20 December 2022, Volume 46 Issue 12
    

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  • Research Progress on Thermal Shock Resistance of Ceramic Materials
    ZHAO Tingting, FAN Likun, LI Yang
    Materials For Mechanical Engineering. 2022, 46(12): 1-8. https://doi.org/10.11973/jxgccl202212001
    Abstract ( ) Download PDF ( )   Knowledge map   Save
    When the thermal stress caused by sudden temperature change of ceramic materials exceeds its strength, materials will happen to crack, peel and even fracture, and then failure. Therefore, the study of thermal shock resistance of ceramic materials becomes a hot spot. The evaluation theory of thermal shock resistance of ceramic materials and the methods for testing and characterizing are described. The methods of improving thermal shock resistance, including strengthening and toughening, improving thermal conductivity, reducing thermal expansion coefficient, and reducing elastic modulus, are reviewed. The external influencing factors of thermal shock resistance are summarized. The development direction of improving thermal shock resistance of ceramic materials in future is proposed.
  • Research Status of Tungsten/Steel Composite Structure Bonding forNuclear Fusion Reactor
    YANG Zonghui, SHEN Yifu, ZHANG Xu, LI Xiaoquan
    Materials For Mechanical Engineering. 2022, 46(12): 9-17. https://doi.org/10.11973/jxgccl202212002
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    In nuclear fusion reactors, joining the plasma material tungsten and structural material low activation steel is a key issue to manufacture tungsten/steel composite structures that can meet extremely harsh working requirements. The difficulties of joining tungsten and steel are introduced, and the research status of bonding technologies of tungsten/steel composite structure, thermal stress and stress reduction method of the joint, and mechanical properties of the joint are described in detail. It is pointed out that improving bonding technology and processes on the basis of systematic test and analysis of thermal conductivity, thermal fatigue resistance and working reliability in high temperature and strong radiation environment, standardizing test methods, and determining the priority and requirements of the key performance of tungsten/steel composite structures are the development direction of the research on tungsten/steel composite structure bonding technologies for nuclear fusion reactors.
    • Testing & Research
  • Electrocatalytic Properties of N-S-Fe Co-doped HierarchicalPorous Carbon Material Co-Synthesized by Dual-template
    DONG Yaqian, ZHANG Yaohui, TANG Bin
    Materials For Mechanical Engineering. 2022, 46(12): 18-23,42. https://doi.org/10.11973/jxgccl202212003
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    N-S-Fe co-doped hierarchical porous carbon material was prepared by MgO/ZnCl2 double template synergy and one-step pyrolysis, and the electrocatalytic performance of oxygen reduction reaction of the material was studied. The results show that the N-S-Fe co-doped hierarchical porous carbon material with carbon nanosheet structure was successfully synthesized, and had large specific surface area of 1140.31 m2·g-1. The ZnCl2 template could be conducive to the formation of micropores and dense active sites. The MgO template promoted the formation of mesopore, which could be beneficial to the mass transfer during electrocatalytic process of oxygen reduction reaction. The material exhibited excellent oxygen reduction electrocatalytic activity, good electrocatalytic stability and persistence, and high electron transfer rates in alkaline electrolytes. The onset potential, half-wave potential and charge transfer resistance were 1.05 V, 0.81 V and 11 Ω·cm2, respectively. After 13h of polarization, 83% of the original current density was retained. The zinc-air battery assembled with the material had open circuit potential of 1.42 V and maximum power density of 182.1 mW·cm-2.
