20 May 2021, Volume 45 Issue 5
    

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  • ZHAO Yong, SU Haijun, ZHANG Jun, LIU Lin, FU Hengzhi
    Materials For Mechanical Engineering. 2021, 45(5): 1-7,44. https://doi.org/10.11973/jxgccl202105001
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    Magnetic field-controlled directional solidification provides a new route to prepare high-quality alloys and castings, and is of great significance for improving the metallurgical quality of products and developing new preparation techniques. The main research progress on the directional solidification of nickel-based superalloys under magnetic field in recent years is summarized. Several typical effects between magnetic field and metal conductive melt are described. The revolution of the directional solidification structures of nickel-based superalloys under static magnetic field, alternating magnetic field, pulsed magnetic field and traveling magnetic field, and the influence of magnetic field on typical solidification defects such as stray grains and on the creep properties of superalloys are systematically summarized. The formation mechanisms of solidification structures and defects under different types of magnetic fields are discussed. Finally, the development trend and breakthrough points of directional solidification of superalloys under magnetic field are prospected.
  • NI Xiaojie, KAI Jiawei, YIN Li, ZHAO Zhongxian, ZHAO Yuantao, WANG Shengze, HU Zhaowei, LI Wenge
    Materials For Mechanical Engineering. 2021, 45(5): 8-14. https://doi.org/10.11973/jxgccl202105002
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    In the severe marine environment of high salts, high humidity, wear and impact of cyclic loads, the key parts of ships are prone to corrosion, wear and fatigue failure. Therefore, the surface of the parts needs to be repaired and remanufactured, such as welding or laser cladding corrosion-resistant and wear-resistant layers on the surface. Mo2NiB2-based cermets have become coating materials for maintenance and remanufacturing due to their high hardness, excellent wear resistance and corrosion resistance, and high temperature oxidation resistance. The application of numerical simulation in research of Mo2NiB2-based cermets is summarized. The preparation processes of Mo2NiB2-based cermets or coatings, as well as the effects of different process parameters on the microstructure and performance of the materials are described in details. It is pointed out that the laser cladding in-situ synthesis technique combined with numerical simulation is the main research direction of Mo2NiB2-based cermets in the future.
  • XUE Chunxu, JIANG Shaoqun, WANG Gang, WANG Zehua, ZHOU Zehua
    Materials For Mechanical Engineering. 2021, 45(5): 15-21,26. https://doi.org/10.11973/jxgccl202105003
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    With Ni60A alloy, Ti, graphite (C), and B4C powders as raw materials and adjusting w(Ti+B4C+C)/w(Ni60A) (w is mass fraction/%) to 0:100, 10:90, 20:80 and 30:70, nickel-based composite coatings were synthesized by reactive plasma cladding on surface of 304 stainless steel. The effects of w(Ti+B4C+C)/w(Ni60A) on the formability, microstructure, hardness and wear resistance of the coating were studied. The results show that the nickel-based composite coatings with Ti+B4C+C were metallurgically bonded to the substrate, and were mainly composed of (Ni, Fe), CrB, TiC and Cr3Si. Increasing w(Ti+B4C+C)/w(Ni60A) improved the precipitation of strengthening phases and decreased the formability. CrB dispersed in the middle and lower part of the coating in gray-black slender strip forms, while in the upper part in small block or rod forms. TiC dispersed in the coating in fine particle forms. When w(Ti+B4C+C)/w(Ni60A) was 20:80, the comprehensive performance of the coating was relatively good; the average microhardness was the highest (948 HV) and the cross-sectional area of the wear scar was about 1/5 that of the pure Ni60A alloy coating. Adhesive wear and oxidative wear mainly occurred in nickel-based composite coatings.
  • HAN Yuchen, XING Shilong, JIANG Chuanhai
    Materials For Mechanical Engineering. 2021, 45(5): 22-26. https://doi.org/10.11973/jxgccl202105004
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    The Ni-W alloy coating was deposited in the electroplating solutions with different content (mass concentration of 0, 5, 10, 20 g·L-1) of Y2O3 nanoparticles. The influence of Y2O3 nanoparticle addition on the microstructure, micromorphology and electrochemical corrosion properties of the coating was studied. The results show that the addition of Y2O3 nanoparticles reduced the surface nodular structures of the coatings, refined the grains, and increased the microscopic strains. When the mass fraction of Y2O3 nanoparticles was between 5-10 g·L-1, the surface roughness of the coating was lower than that without nanoparticles; when the mass fraction of the nanoparticles increased to 20 g·L-1, the surface roughness was larger than that without nanoparticles. The addition of Y2O3 nanoparticles improved the electrochemical corrosion resistance of the coating. When the mass fraction of the nanoparticles was 10 g·L-1, the coating had the best electrochemical corrosion resistance.
