20 May 2018, Volume 42 Issue 5
    

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  • WEI Xin, ZHAO Longhai, TAN Yi, YOU Xiaogang, SHI Shuang, YOU Qifan
    Materials For Mechanical Engineering. 2018, 42(5): 1-8,13. https://doi.org/10.11973/jxgccl201805001
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    Vacuum induction melted Inconel718 alloy was refined by electron beam smelting. The high temperature oxidation behaviour of the alloy before and after electron beam refining was studied and compared by isothermal oxidation tests in the air at 900, 1 000℃. The results show that the average oxidation rate of the electron beam refined alloy oxidized at 900℃ for 120 h was 0.366 20 g·m-2·h-1, smaller than that before refining; the oxidative activation energy was 280.90 kJ·mol-1, higher than that before refining. The outer layer of the oxide film of the electron beam refined alloy oxidized at 900℃ and 1 000℃ for 120 h was composed of Cr2O3 and TiO2, the middle layer consisted of Cr2O3 and a small amount of TiO2 and spinel NiCr2O4, and the inner layer was mainly composed of Al2O3. The content of trace impurity elements distributed evenly in the electron beam refined alloy was relatively small, grain size was larger,and the alloy had a better antioxidant property.
  • LIU Changkui, ZHOU Jingyi, WEI Zhenwei, CHEN Feng, TAO Chunhu
    Materials For Mechanical Engineering. 2018, 42(5): 9-13. https://doi.org/10.11973/jxgccl201805002
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    The heat exposure test at 650℃ for different times was carried out on FGH97 powder metallurgy superalloy. The evolution rule of microstructure was analyzed by scanning electron microscopy, and the γ' phase in the course of evolution was quantitatively characterized. The results show that with the extension of heat exposure time, the shape of γ' phase in the FGH97 powder metallurgy superalloy changed from regular square and triangle to butterfly or octagon, and then to irregular shape such as strip and rod. The cracking occurred in the secondary γ' phase and the amount of tertiary γ'phase particles in the grains decreased. As the heat exposure time increased, the average equivalent diameter of γ' phase in the FGH97 powder metallurgy superalloy first increased and then decreased, the shape factor decreased, the volume fraction increased, and the amount of γ' phase gathered at the grain boundaries increased significantly.
  • LI Guangyu, ZENG Xinrui, WANG Nan, GU Xuezhong, FANG Ziqi
    Materials For Mechanical Engineering. 2018, 42(5): 14-19. https://doi.org/10.11973/jxgccl201805003
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    AISI 316 austenitic stainless steel was modified by plasma source nitriding technique at 450℃ for 6 h. The friction and wear behavior of the stainless steel substrate and surface modified layer against Si3N4 ceramic ball friction pairs was investigated comparatively under different loads by dry friction and wear tests. The wear morphology was observed and the wear mechanism was analyzed. The results show that a high-nitrogen γN phase layer with single face-centered-cubic structure and thickness of 17 μm was prepared on the surface of the tested steel after plasma source nitriding. The atom fraction of nitrogen element of γN phase layer was 15%-20% and the highest micro-hardness was about 1 510 HV0.01. The friction coefficient of the γN phase layer was equivalent to or smaller than that of the substrate under the same load, the specific wear rate was reduced by one order magnitude and the wear resistance was improved. The main wear mechanism of the substrate was adhesive wear. The main wear mechanism of the γN phase layer was oxidative wear under relatively low loads (2-4 N) and abrasive wear under relatively high loads (6-8 N).
  • ZHOU Jixue, CHEN Yanfei, SONG Xiaocun, LIU Hongtao, YANG Yuansheng
    Materials For Mechanical Engineering. 2018, 42(5): 20-26,31. https://doi.org/10.11973/jxgccl201805004
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    AZ31B magnesium alloy and 6061 aluminum alloy dissimilar metal riveted part was micro-arc oxidized. The microscopic morphology, phase composition, electrochemical property and hardness of the oxidation film after micro-arc oxidation for different times were studied. The formation process of the oxidation film on the surface of magnesium alloy and aluminum alloy was comparatively analyzed during micro-arc oxidation. The results show that the connected part was integrally wrapped by the oxidation film after micro-arc oxidation for 10 min. The oxidation film connected with the two alloy substrates tightly and consisted of a compact layer and a loose layer. The oxidation film on the surface of magnesium alloy was composed of MgO and a small amount of silicates and fluoride. The oxidation film on the surface of aluminum alloy consisted of Al2O3 and a small amount of silicates. The micro-arc oxidation improved the corrosion potential of the magnesium alloy and aluminum alloy, reduced the corrosion potential difference between them and effectively alleviated the occurrence of galvanic corrosion.
