20 April 2019, Volume 43 Issue 4
    

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  • LUO Baomin, LI Daoxi, ZHAO Chao, LUO Zongqiang, WANG Zhi, YANG Chao, ZHANG Weiwen
    Materials For Mechanical Engineering. 2019, 43(4): 1-5,24. https://doi.org/10.11973/jxgccl201904001
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    Homogenization annealing treatment at 930℃ for 2.5 h and hot extrusion at 950℃ were conducted on as-cast Cu-17Ni-2.5Sn-1.5Al alloy in sequence. The microstructure and tensile properties of the hot-extruded alloy were studied, and the strengthening mechanism was analyzed. The results show that the microstructure of the hot-extruded alloy was refined obviously to average grain size of about 32 μm. Spherical Ni3Al phase with a diameter of about 10 nm dispersed in the matrix structure. The ultimate tensile strength of the hot-extruded alloy was 922 MPa and the yield strength was 779 MPa. The alloy had three types of strengthening mechanism, namely refinement crystal strengthening, solid solution strengthening and second phase precipitation strengthening. The solid solution strengthening played a main role and accounted for 56% of the total strengthening effect. Aluminum played a solid solution strengthening role and a second phase precipitation strengthening role.
  • LI Guangyu, QI Senpeng, YU Kewei, SUI Shuanglian, YANG Anshen
    Materials For Mechanical Engineering. 2019, 43(4): 6-9,34. https://doi.org/10.11973/jxgccl201904002
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    2Cr13 martensitic stainless steel was treated by plasma source nitriding at 450℃ for 6 h, and then the microstructure, phase composition, wear resistance and corrosion resistance of the steel surface layer before and after nitriding were studied and compared. The results show that after nitriding, an about 18 μm thick compound layer composed of αN, ε-Fe3N and γ'-Fe4N and a nitrogen diffusion layer with obvious refined structure were formed on surface of the stainless steel. The nitrogen atom penetration depth reached 20 μm. The surface hardness of the nitrided stainless steel was up to 1 350 HV and the friction factor was lower than that before nitriding. The wear mechanism changed from adhesive wear before nitriding to oxidative wear after nitriding. The wear resistance after nitriding was obviously higher than that before nitriding. In 3.5wt% NaCl solution, the anodic polarization curve of the stainless steel before nitriding only showed a feature of activation dissolution while after nitriding showed features of activation dissolution, self-passivation and pitting breakdown. After nitriding, the free-corrosion potential increased to -104 mV and the corrosion resistance was improved significantly.
  • WANG Erpeng, LIU Haifei, GUO Wen, LU Mingyang, ZHENG Bingxin, YAN Haiju, ZHANG Xiuhai
    Materials For Mechanical Engineering. 2019, 43(4): 10-14,68. https://doi.org/10.11973/jxgccl201904003
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    Ni-15Cr-5Al-xSi (x=0, 1, 3, 5, mass fraction/%) alloys were prepared by powder metallurgy and then oxidized at 1 000℃ for 100 h. Effects of silicon content on surface phase composition and high temperature oxidation resistance of the alloys were studied. The results show that the alloys with 0 and 1wt% silicon were both anti-oxidant grade, and the alloys with 3wt% and 5wt% silicon were both complete anti-oxidant grade. After oxidation, NiO and Al2O3 oxides were formed on surface of all the four alloys; also, NiAl2O4 and Cr2O3 existed on surface of the alloys with silicon content of 0 and 1wt%, and a small amount of Cr2O3 and NiCr2O4 were found with silicon content of 3wt% and 5wt%. The oxide scale on surface of the alloy with 5wt% silicon was flat and had a dense structure, and the oxide particles were fine and homogeneous. The alloy with 5wt% silicon had the best oxidation resistance at high temperature.
