20 January 2018, Volume 42 Issue 1
    

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  • Oxidation Behaviour of Incoloy800H Alloy in High-Temperature Pure Steam
    YANG Zhen, LU Jintao, LE Ming, ZHOU Yongli, LI Hao, YUAN Yong
    Materials For Mechanical Engineering. 2018, 42(1): 1-6. https://doi.org/10.11973/jxgccl201801001
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    The oxidation behaviour of Incoloy800H alloy in 750℃ and 850℃ pure steam was investigated by discontinuous weighing method, X-ray diffraction, and scanning electron microscopy. The results show that the oxidation kinetics of the tested alloy followed a parabolic law; the oxidation accelerated rapidly with rising temperature. After oxidation in 750℃ steam, an oxide layer mainly composed of (Cr, Mn)2O3 was formed on the surface of the tested alloy, discontinuous bulgy Fe3O4 was distributed on the oxide layer and Cr in the matrix under the oxide layer was oxidized internally to Cr2O3. After oxidation in 850℃ steam, a duplex oxide layer, composed of a thin outer layer of (Fe, Mn)3O4 and a thick inner layer of (Cr, Mn)2O3, was formed on the surface of the tested alloy; beneath the oxide layer, Al was oxidized inernally to Al2O3 along grain boundaries in the matrix.
  • Effects of Ultrasonic Surface Rolling Process on Microstructure and Surface Integrity of Ti-6Al-4V Alloy
    CAI Zhen, ZHANG Xiancheng, TU Shantong
    Materials For Mechanical Engineering. 2018, 42(1): 7-10,17. https://doi.org/10.11973/jxgccl201801002
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    The ultrasonic surface rolling process (USRP) was performed on the annealed Ti-6Al-4V alloy using employing the rectangular-ambulatory-plane machining path. The microstructure and surface integrity of Ti-6Al-4V alloy after USRP were characterized by equipments such as optical microscope, transmission electron microscope, vickers indenter, X-ray diffraction residual stress analyzer and surface three-dimensional topography. The results show that a plastic deformation layer with around 300 μm thickness was formed on the surface of Ti-6Al-4V alloy after USRP. The surface of plastic deformation layer was the equiaxial nanocrystal layer and the subsurface was the long strip shaped nanocrystalline laminar layer with the same grain orientation. The maximum mirco-hardness of Ti-6Al-4V alloy was 390 HV and the surface roughness reduced from 0.76 μm to 0.23 μm after USRP. The residual compressive stress of Ti-6Al-4V alloy increased first and then decreased with the increase of distance from surface.
  • Solid-Liquid Synergistic Sintering Kinetics and Densification Model of B4C Ceramics
    SHI Xiumei, CUI Hong, CHEN Gang, CAO Jianwu, TANG Weihong, ZHANG Lijun
    Materials For Mechanical Engineering. 2018, 42(1): 11-17. https://doi.org/10.11973/jxgccl201801003
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    B4C ceramics with different raw powder ratios were prepared by solid-liquid synergistic sintering with different sintering parameters. The influence of sintering temperature and sintering time on the linear shrinkage of B4C ceramic was studied. The effect of raw powder ratio and sintering temperature on the apparent activation energy was investigated. The solid-liquid synergistic sintering kinetics was analyzed, and the solid-liquid synergisticsintering densification model established considering the sintering temperature, sintering time, raw powder ratio, and green density. The accuracy of the model was assessed. The results show that there was a strong positive correlation between the sintering density predicted by the sintering densification model and sintering density measured, and the average absolute relative error was less than 20%. The model could predict the relationship well between sintering density and the sintering temperature, sintering time, raw powder ratios in the process of solid-liquid synergistic sintering of B4C ceramics.
