20 September 2021, Volume 45 Issue 9
    

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  • Research Progress on Mechanical Property Improving Methods and MachiningMethods for Rare Earth Permanent Magnetic Materials
    Lü Guihong, MA Zheng, XIAO Tenglong, LI Xiaosen, LIU Xialin, AN Shizhong
    Materials For Mechanical Engineering. 2021, 45(9): 1-7. https://doi.org/10.11973/jxgccl202109001
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    Rare earth permanent magnetic materials are widely used in traditional industries, wind power generation and new energy vehicles because of their excellent magnetic properties. However, due to the brittleness of intermetallic compounds, the mechanical properties and machinability of rare earth permanent magnetic materials are poor, which limit their application. The reasons for poor ductility and toughness along with the fracture mechanisms of rare earth permanent magnetic materials are summarized. The methods of improving their mechanical properties in recent years are reviewed, including the optimization of grain size and distribution, the improvement of strength and ductility of the matrix phase, the improvement of strength and ductility of the grain boundary, and the reduction of mechanical property anisotropy. The machining methods of rare earth permanent magnetic materials are described. Finally, a brief prospect for the future development directions of this field is provided.
  • Research Progress on High Thermal Conductivity SiC Ceramics
    WANG Xiaobo, WANG Feng, HE Zhiyong, ZHANG Qifu
    Materials For Mechanical Engineering. 2021, 45(9): 8-12. https://doi.org/10.11973/jxgccl202109002
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    In recent years, the rapid development of integrated circuit, heat exchanger, semiconductor industry has put forward higher requirements for the thermal conductivity of SiC ceramics. The thermal conductivity at room temperature of SiC ceramics is much lower than the theoretical value of single crystal SiC because of the defects such as lattice oxygen, grain boundary and porosity. The effects of additives and sintering process on the thermal conductivity at room temperature of SiC ceramics are reviewed. The future development direction of high thermal conductivity SiC ceramics is prospected.
  • Research Status on Weldability of Duplex Stainless Steeland Corrosion Resistance of Joint
    QIN Qin, TIAN Jinxin, TANG Shijia, YANG Haodong, YAN Ziyi, HUANG Taibo, LI Yunkun
    Materials For Mechanical Engineering. 2021, 45(9): 13-18. https://doi.org/10.11973/jxgccl202109003
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    Dual-phase stainless steel has been widely used because of its good mechanical properties and corrosion resistance, and its weldability has also become an important research object. The welding method and microstructure of the welded joint of duplex stainless steel are introduced, and pitting corrosion, stress corrosion, intergranular corrosion and the generation mechanism of embrittlement and cracks of the welded joint are discussed. Finally, the research direction of duplex stainless steel weldability is prospected.
  • Influence of High Temperature Strain Aging on High Temperature Low-Cycle Fatigue Properties of P92 Steel
    ZHAO Li, HUA Xiaochun, MA Tao, ZHANG Xiaofei, WANG Xiaoyi, RAO Sixian
    Materials For Mechanical Engineering. 2021, 45(9): 19-25. https://doi.org/10.11973/jxgccl202109004
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    The fatigue behavior of P92 steel under different strain amplitudes (0.2%-1.0%) and stress amplitudes (280-350 MPa) was studied by high temperature low cycle fatigue tests at 550 ℃ under stress and strain control, respectively. P92 steel was subjected to strain aging treatment at different prestrains (0-4%) and temperatures (250-350 ℃), and then the high temperature tensile and low cycle fatigue properties were studied. The results show that the relation between strain and fatigue life of P92 steel conformed to Manson-Coffin equation under strain control, and the phenomenon of cyclic hardening and then cyclic softening appeared in P92 steel at low strain amplitudes (below 0.7%). The relation between strain and fatigue life did not follow Manson-Coffin equation under stress control, and the phenomenon of cyclic hardening and then cyclic softening appeared in P92 steel under a high stress amplitude (350 MPa). The strain aging treatment could improve the yield strength of P92 steel, and the high temperature tensile curve showed a Porevin-Le Chatelier yield effect. The relation between strain and life of P92 steel after strain aging treatment under stress control did not follow Manson-Coffin equation, and the low cycle fatigue life greatly decreased.
