20 August 2018, Volume 42 Issue 8
    

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  • Research Progress on Residual Stress in Metal Component Manufactured by Selective Laser Melting
    LI Jiuxiao, LI Mingpei, YANG Dongye, HE Bo
    Materials For Mechanical Engineering. 2018, 42(8): 1-6. https://doi.org/10.11973/jxgccl201808001
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    Residual stress is one of the key factors leading to the failure of metal components manufactured by selective laser melting (SLM). The generation mechanism and the testing methods of residual stress during SLM manufacturing are described; the influence of SLM process parameters on residual stress is summarized; the future direction of residual stress research of SLM manufactured components is prospected.
  • Effect of Dwelling Time on Microstructure and Property of Cemented Carbide/Steel Joint Fabricated by Partial Transient Liquid Phase Bonding
    GUO Yajie, GUO Dong, ZHOU Tingting, GENG Gangqiang
    Materials For Mechanical Engineering. 2018, 42(8): 7-10,32. https://doi.org/10.11973/jxgccl201808002
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    The sandwich structural titanium foil/nickel foil/titanium foil were used as interlayer materials, and then the dissimilar metal joint of YG10 cemented carbide and 40Cr steel was prepared by partial transient liquid phase (PTLP) bonding at 1 000℃ for different dwelling times (1-4 h). The effects of dwelling time on the micromorphology, phase composition and shear strength of the joint were investigated. The results show that the joint had a multilayer structure composed of YG10 cemented carbide/TiC+WC/Co-Ni-Ti/Ni3Ti/nikle layer/Ni3Ti/NiTi/TiC/40 Cr steel, and a transition layer with width of 30-50 μm was formed between cemented carbide and nickle layer, and between steel and nickle layer, respectively. When the dwelling time increased from 1 h to 4 h, the amount of microcavities in the transition layer of the joint decreased, the thickness of the transition layer increased, and the shear strength of the joint increased first and then decreased. After dwelling for 2 h, the shear strength of the joint reached the largest value of 153 MPa.
  • Composition Optimization and High Temperature Sagging Resistance of Aluminum Alloy Core Material in Composite Aluminum Foil
    GAO Xudong, ZHAO Yuanyuan, JIN Li, WANG Fenghua, DONG Jie
    Materials For Mechanical Engineering. 2018, 42(8): 11-17. https://doi.org/10.11973/jxgccl201808003
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    The effects of content of Mn, Si, Zn, Cu and Ce-rich mixed rare earth on the room-temperature mechanical properties and high temperature sagging resistance of the aluminum alloy on the basis of chemical composition of 3003M aluminum alloy were studied by orthogonal test. The chemical composition of aluminum alloy core material for composite aluminum foil was optimized and the sagging resistance mechanism of the aluminum alloy during brazing was analyzed. The results show that Cu element had the greatest effect on the tensile strength of the tested aluminum alloy, while Si, Mn and Cu elements had significant effects on the sagging resistance. The mass fractions of Mn, Si, Zn, Cu and Ce-rich mixed rare earth of the aluminum alloy with the best properties were 0.5%, 2.5%, 0.8%, 1.2%, 0, respectively. The tensile strength of the optimal aluminum alloy was about 40 MPa higher than that of 3003M aluminum alloy, the elongation increased by about 2 percentage points, and sagging distance was shortened by half. During brazing at 610℃, the secondary recrystallization occurred in the optimal aluminum alloy, and the microstructure was composed of dispersed precipitated phase, primary recrystallization grains and coarse long grains with size of about 1 mm.
