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  • Physical Simulation & Numerical Simulation
    XUE He, LU Jingzhi, JIA Yulei, WANG Shuang, WANG Zheng
    Materials For Mechanical Engineering. 2022, 46(11): 92-96. https://doi.org/10.11973/jxgccl202211015
    A three-dimensional finite element model for continuous ball indentation tests was established, and the relationship between residual indentation strains and different material tensile property parameters (elastic modulus of 90-210 GPa, yield strength of 180-300 MPa, strain hardening exponent of 0.1-0.3) was simulated by a single variable method. Finite element simulation of continuous ball indentation tests was performed under 125 sets of material tensile property parameter combinations, and formulas for calculating material tensile property parameters based on residual indentation strains were obtained and verified experimentally. The results show that there was a log-linear relationship between the residual indentation strain and the modulus of elasticity and yield strength, respectively, and a power-law relationship between the residual indentation strain logarithm and the strain hardening exponent. The residual indentation strains of 316L stainless steel measured by the continuous ball indentation test were substituted into the material tensile property parameter calculation formula, and the relative errors between the elastic modulus, yield strength, and strain hardening exponent obtained by inversion and the tensile test results were 1.50%, 1.57%, and 0.22%, respectively, indicating that the stainless steel material tensile property parameter calculation method based on the residual indentation strain could meet the engineering needs.
  • Physical Simulation & Numerical Simulation
    ZHANG Feng, TANG Qiaoyun, CAI Qixing, ZHI Youran, MA Yinzhong
    Materials For Mechanical Engineering. 2022, 46(11): 78-85. https://doi.org/10.11973/jxgccl202211013
    The deformation mechanism and mechanical properties of nanocrystalline copper with a bimodal structure (grain size obeying bimodal distribution in statistics) were systematically investigated by combination of molecular dynamics simulation, visco-plastic constitutive model and nanoindentation test verification. The results show that during the plastic deformation, dislocations were first nucleated and expanded in the fine grain zone of the nanocrystalline copper, and the directions were parallel to each other; while the dislocation slip directions in the coarse grain zone crossed each other, and the larger the size of coarse grains, the more likely dislocation entanglement and cross-slip occurred. The flow stresses of the nanocrystalline copper with a bimodal structure increased with increasing coarse grain size, and the hardness decreased with increasing volume fraction of coarse grains. The stress variation law calculated by the visco-plastic constitutive equation was consistent with that by the empirical formula and molecular dynamics simulation, and the relative error between the flow stresses calculated by the constitutive equation and the empirical formula was less than 5%.
  • Review
    PAN Xincheng, LIN Zhengqi, YANG Liu, DENG Liping
    Materials For Mechanical Engineering. 2023, 47(1): 1-10. https://doi.org/10.11973/jxgccl202301001
    As a commonly used metal material, copper is limited in its application due to its low strength. Because of its excellent comprehensive properties, graphene has attracted wide attention as a potential reinforcement. Graphene reinforced copper matrix composites combine the great properties of both copper and graphene, and have become an research hotspot. The preparation processes and comprehensive properties of graphene reinforced copper matrix composites are introduced. The characteristics of various preparation processes, strengthening mechanism and configuration design are emphatically discussed, and the improvement approaches to solve the two main technical difficulties of weak bonding of composite interface and difficult dispersion of graphene are summarized. Finally, the preparation process of graphene reinforced copper matrix composites is prospected.
  • Review
    CONG Jiaqi, JI Yunping, WANG Lei, KANG Xueliang, LI Yiming, REN Huiping
    Materials For Mechanical Engineering. 2023, 47(2): 1-6. https://doi.org/10.11973/jxgccl202302001
    Selective laser melting (SLM) is one of the most widely used metal additive manufacturing techniques. Many defects are inevitably produced in the SLM formed parts, including pores, surface layer powder spheroidization, cracks and so on. The formation of defects not only affect the smoothness of the forming process, but also damage the internal integrity of the part and reduce its serviceability. The main characteristics of three defects including pores, surface layer powder spheroidization and cracks in SLM formed 316L stainless steel parts are reviewed. The formation mechanisms and influencing factors of these three defects are summarised, and the main measures to control the defects are proposed. Finally, future research directions are put forword.