  • Effect of Doping Amount of Sb2O5 on Electrical Properties of SnO2 Ceramic Piezoresistor Under Co-doping with Y2O3
    YU Peiyuan, ZHAO Hongfeng
    Materials For Mechanical Engineering. 2021, 45(9): 26-29. https://doi.org/10.11973/jxgccl202109005
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    The effect of doping amounts (0,0.05%,0.10%,0.15%, mole fraction) of Sb2O5 on the micromorphology,voltage gradient and grain resistance of SnO2 piezoresistor was studied by scanning electron microscope and impedance meter through co-doping Sb2O5 and Y2O3 (0.05%, mole fraction) into SnO2 ceramic piezoresistor. The results show that with increasing doping amount of Sb2O5, the grain size and interfacial state density of SnO2 piezoresistor increased first and then decreased, and the voltage gradient, nonlinear coefficient and leakage current density decreased first and then increased. When the doping amount of Sb2O5 was 0.10%, the interfacial state density of SnO2 piezoresistor was the largest, the leakage current density was the smallest, the grain resistance was the smallest, and the integrated electrical performance was the best.
  • Effect of In-Situ Synthesis TiC on Microstructure and Properties ofHigh Chromium Cast Iron Surfacing Metal
    WANG Chi, SUN Junsheng, XU Hu, JIN Jun, TANTAI Fanliang, TIAN Hongfang
    Materials For Mechanical Engineering. 2021, 45(9): 30-34. https://doi.org/10.11973/jxgccl202109006
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    Using self-made high chromium cast iron flux-cored welding tape as welding material, single-layer single-pass surfacing tests were carried out by non-melting inert gas arc welding (TIG) on low carbon steel plate. The effect of in-situ synthesis TiC on the microstructure and properties of surfacing metal was studied by adding different mass fraction (0-5.2%) of ferro-titanitum powder in the flux-cored welding tape powder. The results show that after adding ferro-titanium powder to the flux-cored welding tape powder, there was in-situ synthesis TiC phase in the surfacing metal except Cr7C3 hard phase; the size of Cr7C3 decreased, the distribution was relatively uniform, and the number increased significantly. When the mass fraction of ferro-titanium powder in the powder was 5.2%, the refinement of Cr7C3 in the surfacing metal was the most obvious, and the distribution was the most uniform. With increasing ferro-titanium powder content in the flux-cored welding tape powder, the hardness and wear resistance of the surfacing metal increased. The TiC synthesized in situ in the liquid metal could be used as the heterogeneous nucleation core of Cr7C3, which reduced the nucleation resistance of Cr7C3 and thus refined Cr7C3.
  • Preparation and Tensile Behavior of Mini SiCf/SiC Composites with PyC-SiC Codeposition Interface
    LIU Guiliang, HE Zongbei, LIN Haoran, ZHANG Ruiqian, CHEN Zhaoke, WANG Jiping
    Materials For Mechanical Engineering. 2021, 45(9): 35-39,50. https://doi.org/10.11973/jxgccl202109007
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    With third-generation domestic silicon carbide fiber (SiCf) as reinforcement, pyrocarbon (PyC) and SiC codeposition interface layer were simultaneously deposited on the surface of SiCf by chemical vapor infiltration (CVI) with deposition time of 20-70 min. Then SiC was deposited continueously and dense Mini SiCf/SiC composites were prepared. The interface structure and teasile behavier of the composites were studied. The results show that the average thicknesses of the codeposition interface layer were 500, 1 100, 2 100 nm after deposition for 20, 40, 70 min, respectively, and the thickness of the interface layer was uniform; the interface layer was a single layer structure. When the thickness of the codeposition interface layer was 1 100 nm, the Mini composite had moderate interface bonding strength and the largest tensile strength of 626.0 MPa, and the corresponding fracture strain was 0.45%.
  • Development of 500 MPa Grade Forklift Gantry Steel C250b
    HUO Xiwei, GAO Cairu, SONG Yuqing, TIAN Yudong, DU Linxiu, QIAO Peng
    Materials For Mechanical Engineering. 2021, 45(9): 40-44,57. https://doi.org/10.11973/jxgccl202109008
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    Mn-Nb-V-Cr-N series steel was designed in order to meet the requirements of C250b gantry steel customized by users with yield strength of not less than 500 MPa, tensile strength of not less than 610 MPa, percentage elongation after fracture of not less than 17%, and impact energy at -20 ℃ of not less than 27 J. According to the actual production process, the test steel was finishing rolled at different initial rolling temperatures and end rolling temperatures. The microstructure and mechanical properties of the test steel were studied, and the strengthening mechanism of the test steel was discussed. The results show that the designed steel had the chemical composition (mass fraction/%) of 0.16-0.20 C, 0.40-0.50 Si, 1.50-1.60 Mn, 0.35-0.45 Cr, trace Ni and V, and the microstructure of the steel was ferrite + pearlite after finishing rolling and air cooling. When the initial rolling temperature was 920-970 ℃ and the end rolling temperature was 820-870 ℃, the average grain size of the test steel was no greater than 7 μm; the mechanical property parameters of the test steel met the requirements. The contribution of solution strengthening in the test steel to the yield strength was about 240 MPa, that of fine-grain strengthening was 177-191 MPa, and that of precipitation strengthening of the second phase was about 100 MPa.