  • Effect of Mo2S Addition Amount on Microstructure and Properties of MoS2/Ni60A Solid Self-lubricating Coating
    ZHANG Yupeng, WANG Yongdong, CHANG Mengyang, WANG Jinyu
    Materials For Mechanical Engineering. 2022, 46(12): 24-29,35. https://doi.org/10.11973/jxgccl202212004
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    MoS2/Ni60A solid self-lubricating coating was prepared on 35CrMnSi steel substrate by laser cladding with Ni60A alloy powder and MoS2 powder as cladding materials. The effects of MoS2 addition amount (mass fraction of 1%, 3%, 5%, 7%, 9%) on the phase composition, microstructure, microhardness and tribological properties of the coating were investigated. The results show that the coatings with different MoS2 addition had good surface formability and were metallurgical by bonded with the substrate. The main phase of the coatings were MoS2, γ-Ni, NiS, Cr2B. The microstructure of middle and upper position was mainly composed of rod-shaped, fishbone-shaped and radial dendrite. The microstructure of the bottom and fusion line was composed of planar and columnar crystals. With the increase of MoS2 addition, the microhardness of the coating decreased and the wear rate increased, and the friction coefficient decreased first and then increased. When the addition of MoS2 was 3%, the friction coefficient of the coating reached the lowest of 0.43, and a complete solid self-lubricating film was formed on the worn surface; The plough furrow was less and the main wear mechanism was slight abrasive wear.
  • Effect of Gd Addition Amount on Microstructure and Mechanical Properties of Mg-Gd Alloy Fabricated by Wire Arc Addictive Manufacturing
    ZHANG Xinqi, YANG Dongye, TIAN Wenqi, SI Ke, LI Jiuxiao, ZOU Wenbin
    Materials For Mechanical Engineering. 2022, 46(12): 30-35. https://doi.org/10.11973/jxgccl202212005
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    Mg-Gd alloys with Gd mass fraction of 2%,3%,10% were prepared by tungsten inert gas (TIG) arc additive manufacturing technique. The effect of Gd content on the microstructure and mechanical properties of Mg-Gd alloys was studied. The results show that the microstructure of Mg-Gd alloys with different Gd content were all mainly composed of magnesium matrix and the second phase Mg5Gd. With the increase of Gd content, the number and size of the second phase Mg5Gd distributed along the grain boundary increased, the shape changed from round particles to long strips; the Mg grains changed from columnar grains to equiaxed grains. The number and size of pores in the alloy decreased, and the grain size decreased first and then increased, reaching the minimum with 3% Gd. With the increase of gadolinium content, the strength of the alloy increased and the elongation after fracture decreased. The fracture methods were all ductile fracture.
  • Effect of Annealing Temperature on Microstructure and Corrosion Resistance of NiCoCrMn High-Entropy Alloy Laser Cladding Coating
    CHEN Wentao, MA Libing
    Materials For Mechanical Engineering. 2022, 46(12): 36-42. https://doi.org/10.11973/jxgccl202212006
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    NiCoCrMn high-entropy alloy coating was prepared on the surface of 45 steel by laser cladding technique, and then annealed at different temperatures (700, 800, 900, 1000 ℃). The effect of annealing temperature on the microstructure and corrosion resistance of the laser cladding coating was studied. The results show that the as-deposited and annealed NiCoCrMn high-entropy alloy coatings had a single phase face centered cubic solid solution structure. The as-deposited, 700 ℃ annealed, and 800 ℃ annealed NiCoCrMn high-entropy alloy laser cladding coatings consisted of columnar grains, and inside grains a high population of cell substructures along with solidification segregation phenomenon existed. When the annealing temperature exceeded 900 ℃, solidification segregation phenomenon started to disappear. When the annealing temperature reached 1000 ℃, solidification segregation disappeared, and structive recovery and recrystallization occurred, resulting in formation of equiaxed microstructures. The annealing treatment improved the corrosion resistance of the cladding coating, and the corrosion resistance of cladding coating increased with increasing annealing temperature.
