermal stability of the composites with SG-CNTs is a little lower than that of the composites without SG-CNTs.

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Ablation Mechanism of HfC-HfO2 Protective Coating for SiC-Coated C/C Composites in an Oxyacetylene Torch Environment
Yang Yang, Li Kezhi, Liu Guanxi, Zhao Zhigang
J. Mater. Sci. Technol.    2017, 33 (10): 1195-1202.   DOI: 10.1016/j.jmst.2016.11.010
Abstract   HTML PDF (2405KB)  
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Friction Characteristics of Impregnated and Non-Impregnated Graphite against Cemented Carbide under Water Lubrication
Zhang Gaolong, Liu Ying, Guo Fei, Liu Xiangfeng, Wang Yuming
J. Mater. Sci. Technol.    2017, 33 (10): 1203-1209.   DOI: 10.1016/j.jmst.2016.06.013
Abstract   HTML PDF (1759KB)  

The friction behavior of resin-impregnated and non-impregnated graphite sliding against a cemented carbide in dry, oil, and water environments using a ring-ring configuration was investigated. Friction coefficients were recorded at various speeds. The results showed that the impregnated graphite exhibited much better friction properties under water or oil lubrication than non-impregnated graphite, and the impregnated graphite could remain in the stable friction regime under high pressure × velocity (pv). Based on scanning electron microscopy and Raman spectroscopy analyses, the different characteristics between impregnated and non-impregnated graphite were able to be attributed to the structure of the graphite and wettability of the lubricants.

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Ultrahigh hardness of carbon steel surface realized by novel solid carburizing with rapid diffusion of carbon nanostructures
Tao Qing, Wang Jian, Fu Liming, Chen Zheng
J. Mater. Sci. Technol.    2017, 33 (10): 1210-1218.   DOI: 10.1016/j.jmst.2017.04.022
Abstract   HTML PDF (901KB)  

In this study, a novel rapid solid carburizing process with a large diffusion depth using nano-diamonds (NDs) was conducted for low carbon steel. Changes of annealed NDs were obtained by Raman spectroscopy and transmission electron microscopy (TEM), and the results suggested that the NDs experience a stripping process before a special solid-reaction with surface iron atoms from steel substrate. Onion-like carbon (OLC) derived from the annealed NDs provided broken graphitic ribbons as carbon sources that accelerated the rate of adsorption and diffusion. Examination of the surface layer at equilibrium using TEM and X-ray photoelectron spectroscopy (XPS) also revealed the special state of carbon, and an ultrafine mixed phase microstructure was obtained by rapid solid-phase transformation. As a result, a surface hardened layer with ultrahigh hardness and a smooth transition region were realized. We believe that these kinds of diamond or graphitic structures with high activity states have an important influence not only on adsorption and diffusion but also on this special solid-phase transformation.

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Microstructure evolution and mechanical behavior of Ni-based single crystal superalloy joint brazed with mixed powder at elevated temperature
Wang Guanglei, Sun Yuan, Wang Xinguang, Liu Jide, Liu Jinlai, Li Jinguo, Yu Jinjiang, Zhou Yizhou, Jin Tao, Sun Xudong, Sun Xiaofeng
J. Mater. Sci. Technol.    2017, 33 (10): 1219-1226.   DOI: 10.1016/j.jmst.2017.01.027
Abstract   HTML PDF (461KB)  

Brazing of a Ni-based single crystal superalloy has been investigated with the additive Ni-based superalloy and filler Ni-Cr-W-B alloy at 1260 °C, and attentions were paid to the microstructure evolution during brazing and the stress-rupture behavior at 980 °C of such brazed joints after homogenization. Microstructure in the brazed joint generally includes brazing alloy zone (BAZ), isothermally solidified zone (ISZ) and diffusion affected zone (DAZ). Microstructure evolution during this brazing process is discussed at the heating stage, the holding stage and the cooling stage respectively, according to the diffusion path of B atoms. Initially well-distributed γ/γ′ microstructure in the homogenized bonded zone after heat treatment and substantial γ′ rafts enhance the post-brazed joint to obtain a stress-rupture lifetime of more than 120 h at 980 °C/250 MPa. On the other hand, the decreased stress-rupture behavior of post-brazed joint, compared with parenting material, is ascribed to the presence of inside brazing porosity and stray grain boundary, which not only reduces the effective loading-carrying area but also offers preferential sites for creep vacancy aggregation to further soften stray grain boundary. And finally an early fracture of these post-brazed joints through the intergranular microholes aggregation and growth mode under this testing condition was observed.