  • Asymmetric Strain Fatigue Behavior and Life Prediction of 3.5NiCrMoV Steel and 20Cr13 Steel for Steam Turbine
    WU Haili
    Materials For Mechanical Engineering. 2021, 45(9): 45-50. https://doi.org/10.11973/jxgccl202109009
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    Symmetric and asymmetric strain control fatigue tests were performed on 3.5NiCrMoV bainite steel and 20Cr13 martensite steel for steam turbine, and their fatigue behaviors were compared and studied. Morrow model, SWT model and Ellyin model based on symmetric strain fatigue parameters were used to predict asymmetric fatigue life, and the applicability of these models was discussed. The results show that the asymmetric fatigue life of 3.5NiCrMoV steel was not higher than its symmetric fatigue life, and the asymmetric fatigue life of 20Cr13 steel was higher than its symmetric fatigue life. There was a big difference between symmetric and asymmetric cyclic stresses of 3.5NiCrMoV steel, and the symmetric and asymmetric cyclic stresses of 20Cr13 steel were similar. The average stress reduction was a common phenomenon for asymmetric strain control fatigue, and the plastic strain change was the main factor affecting asymmetric fatigue life. The prediction accuracy of the Morrow model depended on the effect of strain ratio on fatigue life. The SWT model was not suitable for fatigue life prediction of 3.5NiCrMoV steel with a large difference between asymmetric and symmetric cyclic stress-strain curves. The Ellyin model had a good prediction effect on the asymmetric fatigue life of 20Cr13 steel with similar asymmetric and symmetric cyclic hardening trends.
  • Effects of Laser Power and Laser Scanning Speed on Microstructure and Property of TC4 Titanium Alloy Formed by Selective Laser Melting
    WU Huimin, LUO Zhiqiang, JIN Shengran
    Materials For Mechanical Engineering. 2021, 45(9): 51-57. https://doi.org/10.11973/jxgccl202109010
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    TC4 titanium alloy samples were formed by selective laser melting, and the influence of laser power (50-300 W) and laser scanning speed (250-1 750 mm·s-1) on the microstructure and properties of the samples was studied. The results show that with the decrease of the scanning speed or the increase of the laser power, the forming quality of the samples was improved, the surface roughness was reduced, and the hardness on longitudinal section increased. The needle-like α' phase and nano-β phase were found in the microstructure of the samples. The size of the α' phase was relatively small, and the content of the β phase was relatively low at the relatively high scanning speed. Changing the scanning speed or the laser power had little effect on the tensile strength of the samples, but the elongation after fracture was relatively high at relatively low laser power or relatively high scanning speeds. When the laser power was 200 W and the scanning speed was 1 150 mm·s-1, the samples had relatively good strength and plasticity matching.
  • Microstructure and Properties of Laser Cladding SiC Reinforced Ni35 Alloy Layer
    CHAI Cheng, LI Xinmei, WANG Songchen, WANG Gen
    Materials For Mechanical Engineering. 2021, 45(9): 58-61,66. https://doi.org/10.11973/jxgccl202109011
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    20wt% SiC reinforced Ni35 alloy cladding layer was prepared on 45 steel surface by laser cladding at different laser power (1 000-1 400W) and scanning speeds (6-10 mm·s-1). The optimal process parameters were determined according to the macromorpholgy of the cladding layer. The microstructure and properties of the cladding layer were studied under the optimal parameters. The results show that the optimal process parameters of the laser cladding layer were as follows: laser power of 1 000 W and scanning speed of 8 mm·s-1. Under these parameters, the microstructure of the cladding layer consisted of dendrites and equiaxed crystals, and the phases included hard phases such as SiC, Ni4B3, CrB, Ni2Si and FeSi. The hardness of the cladding layer was about 3.5 times that of the 45 steel substrate, and the hardness of the heat affected zone was higher than that of the substrate because of laser quenching effect during cladding. The wear mass loss of the cladding layer was obviously less than that of the substrate, and the increase in wear mass loss with the prolonged wear time was small, indicating that the wear resistance of the cladding layer was relatively good. The main wear mode of the cladding layer was adhesive wear after wear for 60 min, and was abrasive wear after wear for 120 min.