  • Dynamic Deformation Behaviour of High Strength Steel Sheet for Automotive
    XIONG Ziliu, LIN Zhangguo, SUN Li, DONG Yikang, LUO Yang, WANG Jian
    Materials For Mechanical Engineering. 2018, 42(8): 18-23,36. https://doi.org/10.11973/jxgccl201808004
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    The room temperature tension tests at strain rates of 0.003 s-1 (quasi-static) and 20-700 s-1 (dynamic) were conducted on DP590 steel sheet and CR340LA steel sheet, and then the dynamic tensile deformation behaviour, strain rate sensitivity and dynamic fracture behaviour of tested steel sheets were studied. The results show that no yield platforms were observed on the dynamic true stress-true strain curves of the two tested steel sheets. After yield, the true stress increased rapidly and then slowly with increasing true strain. The effect of strain rate on yield strength was bigger than that on tensile strength, and the strain rate sensitivity and hardening coefficient of DP590 steel sheet were higher than those of CR340LA steel sheet. The uniform elongation of the two tested steel sheets decreased with strain rate increasing. With increasing strain rate, the dislocation density in DP590 steel sheet increased, and dislocation cells formed at strain rate no less than 200 s-1. Obvious necking occurred during quasi-static stretching of DP590 steel sheet, while no necking occurred during dynamic stretching. With increasing strain rate, the amount of C-shaped dimples on the tensile fracture of DP590 steel sheet decreased, and the amount of equiaxed dimples increased.
  • Effect of Heating Rate for Solid Solution on Microstructure and Properties of Al-10.78Zn-2.78Mg-2.59Cu Aluminum Alloy
    ZHANG Chong, XU Xiaojing, ZHANG Jie, HUANG Peng, DU Donghui, JIA Weijie
    Materials For Mechanical Engineering. 2018, 42(8): 24-28. https://doi.org/10.11973/jxgccl201808005
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    Al-10.78Zn-2.78Mg-2.59Cu aluminum alloy was heated to 470℃ at the heating rates of 3.6℃·h-1 and 180℃·h-1, respectively, then treated by solid solution, and aged subsequently. The effects of heating rate on the microstructure and properties of tested alloy were studied. The results show that the average grain size and the average orientation angle of grain boundaries in tested alloy at the relatively high heating rate was higher, the fraction of low angle grain boundaries was smaller, the mechanical properties were lower and the conductivity was higher than those at the relatively low heating rate. Dimples existed obviously on the tensile fracture of tested alloy at the two heating rates, and the fracture modes were both transgranular. The effect of heating rate on corrosion resistance was little; the intergranular corrosion depth was between 30 μm and 100 μm, the intergranular corrosion grade was 3, and the peeling corrosion grade was PC. The solid solution and aging precipitation strengthening made the most important contribution to yield strength of the tested alloy. Heating up slowly can improve yield strength of the tested alloy effectively.
  • Effect of Graphene Addition Amount on Properties of Pressureless Sintered Graphene/Silicon Carbide Ceramic Composite
    XU Binhuan, LIN Wensong, FU Sujia, HAN Weiyue
    Materials For Mechanical Engineering. 2018, 42(8): 29-32. https://doi.org/10.11973/jxgccl201808006
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    Graphene/silicon carbide ceramic composites were prepared by pressureless sintering silicon carbide powders with addition of 1wt%-5wt% graphenes at 2 190℃ for 1 h. The effects of graphene addition amount on the phase composition, density and mechanical properties of the composite were studied. The results show that the composite was composed of silicon carbide phase and small amount of graphite phase. With the increase of graphene addition amount, the density of the composite decreased, the relative density changed little, the bending strength and fracture toughness increased first and then decreased, and the hardness decreased. When the mass fraction of graphene was 3%, the bending strength of the composite was 395 MPa, the hardness was 89 HRA and the fracture toughness was 6.0 MPa·m1/2; the comprehensive mechanical properties were the highest.
  • Microscopic Characteristics of Melted Mark of Copper Wire in Electrical Fire
    XU Na, SHI Junbo, LI Enxia, CHEN Lizong, LIU Long, GUO Weimin, HU Zhiwen
    Materials For Mechanical Engineering. 2018, 42(8): 33-36. https://doi.org/10.11973/jxgccl201808007
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    The fire melted mark, primary short circuited melted mark and secondary short circuited melted mark of the copper wire were prepared by simulation experiments. The micromorphology of these marks were observed and the microscopic characteristics was summarized. The results show that no holes existed at fracture of the fire melted mark. The microscopic characteristics of the primary short circuited melted mark before and after being treated at high temperature was the same; uniform and fine holes existed at the fracture and the fracture presented an oval pattern. The holes at fracture of the secondary short circuited melted mark varied in size and the fracture presented a honeycomb pattern.