  • Arc Erosion Behavior of W/Cu Current-Carrying Frictional Pairs
    SONG Lianmei, ZHANG Yongzhen, SHANGGUAN Bao
    Materials For Mechanical Engineering. 2018, 42(1): 18-22. https://doi.org/10.11973/jxgccl201801004
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    Current-carrying arc erosion tests of W/Cu current-carrying frictional pairs were carried out by the home-made current-carrying arc tester. The arc erosion behavior and arc erosion mechanism were studied. The results show that with the arcing time increasing, the current of current-carrying arc decreased, the voltage increased, and the electric field intensity first increased then decreased. The current-carrying arc was divided into three stages of ignition, stable burning and extinction. The time intervals of the three stages were about 7%,89% and 4% of the total arcing time. The serious arc erosion of copper specimen occurred at the ignition stage and at the beginning of stable burning stage. With the increase of test current, the existence time interval of the arc in metallic vapour state extended; the width of arc erosion pit on copper specimen surface increased and the depth first increased then decreased. The results were related to the increasing deposition of tungsten with high melting point.
  • Hydrogen Embrittlement Resistance and Influence Factors of 34CrMo4 Steel for High Pressure Cylinder
    YIN Xieping, WU Chuanxiao, JIANG Xijun, GAO Zengliang
    Materials For Mechanical Engineering. 2018, 42(1): 23-27,32. https://doi.org/10.11973/jxgccl201801005
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    To ensure the safe use of high pressure cylinders with the risk of hydrogen embrittlement, the chemical composition analysis, mechanical property testing and hydrogen embrittlement resistance test of 34CrMo4 steel for high pressure cylinder from two domestic steel mills were conducted. The hydrogen embrittlement resistance and influence factors of 34CrMo4 steel from different steel mills were studied and compared. The results show that the main chemical composition of 34CrMo4 steel from different steel mills was basically the same. Due to relatively big differences in the content of the gas elements O, N and H, the harmful elements P and S and the trace elements (V+Nb+Ti+B+Zr), in the grade of non-metallic inclusions, and in the impact properties of the steel, the tensile strength for passing the hydrogen embrittlement test was different, which was 901 MPa and 968 MPa, respectively. The corresponding maximum hydrogen embrittlement indexes were 1.93 and 1.92, respectively. For the high pressure cylinders with the risk of hydrogen embrittlement, the maximum tensile strength and the yield ratio of the materials should be limited. In addition, the content of harmful elements P and S and that of the trace elements (V+Nb+Ti+B+Zr) should be limited.
  • Preparation and Formula Optimization of Glass Fiber Sealing Gasket by Beater-Addition Process
    FENG Hongfei, LIU Meihong, TIAN Shuo, JIAO Jian, KANG Yuchi
    Materials For Mechanical Engineering. 2018, 42(1): 28-32. https://doi.org/10.11973/jxgccl201801006
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    Glass fiber with surface treatment was substituted for asbestos fiber, and then sealing gaskets with different formulas were prepared by beater-addition process. The compressibility, recovery, tensile strength and density of the sealing gaskets were tested. The multiple linear regression was used to study the correlation between the performance and the gasket formula. The gasket formula was optimized by multi-objective optimization function. The results show that the content of components in gasket formula had a great influence on the performance of gaskets. With the increase of the content of glass fiber in the gasket formula, the compressibility increased gradually and recovery, tensile strength and density decreased gradually. The tested values of performance were relatively close to the optimal target values after the components of gasket formula were multi-objective optimized by fgoalattain function, and the gasket had relatively good performance after optimization.
  • Effects of Minor Re Adjustment on Microstructure and High-temperature Stress Rupture Properties of the Third Generation Ni-based Single Crystal Superalloy
    FANG Xiang, ZHANG Jian, ZHAO Yunsong, YANG Zhenyu, XU Jianwei, WU Qinghui, JIANG Hua, LUO Yushi
    Materials For Mechanical Engineering. 2018, 42(1): 33-38,43. https://doi.org/10.11973/jxgccl201801007
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    Two single crystal superalloys with nominal composition of Ni-9Ta-6Al-6W-4Co-2Cr-0.4Mo-xRe (x was 6.2, 6.8, respectively, mass fraction/%) were prepared. The effects of Re content on the microstructure and phase transition temperature of the as-cast alloys and on the microstructure and high-temperature stress rupture property of the heat-treated alloys were investigated. The results show that a slight increase of Re content resulted in the increase of the solidification segregation degree and the γ+γ' eutectic structure content in the as-cast alloys. The peak temperatures of rapid dissolution of eutectic structure increased during the solid solution process. The size of γ' phase in the heat-treated alloys decreased slightly and the topological close-packed phase formation increased in the stress rupture process. The minor increase of Re changed the element partitioning ratios of Re and Cr significantly, improved the solid solution strengthening effect and increased the high-temperature stress rupture properties of the alloys strikingly.