  • Failure Analysis
    CHENG Quanshi, HUANG Qingmei, YE Lingying, XU Yongchun
    Materials For Mechanical Engineering. 2022, 46(10): 106-112. https://doi.org/10.11973/jxgccl202210018
    High lock nuts were made from 7075-T73 aluminum alloy that was obtained by T73 heat-treating 7075-T6 aluminum alloy. After serving in an atmospheric environment for about 3.5 a, many nuts cracked. The crack reason was analyzed by chemical composition analysis, microstructure and fracture morphology observation, residual stress testing and other methods. The results show that stress corrosion cracking occurred in the 7075 aluminum alloy high lock nut during service. After the high lock nut was installed, the circumferential residual tensile stress was generated at the closing part, and the surface oxide film was cracked, making the metal substrate in contact with corrosive media in atmosphere. The second phase precipitated locally and continuously along grain boundaries during the heat treatment from T6 to T73 states, providing channels for crack initiation and propagation. Under the combination of these factors, stress corrosion cracking occurred in the high lock nut.
  • Testing & Research
    DU Wei, HAN Bingyuan, CUI Fangfang, HANG Weixing, CONG Mengqi, XU Wenwen, CHU Jiajie, GAO Xianghan, WU Haidong
    Materials For Mechanical Engineering. 2022, 46(11): 26-32. https://doi.org/10.11973/jxgccl202211004
    A Ni60CuMo alloy coating was prepared by plasma spraying on the surface of ZL109 aluminum alloy for engine piston. The microstructure, phase composition, microhardness and wear resistance under different conditions of the coating were studied. The results show that the coating was composed of alternately overlapping Cr-rich zone and Ni-rich zone, and the bonding mode between coating and substrate was mechanical bonding. The porosity of the coating was 2.48%. The average microhardness was 792.91 HV and was about more than 6 times that of the substrate. The friction coefficient and wear mass loss decreased with increasing test temperature from 25 ℃ to 450 ℃. Under 450 ℃ oil lubrication condition, the average friction coefficient of the coating was 0.037, and the wear mass loss was 7.35 mg, which was only about 1/4 of the substrate. With increasing test temperature, the wear mechanism of the coating changed from peeling failure to oxidation wear and adhesive wear under dry friction condition, and from abrasive wear to abrasive wear and adhesive wear under oil lubrication condition, and finally to adhesive wear.
  • Failure Analysis
    ZHOU Song, FENG Yi, GAO Xiang, SUN Dai, SHEN Juan, WANG Binhua
    Materials For Mechanical Engineering. 2022, 46(11): 102-110. https://doi.org/10.11973/jxgccl202211017
    700L steel trailer frame beam products in an enterprise under lower service lives cracked. The reason for cracking of the beam was analyzed by testing the fracture morphology, chemical composition, microstructure, mechanical properties, fatigue performance and service performance of the cracked beam, and comparing with those of the uncracked beam. The corresponding improvement was put forward. The results show that the structure of the cracked 700L steel trailer frame beam had mixed crystal phenomenon, led to low toughness and fatigue limit. Under the alternating load, stress concentration occurred at the position between the spring support and the reinforcing plate on the lower wing surface of the beam and the connection between the saddle plate and the beam. Microcracks initiated and growth at the stress concentration position, and eventually led to fatigue fracture of the frame beam. To reduce the risk of cracking, the final rolling temperature should be lowered slightly, and C-shaped reinforcing plate was placed near the inner side of the lower wing surface of the gooseneck to decrease stress concentration of the beam under service conditions.