  • Effect of Mo Content on Microstructure and Properties of TiC-High Mn Steel Bonded Carbide Prepared with Pre-alloyed Powders
    LI Guoping, CHEN Wen, LUO Fenghua, DU Yong, LIU Zenglin, YUAN Yong
    Materials For Mechanical Engineering. 2018, 42(8): 37-41,47. https://doi.org/10.11973/jxgccl201808008
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    With Fe-Mo-C pre-alloyed powder, FeMn84C0.4 alloy powder, Ni powder, graphite powder and TiC powder as raw materials, TiC-high Mn steel bonded carbide containing different Mo content, with high Mn steel as adhesive phase and TiC as hard phase, was prepared by sintering. Effects of Mo content on the microstructure and properties of the steel-bonded carbide were studied. The results show that with increasing Mo content, the size of TiC particles in microstructure of the steel-bonded carbide decreased first and then increased, and on surfaces formed (Ti,Mo)C solid solution phase. When being compared with those by adding pure Mo powder, TiC particles in the steel-bonded carbide obtained by adding Mo-containing pre-alloyed powder were relatively fine and relatively round and regular, and (Ti,Mo)C solid solution phase formed relatively easily. With the increase of Mo content, the relative density, hardness, rupture strength and impact toughness of the steel-bonded carbide increased first and then decreased, and reached largest values with Mo content of 1.15wt%; the microstructure and comprehensive properties were relatively good.
  • Systhesis and Catalytic Methanol Oxidation Performance of Pt/TiC/TiO2 Catalyst with Nano-Composite Structure
    CHEN Chuansheng, ZHANG Xueru, ZHENG Jiafang, GUO Yanan, TIAN Cha, ZHANG Qing
    Materials For Mechanical Engineering. 2018, 42(8): 42-47. https://doi.org/10.11973/jxgccl201808009
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    Optimal parameters of TiO2 nanowires prepared by hydrothermal method were determined. TiO2 nanowires prepared with the optimal parameters were treated by carbonization and surface deposited with platinum, and then the Pt/TiC/TiO2 catalyst was obtained. The phase composition, chemical composition and micromorphology of the products in different stages were investigated, and the catalytic methonal oxidation capability of Pt/TiC/TiO2 catalyst was tested. The results show that the optimal hydrothermal parameters were listed as follows:NaOH solution concentration of 1 mol·L-1, hydrothermal temperature of 160℃, and hydrothermal time of 20 h. Consequently, TiO2 nanowires with diameter of about 100 nm and length of over 1 μm were obtained. The TiC/TiO2 nanowires were obtained after carbonization and the surface was coated with platinum nanoparticles after the deposition of platinum. The initial oxidation potential of methanol oxidation catalyzed by Pt/TiC/TiO2 catalyst was 0.34 V (vs Ag/AgCl), about 0.15 V negative shift compared with that by Pt/TiO2 catalyst, and the maximum forward current density was more than 8 times as large as that by Pt/TiO2 catalyst. The carbonization improved the catalytic methanol oxidation capability of Pt/TiO2 catalyst significantly.
  • Optical and Electrical Properties of ZnO/Al(O)/ZnO Film Prepared by Reactive Magnetron Sputtering
    XING Shilong, MIN Guanghui, PANG Tao
    Materials For Mechanical Engineering. 2018, 42(8): 48-52,82. https://doi.org/10.11973/jxgccl201808010
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    ZnO/Al(O)/ZnO films were prepared on polyethylene glycol terephthalate substrate by reactive magnetron sputtering and controlling oxygen flow rate during deposition of the intermediate layer. The effects of oxygen flow rate on micromorphology and surface roughness of Al(O) film and on optical and electrical properties of ZnO/Al(O)/ZnO film were studied. The results show that with increasing oxygen flow rate, the growth mode of Al on the surface of ZnO film changed from three-dimensional island-like to two-dimensional lamellar; the surface toughness of Al(O) film increased first, then decreased and then increased, and reached the lowest value at oxygen flow rate of 6.7×10-3 cm3·s-1. With increasing oxygen flow rate, the transmittance of ZnO/Al(O)/ZnO film increased in the range of relatively long wavelengths, the square resistance increased and the Hall mobility and carrier concentration decreased. Considering optical and electrical properties synthetically, the suitable oxygen flow rate was 6.7×10-3 cm3·s-1.