  • Effect of Hot Extrusion and Heat Treatment on Microstructure and Tensile Properties of 7075 Aluminum Alloy Prepared by Semi-Solid Method
    ZHU Yongbo, YANG Xiangjie, GUI Yunpeng
    Materials For Mechanical Engineering. 2018, 42(1): 39-43. https://doi.org/10.11973/jxgccl201801008
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    7075 aluminum alloy casting rod was prepared by using semi-solid slurry preparation process of low superheat pouring with a shear field (LSPSF), and homogenization treatment, hot extrusion and T6 heat treatment were carried out in sequence. The effect of hot extrusion and heat treatment on microstructure and tensile properties of the aluminum alloy was investigated. The results show that the near spherical grains in the as-cast aluminum alloy changed into irregular shapes in the process of hot extrusion. The relatively obvious grain boundary in the structure of the aluminum alloy was formed after T6 treatment. (110) crystal plane in the microstructure of the aluminum alloy had preferred orientation after treated by hot extrusion and T6 heat treatment. The tensile strength and yield strength of the aluminum alloy treated by hot extrusion increased by 136% and 140% comparing with those of the aluminum alloy in as-cast state, respectively. After T6 heat treatment, the tensile strength and yield strength were further improved. The fracture mode of the aluminum alloy in as-cast state was brittle fracture, and the fracture modes after hot extrusion and T6 heat treatment were both ductile fracture.
  • Microstructure and Mechanical Properties of Welded Joint of NM450 Wear-Resistant Steel Plate
    DONG Xianchun, ZHANG Nan, HAN Nidan, CHEN Yanqing
    Materials For Mechanical Engineering. 2018, 42(1): 44-47,53. https://doi.org/10.11973/jxgccl201801009
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    NM450 wear-resistant steel plates were welded with ER50-6 welding wire by CO2 gas-shield welding. The microstructure, mechanical properties and welding cold crack sensitivity of the joint were studied. The results show that the microstructure of the weld was composed of massive ferrite and needle-shaped ferrite, and that of the coarse-grained heat-affected zone and of the normalized zone was composed of lath martensite and ferrite+cementite, respectively. The hardness of weld metal, coarse-grained zone, normalized zone and incomplete recrystallization zone was 220, 412, 234, 386 HV, respectively. The decomposition of martensite led to the decrease of hardness in the normalized zone and incomplete recrystallization zone. The tensile strength of welded joint was 768 MPa. The impact energy of weld center, heat-affected zone and base metal at -20℃ was 110, 140, 88 J, respectively. The steel had a certain cold crack sensitivity. No cracks were produced for the welding at 32.6℃ without preheating. Both the root crack percentage and cross-sectional crack percentage were 100% for the welding at -1.4℃ without preheating, while no welding cracks were produced after preheating at 80℃.
  • Effect of Al-5Ti-0.2C Refiner on Microstructure and Mechanical Properties of 5356 Aluminum Alloy
    HUANG Yuwei, LI Anmin, DONG Tao
    Materials For Mechanical Engineering. 2018, 42(1): 48-53. https://doi.org/10.11973/jxgccl201801010
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    Effect of mass fraction of Al-5Ti-0.2C refiner and refinement holding time on the microstructure and mechanical properties of 5356 aluminum alloy was studied by using optical microscope, scanning electron microscope, energy disperse spectroscopy and universal material testing machine. The results show that the grain of 5356 aluminum alloy was refined significantly after adding Al-5Ti-0.2C refiner. With the increase of refinement holding time and mass fraction of refiner, the grain size of aluminum alloy decreased first and then increased. The mechanical properties of aluminum alloy were improved after adding the refiner. When the mass fraction of refiner was 3% and refining for 20 min, the elongation of the aluminum alloy was the largest, which was 12.58%, and the aluminum has the best comprehensive mechanical properties.
