20 April 2022, Volume 46 Issue 4

    

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Technical Review
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  Research Status on High-Energy-Density Welding ofFerrite/Austenite Duplex Stainless Steel

  ZHANG Zhiqiang, XU Yutong, ZHANG Tiangang, ZHANG Yuhang, WANG Hao, YANG Fan

  Materials For Mechanical Engineering. 2022, 46(4): 1-11. https://doi.org/10.11973/jxgccl202204001

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  Ferrite/austenite duplex stainless steel has a combination of good ductility and toughness, excellent corrosion resistance and high strength due to its unique microstructure characteristics, and has a wide application prospect in many fields such as marine engineering, petrochemical engineering. High-energy-density welding technique has attracted attention from scholars in recent years because of its narrow heat affected zone, low deformation level, low residual stress, high welding speed and high productivity. The research progress of high-energy-density welding is introduced from two aspects of welding method and process, and then the microstructure and properties of duplex stainless steel with high-energy-density welding and post-weld heat treatment are reviewed. Finally, the problems existing in the current research of high-energy-density welding of duplex stainless steel are pointed out and the future research direction is given.
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  Research Methods of Molten Pool Flow Characteristics inTungsten Inert Gas Welding

  LI Yuanbo, ZHENG Wenxing, YE Tao, MA Shuaichuan, ZHAO Xilong

  Materials For Mechanical Engineering. 2022, 46(4): 12-20. https://doi.org/10.11973/jxgccl202204002

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  The flow of the molten pool during tungsten inert gas (TIG) welding has an important impact on the final geometry, microstructure, residual stress of the weld, and understanding the flow characteristics of the molten pool had a great significance to control the quality and properties of the weld. At present, the research methods of molten pool flow characteristics are mainly divided into experimental test, numerical simulation and dimensional analysis. The status of research methods of the molten pool flow characteristics during TIG welding are summarized, and the characteristics of different research methods are compared and analyzed. The future research direction is prospected.
Testing & Research
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  Microstructure and Properties of FeCoNiCr_0.5Al_0.8 High Entropy Alloy Pulsed Laser Cladding Layer on Pure Titanium Surface

  YIN Zhengsheng, XUE Xinyu, JIANG Yongfeng, LU Tao, ZHAO Lijuan, JI Xiulin

  Materials For Mechanical Engineering. 2022, 46(4): 21-25,31. https://doi.org/10.11973/jxgccl202204003

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  The FeCoNiCr_0.5Al_0.8 high entropy alloy cladding layer was prepared on the surface of TA2 industrial pure titanium by pulsed laser cladding technique, and the microstructure, phase composition, hardness and high temperature oxidation resistance of the cladding layer were studied. The results show that a good metallurgical bonding was formed between the cladding layer and the substrate, there were no defects such as cracks and pores in the cladding layer, and the fusion interface was relatively straight. There were fine equiaxed crystals at the molten pool boundary of the cladding layer and dendrites in the middle of the molten pool. The section structure of the cladding layer was layered distributed fine crystals. The cladding layere was mainly composed of simple face-centered cubic structure Ti₂Ni and AlCTi₂. The average hardness of the cladding layer was 761.23 HV, which was more than 4 times the hardness of the substrate. The cladding layer had excellent high temperature oxidation resistance, and the mass grain per unit area of the cladding layer oxidized at 800℃ for 120 h was about 17 mg·cm^-2, which was about only one third of the substrate.
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  Mechanical Property Changes of Tungsten after Helium Ion Irradiation with Different Damage Degree

  CHEN Wanqi, LI Xinnan, LI Kailun, CHIU Yulung, LIU Wei

  Materials For Mechanical Engineering. 2022, 46(4): 26-31. https://doi.org/10.11973/jxgccl202204004

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  The surface of recrystallized tungsten was irradiated by helium ions with different energy and ion fluence. The microstructure of tungsten with irradiation damage of 0.2,0.5,1.0 dpa was observed. The nanoindentation test was conducted with spherical indenter of different radius (1,5,10 μm) to obtain the indentation stress-strain curve, and the change of mechanical properties and reason for the change were explored. The results show that the thickness of damage layer on tungsten surface was 554-558 nm after irradiation with different damage degree. With increasing damage degree, the density of dislocation loop in tungsten increased obviously. The indentation stress-strain curves of tungsten after irradiation did not exhibit pop-in phenomenon, and the yield strength increased with damage degree, and the indentation elastic modulus basically unchanged. The dislocation loop defect caused by irradiation was the direct cause of the change of mechanical properties of tungsten. The mechanical properties of tungsten had the effect of indentation size. The smaller the indenter radius, the higher the yield strength of tungsten, and the greater the indentation stress when the stress-strain curve of unirradiated tungsten showed pop-in.
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  Effect of TiO₂ Doping on Structure and Properties ofCaO-Al₂O₃-SiO₂ Series Glass