  • Preparation and Properties of Ti3AlC2/Cu Composite
    CHEN Haiji
    Materials For Mechanical Engineering. 2018, 42(8): 53-56. https://doi.org/10.11973/jxgccl201808011
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    The Ti3AlC2/Cu composite was prepared by spark plasma sintering powder mixtures of Cu and Ti3AlC2 with different volume fractions at different temperatures (850,900℃) for 20 min. The effects of Ti3AlC2 content and sintering temperature on the microstructure, relative density, hardness and frictional wear performance of the composite were investigated. The results show that after sintering at 900℃ for 20 min, with the increase of Ti3AlC2 content, the uneven distribution of Ti3AlC2 in Cu matrix became more and more obvious; the relative density of the composite decreased and the hardness increased. Meanwhile, the wear rate and friction coefficient of the composite decreased, indicating the increase of wear resistance, and the wear mechanism changed in the order of cut wear and adhesive wear, adhesive wear and abrasive wear, and cut wear and slightly adhesive wear. The relative density of the composite sintered at 900℃ was higher and the friction coefficient was lower than those at 850℃.
  • Cutting Performance and Wear Mechanism of TiB2-B4C Ceramic Cutting Tool in Cutting Inconel 718 Alloy
    TAN Dawang, GUO Weiming, WU Lixiang, ZENG Lingyong, LIN Huatai
    Materials For Mechanical Engineering. 2018, 42(8): 57-62. https://doi.org/10.11973/jxgccl201808012
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    80vol%TiB2-20vol%B4C (TB2) and 20vol%TiB2-80vol%B4C (TB8) ceramics were prepared by hot-pressed sintering and were made into cutting tools; the ceramic cutting tools were used to machine Inconel 718 alloy at cutting speeds of 50 m·min-1 and 150 m·min-1, respectively. The cutting performance and wear mechanism of the ceramic cutting tools were studied and compared with those of YG cemented carbide cutting tool. The results show that the flexural strength and Vickers hardness of TB2 ceramics were lower than those of TB8 ceramics while the fracture toughness was about 26% higher than that of TB8 ceramics. The life of TB2 ceramic cutting tool was the longest at the two cutting speeds, which was about twice that of TB8 ceramic cutting tool and YG cemented carbide cutting tool. The adhesive wear was the main mechanism for the wear of flank and tool tip of TB2 ceramic cutting tool; the grooves at boundaries were caused by slightly tipping and flaking of cold welding layer. The wear of flank and tool tip of the TB8 ceramic cutting tool mainly contributed to tipping; the formation of grooves at boundaries was due to tipping and large-pieced flaking of cold welding layer.
  • Effect of Cerium Content on Microstructure and Properties of High Speed Steel Surfacing Layer
    LIANG Chen, SHI Haifang, YANG Zhihua, YANG Zhaofang
    Materials For Mechanical Engineering. 2018, 42(8): 63-66. https://doi.org/10.11973/jxgccl201808013
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    High speed steel surfacing layers containing different mass fractions (0-0.4%) of cerium were deposited by tungsten inert gas arc welding on the low carbon steel plate, and then the microstructure, phase composition, hardness and wear resistance of surfacing layers were studied. The results show that with the cerium mass fractions of 0-0.4%, the microstructure of the surfacing layer was composed of martensite, retained austensite and carbides, such as VC, WC and Cr23C6. With the increase of cerium content, the surface hardness and wear resistance of the surfacing layer increased first and then decreased. When the cerium mass fraction was 0.1%, the surface hardness of the surfacing layer reached the highest value of 61.6 HRC, the wear loss had the lowest value of 87.75×102 g·m-2, and the groove formed by wear was the shallowest, indicating that the wear resistance was the best.