  • CAI Yuqing, HU Xiongfeng, QU Shengguan, ZHANG Yalong, LAI Fuqiang, LI Xiaoqiang
    Materials For Mechanical Engineering. 2021, 45(5): 27-33,38. https://doi.org/10.11973/jxgccl202105005
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    Shot peening was conducted on surface of CF53 steel under three shot peening strengths (0.326, 0.401, 0.438 mm), and then pin-on-disk friction and wear tests were carried out under oil lubrication conditions. The surface morphology, microstructure, microhardness and wear resistance of the specimens before and after shot peening were studied and compared. The results show that the surface of the specimens had dimple-like pit morphology after shot peening, and the surface roughness, microhardness and depth of the hardening affected zone increased with the increase of the shot peening strength. Shot peening by three strengths improved the wear resistance of the specimens; the friction coefficients and volume wear rates after shot peening were less than those of the unpeened specimens. The wear resistance of the specimen shot peened with 0.326 mm strength was the best. The wear mechanism of the unpeened specimens was mainly adhesive wear and material shearing off. After shot peening at strength of 0.326,0.401 mm, the wear mechanism was delamination and abrasive wear; at strength of 0.438 mm, the wear mechanism was fatigue wear.
  • MA Changwen, DI Guobiao, WANG Kaikai, HUANG Leqing, LU Shiping
    Materials For Mechanical Engineering. 2021, 45(5): 34-38. https://doi.org/10.11973/jxgccl202105006
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    The on-line quenching and 600 ℃ tempering and the out-line quenching and 600 ℃ tempering treatments were conducted on a high-strength steel plate. The microstructure and mechanical properties by the two processes were studied and compared. The results show that the microstructures of the test steel plate under the two processes were both tempered martensite. After the on-line quenching and tempering treatment, the martensite laths had smaller spacing and longer length. Moreover, the martensite after the on-line quenching and tempering had a higher proportion of dislocation density and more large-angle grain boundaries, and the carbides were finer. The mechanical properties of the test steel plate after the on-line quenching and tempering treatment showed higher strength, but the plasticity and toughness were lower than those after the out-line quenching and tempering treatment.
  • LI Hui, CUI Xin, ZHAO Xiaobing, LIU Xiwu, ZOU Yang
    Materials For Mechanical Engineering. 2021, 45(5): 39-44. https://doi.org/10.11973/jxgccl202105007
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    Fe-based amorphous coating was prepared by plasma spraying technique using Fe-based amorphous alloy powder as raw materials. The effects of simultaneous increase of Ar flow rate (40-80 L·min-1) and H2 flow rate (6-10 L·min-1) on the microstructures, bonding strength with substrate, microhardness, wear resistance and corrosion resistance of the coating were investigated. The results show that the amorphous content of the prepared coatings was relatively high, and the area fraction reached 92.4%-94.8%. Good bonding was formed between the coating and the substrate and no obvious crack was observed. With increasing flow rate of Ar and H2, the porosity of the coating decreased first and then increased, and bonding strength between the coating and the substrate and microhardness of the coating increased first and then decreased. The corrosion resistance of the coating in 0.5 mol·L-1 H2SO4 solution became better and then worse. When Ar flow rate was 60 L·min-1 and H2 flow rate was 8 L·min-1, the coating had the most compact structure with the lowest porosity, the highest bonding strength and microhardness and the best wear and corrosion resistance.
  • YUAN Changwang, HUANG Jiajin, ZHONG Huilong, LI Shengci
    Materials For Mechanical Engineering. 2021, 45(5): 45-49. https://doi.org/10.11973/jxgccl202105008
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    The microstructure and tensile properties of 22MnB5 steel before and after hot stamping at 890 ℃ were studied and compared. The micromorphology evolution during uniaxial tensile of the test steel after hot stamping was investigated by in-situ tensile tests. The results show that the microstructure of the test steel before hot stamping was composed of ferrite and pearlite. After hot stamping, the microstructure changed to martensite, and the strength and the volume of strength and plasticity of the steel increased, while the plasticity decreased. During tensile, the test steel first underwent necking, then the original austenite grain boundaries were destroyed, leading to the initiation of microcracks, and the hole-type cracks were formed by debonding of inclusions. As the tensile continued, the cracks propagated and connected to each other, resulting in the fracture of the steel. A large number of dimples were observed on the tensile fracture surface of the hot stamped test steel, and the fracture form was microvoid coalescence fracture.
