Fatigue & Fracture of Engineering Materials & Structures
Fatigue crack growth behavior in welded joints subjected to elastic-plastic shock waves was investigated using three-point-bend specimens. The results indicate that the fatigue crack growth rate is reduced in the affected region of elastic or plastic waves. The travel of a plastic stress wave reaches 10 to 13 mm depth, but the hardness in this region is not increased although the lattice distortion is high. The crack path morphologies were observed, and reasons for a decrease in crack growth rate are presented.
关键词:
Zhijian LIU
,
Zhiyou LI
,
Wei DUAN
,
Xuanhui QU
,
Baiyun HUANG
,
Siqi ZHANG
材料科学技术（英文）
A LI-B alloy has been prepared using a pretreated amorphous B powder and pure Li ingot as starting materials by continually slow addition of B powder and intensified stirring in the process of melting. The microstructure and the discharge characteristic of the materials have been investigated. Results show that the problem of temperature control in synthesis would be modified by means of continual addition of B powder, the Li7B6 would be more finery distributed in the metal Li by means of intensified stirring. The discharge characteristic of the Li-B alloy using amorphous B as starting materials is almost the same with that of using crystalline B.
关键词:
Materials Letters
Interfacial characteristics of molten Bi-43Sn alloy on amorphous and crystalline Fe(78)B(13)Si(9) during wetting were investigated at 523 K, 573 K, 623 K and 673 K. It is found that an intertnetallic compound exists at the interface of Bi-43Sn alloy on amorphous FC(78)B(13)Si(9), while no intermediate reaction layer is formed at the interface of Bi-43Sn alloy on crystalline Fe(78)B(13)Si(9). For Bi-43Sn alloy/amorphous Fe(78)B(13)Si(9) system, isothermal aging was performed at 323 K, 373 K and 423 K. The layer growth of the intermetallic compound is mainly controlled by a diffusion-controlled mechanism in the temperature range studied because the values of time exponent (n) is approximately equal to 0.5. (c) 2007 Elsevier B. V. All rights reserved.
关键词:
intermetallic compound;amorphous;crystalline;kinetic;diffusion;glass;cu
LIU Jian QIU Baoqin LIU Muyi XIAO Yaofu University of Science and Technology Beijing
,
Beijing
,
China associate professor
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Department of Materials
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University of Science and Technology Beijing
,
Beijing 100083
,
China
金属学报(英文版)
The phase constitution and variation of Nd_(14)Fe_(73)Co_6B_7 alloy after hydriding and subsequent dehydriding treatment at 770℃ have been investigated respectively by means of X-ray diffraction,SEM,TEM and magnetic measurement techniques.The original coarse,as cast grain structure,is dissolved into α-Fe,Nd hydride and Fe_2B mixture with average dimension of 0.1 μm,during hydriding process,and subsequently the triphase mixture recombined into finely unique Nd_2Fe_(14)B phase with dimension of 0.3 μm by desorbing the hydrogen.It was found that the Nd-rich phase distributed at the boundary of as-cast grain structure diffused into matrix Nd_2Fe_(14)B grain during hydriding.It remains during dehydriding and distribute homogeneously around some colonies composed of fine grains of Nd_2Fe_(14)B.
关键词:
Nd_(14)Fe_(73)Co_6B_7
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null
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null
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null
Physical Review B
By using a first-principles plane-wave pseudopotential method, the energetics and electronic structure of Sigma5(210) grain boundary (GB) and the (210) surface of undoped as well as B- and/or H-doped Ni3Al are investigated. The geometric structures of the GBs and surfaces are fully relaxed by minimizing the total energy and interatomic force. The results show that B induces a large lattice expansion but H does not. Both B and H "prefer" to occupy the Ni-rich hole at the GB or surface but not the Ni-deficient one. The segregation energies of B and H as well as the interaction energy between them at the GB and surface are calculated. The calculation indicates that B segregates more strongly to the GB than to the surface, which results in an increase in the Griffith work of the GB and, therefore, in agreement with the experiments, improves the ductility of Ni3Al. Contrary to the case of B, H segregates more strongly to the surface than to the GB, which results in a decrease in Griffith work and confirms H as an embrittler for Ni3Al. The calculation of the interaction energy between B and H demonstrates that B and H repel each other. Consequently, B may block the site of occupation of H at the GB, and restrain the H-induced embrittlement. To understand the mechanism of the obtained energetic features, the electronic densities of states (DOSs) are calculated. A comparison of the total DOSs between the B-doped GB and undoped as well as H-doped ones shows that B increases the hybridization of the GB, which contributes to the enhanced binding of the B-doped GB over the undoped and H-doped ones. When the site of B changes from bulk to GB to surface, the hybridization between B and Ni decreases accordingly. It is proposed that the segregation behavior of B at the GB and surface is dominated by the competition between B(p)-Ni(d) bond energy and the strain energy induced by B. The preference of B for the Ni-rich interstice in Ni3Al is explained by the repulsive interaction between B and Al atoms resulting from the hybridization between their electrons when they are close to each other. The repulsion between B and H can also be explained by the same electronic structure mechanism as that for the B-Al interaction. The segregation of B at surface shifts the DOS of its nearest neighbor Ni to lower energy. This may increase the chemisorption potential energy of H2O on Ni3Al surface and, therefore, decrease the reactivity of the surface, inhibiting the environmental embrittlement of Ni3Al.
