20 July 2021, Volume 45 Issue 7
    

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  • Research Progress on Preparation Technology of Silicon CarbideCeramics with Complex Structure
    WANG Xiaobo, HE Zhiyong, WANG Feng, ZHANG Qifu
    Materials For Mechanical Engineering. 2021, 45(7): 1-6,34. https://doi.org/10.11973/jxgccl202107001
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    Silicon carbide ceramic has high strength and thermal conductivity, and good chemical stability, and is widely used in aerospace, petrochemical, integrated circuits and other fields; however, defects are easy to form in the silicon carbide ceramic during processing because of its high hardness and brittleness, which restricts the application of silicon carbide ceramic with complex structures. The preparation processes of silicon carbide ceramic with complex structures are described, and the advantages and disadvantages of the commonly used preparation technologies, such as cold isostatic pressing combined with pressure-free sintering, gel injection molding combined with reactive sintering, slip casting combined with reactive sintering, 3D printing combined with reactive sintering, are analyzed in order to provide a certain theoretical reference for the preparation of silicon carbide ceramic with complex structures.
  • Research Progress on Toughness Evaluation and of Ductile-Brittle Transition Mechanism of Reactor Pressure Vessel Steel
    RAO Delin, MO Jiahao, GAO Jianbo, LI Jun, ZHANG Shuyan
    Materials For Mechanical Engineering. 2021, 45(7): 7-11. https://doi.org/10.11973/jxgccl202107002
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    The evaluation of mechanical performance of reactor pressure vessel (RPV) steel is the main content of the life extension evaluation of nuclear power plants, and the increase of ductile-brittle transition temperature caused by irradiation damage is the main factor affecting operational safety and life. The toughness and brittleness transition evaluation of RPV steel is carried out by drawing surveillance samples, but the shortage of the surveillance samples forces material workers to study the toughness evaluation using small sample and sample reconstitution technique. The toughness evaluation methods of RPV steel at home and abroad in recent years are discussed, and the application of several nondestructive testing techniques on RPV steel mechanical property testing is described. The research progress on the irradiated embrittlement mechanism of RPV steels, especially the microstructure evolution mechanism of RPV steel under the high irradiation condition, in the past three years at home and abroad is described. Finally, the prospect of toughness evaluation and related mechanism research of RPV steel in China is presented.
  • Effect of Corrosion Product Film on Seabed Corrosion Behavior of X70 Pipeline Steel Weld
    ZHANG Kaili, XIE Fei, WU Ming, WANG Dan, GAI Zuosong, LIU Jin
    Materials For Mechanical Engineering. 2021, 45(7): 12-16,40. https://doi.org/10.11973/jxgccl202107003
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    After corrosion in simulated South China Sea mud solution for 10, 24, 72, 120 h, the morphology and composition of the corrosion products on surface of the weld of X70 pipeline steel were analyzed by scanning electron microscopy and energy spectroscopy. Then the effect of corrosion product film on the corrosion behavior of the weld was studied by slow strain rate tensile tests and potentiodynamic polarization tests. The results show that with increasing corrosion time, the corrosion product films on surface of the weld were thickened. A dense corrosion product film was formed after corrosion for 72 h, and more pores and cracks were formed in the film after 120 h corrosion. With increasing corrosion time, the stress corrosion sensitivity of the weld increased first, then decreased, and then slightly increased. The electrochemical corrosion behavior showed the same change. After corrosion for 72 h, the formation of the dense corrosion product film reduced the stress corrosion sensitivity of the weld and improved the corrosion resistance.