  • Effect of Nb Content on Dendrite Segregation and Carbide Composition and Morphology of H13 Steel
    OUYANG Weihao, ZHOU Jian, GAO Peng, CHI Hongxiao, XIE Guanli, WANG Wenjun
    Materials For Mechanical Engineering. 2022, 46(12): 43-49. https://doi.org/10.11973/jxgccl202212007
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    H13 steel with different mass fractions (0,0.17%,0.38%) of Nb was prepared with vacuum induction furnace. The effect of Nb content on dendrite segregation, and eutectic carbide composition and morphology of H13 steel was studied. The results show that adding Nb could significantly refined the structure of H13 steel and reduce the segregation of the forming elements of interdendritic carbides. With the increase of Nb content, the number and size of eutectic carbides increased significantly, and their morphology changed from blocky or long strip to lamellar or fishbone. The carbides were M7C3, M23C6, M6C and MC. With the increase of Nb content, the number of M7C3 and M23C6 type carbides decreased while the number of M6C and MC type carbides increased; MC type carbides changed from VC to NbC and VC, and the precipitation temperature of MC type carbides increased significantly.
  • Effects of Sc, Zr Modification and Pulse Magnetic Field on Solidified Structure and Hardness of Al-3Fe Alloy
    LI Zhiwei, ZHOU Quan, DONG Jianjun, CHEN Leping, WEI Chenyang
    Materials For Mechanical Engineering. 2022, 46(12): 50-54,59. https://doi.org/10.11973/jxgccl202212008
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    Al-3Fe alloy was prepared with high-purity aluminum and Al-10Fe master alloy as raw materials. In the melting process, 0.3 wt% Sc and 0.1 wt% Zr were added to modify the melt. During the solidification process, pulsed magnetic field with different voltages (100, 200, 300 V) and frequencies (2.5, 5, 10 Hz) were applied. Effects of modification and pulsed magnetic field on the solidified structure and hardness of Al-3Fe alloy were studied. The results show that Sc and Zr modification, applying pulsed magnetic field(100 V, 5 Hz) and their combination could refine solidified structure of the alloy effectively, and the composite treatment had the best refinement effect; Al3Fe phase changed from coarse long needle under untreatment conditions to fine short rod or short needle. Under composite treatment, the length of Al3Fe phase increased first and then decreased with the increase of pulse voltage, and decreased with the increase of pulse frequency. After modification and pulsed magnetic field composite treatment, Brinell hardness of the alloy increased the most.
  • Corrosion Mechanism of J55 Steel Casing in Block ContainingHydrogen Sulfide in Changqing Oilfield
    ZHU Guangshe, ZHANG Xiaobo, YANG Xuefeng, LIU Yang, ZHANG Liyuan, ZHAO Chunyu, YOU Jiaqing, JIANG Feng, LIU Man, LIU Sijia
    Materials For Mechanical Engineering. 2022, 46(12): 55-59. https://doi.org/10.11973/jxgccl202212009
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    The corrosion product composition and morphology on the surface of J55 steel casing in H2S containing block in Changqing Oilfield and in different corrosive enviroments (pure CO2, pure H2S, different partial pressure CO2+H2S enviroments) were analyzed by energy spectrum analyzer, scanning electron microscope and X-ray diffractometer. The corrosion rate was calculated, and the corrosion mechanism of J55 steel casing in H2S containing block was studied. The results show that the coarse-grained FeCO3 corrosion product film with low compactness was formed in a single CO2 environment for J55 steel, whose corrosion rate was high. The addition of H2S made J55 steel form a fine-grained and dense FeS corrosion product film in CO2+H2S environments, which could protect the base metal and significantly reduce the corrosion rate of J55 steel. The corrosion mechanism of J55 steel in sulfur-containing block of Changqing Oilfield was CO2+H2S corrosion dominated by H2S corrosion.
