W.B. Han
,
K.F. Zhang
,
B. Wang
,
D.Z. Wu
金属学报(英文版)
The superplasticity and diffusion bonding of IN718 superalloy were studied in this article. The strain rate sensitivity index m was obtained at different temperatures and various initial strain rates using the tensile speed mutation method; m reached its maximum value 0.53 at an initial strain rate of 1×10-4s-1 at 1253K. The diffusion bonding parameters, including the bonding temperature T, pressure p, and time t, affected the mechanism of joints. When the bonded specimen with 25μm thick nickel foil interlayer was tensile at room temperature, the shear fracture of the joints with nickel foil interlayer took place at the IN718 part. Microstructure study was carried out with the bonded samples. The microstructure shows an excellent bonding at the interfaces. The optimum parameters for the diffusion bonding are: T = 1273-1323K, p = 20-30MPa, t = 45-60min.
关键词:
superplasticity
,
null
,
null
,
null
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）
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
,
Department of Materials
,
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
,
null
,
null
Journal of Materials Research
The morphology of the dark and bright regions observed by transmission electron microscopy for the Zr(64.13)Cu(15.75)Ni(10.12)Al(10) bulk metallic glass strongly depends on the ion beam parameters used for ion milling. This indicates that the ion beam could introduce surface fluctuation to metallic glasses during ion milling.
关键词:
room-temperature
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
,
光催化剂
,
B-Er共掺杂
,
甲基橙