  • Compression-Compression Fatigue Behavior of Open-Cell Foam Copper
    YANG Yang, CHEN Jian, LI Cong, JIANG Xueao
    Materials For Mechanical Engineering. 2021, 45(7): 17-21. https://doi.org/10.11973/jxgccl202107004
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    Uniaxial quasi-static compression and compression-compression fatigue tests were performed on open-cell foam copper with the same pore size. The compression characteristics and fatigue behavior of open-cell foam copper were analyzed, and the fatigue failure mode and failure mechanism were discussed. The results show that the compressive stress-strain curve of open-cell foam copper consisted of elastic deformation stage, platform stress stage, and compaction stage. During compression-compression fatigue process, the open-cell foam copper mainly experienced fatigue damage accumulation zone, strain surge zone, and continuous failure zone. The lower the stress level, the longer the life of open-cell foam copper. Under the action of shearing force, the middle part of the open-cell foam copper formed an extruded zone with a certain angle to the horizontal direction. As the accumulated strain increasing, the pore structure in the extruded zone continued to be destroyed and formed an almost horizontal crush zone. The fatigue failure mechanism of open-cell foam copper was the peeling, necking, fracture of pore edges, and cracking of pore junction.
  • Effects of CeO2 Content, Boronizing Temperature and Time on Microstructureand Properties of H13 Steel Boronized Layer
    ZHANG Yanwei, ZHENG Quan, FAN Yu, MEI Shunqi, LYGDENOV Burial, GURYEV Alexey
    Materials For Mechanical Engineering. 2021, 45(7): 22-26. https://doi.org/10.11973/jxgccl202107005
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    The surface of H13 steel was boronized, and the effect of the content of rare earth CeO2 (0, 2wt%, 4wt%, 6wt%), boronizing temperature (850, 900, 950, 1 000 ℃) and boronizing time (2, 3, 4, 5 h) on the microstructure and properties of the boronized layer were studied. The results show that the thickness of the boronized layer increased first and then tended to be stable with increasing boronizing temperature and time. When the content of CeO2 increased from 0 to 2wt%, the diffusion activation energy of boron atoms did not change much, and decreased obviously from 2wt% to 4wt%, and the thickness of the boronized layer increased faster. The content of CeO2 increased from 4wt% to 6wt%, the diffusion activation energy basically unchanged, the thickness of the boronized layer increased slower. The boronized layer with 4wt% CeO2 formed at 950 ℃ for 4 h had the least holes, the most dense microstructure, the highest hardness, and the best wear resistance.
  • Effect of CeO2 Adding Content on Microstructure and Properties of Laser Cladding WC Reinforced Nickel-Based Alloy Coating
    XU Huanhuan, LIN Chen, LIU Jia, ZHANG Liang, SHEN Jingyi
    Materials For Mechanical Engineering. 2021, 45(7): 27-34. https://doi.org/10.11973/jxgccl202107006
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    The mixed powders with nickel-coated tungsten carbide powder and CeO2 powder was used as raw materials, WC reinforced nickel-based alloy coating was prepared on the surface of 42CrMo steel by laser cladding technique. The effect of mass fraction (0-2.0%) of CeO2 in raw materials on the phase composition, microstructure, hardness and wear resistance of the coating was investigated. The results show that the phase of the coating with CeO2 was composed of γ-(Ni, Fe) solid solution, Ni3Fe, WC, Cr23C6, M7C3 (M=Fe, Cr) and a small amount of CeNi3. A good metallurgical bond was formed between the coating and the substrate. When the mass fraction of CeO2 was 1.0%, the structure was dense and uniform, and the refinement effect was the most obvious. With increasing CeO2 content, the hardness of the coating increased first and then decreased, and the friction coefficient and the amount of wear decreased first and then increased. The average hardness of the coating with 1.0% CeO2 was the highest, which was 956.0 HV, and increased by 29% compared with that without CeO2; the average friction coefficient and the average wear volume were the smallest, which were 0.383 and 11.25×10-3 mm3, and were reduced by 27% and 20% compared with those without CeO2, respectively. The wear resistance of the coating with 1.0% CeO2 was the best, and the wear mechanism of the coating was slight abrasive wear.