  • SHI Ke, WANG Wendong, SI Mingming, WANG Fei, ZHANG Chao
    Materials For Mechanical Engineering. 2021, 45(5): 50-55. https://doi.org/10.11973/jxgccl202105009
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    Two kinds of graphite with different hardness and strength were inlaid in the Cu-15Ni-8Sn alloy matrix. The friction pairs of Cu-15Ni-8Sn copper alloy inlaid graphite material and 05Cr17Ni4Cu4Nb precipitation hardened stainless steel were obtained. The friction and wear properties of the material under different loads (490,980,1 470 N) and different lubrication conditions (dry friction and wet friction) were studied. The results show that under dry friction condition, the friction coefficient of the materials almost increased with load, and the dry friction coefficient of the material with higher hardness and strength graphite was smaller than that of the material with lower hardness and strength graphite. Under wet friction condition, the friction coefficient of the material with higher hardness and strength graphite increased with load, but was similar with that under dry friction condition. With increasing load, the wear loss under dry friction and wet friction increased. The wear mechanism of graphite was abrasive wear accompanied with fatigue wear under dry friction condition, and was abrasive wear and erosive wear under wet friction condition.
  • SHANG Changpei, YANG Fan, XIA Zhiping
    Materials For Mechanical Engineering. 2021, 45(5): 56-62. https://doi.org/10.11973/jxgccl202105010
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    The WE54 alloy in T4 and T6 states were deformed by quasi-static compression and air-hammer forging (high speed). The microstructures, hardness and compression performance before and after deformation were investigated. The results show that after the quasi-static deformation and high speed deformation, twins appeared in some deformed grains of WE54 alloys in T4 and T6 states, and secondary twins were fomed in some coarse twins. These twins exhibited parallel arrangement or intersection features. The deformed grain size remained invariable in the T4 and T6 alloys after deformation at different speeds, but the refining structure due to the sectioning of matrix by newly formed twins was helpful for the improvement of Vickers hardness and compression performence. Compared with the quasi-static compression, the high speed deformation promoted the twinning mechanism to coordinate deformation, therefore induced more twin boundaries to refine the matrix and enhance the hardness and yield strength of the deformed alloys.
  • WANG Pengbo, ZHANG Yongqiang, FU Can, JU Jianbin, YI Rigui
    Materials For Mechanical Engineering. 2021, 45(5): 63-66,83. https://doi.org/10.11973/jxgccl202105011
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    Resistance spot welding was conducted on CP780 galvanized complex-phase steel plate with 1.5 mm thickness. The welding current window, microstructure and mechanical properties of the steel plate were studied. The electrode life during the resistance spot welding was evaluated. The results show that the welding current window for the resistance spot welding of the test steel plate expanded from 6.0-8.0 kA. The microstructure of the weld under the maximum and minimum welding currents mainly consisted of lath martensite, and that of the heat affected zone consisted of martensite and some ferrite. The hardness of the nugget under the maximum and minimum welding currents was higher than that of the heat affected zone, and softening zones were found in the heat affected zone. The maximum shear force and positive tensile force of the spot weld joint at the maximum welding current were 21.80 kN and 10.56 kN, which were 51.8% and 38.0% higher than those at the minimum welding current, respectively. After continuous welding 2 000 points at the maximum welding current, the nugget diameter was still larger than the critical nugget diameter, indicating the electrode life exceeded 2 000 points.