  • KONG Weihai, WAN Zhang, AI Zhibin, ZHANG Qiang, HU Pan
    Materials For Mechanical Engineering. 2019, 43(4): 15-19,63. https://doi.org/10.11973/jxgccl201904004
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    Passivation film performance on surface of S22053 stainless steel in 6wt% FeCl3 solution was studied by methods such as anodic polarization, constant potential film formation polarization, electrochemical impedance spectroscopy and Mott-Schottky test. The results show that the film formation potential of S22053 stainless teel was between 0.3-0.9 V. The maximum module value of impedance increased with increasing film formation potential in the range of 0.3-0.8 V, indicating that the stability of the passivation film was enhanced; in the range of 0.8-0.9 V, the opposite was true. The passivation films, formed after polarization at different film formation potentials for 30 min, showed an n-type semiconductor characteristic in the scanning potential range of 0-0.6 V, and a p-type semiconductor characteristic in the range of 0.6-0.9 V. The change of the passivation film thickness with the film formation potential obtained by electrochemical impedance spectroscopy was consistent with the change of the space charge layer thickness with the film formation potential obtained by Mott-Schottky curves; both reached peak values at film formation potential of 0.8 V.
  • WANG Xiaoqi, LIU Shengke
    Materials For Mechanical Engineering. 2019, 43(4): 20-24. https://doi.org/10.11973/jxgccl201904005
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    12wt%Mg2Si/A356-1.2wt%Fe Fe-rich recycled Al matrix composite was prepared. The effects of vibration frequency (100, 150, 200 Hz) and Mn to Cr mass ratio (0:1, 3:7, 1:1, 7:3, 1:0) of modifier on the as-cast microstructure and property were studied. The microstructure and tensile strength of the composite and A356-0.5wt%Fe recycled Al alloy after solid solution and aging were analyzed and compared. The results show that the mechanical vibration helped the refinement and even distribution of eutectic Si phase, Mg2Si phase and Fe-rich phase in the unmodified composite, resulting in the improvement of tensile strength at room temperature of the composite. After modification with Mn/Cr, the Fe-rich phase changed from needle-like to fish-bone shape, granular or chinese-character shape. When Mn to Cr mass ratio was 1:1, the tensile strength at room temperature reached the maximum value of 125 MPa. At vibration frequency of 200 Hz and with Mn to Cr mass ratio of 1:1, α-Fe (Al8Fe2Si) phase with hexagonal crystal shape was formed in the composite after solid solution and aging, while in the A536-0.5wt%Fe recycled Al alloy formed β-Fe (Al5FeSi) phase with monoclinic crystal shape. The tensile strength at room temperature and at 200, 300℃ of the composite was higher than those of the A536-0.5wt%Fe recycled Al alloy.
  • LU Yao, XU Sha, XING Yanfeng
    Materials For Mechanical Engineering. 2019, 43(4): 25-29. https://doi.org/10.11973/jxgccl201904006
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    Cold metal transfer (CMT) lap welding was performed on 6061 aluminum alloy sheet (aluminum sheet) and DP590 steel sheet. The welding process parameters were optimized by orthogonal method. BP neural network was used to predict welding deformation amount of the aluminum/steel sheets. The predicted results were applied to the aluminum/steel sheets, and then the welding deformation amounts were measured. The results show that the optimal process parameters were listed as follows:wire feed speed of 3.6-3.9 m·min-1, welding speed of 0.66-0.70 m·min-1, arc length correction of 0-5% and aluminum sheet thickness of 1.5-2.0 mm. The maximum test force that the joint welded with the optimal process parameters can withstand was up to 3 400 N, and the maximum thickness of the metal compound transition layer in weld was about 7.43 mm. The prediction results for welding deformation amount by the BP neural network were in good agreement with the experimental results. After anti-deformation, the welding deformation of the aluminum/steel sheets decreased significantly, with deformation amount decreasing from 0.67 mm to 0.12 mm, indicating that the prediction method was valid.
  • LIN Chen, WANG Qingchun, LIU Xuemei
    Materials For Mechanical Engineering. 2019, 43(4): 30-34. https://doi.org/10.11973/jxgccl201904007
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    With tourmaline as heat dissipation raditor and copper as binding phase, copper-tourmaline composite heat dissipation materials containing 15wt%-30wt% copper were prepared by powder metallurgy. The microstructure, relative density, heat dissipation performance, bending strength and fracture morphology of the composites were studied. The results show that with increasing copper content, the structure of the composite became homogenous and dense, the relative density increased and the heat dissipation performance was improved. The composites with different copper content had better heat dissipation performance than T2 copper had, and the natural cooling rate was 1.95-2.78 times higher than that of T2 copper. With increasing copper content, the bending strength of the composite increased. When the copper content was no less than 20wt%, the bending strength was all above 30 MPa, meeting the strength requirement of electronic packaging materials. When the copper content increased up to 25wt%, a certain number of dimples were observed on fracutre surface of the composite, illustrating a ductile fracture feature.