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Hydrogen transport in metals: Integration of permeation, thermal desorption and degassing
Galindo-Nava E.I., Basha B.I.Y., Rivera-Díaz-del-Castillo P.E.J.
J. Mater. Sci. Technol.    2017, 33 (12): 1433-1447.   DOI: 10.1016/j.jmst.2017.09.011
Abstract   HTML PDF (3757KB)  

A modelling suite for hydrogen transport during electrochemical permeation, degassing and thermal desorption spectroscopy is presented. The approach is based on Fick's diffusion laws, where the initial concentration and diffusion coefficients depend on microstructure and charging conditions. The evolution equations are shown to reduce to classical models for hydrogen diffusion and thermal desorption spectroscopy. The number density of trapping sites is found to be proportional to the mean spacing of each microstructural feature, including dislocations, grain boundaries and various precipitates. The model is validated with several steel grades and polycrystalline nickel for a wide range of processing conditions and microstructures. A systematic study of the factors affecting hydrogen mobility in martensitic steels showed that dislocations control the effective diffusion coefficient of hydrogen. However, they also release hydrogen into the lattice more rapidly than other kind of traps. It is suggested that these effects contribute to the increased susceptibility to hydrogen embrittlement in martensitic and other high-strength steels. These results show that the methodology can be employed as a tool for alloy and process design, and that dislocation kinematics play a crucial role in such design.

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Precipitation and hot deformation behavior of austenitic heat-resistant steels: A review
Zhou Yinghui, Liu Yongchang, Zhou Xiaosheng, Liu Chenxi, Yu Jianxin, Huang Yuan, Li Huijun, Li Wenya
J. Mater. Sci. Technol.    2017, 33 (12): 1448-1456.   DOI: 10.1016/j.jmst.2017.01.025
Abstract   HTML PDF (6076KB)  

The austenitic heat resistant-steels have been considered as important candidate materials for advanced supercritical boilers, nuclear reactors, super heaters and chemical reactors, due to their favorable combination of high strength, corrosion resistance, perfect mechanical properties, workability and low cost. Since the precipitation behavior of the steels during long-term service at elevated temperature would lead to the deterioration of mechanical properties, it is essential to clarify the evolution of secondary phases in the microstructure of the steels. Here, a summary of recent progress in the precipitation behavior and the coarsening mechanism of various precipitates during aging in austenitic steels is made. Various secondary phases are formed under service conditions, like MX carbonitrides, M23C6 carbides, Z phase, sigma phase and Laves phase. It is found that the coarsening rate of M23C6 carbides is much higher than that of MX carbonitrides. In order to understand the thermal deformation mechanism, a constitutive equation can be established, and thus obtained processing maps are beneficial to optimizing thermal processing parameters, leading to improved thermal processing properties of steels.

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Recent progress in medium-Mn steels made with new designing strategies, a review
Hu Bin, Luo Haiwen, Yang Feng, Dong Han
J. Mater. Sci. Technol.    2017, 33 (12): 1457-1464.   DOI: 10.1016/j.jmst.2017.06.017
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After summarizing the relevant researches on the medium Mn steels in references, two new targets on the tensile properties have been defined. One is that both transformation-induced (TRIP) and twinning-induced plasticity (TWIP) could be realized for the steel with a relatively low Mn content, which exhibits the similar tensile properties to the classical TWIP steels with higher Mn content. The other is to achieve ultrahigh ultimate tensile strength (>1.5 GPa) without sacrificing formability. To achieve these goals, new designing strategies was put forward for compositions and the processing route. In particular, warm rolling was employed instead of the usual hot/cold rolling process because the former can produce a mixture of retained austenite grains with different morphologies and sizes via the partial recrystallization. Consequently, the retained austenite grains have a wide range of mechanic stability so that they can transform to martensite gradually during deformation, leading to enhanced TRIP effect and then improved mechanic properties. Finally, it is succeeded in manufacturing these targeted medium Mn steels in laboratory, some of them even exhibit better tensile properties than our expectation.

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Effect of pre-annealing prior to cold rolling on the precipitation, microstructure and magnetic properties of strip-cast non-oriented electrical steels
Xu Yunbo, Jiao Haitao, Zhang Yuanxiang, FengFang, Lu Xiang, Wang Yang, Cao Guangming, Li Chenggang, Misra R.D.K.
J. Mater. Sci. Technol.    2017, 33 (12): 1465-1474.   DOI: 10.1016/j.jmst.2017.08.002
Abstract   HTML PDF (4877KB)  

