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Zhang X.,Nanjing Institute of Technology | Zhang X.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Wang Q.,Nanjing Institute of Technology | Wang Q.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | And 6 more authors.
Materials Letters | Year: 2015

Mg-5Gd-1Zn-0.6Zr (GZ51K, wt%) alloy was heat treated at different temperatures in order to study the effect of long period stacking ordered (LPSO) structure on corrosion behavior of the alloy for biomedical applications. The results show that the volume fraction of the LPSO structure increases firstly, then decreases and disappears with increasing heat treatment temperature. The LPSO structure is of great importance to the corrosion behavior of the alloy. More volume fraction of the LPSO structure leads to better corrosion resistance of the alloy, while the GZ51K alloy without the LPSO structure shows rapid corrosion rate and severely localized corrosion. © 2014 Elsevier B.V. All rights reserved.

Lu F.,Hohai University | Ma A.,Hohai University | Ma A.,Nanjing University of Science and Technology | Jiang J.,Hohai University | And 6 more authors.
Corrosion Science | Year: 2015

Microstructural evolution of a new Mg-Al-Gd alloy during heat treatment and its corrosion behavior in 1wt.% NaCl solution were investigated by morphological observation, hydrogen evolution and electrochemical measurements. The microstructure of the as-cast alloy mainly consists of α-Mg, network-like Mg5Gd and polygonal Al2Gd phases, while a considerable part of Mg5Gd ones dissolve after T4 treatment. After T6 treatment, profuse micro-sized needle-like precipitates including crossed Mg5Gd-type and parallel Mg12ZnY-type ones appear and occupy different grains. These precipitates, resulting in homogeneous corrosion, continuous and compact oxidation film on the surface, have significantly improved the corrosion resistance of the Mg alloy. © 2015 Elsevier Ltd.

Wang J.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Wang J.,Nanjing Institute of Technology | Dong J.-X.,University of Science and Technology Beijing | Zhang M.-C.,University of Science and Technology Beijing
Rare Metals | Year: 2016

Dynamic recrystallization (DRX) mechanisms of a nickel-based corrosion-resistant alloy, G3, were investigated by hot compression tests with temperatures from 1050 to 1200 °C and strain rates from 0.1 to 5.0 s−1. Deformation microstructure was observed at the strain from 0.05 to 0.75 by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). Work hardening rate curves were calculated to analyze the effect of deformation parameters on the nucleation process. Results indicate that strain-induced grain boundary migration is the principal mechanism of DRX. Large annealing twins promote nucleation by accumulating dislocations and fragmenting into cell blocks. Continuous dynamic recrystallization is also detected to be an effective supplement mechanism, especially at low temperature and high strain rate. © 2016 The Nonferrous Metals Society of China and Springer-Verlag Berlin Heidelberg

Tan L.,Nanjing Institute of Technology | Tan L.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Xu J.,Nanjing Institute of Technology | Zhang X.,Jinling Institute of Technology | And 4 more authors.
Applied Surface Science | Year: 2015

Novel g-C3N4/CeO2 nanocomposites were synthesized through a simple mixing-calcination method. The structure, morphology and composition of g-C3N4/CeO2 nanocomposites were characterized by X-ray powder diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), field emission scanning electron microscopy (FESEM), energy dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), as well as X-ray photoelectron spectroscopy (XPS). The results indicated that CeO2 nanoparticles with a diameter of 50-100 nm were uniformly loaded on the surface of g-C3N4. Furthermore, the catalytic effect of our prepared novel g-C3N4/CeO2 nanocomposites on the thermal decomposition of ammonium perchlorate (AP) was investigated by utilizing thermogravimetric and differential thermal analyses (TG-DTA). Compared with pure g-C3N4 and CeO2, the g-C3N4/CeO2 nanocomposites were proved to catalyze the thermal decomposition of AP more effectively. Upon addition of g-C3N4/CeO2 nanocomposites, the high weight-loss decomposition temperature of AP was decreased by up to 74.6 °C, which is quite more than that upon the addition of pure g-C3N4 and CeO2. The proposed mechanism demonstrated that this situation was presumably attributed to a synergistic effect between g-C3N4 and CeO2. © 2015 Elsevier B.V. All rights reserved.

Li Z.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Huang Y.,Nanjing Institute of Technology | Kong F.,Nanjing Institute of Technology
Metallurgical and Mining Industry | Year: 2015

In this paper, the influence of flow stress models on FEM simulation results is discussed; the flow stress of AISI 5140 steel at different T, ε and ε in the temperature of warm-hot forging is measured by a uniaxial compression experiment with a thermomechannical simulator. The experimental results show that flow stress is very complex within the temperature range of warm-hot forging; and the traditional interpolation method adopted in FEM simulation on the basis of cold or hot flow stress models is not scientific. To improve FEM simulation precision, a flow stress mathematic model should be calibrated by experiment. Finally, the calibrated flow stress model of AISI 5140 steel is applied in the FEM simulation of the warm-hot forging process of the splined shaft of an automobile. Comparison between the results of FEM simulation and the warm-hot forging experiment indicates that the flow stress model calibrated by experiment is scientific and effective. © Metallurgical and Mining Industry, 2015.