  CHEN Chao, ZHU Qingong, WANG Huanping, XU Shiqing, CAO Yongsheng, PEI Weiwei

  Materials For Mechanical Engineering. 2022, 46(4): 32-36. https://doi.org/10.11973/jxgccl202204005

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  CaO-Al₂O₃-SiO₂ (CAS) series glass with TiO₂ doping amount (mole fraction) of 0-5.0% was prepared by traditional melt cooling method, and the effect of TiO₂ doping amount on the micro structure, thermal stability and bending strength of the glass was studied. The results show that TiO₂ mainly existed in the form of[TiO₅] unit in CAS series glass network. With increasing TiO₂ doping amount, the number of[TiO₅] unit and Ti-O-Si bond in the glass, the number of bridge oxygen in the glass network, and optical band gap of the glass all first increased and then decreased, and all reached the largest value when the TiO₂ doping amount was 4.0%. With increasing TiO₂ doping amount, the thermal stability and flexural strength of CAS series glass first increased and then decreased. When the doping amount of TiO₂ was 4%, the comprehensive performance was the best, and the glass transition temperature, bending strength and optical band gap were 798.24℃, 95.58 MPa and 3.75 eV, respectively.
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  Effect of Temperature on High-Cycle Fatigue Properties of 2CrMo Alloy Steel for Turbine Rotor

  GAO Qianqian, HU Benrun, ZUO Qiang

  Materials For Mechanical Engineering. 2022, 46(4): 37-41. https://doi.org/10.11973/jxgccl202204006

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  The tensile test and axial stress controlled high-cycle fatigue test were carried out on an imported 2CrMo alloy steel for turbine rotor at room temperature and high temperature (450, 500, 566℃). The high-cycle fatigue stress-life curves of the steel were obtained based on test data, and curved surface of median life was obtained by generalized curved surface of median model. The effect of temperature on the high-cycle fatigue properties was studied. The results show that yield strength, tensile strength and elastic modulus decreased with increasing temperature. High-cycle fatigue life decreased with increasing temperature at the same stress level. The influence of stress level on fatigue life was great at high stress ratio (0.5,0.8). The high-cycle fatigue fracture under low stress ratio (-1,-0.3) was a typical high-cycle fatigue fracture under axial load; the fatigue source was multi-source at high temperature and a single crack source at room temperature. At high stress ratio (0.5,0.8), high-cycle fatigue fracture presented tensile fracture characteristics; fracture had obvious radial zone, fiber zone and shear lip zone at room temperature, and had only fiber zone and shear lip zone at high temperature.
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  Microstructure and Hardness of CMT Wire-Arc Additive Manufactured H13 Steel Formed Parts in Different Deposition Paths

  LI Xufeng, LIN Jian, XIA Zhidong, HAN Wentao, LEI Yongping, WANG Zhaoyang

  Materials For Mechanical Engineering. 2022, 46(4): 42-47,55. https://doi.org/10.11973/jxgccl202204007

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  H13 steel formed part was prepared by cold metal transfer wire-arc additive manufacturing in different deposition paths. Based on the thermo-elastic-plastic finite element method, the thermal history of the formed part was studied. The microstructure and hardness evolution of formed part was studied by tests. The results show that the thermal history of the 5-layer single-pass and single-layer 5-pass formed part deposited in the codirection and bidirection path was basically the same. The peak temperature of the middle point of the third layer of bidirection deposited 5-layer single-pass formed part was much higher than that of the middle point of the third pass of bidirection deposited single-layer 5-pass formed part, and the heat accumulation effect of the 5-layer single-pass formed part was more obvious. The lath martensite structure of 5-layer single-pass formed part was coarsened than that of single-layer 5-pass formed part. The hardness of the codirection deposited 5-layer single-pass formed part at the same height was slightly higher than that of bidirection deposited formed part, and the hardness of the codirection deposited and bidirection deposited 5-layer single-pass formed part was basically the same. The average hardness of the 5-layer single-pass formed part was slightly smaller than that of single-layer 5-pass formed part.
Material Properties & Application
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  Effect of Mo Content on Cold and Thermal Fatigue Properties of4Cr5MoV Hot Work Die Steel