A novel processing route involving strip casting, pre-annealing treatment, cold rolling and recrystallization annealing was applied to a Fe-2.6%Si steel to improve the magnetic properties. The impact of as-cast strip pre-annealing on the microstructure, texture, precipitation and magnetic properties were investigated by electron probe micro-analysis, transmission electron microscopy, and X-ray diffraction analysis, etc. It was found that the precipitation of second-phase particles during strip casting was restrained by rapid solidification. The absence of pre-annealing led to the occurrence of a large amount of 20-50 nm MnS precipitates in the final annealed sheets, which is responsible for fine grains and high core loss (4.01 W/kg) due to grain boundary pinning effect. Although the microstructure and texture of 900-1000 °C pre-annealed samples were similar to those of as-cast strip, significant grain coarsening together with the strengthening of λ-fiber texture was observed in the 1100 °C pre-annealed strips. In comparison with the case of as-cast strip, a higher amount of large-sized precipitates consisting of manganese sulfide and/or aluminum nitride occurred in matrix after pre-annealing. Correspondingly, in the final annealed sheets, the number density of precipitates with sizes smaller than 100 nm was substantially reduced, and 100-200 nm and 200-500 nm sized particles became more dominant in samples subjected to 30-min and 120-min pre-annealing treatments respectively. In addition, the average grain size of final annealed sheets increased with the pre-annealing temperature and time because of the weakened pining effect of coarsen precipitates. Ultimately, the magnetic induction of samples subjected to pre-annealing was slightly increased and ranged from 1.73 T to 1.75 T owing to the enhancement of {100} recrystallization texture, and simultaneously the core loss significantly decreased until a minimum of 3.26 W/kg was reached. Nevertheless, large number of 200-500 nm particles presented during pre-annealing for 120 min could weaken the improvement in core loss which is likely associated with the pinning effect on magnetic domain wall.

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Effect of substitution of Si by Al on the microstructure and mechanical properties of bainitic transformation-induced plasticity steels
Zhu Kangying, Mager Coralie, Huang Mingxin
J. Mater. Sci. Technol.    2017, 33 (12): 1475-1486.   DOI: 10.1016/j.jmst.2017.09.002
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The effect of partial or full substitution of Si by Al on the microstructure and mechanical properties has been extensively studied in multi-phase transformation-induced plasticity (TRIP) steels with polygonal ferrite matrix, but rarely studied in bainitic TRIP steels. The aim of the present study is to properly investigate the effect of Al and Si on bainite transformation, microstructure and mechanical properties in bainitic steels in order to provide guidelines for the alloying design as a function of process parameters for the 3rd generation advanced high strength steels (AHSS). It is shown from the dilatometry study, microstructural investigations and tensile properties measurements that the Al addition results in an acceleration whereas Si addition leads to a retardation in bainite transformation kinetics. The addition of Al retards the decomposition of austenite into pearlite and carbides at holding temperatures higher than 450 °C whereas Si retards the decomposition of austenite into carbides at temperatures lower than 450 °C. Consequently, the Al-added bainitic steel has a better strength-elongation combination at bainitic holding temperatures higher than 450 °C while Si-added steel has a better strength-elongation combination at temperatures lower than 450 °C. The higher yield strength of Al-added steel is mainly attributed to its finer bainitic lath. The higher tensile strength of Si-added steel is not only related to the stronger contribution of Si on work hardening during deformation, but also due to the higher volume fraction of martensite or martensite/austenite (MA) blocks in all heat treatment conditions, as well as the lower mechanical stability of retained austenite in this steel.

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Effect of rhenium on the microstructure and mechanical behavior of Fe-2.25Cr-1.6W-0.25V-0.1C bainitic steels
Antonio Jiménez José, Carsí Manuel, Antonio Ruano Oscar
J. Mater. Sci. Technol.    2017, 33 (12): 1487-1493.   DOI: 10.1016/j.jmst.2017.08.001
Abstract   HTML PDF (3775KB)  

A new ferritic creep resistant steel has been developed by eliminating Nb and adding 1.5 mass % Re to a ferritic steel grade T/P23 with the aim of enhancing its mechanical properties at high temperature. Cast ingots of both steels, new grade and ASTM T/P 23, were hot rolled at 900 °C and then submitted to a thermal treatment consisting of solubilization at 1050 °C and tempering at 700 °C. Tempered bainitic microstructures obtained contain second phases reinforcing carbide particles, mainly M6C and M23C6 at the boundaries of both, prior austenite grains and bainitic ferrite laths, as well as MC within the grains. Mechanical properties at temperatures ranging from 540 to 600 °C were studied by strain-rate-change tests in compression at strain rates between 10-7 and 10-4 s-1. These tests showed high stress exponents (n ≥ 20) and activation energies (Q ≈ 400 kJ/mol) for both alloys, which were associated with a dislocation movement mechanism with a strong interaction between dislocations and precipitates. On the other hand, a creep exponent of 5 was derived for the stress dependence of minimum creep rate from conventional-type creep tests at 600 °C. Although this stress exponent is usually related to a dislocation climb controlled creep mechanism, remarkable microstructural degradation observed with increasing creep time makes difficult to elucidate the true deformation mechanism controlling creep.

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