  • Effect of Final Rolling Temperature on Microstructure and Corrosion Resistance of Sn-Containing Ferritic Stainless Steel
    HUA Guoxiang, LIU Xiuting, GAO Feng
    Materials For Mechanical Engineering. 2022, 46(12): 60-66. https://doi.org/10.11973/jxgccl202212010
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    The hot rolling (starting rolling temperature of 1 150 ℃, and final rolling temperatures of 730,800,870,940 ℃) and annealing (950 ℃×5 min), and cold rolling and annealing (900 ℃×2 min)treatments were carried out on the smelting Sn-containing ferritic stainless steel. The effects of final rolling temperature on the microstructure of the cold rolled annealed sheet, the corrosion resistance to H2SO4 and FeCl3 and electrochemical properties were studied. The results show that the microstructures of the cold rolled and annealed sheet at different final rolling temperatures were composed of γ fibre recrystallized grains. With the decrease of the final rolling temperature, the grain size of cold rolled and annealed Sn-containing ferritic stainless steel sheets decreased. When the final rolling temperature was 800 ℃, the grain size was 10-20 μm, and the size distribution was the most uniformly. With the decrease of final rolling temperature the resistance to H2SO4, FeCl3 corrosion and electrochemical corrosion rate decreased first and then increased, and when the finish rolling temperatures was 800 ℃, both achieving the minimum values.
    • Material Properties & Application
  • Effect of Ni Content in Flux-Cored Wire on Microstructure andProperties of 25Cr2Ni4MoV High Strength Steel Welded Joint
    ZHANG Min, ZHANG Lin, WANG Boyu, JIA Fang, XIA Tuo
    Materials For Mechanical Engineering. 2022, 46(12): 67-71. https://doi.org/10.11973/jxgccl202212011
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    Based on the chemical composition of 25Cr2Ni4MoV steel, three metal flux-cored wires with different nickel mass fractions (15%,19%,23%) were designed, and then the 25Cr2Ni4MoV steel plate was welded by metal active gas shielded arc welding. The effect of Ni content in the flux-cored wire on the microstructure and mechanical properties of the joint was studied. The results show that the weld microstructures of the joints were all composed of lath martensite, bainite and a small amount of acicular ferrite. With the increase of Ni content in the flux-cored wire, the lath martensite structure in the weld was refined first and then coarsened; the elongation and impact absorption energy of the joint increased, and the strength increased first and then decreased. When the mass fraction of Ni in the flux-cored wire was 19%, the tensile strength of the joint reached the highest value of 920 MPa, and the impact absorption energy was 48 J; the joint had good matching of strength and toughness.
  • Preparation and Thermophysical Properties of Dual-phase High-Entropy Ceramics (La0.2Eu0.2Gd0.2Y0.2Yb0.2)2Zr2O7
    YANG Hongbo, LIN Guangqiang, LI Hongyi, WANG Wenjun, LIU Huijun, WANG Yuansheng, ZENG Chaoliu
    Materials For Mechanical Engineering. 2022, 46(12): 72-78,84. https://doi.org/10.11973/jxgccl202212012
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    High-Entropy ceramics (La0.2Eu0.2Gd0.2Y0.2Yb0.2)2Zr2O7 were prepared by high-temperature solid state reaction method with La2O3, Eu2O3, Gd2O3,Y2O3, Yb2O3 and ZrO2 powder as raw materials. The preparation process was determined and the microstructure, phase composition, thermophysical properties of the high-entropy ceramics were studied. The high temperature thermal stability was analyzed. The results show that the dual-phase high-entropy ceramics with complete solid solution were obtained by sintering at 1 500 ℃ for 5h followed under furnace cooling. The high-entropy ceramics presented the dual-phase coexistence characteristics of pyrochlore/fluorite with grain size of 200—800 nm; the element distribution was uniform. The thermal conductivity at 800 ℃ of the high-entropy ceramics was 50% of currently used 8YSZ ceramics, and the thermal expansion coefficient was equivalent to that of 8YSZ ceramics. the high-entropy ceramics also showed excellent high temperature thermal stability.