  • Long-Period Corrosion Behavior of 304L Stainless Steel inNitric Acid Industrial Environment
    LIU Xiwu, LI Hui, ZOU Yang, ZHAO Xiaoyan, CUI Xinan
    Materials For Mechanical Engineering. 2021, 45(7): 35-40. https://doi.org/10.11973/jxgccl202107007
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    The long-period corrosion behavior of 304L stainless steel was investigated by three long-period field hanging coupon immersion corrosion tests in the environment of a syngas ethylene glycol plant with temperatures of 116-128 ℃ and nitric acid mass fractions of 2%-20%. The results show that different degrees of intergranular corrosion and corrosion thinning occurred in 304L stainless steel after three long-period hanging coupon immersion corrosion under different conditions. The corrosion degree of stainless steel was the most serious under the condition of nitric acid mass fraction of 2%-8%, temperature of 116 ℃ and time of 156 d, and grain peeling occurred; the general corrosion rate was greater than 2 mm·a-1, and the corrosion degree was serious corrosion. Pd in the catalyst of nitric acid reduction reactor was the main medium that rapidly accelerated the corrosion of 304L stainless steel. Pd and 304L stainless steel formed galvanic effect, thereby accelerating the corrosion of 304L stainless steel. 304L stainless steel was not recommended as the selection material for the de-heavy tower bottom area under the process condition.
  • Effect of Postweld Heat Treatment on Microstructure and MechanicalProperties of Cu-Cr-Zr Alloy Friction Stir Welding Joint
    QIU Yiqing, FAN Zhunan, LIU Lijun, YAN Xiang, LIU Jufeng
    Materials For Mechanical Engineering. 2021, 45(7): 41-45,50. https://doi.org/10.11973/jxgccl202107008
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    Friction stir butt welding of 5 mm thick Cu-Cr-Zr alloy plate was carried out, and the joint was heat treated at different aging temperatures (400, 450, 500 ℃). The effects of heat treatment on the microstructure and mechanical properties of the joint were analyzed. The results show that after postweld heat treatment, the grain size in the nugget zone did not change significantly, and the bended grains in the thermo-mechanically affected zone basically disappeared. After postweld heat treatment, the strengthened precipitates soluted in the matrix during the welding process re-precipitated; the over-aging of the joint after postweld heat treatment at 500 ℃ occurred. After postweld heat treatment, the hardness and tensile strength of the joint obviously increased. The hardness was distributed in a “W” shape and the lowest hardness appeared in the thermo-mechanically affected zone. The hardness and tensile strength hardness of joint after postweld heat treatment at 450 ℃ were both largest; the hardness of the nugget zone was 83% of the base metal, and the tensile strength of the joint was 270 MPa which increased by 50 MPa compared with that before postweld heat treatment.
  • Effect of Displacement Amplitude on Fretting Wear Behavior of ZG230-450 Cast Steel
    LIU Yu, QIAO Jianchun, LI Mingsheng, QI Wei
    Materials For Mechanical Engineering. 2021, 45(7): 46-50. https://doi.org/10.11973/jxgccl202107009
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    Fretting wear test was carried out on ZG230-450 cast steel with different displacement amplitudes (60-140 μm). The effects of displacement amplitude on friction coefficient, wear volume and wear mechanism were studied. The results show that with increasing displacement amplitude, the fretting wear behavior of the cast steel changed from mixed slip to complete slip, and the dissipated energy increased gradually. Under the mixed slip state, the friction coefficient rapidly entered the stable stage after the rising stage, and under the complete slip state, the friction coefficient went through the rising stage, the fluctuation stage and the stable stage. The larger the displacement amplitude, the more the reciprocating motions needed to enter the stable stage. With increasing displacement amplitude, the wear scar area and wear volume both increased, and the wear mechanism changed from the adhesive wear and the delamination wear to the abrasive wear and the delamination wear.