关键词:
intergranular fracture;environmental embrittlement;polycrystalline;ni3al;water dissociation;first-principles;metal-surfaces;boron;segregation;ductility;hydrogen
Applied Surface Science
The Al-Mn alloy coatings were electrodeposited on AZ31B Mg alloy in AlCl(3)-NaCl-KCl-MnCl(2) molten salts at 170 degrees C aiming to improve the corrosion resistance. However, in order to prevent AZ31B Mg alloy from corrosion during electrodeposition in molten salts and to ensure excellent adhesion of coatings to the substrate, AZ31B Mg alloy should be pre-plated with a thin zinc layer as intermediate layer. Then the microstructure, composition and phase constituents of the coatings were investigated by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDX), and X-ray diffraction (XRD). It was indicated that, by adjusting the MnCl(2) content in the molten salts from 0.5 wt% to 2 wt%, the Mn content in the alloy coating was increased and the phase constituents were changed from f.c.c Al-Mn solid solution to amorphous phase. The corrosion resistance of the coatings was evaluated by potentiodynamic polarization measurements in 3.5% NaCl solution. It was confirmed that the Al-Mn alloy coatings exhibited good corrosion resistance with a chear passive region and significantly reduced corrosion current density at anodic potentiodynamic polarization. The corrosion resistance of the alloy coatings was also related with the microstructure and Mn content of the coatings. (C) 2009 Elsevier B. V. All rights reserved.
关键词:
Magnesium alloy;Electrodeposition;Al-Mn alloy;Zn intermediate layer;Corrosion resistance;sodium chloride bath;corrosion-resistance;aluminum;improvement;deposition;powder;melts
王敏
,
车寅生
,
董占军
,
祝雷
,
牛超
,
董多
,
郑浩岩
材料热处理学报
采用柠檬酸络合法分别合成了B掺杂及B-Er共掺杂BiVO4可见光光催化剂,并对材料进行了XRD、SEM、EDS、BET和UV-vis等表征和分析.以光催化降解甲基橙溶液为探针反应,考察掺杂对BiVO4可见光催化活性的影响.结果表明:掺杂没有改变BiVO4晶型,掺杂前后均为单斜型,但B-Er共掺杂BiVO4的晶体粒径较单掺杂B和纯BiVO4减小.由UV-vis知,B-Er共掺杂BiVO4的光吸收强度大于单掺杂和纯BiVO4,光谱吸收红移程度大于单掺杂.B和Er共掺杂纳米BiVO4光催化剂产生协同效应,其光催化性能优于单掺杂B.当固定B为4％掺杂时,Er掺杂量为1％制备的B-Er共掺杂BiVO4,60 min对甲基橙的降解率达96.62％,较单掺杂B(37％)和纯样(20％)有明显提高.
关键词:
钒酸铋
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光催化剂
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B-Er共掺杂
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甲基橙
郑一雄
,
姚士冰
,
周绍民
应用化学
doi:10.3969/j.issn.1000-0518.2008.02.021
在W/O型反相微乳液体系中,以KBH4为还原剂制得近乎单分散的Ni-La-B非晶态合金纳米团簇. 采用扫描电子显微镜、透射电子显微镜、X射线衍射、差示扫描量热仪和X射线光电子能谱(XPS)等测试技术对样品进行了表征. 结果表明,团簇呈球形,尺寸为10～15 nm,分布较均匀,基本呈单分散. 升温速率为20 K/min时,DSC曲线在657.6和724.3 K处出现2个强放热峰,其晶化温度明显高于水溶液体系以KBH4为还原剂制备的Ni-B非晶态合金纳米颗粒,表明样品具有良好的热稳定性. X射线衍射测试鉴识出DSC曲线揭示的2个相转变过程,Ni-La-B非晶态合金晶化成Ni-La-B晶态合金和Ni-La-B晶态合金转化成纳米晶Ni-La和单质B. 相转变活化能的测定表明,后1个晶态合金的相转变过程的速率比前1个非晶态合金的快.
关键词:
Ni-La-B非晶态合金
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微乳液
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纳米团簇
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晶化
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单分散
雷秀兰
,
易翔
,
袁洋
,
曾延波
,
李蕾
应用化学
doi:10.3724/SP.J.1095.2011.00418
以罗丹明B为模板分子,丙烯酰胺为功能单体,乙二醇二甲基丙烯酸酯为交联剂,采用沉淀聚合法制备了罗丹明B分子印迹聚合物(MIP)微球,并用扫描电子显微镜表征.采用紫外分光光度法测定了印迹分子罗丹明B与功能单体丙烯酰胺二者之间的结合常数(K=5.303 × 10(3)(mol/L)(-1))和化学计量比(n=1).考察了沉淀剂的种类和用量对聚合物微球的影响.将分子印迹聚合物微球应用于固相萃取材料自制固相萃取柱,从加标罗丹明B的红椒粉中萃取罗丹明B.本文优化了固相萃取条件,高效液相色谱检测表明,在一定的萃取条件下,分子印迹聚合物对加标量为0.479 mg/kg的辣椒中罗丹明B的萃取加标回收率可达91.7%～103.5%.
关键词:
分子印迹聚合物微球
,
罗丹明B
,
沉淀聚合
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固相萃取