  • YU Junfeng, YANG Guang, WANG Jing, XING Yunying, WANG Xiuyun
    Materials For Mechanical Engineering. 2018, 42(5): 27-31. https://doi.org/10.11973/jxgccl201805005
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    ERNiCrMo-3 nickel-based alloy welding wire was deposited on the surface of X70 pipeline steel by manual tungsten inert gas welding. The microstructure, element distribution and hardness distribution of the interface between the surfacing layer and base metal were analyzed. The initiation and propagation mode of hydrogen induced cracks were studied by electrochemical hydrogen charging method. The results show that the microstructure of fine grained region in heat affected zone of the interface between nickel-based alloy surfacing layer on X70 pipeline steel and base metal was fine ferrite and a small amount of pearlite. The microstructure of coarse grained region near fusion line was coarse ferrite. The microstructures of the fusion zone and surfacing layer were martensite and dendritic austenite, respectively. The impact fracture of surfacing layer showed a ductile fracture feature, the base metal showed a cleavage or quasi-cleavage brittle fracture feature, and fusion zone showed a mixture transition feature with deformation characteristics composed of shallow dimples and quasi-cleavage. The hardness of both the surfacing layer and fusion zone was higher than that of the base metal. The hydrogen induced cracks of the surfacing layer originated around the inclusions of Al2O3 and monatomic silicon, and propagation mode was intergranular and transgranular propagation.
  • WEN Naimeng, REN Yuling
    Materials For Mechanical Engineering. 2018, 42(5): 32-34,39. https://doi.org/10.11973/jxgccl201805006
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    The hot-dipped 55%Al-Zn steel sheet was baked at 300,350,400,450℃, respectively, and the changes of the gloss, mass per unit area, morphology, chemical composition and bonding performance of the hot-dipped aluminum zinc steel sheet baked for 24 h at different temperatures were studied. The heat resistance of the steel sheet was analyzed. The results show that the performance of the plating did not change after baking at 350℃ or below for 24 h. When baked at 400℃ for 24 h, the gloss of the plating declined slightly, the cracks appeared on the surface, but the surface morphology, chemical composition, mass per unit area and bonding performance changed little. When baked at 450℃ for 24 h, the gloss and mass per unit area of the plating decreased obviously, the bonding performance got worse, and part of the plating flaked off.
  • LIU Xiufeng, GE Yangyang, GE Dayong, LI Jiahui, GUO Cong, DAI Xiuhong, LIU Baoting
    Materials For Mechanical Engineering. 2018, 42(5): 35-39. https://doi.org/10.11973/jxgccl201805007
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    Na0.5Y0.5TiO3 (NYT) ferroelectric thin film was prepared on the substrate of single-crystal niobium doped strontium titanate (Nb:STO) with[001] orientation by radio frequency magnetron sputtering. The phase composition, microstructure, ferroelectric properties and electrical transport properties of the ferroelectric thin film were studied. The results show that the NYT thin film had a[001] oriented epitaxial structure, the surface was smooth, the interface was clear, and the crystalline quality was good. The NYT thin film had ferroelectric properties with remanent polarization of 0.3 μC·cm-2 and coercive field of 178 kV·cm-1. The Schottky barrier was found at the NYT thin film/electrode interface. The reverse-biased Schottky junction decreased the leakage current density significantly and increased the breakdown electric field strength of NYT thin film. The current conduction in the forward-biased state of Schottky junction complied with the space charge limited current mechanism controlled by trapping state.
  • LIU Yan, LI Zongyi, ZHANG Xiaogang, ZHANG Hao
    Materials For Mechanical Engineering. 2018, 42(5): 40-44. https://doi.org/10.11973/jxgccl201805008
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    Selective laser melting forming was applied to 316L stainless steel powder. The effects of laser power, scanning speed and scanning interval on the relative density, tensile properties and micromorphology of formed samples were analyzed by the orthogonal method, and the optimal process parameters were obtained. The results show that the tensile strength, yield strength and relative density of the formed sample increased and then decreased with increasing laser power or scanning speed, and increased with increasing scanning interval. The elongation decreased and then increased with increasing laser power, increased with increasing scanning speed, and changed little with increasing scanning interval. The optimal process parameters obtained were as follows:laser power of 310 W, scanning speed of 960 mm·s-1 and scanning interval of 0.13 mm. The relative density, tensile strength and yield strength of the formed sample with the optimal process parameters were the highest of 99.53%, 613 MPa and 320 MPa, respectively, and the elongation was 44.6%; the formed sample had a smooth surface and small pores; the tensile fracture showed small and uniform dimples and less balling phenomena.