  • Structure of Zeolitic Imidazolate Frameworks Derived Carbon-based Compositeand Properties of Its Supercapacitor
    YE Yanqiu
    Materials For Mechanical Engineering. 2021, 45(7): 51-56,74. https://doi.org/10.11973/jxgccl202107010
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    Zeolite imidazolate framework particles were embedded into polypyrrole tubes (mass of 30,60,120 mg) by in-situ growth method, and then carbon-based composites were prepared by carbonization and activation with one-step heat treatment. The microstructure and electrochemical properties of the materials and the electrochemical performance of the assembled double-layer supercapacitor were studied. The results show that the composites were composed of carbon nanotubes and nitrogen-doped carbon particles on the outer surface of the tubes; the composites had large specific surface area and high nitrogen content, and the micropore diameter was concentrated at about 1 nm. The composites had good charge-discharge reversibility and rate performance, and exhibited typical double-layer capacitance behavior. The electrochemical performance of the composites with 60 mg polypyrrole tubes was the best under the same condition, and the composite had the largest specific capacitance of 283 F·g-1 at current density of 1 A·g-1. The symmetrical supercapacitor assembled by the composite had excellent cycle stability with specific capacitance retention rate of 91.5% after 3 000 cycles at charge-discharge current density of 2 A·g-1 and with energy density of 9.15 Wh·kg-1.
  • Collision Failure Simulation of Spotweld of DP590 High-Strength Steel Considering Welding Heat-Affected Zone
    ZHENG Hao, OUYANG Jun, WANG Yuchao, LI Wei, LIU Heng, ZENG Zicong, LIU Yanmei
    Materials For Mechanical Engineering. 2021, 45(7): 57-62,68. https://doi.org/10.11973/jxgccl202107011
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    By spotweld tearing tests (lap-shear tension, coach-peel tension and KS-Ⅱ tension), the collision failure mechanical response of DP590 high-strength steel spotweld under different stress conditions was studied. The spotweld modeling method was proposed by considering bending moment transmission and welding heat-affected zone. With the CrachFEM material model of DP590 steel and by the benchmarking of the spotweld tearing test results and simulation, the correction coefficients of the CrachFEM material model for the heat-affected zone were obtained. The simulation was verified by three-point bending crush tests of the subsystem. The results show that all the spotweld samples were torn in the heat-affected zone. The force-displacement curve obtained by the subsystem test was in good agreement with the simulation, and the relative error of the failure load obtained by the simulation and the test was below 1%, indicating that the proposed spotweld failure simulation method could accurately predict the collision failure behavior of DP590 high-strength steel spotweld.
  • Optimization of Injection Process Parameters for Composite Parts by BP Neural Network and Genetic Algorithm
    WANG Bo, ZHAO Dongping, LI Feng, ZHAO Shimin, WANG Yizhuo
    Materials For Mechanical Engineering. 2021, 45(7): 63-68. https://doi.org/10.11973/jxgccl202107012
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    Taking warpage deformation of the aircraft nose radome under different process parameters obtained by Moldflow software as training samples, a back propagation (BP) neural network model was established between the process parameters of the radome model and its warpage deformation values. Then genetic algorithm was used to optimize the process parameters, and the process parameters of the radome model with the smallest warpage deformation value was obtained. The results show that with the same process parameters, the warpage deformation value of the radome model obtained by BP neural network was similar to that simulated by Moldflow software, and the relative error was less than 4%, which proved the reliability of BP neural network. The simulated optimal molding process parameters of the radome model were injection temperature of 295 ℃, mold temperature of 80 ℃, injection time of 0.75 s, pressure holding time of 8 s, and pressure holding pressure of 125 MPa; the warpage deformation value was the smallest of 0.121 3 mm. The maximum warpage deformation of the radome model was 0.126 0 mm after injection molding with the optimal molding process parameters, and the ralative error between the experimental result and the predicted result was less than 3.7%, which verified the accuracy of the method of combining BP neural network and genetic algorithm.