  • Review
    ZHOU Qiong, WEN Yadong, ZHANG Ergeng, HUANG Biao, LI Yaodong, LIANG Dandan, CHEN Qiang
    Materials For Mechanical Engineering. 2022, 46(10): 1-7. https://doi.org/10.11973/jxgccl202210001
    Diamond-like carbon (DLC) is a kind of metastable amorphous material containing diamond structure (sp3 hybrid bond) and graphite structure (sp2 hybrid bond), and has excellent characteristics such as high hardness, corrosion resistance, low friction coefficient, wear resistance. However, DLC also has problems such as large internal stress, poor thermal stability and sensitive tribological behavior caused by different preparation process and deposition parameters, which greatly limits its industrial application. The affecting factors of DLC film tribology properties are summarized from two aspects of the intrinsic factors and external factors. The improvements of DLC film tribology properties are discussed from heterogeneous elements doping and surface texture. The research trend of tribological properties of DLC film is prospected.
  • Testing & Research
    ZHANG Feng, YOU Xiaogang, TAN Yi, ZHUANG Xinpeng, CUI Hongyang, WANG Yiling, CHANG Kai
    Materials For Mechanical Engineering. 2022, 46(11): 9-19. https://doi.org/10.11973/jxgccl202211002
    FGH4096 alloy was treated by melt overheating process under different melt overheating temperatures (1 415,1 463,1 523 ℃) and overheating times (10, 20, 30 min). The influence of melt overheating on the purification behavior and solidification microstructure of the alloy was studied. The results show that with increasing melt overheating temperature or prolonging overheating time, the secondary dendrite spacing decreased gradually. With increasing overheating temperature, the segregation degree of the elements in the alloy decreased, but the influence of the overheating time on the segregation degree was not significant. When the overheating temperature was 1 415-1 463 ℃, carbon-oxygen reaction mainly occurred in the melt , and the nitrogen absorption reaction was weak, resulting in low oxygen and nitrogen content. When the melt overheating temperature was 1 463-1 523 ℃, MgO crucible decomposition reaction and absorbed nitrogen reaction occurred, resulting in high oxygen and nitrogen content in the alloy.
  • Review
    SUN Hui, WU Huibin, XU Yaowen
    Materials For Mechanical Engineering. 2023, 47(1): 11-18. https://doi.org/10.11973/jxgccl202301002
    High entropy alloys have great development potential in industry with the advantages of high strength,high hardness and corrosion resistance. The phases of typical high entropy alloys include solid solution phases, such as face-centered cubic (FCC) phase,body-centered cubic (BCC) phase and hexagonal close-packed (HCP) phase, and amorphous phases. The unique phase structure has an important influence on mechanical behaviors of high entropy alloys. The mechanical behaviors of high entropy alloys with different phase structures are reviewed, and the research progress on phase structure prediction methods of typical high entropy alloys, including empirical rule, CALPHAD method, first-principles calculation and machine learning method, are summarized. The future development direction of phase structure prediction of high entropy alloys is given.
  • Testing & Research
    ZHANG Wei, JIANG Shengqiang, DUAN Chunyan, XIAO Xiangwu, TAN Yuanqiang
    Materials For Mechanical Engineering. 2023, 47(2): 21-25. https://doi.org/10.11973/jxgccl202302004
    IN718 nickel-based superalloy powder was spreaded at different scraper moving speeds (28.23, 63.55, 91.11, 125.25 mm·s-1), and the powder layer thickness was 0.3, 0.5, 0.7, 0.9 mm, respectively. The powder at different positions with the same volume of the powder layer was collected by a self-made device for testing powder uniformity and weighted. The influence of the scraper moving speed and the powder layer thickness on the powder spreading uniformity was studied by calculating mass standard deviation. The results show that the mass standard deviation of the powder layer increased with the increase of the scraper moving speed or the powder layer thickness, indicating the powder spreading uniformity became worse; the scraper moving speed had a greater effect on the powder spreading uniformity. The optimal process parameter combination to obtain the best powder spreading uniformity was listed as follows:scraper moving speed of 28.23 mm·s-1 and powder layer thickness of 0.3 mm.