  • TANG Huili, REN Yu
    Materials For Mechanical Engineering. 2018, 42(5): 45-49,77. https://doi.org/10.11973/jxgccl201805009
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    Ordered mesoporous CuO was prepared by a nitrate combustion method with mesoporous silica KIT-6 as template, and characterized by X-ray diffractometer, transmission electron microscope, and specific surface area and porosity analyzer. The results show that the prepared mesoporous CuO had a highly ordered mesoporous structure and a nanosized crystal structure with bi-modal pore size distribution centered at 3.7 nm and 10 nm. With the sintering temperature increasing from 300℃ to 700℃, the mesoporous structure of mesoporous CuO contracted, the grain size increased, and the specific surface area decreased. The mesoporous CuO had the stable electrochemistry performance and small molecular gas adsorption performance, which had a discharge capacity over 600 mAh·g-1 after 50 cycles of charge-discharge at current density of 100 mA·g-1, and adsorption capacities of 1.2, 0.75 mmol·g-1 for NO and CO, respectively.
  • DENG Suhuai, MA Yue, ZHANG Huifeng, LÜ Naibing
    Materials For Mechanical Engineering. 2018, 42(5): 50-54. https://doi.org/10.11973/jxgccl201805010
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    Microstructure and properties of high carbon chromium steel with 4wt% aluminum after annealing treatment were studied by means of optical microscope, scanning electron microscope and hardness tester, and compared with those of Al-free high carbon chromium steel. The results show that the density of the high carbon chromium steel with 4wt% aluminum was 7.33 g·cm-3 which was reduced by 6% than that of the Al-free high carbon chromium steel, the critical transition points increased, two phase region was expanded, the suitable annealing temperature increased by 100℃, and the hardness was higher than that of the Al-free high carbon chromium steel. The Al-free high carbon chromium steel was a hypereutectoid steel, while the high carbon chromium steel with 4wt% aluminum was a hypoeutectoid steel. Aluminum dissolved in ferrite completely and changed the precipitation sequence of second phases, therefore the ferrite phase was formed before carbide phase.
  • CHEN Yeqing, WU Yiwen, QIN Ziwei, ZHOU Xiao, WANG Hongbin
    Materials For Mechanical Engineering. 2018, 42(5): 55-58,62. https://doi.org/10.11973/jxgccl201805011
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    GCr15 bearing steel was treated by quenching+tempering, quenching+tempering+deep cryogenic, quenching+deep cryogenic+tempering, quenching+tempering+deep cryogenic+tempering treatment, respectively, and the influence of deep cryogenic treatment on microstructure, hardness and wear resistance of GCr15 bearing steel was discussed. The results show that comparing with that treated by traditional quenching+tempering treatment, the content of retained austenite in the samples treated by the process with addition of deep cryogenic treatment decreased, the hardness increased and wear resistance was improved. The content of retained austenite in the sample treated by quenching+deep cryogenic+tempering was the lowest, the hardness was the highest, the wear resistance was the best, and the wear loss was reduced by 6% compared with that treated by quending and tempering treatment. The deep cryogenic treatment improved the fatigue wear resistance and abrasive wear resistance of GCr15 bearing steel.
  • LI Tianyi, MA Chao
    Materials For Mechanical Engineering. 2018, 42(5): 59-62. https://doi.org/10.11973/jxgccl201805012
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    The effect of mass fraction of hydrochloric acid, temperature and soaking time on the hydrochloric decomposition rate of thermoplastic polyurethane modified polyoxymethylene (TPU/POM) plastics with different formulas was studied. The optimum process parameters for the decomposition of the TPU/POM plastics were determined and the appearance of the sample after decomposition was observed. The results show that the decomposition rate of TPU/POM plastics sample increased with the increase of hydrochloric acid mass fraction, temperature and soaking time. The optimum process parameters for the complete decomposition of POM in the sample were listed as follows:the hydrochloric acid mass fraction of 20%, the temperature of 50℃ and the soaking time of 6 h or the hydrochloric acid mass fraction of 20%, the temperature of 60℃, and the soaking time of 2 h or 3 h. With the optimum parameters, the morphology of decomposed sample was changed to a porous cylinder shape with a smaller diameter from tiny particle shape with increasing content of TPU.