  • ZHANG Weichen, LI Jiuxiao, YANG Dongye, ZHANG Xinyue, ZHENG Lixin, ZHANG Yutong, HE Linghuan
    Materials For Mechanical Engineering. 2021, 45(5): 67-70,75. https://doi.org/10.11973/jxgccl202105012
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    With Ti-6Al-4V titanium alloy powder and LaB6 powder as raw materials, the in-situ synthesized TiB+La2O3/TC4 titanium matrix composite and TC4 titanium alloy were prepared by selective laser melting. The phase compostion, microstructure, hardness and compressive strength of the composite and the titanium alloy were studied and compared. The results show that the microstructures of the composite and the titanium alloy were both composed of columnar β grains and acicular α' martensite distributed in grains. The size of the β grains and α' martensite clusters of the composite were smaller, and the proportion of large angle grain boundary was higher. TiB and La2O3 reinforcements were formed by in-situ reaction of LaB6 and titanium. TiB was elongated and distributed along a certain direction. La2O3 was in shape of small spheres, and dispersed on grain boundaries and in grains. The microhardness and room temperature/high temperature compressive strength of the composite were higher than those of the titanium alloy.
  • YU Shihao, LI Jiaqi, ZHANG Linlang
    Materials For Mechanical Engineering. 2021, 45(5): 71-75. https://doi.org/10.11973/jxgccl202105013
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    A finite element model of in-mold melting diffusion of V9Cr4 high-vanadium alloy was established with ANSYS software, and then the temperature change at different spots in the high-vanadium alloy rod was simulated during solidification after casting 5CrNiMo alloy liquid. According to the simulation that the axial temperature of the alloy rod changed little, the three-dimensional diffusion of alloy elements was simplified to two-dimensional diffusion, and the mathematical model for vanadium content distribution along radial direction was established. The vanadium content along radial direction was calculated and was verified by experiments. The results show that the temperatures of the alloy rod were higher than its solidus temperature during casting, indicating the metallurgical bonding between the high-vanadium alloy and 5CrNiMo alloy. The diffusion time of vanadium was determined to be 810 s from the temperature distribution curve. This diffusion time was substituted into the mathematical model for vanadium content distribution and then the vanadium content at different spots was obtained. The relative errors between the calculated content and the testing results were less than 1%, indicating that the established finite element model of in-mold melting diffusion was accurate, and its simulation could be used to calculate the vanadium content distribution.
  • BAO Zhiqiang, ZHANG Yong, ZHANG Zhuzhu, FAN Weijie, MENG Lili
    Materials For Mechanical Engineering. 2021, 45(5): 76-83. https://doi.org/10.11973/jxgccl202105014
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    Quasi-static compression at low strain rates (10-4, 10-3, 10-2 s-1) and dynamic compression at high strain rates (850-4 500 s-1) were conducted on 38CrMoAl high strength steel with a hydraulic testing machine and a split Hopkinson pressure bar test device. The dynamic compressive mechanical properties of the steel and the microstructure after dynamic compression were studied. Considering the strain rate enhancement effect and adiabatic effect, the Johnson-Cook (J-C) constitutive model was modified, and was verified by experiments. The results show that the true yield strength of the test steel increased with the increase of the compressive strain rate, indicating an obvious strain rate enhancement effect. After compression at high strain rates, the strengthening zone with certain corrosion resistance appeared in the microstructure of the test steel. The average relative errors between the prediction by the modified J-C constitutive model and the experimental values of the true stresses were 1.76%-3.99%, indicating that the modified J-C constitutive model could describe the dynamic compressive mechanical properties of 38CrMoAl steel accurately.
  • JING Ya, ZHONG Fei, YUAN Guangjian, CAO Xian, WANG Runzi, ZHOU Guoyan, ZHANG Xiancheng
    Materials For Mechanical Engineering. 2021, 45(5): 84-90,95. https://doi.org/10.11973/jxgccl202105015
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    With the crystal plastic constitutive model, the uniaxial tensile and fatigue test data were fitted to obtain the relevant parameters that meet the simulation conditions, which was realized by generating the representative volume elements of macroscopic specimens. The effect of mesh size on the simulation was analysed. The cumulative plastic slip and energy dissipation were used as indicators to predict the fatigue crack initiation life, and the influence of notch size on the fatigue crack initiation life was studied.The results show that the fatigue crack initiation life of the notched specimen obtained by the established model was within two times the error band of the fatigue crack initiation life obtained in the test, indicating the model had good prediction accuracy. When the notch size was small, the fatigue crack initiation life of the specimen significantly reduced with increasing notch size; when the notch size was larger than the critical notch size, the fatigue crack initiation life of the specimen was hardly affected by the notch size.