  • Dynamic Constitutive Relation of GH4169 Superalloy Based on Z-A Model
    ZOU Pin, ZHAO Zhenhua, YAN Huansong, KONG Zukai, LIU Lulu, GUAN Yupu, CHEN Wei
    Materials For Mechanical Engineering. 2018, 42(8): 67-71,77. https://doi.org/10.11973/jxgccl201808014
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    The flow stress-strain curves of GH4169 superalloy at the temperatures of 20-400℃ and strain rates of 1 000-3 000 s-1 were studied by split Hopkinson bar test. The relationship between stress and strain was described by Zerilli-Armstrong (Z-A) constitutive model, the parameters of constitutive model were determined, and the model was verified by experiments. The results show that GH4169 superalloy had obvious strain rate strengthening effect and temperature softening effect. The relationship between flow stress and strain was nearly linear. The established Z-A constitutive model accurately described the rheological behavior of GH4169 superalloy at different temperatures and different strain rates, and the average value of average relative errors of the model was 2.65%.
  • Numerical Simulation of Microstructure Distribution in Tooth of 42CrMo Steel Gear during Step Quenching
    KONG Dewu, LÜ Kun, HUANG Qunfeng, TANG Zheng
    Materials For Mechanical Engineering. 2018, 42(8): 72-77. https://doi.org/10.11973/jxgccl201808015
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    42CrMo steel gear model was established, and then the microstructure distribution in the gear tooth during step quenching was simulated with Sysweld software and verified by experiments. The results show that after being cooled in the nitrate solution until the surface temperature was about 175℃, the bainite content in structure of the gear tooth increased with the distance from the surface increasing; the martensite content in the subsurface layer was the highest (90%, area fraction, the same as below), followed by that in the core (66%), and that in the surface layer was the lowest (58%). After step quenching, the surface microstructure of the gear tooth consisted of 90% martensite and 10% retained austenite, and the core microstructure was composed of 66% martensite and 34% bainite. The retained austensite content at surface of gear tooth after quenching, measured by experiments, was 7.5%, the martensite and bainite content in core was about 69% and 31%, respectively. The experimental results were consistent with the simulation.
  • Effects of Thermal Cycle on Microstructure and Cryogenic Toughness of Coarse-Grained Heat Affected Zone of 9Ni Steel Joint
    YANG Xiuzhi, ZHANG Lichao, LI Xuan, HUA Wenlin, YANG Chunjie, DONG Chunfa, XIAO Xinhua
    Materials For Mechanical Engineering. 2018, 42(8): 78-82. https://doi.org/10.11973/jxgccl201808016
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    Coarse-grained heat affected zone (CGHAZ) samples of 9Ni steel joint were prepared with Gleeble-3500 type thermal simulator at t8/5 (cooling time from 800℃ to 500℃) of 6,10,30,60,100 s, respectively, and then cryogenic impact tests were carried out on the samples. The effects of t8/5 on the microstructure and cryogenic toughness of CGHAZ were investigated. The results show that the microstructure of CGHAZ was mainly composed of lath martensite. The granular bainite appeared at t8/5 of 30 s and the amount increased with increasing t8/5. With increasing t8/5, the size of martensite lath in CGHAZ increased slightly and then decreased; the ductile-brittle transition temperature rose and then decreased. The impact energy at -100℃ and -125℃ of CGHAZ prepared at different values of t8/5 was higher than 200 J. With decreasing impact temperature, the impact fracture morphology changed from dimple to quasi-cleavage.
  • Reason for Fracture of Guard Board for Vehicle Cooling Device
    CHEN Lizong, SHI Junbo, XU Na, DING Ning, GUO Weimin, LIU Long
    Materials For Mechanical Engineering. 2018, 42(8): 83-86. https://doi.org/10.11973/jxgccl201808017
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    A guard board for vehicle cooling device fractured at the position for fixing nuts. Reason for fracture was analyzed by the methods such as microstructure analysis, fracture morphology observation and chemical composition detection. The results show that the guard board factured in a fatigue manner. Two fatigue crack sources existed on fracture. One was located in weld fusion zone of internal surface of the guard board and the nut, and the other was located in welding heat affected zone on outer surface. The crack propagation by alternating loading led to fracture of the guard board. Welding defects were the main cause of fatigue cracking.
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