    • Physical Simulation & Numerical Simulation
  • Fatigue Life Prediction of Pre-corroded Aluminum Alloy Based on Fractal Dimension Method
    WANG Yonggang, GUO Yibing, DONG Yijun, ZHOU Song, ZHI Shanjie, ZHANG Jingkuo, LU Yaping, LI Dongya, WANG Shuang
    Materials For Mechanical Engineering. 2022, 46(12): 79-84. https://doi.org/10.11973/jxgccl202212013
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    The surface corrosion morphology of 2xxx aluminum alloy specimens pre-corroded with 3.5% mass fraction NaCl solution for different times was analyzed by digital image processing technique. The three-dimensional corroded morphology was described by Differential Box-Counting method. The relationships between fractal dimension, corrosion time and fatigue life were analyzed, and the fatigue life prediction model based on fractal dimension was established and verified by experiments. The results show that the relationship between the fractal dimension and corrosion time was a power function, while the fractal dimension was linear with the fatigue life. The prediction results of the established life prediction model for low cycle fatigue lives were relatively conservative, and the relative error with the test result was within 25%. The prediction results for high cycle fatigue lives were relatively accurate, and the relative error of the test result was reduced to less than 15%. The fatigue limit calculated by life prediction model was close to the test value, and the relative error of less than 5%.
    • Failure Analysis
  • Corrosion Cause of 3Cr Steel Tubing in a Gas Injection Well
    JI Nan, LI Changliang, SONG Wenwen, ZHAO Mifeng, LONG Yan, XIE Junfeng
    Materials For Mechanical Engineering. 2022, 46(12): 85-90,97. https://doi.org/10.11973/jxgccl202212014
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    Corrosion was observed on the 3Cr steel tubing of a gas injected well in western oilfield. The corrosion causes of the tubing were analyzed by macroscopic inspection, mechanical property measurement, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. The results show that under the nitrogen injection drive condition, dissolved oxygen corrosion mainly occurred in the inner and outer walls of tubing, and dissolved oxygen corrosion and crevice corrosion mainly occurred in the pin end face of the tubing. The corrosion of tubing was caused by the mismatch between the tubing material properties and the corrosion environment in actual service, which was ascribed to the formation of oxygen corrosion environment in the inner and outer walls and end face of tubing due to the oxygen contained in the injected nitrogen.
  • Cause of Pin Fracture for Low Pressure Rotor Blade Fork-Type Blade Root
    DENG Hui, WU Wensheng, WU Xuliang, YUAN Hongyu, XIE Zhaozeng
    Materials For Mechanical Engineering. 2022, 46(12): 91-97. https://doi.org/10.11973/jxgccl202212015
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    In a 660 MW ultra-supercritical machine of a coastal power plant, cracking occurred at the end of the secondary blade fork-type blade root pins of the A and B low-pressure rotors, and the cracking causes of the pins were studied by macro/micromorphology observation, chemical composition analysis, microstructure observation and mechanical property tests. The results show that stress corrosion cracking occurred in the pin. The microstructure of cracking pin steel was uneven, and macroscopic coarse grains existed. The stress corrosion sensitivity of the material was higher. Corrosive media existed in the pin hole, which caused corrosion pits forming on the surface of the pin. The corrosion products contained chlorine, sulfur and other elements. In the process of high-speed rotation of the steam turbine, the pin bore the bending stress caused by the centrifugal force of the blades, and microcracks germinated at the corrosion pit. Stress corrosion cracking occurred.
  • Cracking Cause of Incoloy 800HT Alloy High-Temperature Steam Pipeline Butt Weld in Styrene Plant
    CHEN Gang, LI Zhifeng, LU Baoxi, YANG Lijun
    Materials For Mechanical Engineering. 2022, 46(12): 98-102. https://doi.org/10.11973/jxgccl202212016
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    Cracks were found in the regular inspection of Incoloy 800HT alloy high temperature steam pipeline used for 13 a, and the causes of cracks were analyzed by tensile test, bending test, metallographic examination and micromorphology observation. The results show that the tensile and bending specimens both fractured on the weld fusion line. A large number of precipitated phases existed on the fusion line, and the precipitated phases were mainly carbides formed by alloying elements chromium and molybdenum. The phase led to the decrease of high temperature mechanical properties of the alloy and the generation of stress concentration. Creep holes were generated near the precipitated phase and evolved into creep cracks after long-term high temperature use.
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