Zhang Y.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Zhang Y.,Nanjing Institute of Technology | Mei Y.F.,Nanjing Institute of Technology | Zhou N.,Nanjing Institute of Technology | And 2 more authors.
Materials Science Forum | Year: 2016

The high-temperature mechanical properties and microstructure of HK40 heat-resistant steel with different content of Al were investigated. The results from scanning electron microscope and transmission electron microscope showed that a large amount of spheroidal and dispersed γ′ phase were observed HK40 steel with 4.72wt.% and 7.10wt.% Al. The diameter of γ′ phase decreases from about 1.5μm to 50nm after solution treatment of 1200℃ for 5h. The results of short term tensile test showed that tensile strength at 900℃ decreased and the elongation was improved with increasing Al content. The oxides in the alloy with 4.72wt.% and 7.10wt.% Al were more uniform and finer than that in the alloy with and without 1.68wt.% Al. © 2016 Trans Tech Publications, Switzerland.

Wang J.,Nanjing Institute of Technology | Wang J.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Shang X.,Nanjing Institute of Technology
Jinshu Rechuli/Heat Treatment of Metals | Year: 2015

Microstructure evolution and corresponding room temperature hardness of GH738 alloy were investigated under multistage heat treatment process, which contained solution, stabilization and aging. Qualitative model were then constructed. The results show that continuous carbides at grain boundaries and γ' with similar size are observed when the solution temperature is higher than that of γ' solvus. On the other hand, discontinuous carbides appear at grain boundaries when the solution temperature is lower than that of γ' solvus at low stabilization temperature. Furthermore, two kinds of γ'phase with different sizes are obtained in grains. GH738 alloy can obtain the maximum hardness at room temperature after stabilization treatment of 850 ℃×100 min. © 2015, Chinese Mechanical Engineering Society of Heat Treatment. All right reserved.

Yang S.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Yang S.,Nanjing Institute of Technology | Yan X.,Nanjing Institute of Technology | Yang K.,Nanjing Institute of Technology | Fu Z.,South China University of Technology
Vacuum | Year: 2016

This manuscript reports the synthesis of nanoscale Al2O3-reinforced Al0.4FeCrCoNi1.2Ti0.3 high entropy alloy composites (HEACs) by mechanical alloying (MA) and spark plasma sintering (SPS). The effects of 12 wt% Al2O3 on the microstructure and mechanical properties were investigated. A major FCC phase along with BCC and Al2O3 were observed after SPS. Many deformation twinnings were found in HEACs from the SAED pattern. In the composite with 12 wt% Al2O3 quality fraction, the fracture strength, plastic strain and Vickers hardness of HEACs were as high as 2250 ± 10 MPa, 20.0 ± 0.50% and 743 ± 12Hv, respectively. © 2016 Published by Elsevier Ltd.

Gu J.,Nanjing University of Aeronautics and Astronautics | Gu J.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Gu J.,Nanjing Institute of Technology | Sun H.,Nanjing University of Aeronautics and Astronautics | Fang C.,Nanjing University of Aeronautics and Astronautics
Smart Materials and Structures | Year: 2015

A multi-branch thermoviscoelastic-themoviscoplastic finite deformation constitutive model incorporated with structural and stress relaxation is developed for a thermally activated shape memory polymer (SMP) based syntactic foam. In this paper, the total mechanical deformation of the foam is divided into the components of the SMP and the elastic glass microballoons by using the mixture rule. The nonlinear Adam-Gibbs model is used to describe the structural relaxation of the SMP as the temperature crosses the glass transition temperature (Tg). Further, a multi-branch model combined with the modified Eying model of viscous flow is used to capture the multitude of relaxation processes of the SMP. The deformation of the glass microballoons could be split into elastic and inelastic components. In addition, the phenomenological evolution rule is implemented in order to further characterize the macroscopic post-yield strain softening behaviors of the syntactic foam. A comparison between the numerical simulation and the thermomechanical experiment shows an acceptable agreement. Moreover, a parametric study is conducted to examine the predictability of the model and to provide guidance for reasonable design of the syntactic foam. © 2015 IOP Publishing Ltd.

Yuping L.,Nanjing Institute of Technology | Yuping L.,Jiangsu Key Laboratory of Advanced Structural Materials and Application Technology | Yunfei W.,Hengdian Group DMEGC Magnetics Co. | Daxin B.,Hengdian Group DMEGC Magnetics Co.
Journal of Materials Science: Materials in Electronics | Year: 2016

In order to fabricate high magnetic performance La–Co substituted Sr–Ca hexagonal ferrites, an improved ceramics process was proposed in this study. The particle size of the ferrite powder was measured by laser diffraction particle size analyzer. The microstructures of the sintered ferrites were observed by scanning electron microscopy. The magnetic properties of the sintered ferrite magnets were measured by B–H loop recorder. The results show that, sub-micrometer ferrite powder with narrow particle size distribution could be produced by microwave reheating–remilling treatment. Ferrite magnet with fine grained microstructure and enhanced coercivity could be synthesized by using the powder as precursor. © 2016 Springer Science+Business Media New York

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