  • HAN Shuang, DUAN Haitao, YANG Xuejun, GU Kali
    Materials For Mechanical Engineering. 2018, 42(5): 63-68,73. https://doi.org/10.11973/jxgccl201805013
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    The surface of ductile cast iron was treated by ultrasonic machining. The three-dimensional morphology, surface roughness and microstructure of the surface of non-machining area and machining area were studied by using white light confocal microscope, scanning electron microscope, optical microscope and Vickers hardness tester. The results show that the ultrasonic machining had little effect on the size of the sample, and the continuous polishing was achieved. The transition zone between non-machining area and machining area had a butterfly shaped protrusion with height of about 30 μm. The surface roughness of the sample was reduced by ultrasonic machining significantly. The arithmetical mean deviation of the profile changed from 1.465 μm before machining to 0.948 μm, being reduced by 35.29%. The grains in the surface layer of the sample were refined obviously after ultrasonic machining; the surface hardness of the sample increased. The effect depth of ultrasonic machining on the hardness of the sample was about 0.6 mm.
  • CAI Zhenjie, WANG Jiaqi
    Materials For Mechanical Engineering. 2018, 42(5): 69-73. https://doi.org/10.11973/jxgccl201805014
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    Polyetheretherketone (PEEK)composites containing polytetrafluoroethylene (PTFE)micro-powder with different content were prepared by mechanical mixing at room temperature and hot compressing molding. The mechanical properties, friction and wear properties and wear morphology of the composite were studied, and the friction and wear mechanism was discussed. The results show that with increasing content of PTFE micro-powder, Rockwell hardness and compression strength of the composite decreased; the friction coefficient decreased and the volume wear loss decreased first and then increased under dry friction condition. The volume wear loss under dry friction condition was the smallest when the mass fraction of PTFE micro-powder was 5%. The friction coefficient and volume wear loss under oil and water lubrication conditions were both smaller than that under dry friction condition. The volume wear loss decreased under oil lubrication condition and increased under water lubrication condition with the increase of PTFE micro-powder content. The wear mechanism of composite under dry friction condition was mainly abrasive wear accompanied by fatigue wear; a small amount of lamellar PTFE wear debris and enrichment of carbon fiber were found on the surface of the composite under oil lubrication condition; the surface of the composite was covered by PTFE micro lamella, and micro cracks and cavities existed in the local area under water lubrication condition.
  • LIU Jiao, ZHENG Hui, FAN Zhao
    Materials For Mechanical Engineering. 2018, 42(5): 74-77. https://doi.org/10.11973/jxgccl201805015
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    The leakage of the weld of an elbow in the sequence after pneumatic control valve of drain pipe of high pressure cylinder extraction line occurred in a nuclear power plant. The failure analysis of the weld was carried out by means of the macroscopic morphology and microstructure observation, fracture morphology analysis, and vibration and strain measurement. The results show that the intermittent opening and closing of the pneumatic control valve resulted in the large alternating stresses in the weld, which was greater than the fatigue strength and led to fatigue cracking. The residual tensile stress existing in the weld promoted the extension of the cracks. Turning the intermittent drain into continuous drain by adding one bypass drain pipe on the pneumatic control valve return road could avoid the occurrence of such failure effectively.
  • MIAO Chunhui, ZHANG Tao, CHEN Guohong, WANG Ruomin, LI Jianlin, TANG Quan
    Materials For Mechanical Engineering. 2018, 42(5): 78-81,86. https://doi.org/10.11973/jxgccl201805016
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    The microstructure, micro area composition, electrochemical corrosion property and corrosion product composition of the corroded Al-Mg-Cu alloy drainage plate were investigated and compared with those of the new drainage plate. The reason for corrosion failure was analyzed. The results show that the corrosion of the Al-Mg-Cu alloy drainage plate was caused by acid rain containing sulphur element; the thermal effect of electric current led to the aged structure of the drainage plate, and the precipitation and coarsening of θ phase decreased the corrosion resistance of the drainage plate further.
  • HU Jie
    Materials For Mechanical Engineering. 2018, 42(5): 82-86. https://doi.org/10.11973/jxgccl201805017
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    The fracture morphology, microstructure, chemical composition and tensile properties of a damaged rail head were tested by scanning electron microscope, optical microscope, direct reading spectrometer and tensile testing machine. The reason for formation of longitudinal-transverse kidney-shaped fatigue cracks was discussed and the solutions were proposed. The results show that under the cyclic working stress, the strip crack source was formed at the location of coarse inclusions distributed along the rolling direction in the wheel-rail contacted stress area of the rail head, and then fatigue propagation of the cracks occurred resulting in the formation longitudinal-transverse kidney-shaped fatigue cracks. Improving the purity of the rail steel, strengthening the control and inspection of metallurgical quality of the rail steel and reducing the quantity and refining the size of non-metallic inclusions were the main solutions to prevent the formation of longitudinal-transverse kidney-shaped fatigue cracks.