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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

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. Source

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

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 Source

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

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. Source

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

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. Source

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

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. Source

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