  • Hot Deformation Behavior and Processing Map of WE43 Magnesium Alloy
    HE Weiwei, CHEN Junzhou, HAO Min, DAI Shenglong
    Materials For Mechanical Engineering. 2021, 45(7): 69-74. https://doi.org/10.11973/jxgccl202107013
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    The hot compression test of WE43 magnesium alloy at deformation temperature of 300-500 ℃ and strain rate of 0.000 5-0.5 s-1 was carried out on Gleeble 3800 numerical control thermo-mechanical physical simulator, and the hot deformation behavior of the alloy was investigated. The processing map at strain of 0.6 was established, and the optimum hot working parameter range for WE43 magnesium alloy was determined by combination with microstructure evolution. The results show that the true stress of WE43 magnesium alloy increased with decreasing deformation temperature or increasing strain rate, and the true strain corresponding to the peak stress decreased with decreaseing strain rate or increasing deformation temperature. The optimum thermoplastic working ranges for WE43 magnesium alloy were deformation temperature of 410-500 ℃ and strain rate of 0.05-0.005 s-1; at the same time, the hot deformation softening mechanism of the alloy was mainly dynamic recrystallization, and the grain size was relatively uniform with average grain size of less than 100 μm.
  • Causes of Abnormal Wear of Titanium Alloy Flexible Shaft
    ZHANG Honglin, WANG Yupeng, MI Kaifu, GUO Tianming, ZHANG Yingjin
    Materials For Mechanical Engineering. 2021, 45(7): 75-81,87. https://doi.org/10.11973/jxgccl202107014
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    A titanium alloy flexible shaft for drilling had a bright band at the reducer near the plug end after a period of drilling and start-up. The cause of the bright band was analyzed by force analysis, macroscopic and microscopic morphology observation, chemical composition analysis, mechanical property test, and finite element simulation. The method of prolonging the life of titanium alloy flexible shafts was put forward. The results show that fretting wear occurred at the reducer of the flexible shaft, and the fretting wear was mainly caused by the shear stress and the relative displacement between body part of flexible shaft and plug parts. The fretting wear resulted in the initiation of cracks at the reducer of the flexible shaft. Under the alternating load and torque, the cracks propagated, resulting in the fretting fatigue. The cracks originated uniformly from the periphery and propagated with transgranular forrn. The surface hardness and wear resistance of the titanium alloy increased after the coating layer was prepared by supersonic flame spraying technique, which could restrain the peripheral origin cracks caused by fretting wear, thus prolonging the life of the flexible shaft.
  • Fracture Cause of Correction Roller in Hot-dip Galvanizing Line
    ZHANG Ying, WANG Qiongqi, HUANG Jibo, LI Yuanjun, LI Chaoxiong, TAN Xinghai, WANG Weize, TU Shantong
    Materials For Mechanical Engineering. 2021, 45(7): 82-87. https://doi.org/10.11973/jxgccl202107015
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    A correction roller in a hot-dip galvanizing line fractured at the transition fillet of its shaft head during operation. The fracture cause of the correction roller was analyzed by chemical composition analysis, tensile property testing, microstructure observation, micro-area composition analysis, non destructive testing and stress analysis. The results show that the failure mode of the correction roller was multi-source fatigue failure caused by complex loads including bending load and torsion. The pits on the outer surface of the transition fillet of the correction roller shaft head and the stress concentration here promoted the initiation of multiple fatigue cracks on the surface. The fatigue cracks propagated under high loads, and finally the fracture of the correction roller occurred. In order to avoid the reoccurrence of such failure, it was recommended to use the larger radius of the transition fillet to reduce the stress concentration degree at the transition fillet, improve the surface quality and strengthen nondestructive testing before putting into operation.
