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Li H.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin Key Laboratory of Advanced Joining Technology | Han Y.,Tianjin Key Laboratory of Advanced Joining Technology | Xu Y.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Journal of Alloys and Compounds

Effect of Cu-doping on the microstructure and transport properties of p-type thermoelectric BiSbTe alloy is studied. Quaternary Cu-Bi-Sb-Te alloys with general formula of CuxBi0.5-xSb1.5Te 3(x = 0, 0.04, 0.07, 0.1) are prepared by mechanical alloying and spark plasma sintering. The results show that the doping of copper has significant effect on the microstructure of the samples. With x increasing up to 0.07, the alloys begin to present an especial microstructure which consists of fault structure and dispersed pores. The electrical conductivities of the specimens are obviously improved to 1.9 × 105 S m-1 which is about 35% higher than the maximum value observed in pure Bi0.5Sb 1.5Te3 alloy by far. The maximum power factor value of 1.9 × 10-3 Wm-1 K-2 is obtained for the Cu0.1Bi0.4Sb1.5Te3 alloy between 325 and 450 K, being approximately twice as large as those of ternary Bi 0.5Sb1.5Te3 alloy obtained in our work around the temperature at which the maximum power factor is achieved. Nano-scale dispersed pores in Cu0.07-Bi0.43Sb1.5Te 3 and Cu0.1Bi0.4Sb1.5Te3 alloy have significant effect on the reduction of lattice thermal conductivity. ZT of 1.39 can be obtained for Bi0.5Sb1.5Te3 alloy at 390 K. © 2013 Elsevier B.V. All rights reserved. Source

Zhao L.,Tianjin University | Zhao L.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.,Tianjin University | Xu L.,Tianjin University | And 2 more authors.
Engineering Fracture Mechanics

Effects of constraint induced by crack depth on creep crack behavior of P92 steel was investigated by experimental investigation and numerical simulation. Creep crack growth tests were carried out on compact tension specimens with different crack depths. It revealed that the high constraint affected creep crack initiation time and steady creep crack growth rate. Then, the crack-opening stress distribution at crack tip during creep crack growth process was obtained by finite element method (FEM) analysis. The corresponding variation of constraint parameter Q was also obtained. Finally, a C--Q approach was employed to characterize the creep crack growth rate. © 2012 Elsevier Ltd. Source

Cui C.,Tianjin University | Cui C.,Tianjin Key Laboratory of Advanced Joining Technology | Ye F.,Tianjin University | Ye F.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Surface and Coatings Technology

Fe-based alloy coatings were deposited onto Fe360A (ISO 630) substrates by the High Velocity Oxy-Fuel (HVOF) technique. A Nd:YAG laser was used to remelt surfaces of the coatings. The experimental parameters were determined using an orthogonal experimental design approach. The microstructure and microhardness were studied using a metallographic microscope and a microhardness tester. The phase compositions were investigated by X-Ray Diffractomer (XRD). The effect of laser surface remelting on the corrosion resistance of Fe-based alloy coatings was evaluated by electrochemistry methods using a 10wt.% NaOH solution. It was found that there were four types of typical shapes of laser surface remelting pools. Large holes inside the coatings could be avoided when the remelted thickness was equal to or greater than the thickness of as-sprayed coatings. The microstructure of the laser surface remelted coatings was homogeneous, and its microhardness was promoted from an average of 600 HV 0.1 to 900 HV 0.1 because of emergence of the high hardness compounds such as SiO 2 and Fe 3Si after laser surface treatment. The remelted thickness was found to have a linear relationship with the laser power density, while the microhardness of laser surface remelted coatings exhibited a parabolic relationship. Analysis of the polarization curves showed that the free corrosion current density of laser surface remelted coatings could be lowered down from 25.63μA/cm 2 to 12.99μA/cm 2. Results of the electrochemical impedance spectroscopy (EIS) also indicated that laser surface remelting could improve the corrosion resistance of Fe-based alloy coatings. © 2011 Elsevier B.V. Source

Han Y.D.,Tianjin University | Han Y.D.,Tianjin Key Laboratory of Advanced Joining Technology | Jing H.Y.,Tianjin University | Jing H.Y.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Materials Chemistry and Physics

In this study, the effect of microstructure at the base metal (BM), the fine grain heat affected zone (FGHAZ), the coarse grain HAZ (CGHAZ) and weld metal (WM) under different welding heat input on hydrogen permeation in X80 steel weldments have been investigated. Base metal showed the highest effective diffusivity. With each heat input, the effective hydrogen diffusivity in FGHAZ is comparable to that of the base metal. The effective hydrogen diffusivity in weld metal was lower than that in CGHAZ. With increasing the welding heat input, the effective diffusivity in different zones of the weldment decreased correspondingly. Non-metallic inclusions were not detected in each specimen. Constituents in microstructure under low heat input are likely to agglomerate during accelerated cooling. The retained hydrogen may create an unpredictable susceptibility to hydrogen cracking at the CGHAZ even existing during service. © 2011 Elsevier B.V. Source

Liu Y.,Tianjin University | Liu Y.,Tianjin Key Laboratory of Advanced Joining Technology | Wang L.,Tianjin University | Wang L.,Tianjin Key Laboratory of Advanced Joining Technology | And 2 more authors.
Journal of Materials Processing Technology

Ultrasonic surface rolling (USRP) is a newly developed process in which ultrasonic vibration and static force are applied on work-piece surface through the USRP operator to generate a nanostructured surface layer with mechanical behaviors highly improved. Compared with other surface severe plastic deformation (S2PD) methods, it can realize mechanized machining and be directly used for preparing final product. Notwithstanding the excellent performance of USRP, elaborate relation between process parameters and surface layer characteristics is still inadequacy due to inconvenient and costly experimental evaluation. Therefore, in this paper a three-dimensional finite element model (FEM) has been developed to predict the treatment conditions that lead to surface nanocrystallization. Simulated results of surface deformation, stress and strain are investigated to assess the formation of nanostructured layer. The numerical results from the FEM corresponds well with the values measured experimentally, indicating that this dynamic explicit FEM is a useful tool to predict the processing effects and to relate the treating parameters with the surface layer in terms of the size of nanostructured layer, residual stress and work hardening. © 2011 Published by Elsevier B.V. All rights reserved. Source

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