  DENG Junjie, ZHOU Jian, LIU Jianxiong, CHI Hongxiao, LIN Peng

  Materials For Mechanical Engineering. 2022, 46(4): 48-55. https://doi.org/10.11973/jxgccl202204008

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  The surface and section crack morphology, microstructure and hardness changes of 4Cr5MoV hot work die steel containing different mass fraction (1.8%, 3.2%) of Mo were analyzed by self-constrained cold and thermal fatigue test from room temperature to 600℃. The effect of Mo content on cold and thermal fatigue properties of hot work die steel was studied. The results show that after 1 000 cold and hot fatigue cycles, the cracks on the surface of test steel containing 3.1wt% Mo were thin and sparse, and the crack number was significantly less than that of the test steel containing 1.8wt% Mo; the test steel containing 3.1wt% Mo had higher temper softening resistance, and high surface hardness could delay the initiation of cold and thermal fatigue cracks in the die steel. After 2 000 cold and thermal fatigue cycles, the crack propagation depth of the test steel containing 3.1wt% Mo was greater than that of the test steel containing 1.8wt% Mo, indicating the crack propagation rate was larger, which was related to the low impact toughness at room temperature and coarsening of a large amount of carbides of the test steel containing 3.1wt% Mo.
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  Friction and Wear Properties of Friction Pair Between SA533 Gr.B Alloy Steeland Graphite under Different Conditions

  TIAN Hongzhi, WANG Wendong, WANG Fei

  Materials For Mechanical Engineering. 2022, 46(4): 56-62. https://doi.org/10.11973/jxgccl202204009

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  Two kinds of graphite with different graphitization degree and compressive strength were combined with SA533 Gr.B alloy steel to form friction pair. The friction and wear properties under different lubrication conditions were tested by ring block friction testing machine, and the wear morphology was observed. The results show that in the stable stage of dry friction, the friction coefficient of the friction pair between alloy steel and graphite with high graphitization degree and low compressive strength was greater than that with graphite with low graphitization degree and high compressive strength, and the wear rate of graphite with low graphitization degree and high compressive strength was smaller. Under the condition of wet friction in boric acid solution, the friction coefficient of the friction pair between alloy steel and different graphite had little difference and fluctuated, and the wear rate of graphite was higher than that under dry friction. The transfer film formed by graphite with low graphitization degree and high compressive strength on alloy steel surface under shear stress was thick and closely bonded with steel substrate. The wear mechanism of graphite under dry friction condition and wet friction condition in boric acid solution was mainly abrasive wear.
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  Corrosion Behavior of L360N Pipeline Steel Under Action ofSulfate-Reducing Bacteria in Produced Water of a Shale Gas Field

  LIU Xinyue, ZHANG Lan, YUE Ming, HE Sha, ZHAO Qiyue

  Materials For Mechanical Engineering. 2022, 46(4): 63-68,74. https://doi.org/10.11973/jxgccl202204010

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  Taking three kinds of separator produced water of the gathering and transportation pipeline in a shale gas field containing 10³,10⁵,10 sulfate-reducing bacteria (SRB) per 1 mL water sample (named as 1^#, 2^#, 3^# water sample) as the test medium, the corrosion behavior of L360N pipeline steel immersed in different water samples for 14 d was studied. The results show that the more SRB in the water sample, the higher the corrosion rate, and the more serious the corrosion of pipeline steel. After immersing in 1^# water sample for 14 d, the surface of pipeline steel contained FeS, and the high concentration of HCO₃^- contributed to the formation of corrosion product film. After immersing in 2^# water sample, the content of FeS on the surface of pipeline steel was the highest, and the corrosion products distributed in uneven clusters; high concentration Cl^- and low concentration HCO₃^- together accelerated the damage of the film layer. After immersing in 3^# water sample, the surface of pipeline steel was relatively smooth with few corrosion products and the lowest corrosion degree.
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  High Temperature Creep Behavior of Overage Serviced 10CrMo910 Steel forPower Station

  GAO Yuemin, DU Haoyang, YE Feng, CUI Lun

  Materials For Mechanical Engineering. 2022, 46(4): 69-74. https://doi.org/10.11973/jxgccl202204011