  • Microstructure and Mechanical Properties of Laser Welded Dissimilar Joint of DP780/HC660 Dual-phase Steels with Different Thicknesses
    LIANG Jingwei, QIU Xiaoming, HU Qingwei, LIU Wensheng, LIU Yongcheng
    Materials For Mechanical Engineering. 2018, 42(1): 54-58,63. https://doi.org/10.11973/jxgccl201801011
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    1.2 mm thick DP780 dual-phase steel and 1.0 mm thick HC660 dual-phase steel were butt welded by CO2-laser welding. The microstructure and mechanical properties of the dissimilar joint were studied. The results show that the microstructure of weld zone in the welded joint consisted of coarse lath martensite and a little ferrite. The microstructure of heat affected zone was uneven and could be divided into coarse grained zone, fine grained zone and intercritical zone. The microhardness of the welded joint was asymmetrically distributed around the weld zone center. The average microhardness of the weld zone, heat affected zone and base metal decreased successively. A softening phenomenon was observed in the heat affected zone. The tensile strength of the welded joint was close to that of the HC660 dual-phase steel, while the elongation was reduced to 7.8%. Fracture occurred in HC660 dual-phase steel near heat affected zone. The fracture mode was ductile fracture.
  • Effect of Single Overload on Fatigue Crack Growth Rate of 2205 Duplex Stainless Steel
    GENG Yue, CHEN Ji
    Materials For Mechanical Engineering. 2018, 42(1): 59-63. https://doi.org/10.11973/jxgccl201801012
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    The fatigue crack growth test of 2205 duplex stainless steel at overload ratios of 1.0, 1.5, 2.5 and 3.5 was carried out by using an electro-hydraulic servo fatigue tester. The effect of single overload on the fatigue crack growth rate was studied. The results show that the bigger the overload ratio was, the longer the stagnation time of crack growth of 2205 duplex stainless steel was and the greater the reduction of fatigue crack growth rate was. When the overload ratio was less than 3.5, the crack tip passivated or closed due to the single overload, and the fatigue crack growth rate dropped obviously or even stagnated temporarily. When the overload ratio was 3.5, the crack tip deflected and bifurcated, and the fatigue crack growth stopped completely.
  • Microstructure and Properties of Sn-Zn-In-Bi-Al Solder Alloy for Sputtering Target Bonding
    YAN Huijiang, ZHANG Jianxin, BU Lijing, ZHU Chaogang, YANG Yong, CHU Zhenhua, DONG Yanchun, HE Jining, LIU Na
    Materials For Mechanical Engineering. 2018, 42(1): 64-67,71. https://doi.org/10.11973/jxgccl201801013
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    Four solder alloys of Sn-7.0Zn-xIn-3.8Bi-0.2Al (x=0, 4.5, 5.0, 5.5) were prepared by microalloying method. The influence of the In content on the microstructure, melting point, wettability, electrical conductivity, thermal conductivity of the solder alloys were studied, and compared with the performance of traditional pure In and Sn solders. The results show that the solder alloys consisted essentially of β-Sn and Zn-rich phases. The melting point of the solder alloys gradually decreased and the wettability, electrical conductivity, thermal conductivity increased with the increase of In content.The melting point and wettability of Sn-7.0Zn-5.0In-3.8Bi-0.2Al solder alloy were better than those of pure Sn solder and close to those of of pure In solder. The resistivity and thermal conductivity of the solder alloy were close to those of of pure Sn solder.It was confirmed that Sn-7.0Zn-5.0In-3.8Bi-0.2Al solder alloy was suitable for sputtering target bonding.
  • Effect of Hot Extrusion on Microstructure and Tensile Strength of Powder Metallurgy 6061 Aluminum Alloy
    YUAN Guosen, YANG Zhanyao
    Materials For Mechanical Engineering. 2018, 42(1): 68-71. https://doi.org/10.11973/jxgccl201801014
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    In order to improve the density and mechanical property of 6061 aluminum alloy prepared by powder metallurgy, hot extrusion process was applied to the 6061 alloy in sintered state. The effect of hot extrusion on microstructure and tensile strength of 6061 aluminum alloy was researched. The results show that the microstructure of the aluminum alloy in sintered state was equiaxed grain distributed uniformly. After hot extrusion, the grains were distributed like bandings and grain size decreased. The relative density of the aluminum alloy in sintered state was 96.67% and relative density of the aluminum alloy after hot extrusion increased to 98.14%. The tensile strength increased from 112 MPa to 248 MPa after hot extrusion. The fracture type of the aluminum alloy in sintered state was ductile fracture and fracture type of the aluminum alloy in hot-extruded state was mixed mode of ductile fracture and intergranular fracture.