  • Cracking Reason for Mixing Hydrocarbon Spherical Tank
    LI Zhihui, LI Zhifeng
    Materials For Mechanical Engineering. 2021, 45(7): 88-93,103. https://doi.org/10.11973/jxgccl202107016
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    During the inspection of a hydrocarbon mixing spherical tank, a large number of surface cracks were found at the lower plate girth weld position. The residual stress at the crack concentration position was tested by X-ray stress tester, and the cause of cracking of the spherical tank was analyzed by chemical composition analysis, mechanical property test and fracture micromorphology observation. The results show that the sulfide stress corrosion cracking occurred at the fusion line and heat affected zone in the lower plate girth weld of the spherical tank. Under the action of corrosive medium and large residual tension stress, the cracks initiated in the heat affected zone of the lower plate girth weld with the largest residual tension stress, and then propagated to the fusion line in the transgranular and intergranular forms. Reasonably selecting materials before welding, selecting suitable welding and heat treatment technology and improving the quality of stress relief heat treatment after spherical tank installation should be taken to reduce the residual stress; isolating corrosive media and removing hydrogen sulfide or water from the media were used to reduce the sensitivity of cracking.
  • Cracking Cause of GH738 Superalloy Turbine Casing
    LI Yanming, MENG Lingqi, TONG Wenwei, LIU Huan
    Materials For Mechanical Engineering. 2021, 45(7): 94-99,110. https://doi.org/10.11973/jxgccl202107017
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    The cause of cracking of GH738 super alloy turbine casing in an aeroengine was analyzed by morphology observation, component analysis, microstructure observation, performance testing and thermal simulation experiments, and the crack type and generating mechanism were discussed. The results show that the crack type in the failed casing was fatigue crack, and the crack source was located on the outer surface of the casing fixture fringe. The local temperature of the casing fixture fringe was 850-900 ℃, and exceeded the allowable service temperature (810 ℃) of GH738 alloy, which led to decrease of volume fraction of γ' phase in microstructure, and the mechanical properties and fatigue resistance of the alloy decreased, thereby promoted the premature fatigue cracking of the casing.
  • Cracking Cause of Exhaust Valve Turbulence Hood at Turbine Side of a Nuclear Power Plant
    LEI Xin, FANG Li, JIAO Shaoyang, CHEN Jun, CHEN Chao, TAI Jiang
    Materials For Mechanical Engineering. 2021, 45(7): 100-103. https://doi.org/10.11973/jxgccl202107018
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    The cracking reason of the exhaust valve turbulent hood at turbine side of a nuclear power plant was analyzed by fracture morphology observation, chemical composition test, microstructure analysis and mechanical performance test. The results show that the cracking mode of the turbulent hood was fatigue brittle cracking. The chemical composition of material did not meet the standard, which reduced its strength. The positioning holes on the upper end of the turbulence hood were not centered during installation. The wear and vibration produced by the airflow during working process made a relatively large stress concentration in this location, leading to crack initiation in outer flange surface of the turbulence hood. Under long-term cyclic thermal stresses, the cracks propagated along the section with the smallest bearing capacity, leading to cracking of the turbulent hood. It was suggested to take material re-inspection measures , thereby reducing the inflow of unqualified materials and to take strict requirements for installation process to avoid misalignment, thereby reducing stress concentation caused by wear and vibration.
  • Fracture Cause of Electric Gate Valve Stem in a 1 000 MW Ultra-Supercritical Unit
    PENG Bo, WANG Jianguo, PEI Guanghui, XIN Linxiang, WANG Zhichun
    Materials For Mechanical Engineering. 2021, 45(7): 104-110. https://doi.org/10.11973/jxgccl202107019
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    A electric gate valve stem at the outlet of feedwater pump in a 1 000 MW ultra-supercritical unit fractured during valve opening. The fracture cause of the stem was analyzed by macromorpholgy observation, chemical composition analysis, mechanical performance test and microstructure observation. The results show that the microstructure of the stem was nonuniform, and there was local porosity in the center area. A lot of striped or massive ferrite existed in the microstructure resulting in insufficient plasticity and uneven comprehensive mechanical properties of the stem. The serious jam occurred between the valve disc and the slide rail on the outlet side during valve opening. The machining quality of the annular platform surface of the stem was poor, and the transition arc angle of the variable section root of the annular platform at the bottom of the stem was small. The cracks initiated at the stress concentration area of the variable cross-section root of the annular platform when opening the valve, and then expanded quickly, resulting in the brittle fracture of the stem finally.
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