  • YANG Qin, GUO Yonghuan, XU Dongqin, YAN Tian
    Materials For Mechanical Engineering. 2021, 45(5): 91-95. https://doi.org/10.11973/jxgccl202105016
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    12 groups of welding process parameters (welding current at 60, 70, 80, 90, 100, 110 A, welding speed at 1.96, 2.88 mm·s-1) were set by uniform experimental design. The welding finite element model of DP780 dual phase steel was established. By the simulation and experiments, the optimal welding current and welding speed were determined with the minimum deformation of the joint as the index. The temperature field and the content of martensite in coarse-grained zone of heat affected zone (CGHAZ) of the joint were simulated by the welding finite element model, and verified by the thermal simulation experiment. The results show that the deformation of the welded joint was the smallest with the welding current of 100 A and the welding speed of 1.96 mm·s-1, and the relative error between the finite element simulation and the experimental result was 3.528%, indicating that the model was accurate. By the finite element simulation, the area with a distance of 2.44-6.97 mm from the weld center was the CGHAZ. The area fraction of martensite in CGHAZ was 43%, which was close to that (44%) in the CGHAZ sample prepared by the thermal simulation experiment, indicating that the established model could be used to simulate the CGHAZ structure.
  • LIU Peixing
    Materials For Mechanical Engineering. 2021, 45(5): 96-99,104. https://doi.org/10.11973/jxgccl202105017
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    Samples were taken from different positions of U-shaped parts of CR1500HF hot-forming steel, and tensile tests with strain rates from 1 to 500 s-1 were carried out. The difference in tensile properties at different positions and the effect of strain rate on the tensile properties of the hot-stamped parts were studied.The material tensile finite element model was established to analyze the high-speed tensile performance of the steel and the stress distribution at the clamping end of the tensile specimen. The results show that the tensile strength and yield strength on side-wall of the hot-stamped U-shaped part were lower than those at flange and bottom positions; therefore, in the collision analysis, it was necessary to consider the influence of the strength reduction at some positions due to insufficient cooling. With increasing strain rate, the yield strength and tensile strength at different positions of the U-shaped part increased. The true stress-true plastic strain curves simulated with the tensile finite element model were in good agreement with those obtained by combined S-H constitutive model; the root-mean-square errors of the true stress at strain rate of 1, 500 s-1 were 19.98,39.48 MPa, respectively. During high-speed tensile, most of the clamping end of tensile specimens were in elastic deformation stages, and the distance between the attachment position of the strain gauge and the arc of the specimen should be greater than 19 mm.
  • ZHOU Xiaogang, JI Feifei
    Materials For Mechanical Engineering. 2021, 45(5): 100-104. https://doi.org/10.11973/jxgccl202105018
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    TC4 titanium alloy plates were subjected to laser shot peening for different times and then subjected to high cycle fatigue tests. The fatigue properties and fracture mechanism of the alloy were studied. Considering the retardation effect of the residual compressive stress and the mesoscopic size of grain boundaries on the microcrack growth, the suppression parameter, open stress intensity factor and residual stress intensity factor were introduced to modify the Paris formula. Then a prediction model for fatigue microcrack growth after laser shot peening was established and verified by experiments. The results show that with the increase of the number of shot peening, the fatigue strength and fatigue life of the TC4 titanium alloy increased, and the fracture mode changed from brittle fracture to ductile fracture. The relative errors of the fatigue life predicted by the fatigue microcrack prediction model and the test results were less than 10%, indicating that the model was accurate.
  • LUO Yi, YANG Yang, JIANG Xiaobin, WANG Huazhong
    Materials For Mechanical Engineering. 2021, 45(5): 105-110. https://doi.org/10.11973/jxgccl202105019
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    Causes of elbow perforation of 20 steel pipeline for crude oil in an oil field were analyzed by microscopic/macroscopic morphology analysis, chemical composition analysis, metallographic analysis, corrosion product analysis, water quality analysis, and force simulation, and so on. The results show that the ceramic coating on inner wall surface of the elbow had some quality defects such as pores and bubbling. The thickness at relatively large curvature area of the outer arc was the smallest, forming a low-lying area. The water in the crude oil was easy to produce CaCO3 scales, which deposited in the low-lying area and the corrosion under scales occured. Under the synergistic action of CO2, H2S, sulfate-reducing bacteria and Cl- in the crude oil medium inside the elbow, corrosion perforation was formed in the area with large curvature of outer arc where the fluid impact force was the largest and the coating damage was the most serious.