  • Properties of Nano Graphite/Hydrogenated Nitrile Rubber Composite by Solution Blending Masterbatch Method
    WU Kepeng, WEN Bocheng, ZHOU Guangwu
    Materials For Mechanical Engineering. 2021, 45(9): 62-66. https://doi.org/10.11973/jxgccl202109012
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    The nanographite composite/hydrogenated nitrile rubber (HNBR) was prepared by the solution blending masterbatch method, and the microstructure, vulcanization properties, mechanical properties, wear resistance were studied and compared with those of the composite prepared by the traditional mechanical blending method. The results show that the solution blending masterbatch method could make the nano graphite more uniformly disperse in the HNBR matrix. Compared with the composite by the traditional mechanical blending method, the composite prepared by the solution blending masterbatch method had better vulcanization and mechanical properties; the maximum comprehensive torque, elastic modulus, crosslinking degree, vulcanization speed increased by 35%, 44%, 32%, 46%, respectively, but the effect of the process on the improvement of tensile strength and wear resistance of the composites was not obvious.
  • Microstructure and Properties of Laser Cladding WC Reinforced Ni-Based Alloy Cladding Layer on AlSi7Mg Aluminum Alloy Surface
    WU Xiaoquan, YAO Dengcan, ZHANG Daoda, YAN Hong, HU Zhi
    Materials For Mechanical Engineering. 2021, 45(9): 67-72. https://doi.org/10.11973/jxgccl202109013
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    Single-track and multi-track WC reinforced Ni-based alloy cladding layers were prepared on surface of AlSi7Mg aluminum alloy by laser cladding. The microstructure, phase composition, dilution ratio and microhardness of the cladding layers were investigated. The results show that when the laser scanning speed increased from 3.3 mm·s-1 to 6.0 mm·s-1, pores and cracks in the single-track laser cladding layer became less. At the scanning speed of 4.6 mm·s-1, spot diameter of 1.0 mm and overlap of 20%, the WC particles in the multi-track cladding layer mainly distributed at interface between the cladding zone and transition zone, and the cracks and pores were located at the overlap and the bottom of the cladding layer, respectively. The dilution ratios of the first-track cladding layer and the last-track (the fifth-track) cladding layer were 10% higher than those of the second-track to fourth-track cladding layers. Intermediate phases, such as AlNi, Al3Ni, M7C3 and M23C3, were formed in the WC reinforced Ni-based alloy cladding layers. The average dilution ratio of the layers was about 45% and the microhardness was about 1 100 HV.
  • Low Cycle Fatigue Characteristics and Life Prediction of N80Q Steel
    CUI Lu, WU Peng, YANG Chenghui, KANG Wenquan, LI Zhen, WEI Wenlan, WANG Peng
    Materials For Mechanical Engineering. 2021, 45(9): 73-78. https://doi.org/10.11973/jxgccl202109014
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    Low cycle fatigue tests of N80Q steel for oil well casing were carried out on Instron 8862 fatigue tester under complete symmetrical cycle loads (mean strain of 0) and non-symmetrical cycle loads (mean strain of 0.5% and 1.0%). The low cycle fatigue characteristics of the steel were studied, and the prediction accuracy of low cycle fatigue life models considering different factors was discussed. The results show that the plastic strain energy increased linearly with increasing strain amplitude, and the mean strain had little effect on the plastic strain energy. There was no stress relaxation behavior of N80Q steel under different strain amplitudes (0.5%-2.0%) and symmetric load or under strain amplitude greater than 1.0% and asymmetric load. When the strain amplitude was less than 1.0% under asymmetric load, the stress relaxation behavior was obvious; the larger the initial mean stress, the more obvious the stress relaxation behavior. The empirical model considering the influence of maximum stress, stress range, strain range and mean strain had higher prediction accuracy, and the predicted lives were mainly dispered in 1.2 time scatter band.
  • Calculation and Finite Element Simulation of Ultimate Collapse Strength of Drivepipe
    LIU Hongtao, XU Aiyan, ZHAO Mifeng, JI Bingyin, ZHOU Bo, SHI Jiaoqi, HU Fangting
    Materials For Mechanical Engineering. 2021, 45(9): 79-82. https://doi.org/10.11973/jxgccl202109015
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    Geometric size measurement, tensile test, and residual stress test were performed on 110 steel drivepipe, and the average ultimate collapse strength of the drivepipe was calculated by the first order second moment method. Collapse test was carried out on the drivepipe, and the ultimate collapse strength of the drivepipe was simulated by finite element model. The calculated results, simulated results and tested results of the ultimate collapse strength were compared. The results show that the calculated results of the average ultimate collapse strength of test drivepipe was higher than the target confidence level and close to the tested results. The calculation method was suitable for calculating the ultimate collapse strength of test drivepipe. The finite element simulated results of the ultimate collapse strength of each drivepipe were close to the tested results, and the relative errors were less than 5.8%, and the finite element simulation was accurate.