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  The high temperature creep tests at different temperatures (535,560,580℃) were conducted on 10CrMo910 steel main steam pipe for generator unit in a thermal power station, which had been running for more than 2×10⁵ h, and the high temperature creep behavior and microstructure evolution of the steel were studied. The results show that after high temperature creep at different temperatures, the grains of overage serviced 10CrMo910 steel were obviously deformed, recrystallization occurred in bainite and ferrite matrix, and precipitates coarsened; creep holes became larger and deeper, and creep damage was aggravated. With increasing creep temperature, the creep fracture time decreased from 4 633 h to 2 314 h, and the high temperature creep rupture strength decreased from 87.7 MPa to 58.3 MPa, indicating the high temperature creep property of 10CrMo910 steel decreased. The creep fracture was dimple-like without obvious shear tear zone and with obvious secondary cracks and precipitates, and the fracture mode was quasi cleavage fracture.
Physical Simulation & Numerical Simulation
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  Numerical Simulation of Close-Coupled Annular Nozzle Atomization Process in Vacuum Induction Gas Atomization Technology

  SUN Yingjian, ZHOU Lijie, GONG Xiang, ZHANG Pengcheng, HAO Ruilin

  Materials For Mechanical Engineering. 2022, 46(4): 75-81. https://doi.org/10.11973/jxgccl202204012

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  The volume of fluid approach was coupled the Reynolds stress model and the discrete phase model combined with the Taylor analogy break-up instability breaking model to simulate the primary atomization and secondary atomization for the close-coupled annular nozzle by computational fluid dynamics software Fluent19.2, and the simulation was verified by experiment. The results show that the primary atomization resulted in the forming of an annular liquid film at the bottom of the delivery tube. The primary atomization at the tip of the liquid film was mainly the result of turbulent shear at the free boundary of the gas jet, and the diameter of the droplets formed by the primary atomization satisfied the normal distribution. As the outside of the dispersed droplet group contacted the gas jet, the secondary atomization gradually started from the outside of the droplet group to the core, but the droplets those did not contact with the gas jet maintained a high degree of superheat. The simulated diameter of the powder after secondary atomization by the close-coupled annular nozzle was in good agreement with test results, and the relative error was less than 5%, which verified the accuracy of simulation.
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  Comparison of Meso Finite Element Modeling Methods for Particle Reinforced Metal Matrix Composites

  LIU Junhua, ZHANG Juan, ZHANG Chen, HUANG Xingmin

  Materials For Mechanical Engineering. 2022, 46(4): 82-88,94. https://doi.org/10.11973/jxgccl202204013

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  Taking TiB₂ particle reinforced iron matrix composites prepared by in-situ formation method as research object, the parameters of power hardening model of matrix were determined by nano indentation test and finite element inverse analysis. The two-dimensional meso real structure model and body cell model with particle random distribution were established, and then the uniaxial tensile test was simulated. The true stress-true strain curve was calculated by equivalent macro method, and the simulation of the two models were compared. The effect of boundary condition on the simulation was discussed. The results show that boundary conditions had little effect on the simulated true stress-true strain curve during uniaxial tension. The true stress-true strain curves by simulating uniaxial tension with the two models had little difference, which were consistent with test results, and the relative error was less than 5%. The error of elastic modulus and yield strength by simulation with real structure model was smaller than that with body cell model. The local microscopic equivalent stress field and strain field of matrix and particle by simulation with different models were obviously different.
Failure Analysis
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  Fracture Cause of Flame Tube Fairing in an Aeroengine

  LIU Huan, GAO Jianhui, CHI Qingxin, MEN Yubin, TONG Wenwei, LI Yanming

  Materials For Mechanical Engineering. 2022, 46(4): 89-94. https://doi.org/10.11973/jxgccl202204014

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  Fracture occurred in flame tube fairing of an aeroengine during working process. Fracture causes were analyzed by macro and micro morphology observation, surface quality inspection, metallographic inspection, fatigue test and dynamic stress test. The results show that the fracture mode of the fairing was high-cycle fatigue fracture, and the fatigue crack source was located at the corner stress concentration area of the fairing. Large grain size of original forging of the fairing decreased the fatigue strength, which was one of the main causes for fatigue fracture of the fairing. The load at the corner stress concentration area of the fairing was too large under the action of the maximum vibration stress, which was significantly higher than its dynamic strength reserve. This was another main reason for the fatigue fracture of the fairing. The abnormal axial scratches at the corner stress concentration area of the fairing further increased the stress concentration factor and promoted the initiation of fatigue cracks.