  • Yield Strength and Strain Hardening Exponent of Metal Material Evaluated by Micro-load Continuous Ball Indentation Method
    JIN Zhuang, ZHAO Jianping
    Materials For Mechanical Engineering. 2018, 42(1): 72-77. https://doi.org/10.11973/jxgccl201801015
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    The method of testing mechanical properties of materials by existing ball indentation was improved and the load-depth curve of metal material was obtained by a continual cycle loading method instead of multipoint single loading method. The dimensionless functions and related apparent strain function during indenter pressing into metal material were fitted by dimensional analysis and finite element anslysis, and the elastic-plastic parameters and stress-strain curves of different metal materials were obtained and verified by the test data. The results show that the error of elastic-plastic parameters between the caculation results obtained by this method and the test data was about 5%. The stress-strain curves were in good agreement.
  • Effects of Uneven Wall-Thickness on Creep Lifetime of P92 Steel Pipe Bend Subjected to In-plane Bending
    LAN Xiang, XU Hong, YANG Le, NI Yongzhong
    Materials For Mechanical Engineering. 2018, 42(1): 78-83,88. https://doi.org/10.11973/jxgccl201801016
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    Based on high temperature creep test of P92 steel pipe bend subjected to in-plane bending the high temperature creep process of the pipe bend with different eccentricity subjected to in-plane bending was simulated by finite element method. The stress and damage at different positions of the bend were analyzed. The relationship model between the eccentricity of pipe bend and the creep lifetime was established and verified by the experimental results. The results show that the creep life of the pipe bend with extrados reduction increased with the increase of eccentricity and had a linear relationship. The creep life of the pipe bend with flank reduction decreased with the increase of eccentricity and showed a slowing trend. The experimental results verified the accuracy of the relationship model and the relationship model could be used to estimate the creep life of pipe bends with uneven wall-thickness subjected to plane bending accurately.
  • Residual Stress Reduction of 7050 Large-Scale Aluminum Alloy Forging Based on Segmented Cold-Pressing Method
    YAO Shijie, XIA Weijun, YUAN Wuhua, CUI Mingliang
    Materials For Mechanical Engineering. 2018, 42(1): 84-88. https://doi.org/10.11973/jxgccl201801017
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    The quenching-induced residual stress of 7050 large-scale aluminum alloy forging was reduced by segmented cold-pressing method. The value and distribution of the residual stress of the forging before and after segmented cold-pressing were simulated by Deform-3D finite element software, and the residual stress of the forging was tested by the blind hole method. The results show that the residual stress of the forging was effectively reduced after segmented cold-processing. The residual stresses measured were less than 130 MPa and the 70.3%-97.4% reduction was achieved. The reduction range of residual stresses in the non-lap zone was bigger than that in the lap zone. The simulation results agreed with the test results.
  • Failure Reason of the Blade of Top Gas Energy Recovery Turbine
    LIU Mingxia, CHANG Gengrong, FU Fuxing, HE Binfeng, MA Fei, CHEN Mingke, YU Lijun, DAI Jun, XU Kewei
    Materials For Mechanical Engineering. 2018, 42(1): 89-94. https://doi.org/10.11973/jxgccl201801018
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    Cracks were found in the first and second stage rotor blade root section of a wet-typed top gas energy recovery turbine (TRT) after operation for 3 a. In order to investigate the cause for cracks, the failure analysis of the blade was performed by macroscopic morphology observation, chemical composition analysis, tensile property test and microscopic morphology observation. The results show that the blade failure was a typical corrosion fatigue damage. The cracks were located in the middle of the first tenon of the blade root. The cracks were initiated from corrosion pits on the contact surface of blade root and shaft groove. Under the effect of complex alternating stress, cracks propagated further, which eventually led to the abnormal vibration and the shut-down of the TRT.
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