  • LI Xudong, LIU Yugai, LI Xiaohui, CHEN Dejin, FENG Shaobo, CAI Xuanlong
    Materials For Mechanical Engineering. 2019, 43(4): 35-38,43. https://doi.org/10.11973/jxgccl201904008
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    A flat multiple composite film cover was designed. The film cover had weak areas with V-shaped grooves along circumference and radial direction. The weak areas were bonded with ER3600 epoxy resin, and the resin layer was enhanced with the glass fiber mat reinforced epoxy resin on it. Non-weak areas were all made up of the glass fiber mat reinforced epoxy resin. The property of the film cover was verified by finite element method and bursting test. The results show that the failure pressure of the film cover predicted by the finite element method was about 0.15 MPa, and that by test was about 0.135 MPa. The simulation and test results are close. The film cover broke up into four parts along the weak areas, the circumferential root fracture occurred, and non-weak areas kept intact. It was indicated that the designed film cover meets the technical requirements.
  • SUN Chunlian, WANG Binbin
    Materials For Mechanical Engineering. 2019, 43(4): 39-43. https://doi.org/10.11973/jxgccl201904009
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    Ca0.925Sm0.05Cu3-yMgyTi4O12 (y=0, 0.05, 0.10, 0.15, 0.20, molar fraction/%) thin films were prepared on Si(100) substrate by sol-gel method. Effects of Mg doping amount on phase composition, micromorphology, dielectric property and pressure-sensitive performance of the film were studied. The results show that the thin films with different doping amounts of Mg were mainly composed of polycrystalline CaCu3Ti4O12 phase and a small amount of SiC and CaTiO3 phases. With increasing Mg doping amount, the grain size and relative dielectric constant of the film increased. After doping with 0.10mol% Mg, the film had the highest density and the smallest dielectric loss at relatively low frequencies. The thin films with different doping amounts of Mg exhibited a nonlinear relationship between current density and electric field strength. When the film was doped with 0.10mol% Mg, its nonlinear coefficient was the largest, and leakage current was relatively small.
  • TANG Bin, SUN Xiao, DU Qiang, ZHU Jie
    Materials For Mechanical Engineering. 2019, 43(4): 44-47,52. https://doi.org/10.11973/jxgccl201904010
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    A certain type aircraft refueling probe was subjected to wear and spalling in the chrome-plated layer of the extenal guide rail. WC-17Co alloy coating by high-velocity oxygen fuel (HVOF) spraying was used to repair the guide rail. The micromorphology, mechanical properties and wear resistance of the HVOF coating was studied. The refueling probe with the repaired guide rail was subjected to 20 full-stroke extending and retracting simulation tests, 30 ground running tests and 50 air flight running tests. The results show that the hardness of the HVOF coating was up to 1 041 HV and the bonding strength with the guide rail substrate was greater than 85.4 MPa. The toughness of the coating was good, the wear resistance was higher than that of electroplated chrome layer, and the wear degree of the grinding surface was small when paired with the electroless nickel plated wheel. After extending and retracting simulation tests and running tests of the probe assembled with the repaired guide rail, the HVOF coating on the guide rail showed no wear features and the repaired guide rail was in good condition.