  • Dynamic Mechanical Properties and Constitutive Relation of SiCp/Al Composites under High Strain Rate
    WU Xiaoping, Lü Qinli, YANG Kuan, YANG Zhongyuan, JI Hong
    Materials For Mechanical Engineering. 2021, 45(9): 83-87. https://doi.org/10.11973/jxgccl202109016
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    Dynamic compression tests of the 15% (volume fraction) SiCp/Al composite were carried out by separate Hopkinson compression bar device, and the dynamic mechanical properties and microstructure evolution of the composite at high strain rates of 500-2 000 s-1 were studied. With the experimental data, stress-train curves were predicted by the Johnson-Cook constitutive model containing the adiabatic temperature rise softening term relating to strain rate and plastic strain, and the predicted results of the model were compared with the experimental results. The results show that the strain rate strengthening effect of the composites was not obvious, but the composites showed a significant strain strengthening. With increasing strain rate, the deformation types of the composite changed from uniform deformation to localized deformation, the fracture of the reinforcing particles was serious, and the adiabatic shear bands were formed and extended in local areas. The relative error between the stress-strain curves calculated by the modified Johnson-Cook constitutive model containing the adiabatic temperature rise softening term and the experimental results was less than 17%.
  • Diffusion Bonding/Stretching Forming Process of TC4 Titanium Honeycomb Core
    ZHOU Xianjun, WU Yong, CHEN Minghe, XIE Lansheng, QIN Zhonghuan
    Materials For Mechanical Engineering. 2021, 45(9): 88-93. https://doi.org/10.11973/jxgccl202109017
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    The diffusion bonding/stretching forming process of TC4 titanium alloy honeycomb core was simulated by ABAQUS finite element simulation software, and the optimal stretching length was obtained by the simulation. The cell outline, wall thickness distribution and diffusion bonding interface morphology of honeycomb core were studied by diffusion bonding/stretching forming tests. The results show that after TC4 titanium alloy laminate was obtained by diffusion bonding at 920 ℃/3 MPa/60 min and then stretched for 75 mm at 800 ℃ and strain rate of 1 mm·s-1 to form honeycomb core. The regular hexagonal cells were formed in the honeycomb core, which verified the feasibility of preparing honeycomb core by diffusion bonding/stretching forming process. The cells of honeycomb core middle part had good quality and relatively high dimension accuracy, with the average height of 16.2 mm, average width of 21.5 mm, bending round corner of 2.5 mm, and the maximum thinning rate of 5.37%. There was no obvious hole defect in the welding area of laminate, and the welding rate exceeded 95%; after stretching there was no tear in the diffusion bonding area, and no cracks in the bending round corner area.
  • Nonlinear Mechanical Behavior of ω-Type Rail Fastening Spring Clip
    JIANG Xiujie, LIU Yan, TANG Jixin, LI Qiutong, ZHAO Wei, LIU Huan
    Materials For Mechanical Engineering. 2021, 45(9): 94-102. https://doi.org/10.11973/jxgccl202109018
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    Taking ω-type SKL15 spring clip in Vossloh300-1 rail fastening system as research object, the rail fastening system model was established by finite element software, and the mechanical behaviors of the spring clip were simulated under the conditions of three material properties (linear elastic model, bilinear model and elastic-plastic model obtained by tensile tests) and two contact properties (binding constraint and nonlinear contact). The validity of the models was verified by fatigue tests, and the influence of the material properties of the clip and the contact properties between the spring clip and embedded block on the nonlinear mechanical behavior of the spring clip was studied. The results show that when the contact relationship between the spring clip and the embedded block was nonlinear and the constitutive model of the spring clip was elastic-plastic model, the maximum principal strain direction and the maximum principal strain at the heel of the spring clip obtained by finite element simulation were consistent with the test results; the relative errors of them were 5% and 3.4%, respectively, which verified the validity of the finite element model. The mechanical behaviors of the spring clip obtained by defining spring clip material with nonlinear contact and the elastic-plastic constitutive model were close to the actual condition.
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