  • LI Anmin, XU Fei, GUO Baohang, KONG Deming, WANG Fuwei
    Materials For Mechanical Engineering. 2019, 43(4): 48-52. https://doi.org/10.11973/jxgccl201904011
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    AlNiFeCuCoCrVx (x=0, 0.1, 0.2, 0.3, 0.4, 0.5, atomic ratio) high-entropy alloys were prepared by smelting in a WK-Ⅱtype non-consumable vacuum arc furnace.The microstructures and mechanical properties of the alloys were studied. The results show that the microstructures of all the tested alloys had a typical dendritic structure, consisting of face-centered cubic (FCC) solid solution, body-centered cubic (BCC) solid solution and intermetallic compound phases. With the addition of vanadium, Fe2AlV phase precipitated and mainly distributed in the dendrites. With increasing vanadium content, the hardness of the alloy increased first, then decreased and then increased. The addition of vanadium was not good for the compressive property of the alloy. Moreover, with increasing vanadium content, the compressive strength decreased first, then increased, and then decreased.
  • CHEN Jian, CHEN Yuxin, HUANG Tao, WANG Bing, LIU Qingyou
    Materials For Mechanical Engineering. 2019, 43(4): 53-58. https://doi.org/10.11973/jxgccl201904012
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    Cyclic wet-dry corrosion testing was conducted on weathering steels containing Cr with two mass fractions (1.990%, 3.194%) in simulated high temperature and humidity environment of the South China Sea with a periodic wheel immersion accelerated corrosion chamber. Then electrochemical tests were conducted on the weathering steels after cyclic wet-dry corrosion for different times. The corrosion resistance of the weathering steels was studied and compared with that of Q235 steel (Cr mass fraction of 0.164%). The results show that the higher the Cr content, the lower the corrosion rate of the tested steel. In the initial stage of corrosion, the steel containing 3.194% Cr had the smallest free-corrosion current density, relatively large capacitance arc radius and the largest charge transfer resistance and total resistance (rust layer resistance+charge transfer resistance), showing the best corrosion resistance. In the final stage of corrosion, due to accelerated corrosion, the rust layer resistance, charge transfer resistance and total resistance of the steel containing 3.194% Cr were lower than those of the steel containing 1.990% Cr.
  • GU Jiaxing, YAN Shanglei, DUAN Chenfeng, XIONG Qi
    Materials For Mechanical Engineering. 2019, 43(4): 59-63. https://doi.org/10.11973/jxgccl201904013
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    Single-pass and double-pass welding were carried out on both sides of A7N01 aluminum alloy T-joint by metal inert-gas welding (MIG welding), respectively. The microstructure, microhardness and fatigue property of the joint were studied, and the influence of sing-pass and double-pass welding was analyzed. The results show that on the single-pass welding side, the microstructure was composed in order of fine grains, columnar grains and equiaxial grains, from fusion zone to weld center. The microstructure near fusion line on the double-pass welding side was similar to that on the single-pass welding side; near the interface between the two welds, columnar crystals were formed, and the columar crystals in the weld of the first pass was relatively coarse. Softening zone existed in base metal on both sides of the joint, and the softening degree on the single-pass welding side was more obvious. The joint by single-and double-pass welding on both sides, respectively, had a shorter fatigue life than the joint by single-pass welding on both side had; the fatigue crack originated on surface of the weld toe and propagated inside; the fracture presented a mixed fracture mode of quasi-cleavage fracture and ductile fracture.
  • WANG Dan, WAN Jun
    Materials For Mechanical Engineering. 2019, 43(4): 64-68. https://doi.org/10.11973/jxgccl201904014
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    Three tools made of polycrystalline cubic boron nitride (PCBN), TiAlN coated cemented carbide (two tool tip corner radii) and Al2O3+TiC coated cemented carbide, respectively, were used to turn TC4 titanium alloy workpiece. Wear width on flank face of the tools and surface roughness of the workpiece were measured, wear morphology of the tools was observed and wear mechanism was analyzed. Meanwhile, effects of tip corner radius on surface roughness of the workpiece and chip morphology were studied. The results show that the TiAlN coated cemented carbide tool had a longer service life than the other two tools. After machining with the TiAlN coated cemented carbide tool, the workpiece had the smallest surface roughness and the best surface quality; the wear form of the tool was mainly abrasive wear and adhesive wear. The failure mode of the PCBN tool was mainly collapse of the rake face and flank face, while the wear form of the Al2O3+TiC coated cemented carbide tool was mainly diffusion wear. Increasing tip corner radius was beneficial to improving chip breaking ability of the TiAlN coated cemented carbide tool and surface quality of the workpiece.
  • NIE Wenjun, XING Li, LIU Fencheng, KE Liming, FAN Hao
    Materials For Mechanical Engineering. 2019, 43(4): 69-72,78. https://doi.org/10.11973/jxgccl201904015
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    5A06 aluminum matrix composite reinforced with 3vol% carbon nanotubes (CNTs) was fabricated by rotational friction extrusion (RFE) method. The microstructure, microhardness and wear resistance of the composite were investigated and compared with those of 5A06 aluminum alloy before and after RFE processing. The results show that the microstructure of the aluminum alloy changed from coarse long-strip-like grains before RFE processing to fine equiaxed grains after RFE processing, but the increase range of the microhardness was small. The grains in the composite were further refined and the hardness increased obviously. The RFE processing had little influence on the friction factor and wear loss rate of the aluminum alloy. The friction factor and wear loss rate of the composite decreased by 17.6% and 34.7% that of the aluminum alloy before RFE processing, respectively. The worn surface of the composite was smooth and complete with plastic deformation and less ploughing; the wear mechanism was surface plastic deformation and slight abrasive wear. The worn surface of the aluminum alloy before and after RFE processing had relatively more grooves and ploughing; the wear mechanism was adhesion wear and abrasive wear.
  • WEI Jianlan, ZHAO Jizhong, DING Li, ZHANG Xu, KAN Qianhua, KANG Guozheng
    Materials For Mechanical Engineering. 2019, 43(4): 73-78. https://doi.org/10.11973/jxgccl201904016
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    Nano-indentation tests were conducted on hardening layer and base metal of laser-quenched U71Mn steel rail, and then the elastic modulus and nanohardness were calculated from the load-depth curves. An axisymmetric finite element model for nano-indentation of the hardening layer was established, and then the material parameters for isotropic power-hardening model were determined by the reverse analysis of the load-depth curves on the basis of the isotropic power-hardening model combined with iterative method. The validity of the reverse analysis was verified. The results show that the average elastic modulus and nanohardness of the hardening layer were 220.3, 11.8 GPa, improved by 4.9%, 187.8% those of the base metal, respectively. The elastic modulus and nanohardness distributed relatively homogeneously in the hardening layer and only changed sharply at the boundary. By the reverse analysis, the representative stress of the hardening layer was 3 146.0 MPa, the representative strain was 0.038, the strain hardening index was 0.64, and the nominal yield strength was 498.3 MPa. The stress-strain curves obtained by the reverse analysis and determined by given parameters were highly consistent, indicating the validity of the reverse analysis method.
  • HUANG Zidong, WEI Liangxin, HONG Zehao, HUANG Rutao, ZHENG Ruisheng, LUO Qing
    Materials For Mechanical Engineering. 2019, 43(4): 79-82,86. https://doi.org/10.11973/jxgccl201904017
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    The excessive amount of chromium ion precipitation in 430 stainless steel pot after dry burning test was determined by heavy metal migration test. The reason for exceeding was analyzed by chemical composition analysis, microstructure observation, electrochemical property testing, and so on. The results show that during the dry burning, the 430 stainless steel pot was in the precipitation temperature range of chromium-rich σ phase. The chromium-rich σ phase was prone to precipitate and caused chromium depletion around it. In corrosive solutions, the electrochemical reaction occurred between the σ phase and the chromium-depleted region, led to the ionization of chromium in the chromium-depleted region and the falling off of the chromium-rich σ phase, and eventually resulted in the excessive precipitation of chromium ion.
  • FU Yangyang, WANG Rong
    Materials For Mechanical Engineering. 2019, 43(4): 83-86. https://doi.org/10.11973/jxgccl201904018
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    Outer ring of a pitch bearing in a wind turbine generator fractured when used for a period of time. The reason for the fracture was analyzed by methods such as macro-inspection, chemical composition analysis, mechanical property test, fracture morphology and microstructure observation. The results show that the bearing outer ring fractured in a fatigue mode. Pits on inner surface of the bolt hole were generated by corrosive mediums, resulting in stress concentration points. By a relatively large external force, the cracks originated at the pits where existing obvious stress concentration, and consequently led to fatigue fracture.