  • Materia Testing and Equipment
    QIAO Jixin, SHEN Junjie, WANG Xinyu
    Materials For Mechanical Engineering. 2022, 46(10): 92-97. https://doi.org/10.11973/jxgccl202210016
    Cold rolling deformation with deformation amounts of 0, 20%, 50% was conducted on Sanicro 25 austenitic heat-resistant steel. The effects of the cold deformation on the microstructure, texture and mechanical properties of the steel were investigated by microstructure observation, electron backscatter diffraction, X-ray diffraction, tensile tests and hardness tests. The results show that no new phases were formed in the test steel during cold deformation under the test conditions. With the increase of cold deformation, the numbers of twins and dislocation density in the test steel were improved. The grain orientation 〈111〉, 〈001〉 of the test steel in the inverse pole figure z direction was unstable orientation. A new {112}〈110〉 texture was produced by cold deformation. With the increase of cold deformation, the strength of Rotated cube {001}〈110〉 and Goss {110}〈001〉 textures of the test steel generally showed a weakening trend, the tensile strength, yield strength and hardness increased, and the ability to resist plastic deformation was weakened.
  • Materia Testing and Equipment
    WANG Yibo, LI Shuxin, SHU Jianming, CHEN Yinjun
    Materials For Mechanical Engineering. 2022, 46(11): 66-70. https://doi.org/10.11973/jxgccl202211011
    A tempering process (150 ℃×2 h tempering+superfinishing) was added after grinding of the original manufacturing process of GCr15 bearing steel ring (raw material forging→annealing→turning→quenching→tempering→grinding→assembly). The microstructure, residual stress and roundness of the bearing ring were studied and compared before and after adding tempering process, and the effect of adding tempering process on the deformation was analyzed. The results show that after adding tempering process, the microstructure of the bearing ring still mainly consisted of lath matensite, retained austenite and spherical carbide particles; comparing with those under the original process, the fine carbide particle amount increased and the retained austenite content decreased. After adding tempering process, the roundness of the inner and outer surfaces of the bearing ring was reduced by 80% and 60%, respectively, indicating the deformation was reduced significantly. After adding tempering process, residual stresses in the ring decreased and tended to be evenly distributed, and the further precipitation of fine carbides inhibited the strain-induced martensitic transformation, thereby the deformation of the bearing ring decreased and the dimensional stability increased.
  • Testing & Research
    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
    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.
  • Review
    YANG Zonghui, SHEN Yifu, ZHANG Xu, LI Xiaoquan
    Materials For Mechanical Engineering. 2022, 46(12): 9-17. https://doi.org/10.11973/jxgccl202212002
    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.
  • Review
    ZHAO Tingting, FAN Likun, LI Yang
    Materials For Mechanical Engineering. 2022, 46(12): 1-8. https://doi.org/10.11973/jxgccl202212001
    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.
  • Testing & Research
    ZHAO Longhai, TAN Yi, BAI Rusheng, YOU Xiaogang, ZHUANG Xinpeng, CUI Hongyang
    Materials For Mechanical Engineering. 2022, 46(10): 15-20,26. https://doi.org/10.11973/jxgccl202210003
    Based on the model of element volatilization pattern of electron beam refined Inconel 718 alloy, the short-time and long-time melting electron beam smelting layered solidification processes were designed,and the element volatilization pattern of Inconel 718 alloy prepared by electron beam smelting layered solidification and the influence of the smelting time and the layer mass on the element volatilization behavior were investigated. The results show that in order to achieve precise element controlling of Inconel 718 alloy by electron beam smelting layered solidification, the layer mass should be controlled to at least 450 g when the electron beam power was 12 kW and the refining time was 10 min. During the electron beam smelting layered solidification, the melting time should be reduced as much as possible (less than 240 s), and the electron beam power should directly increase to 12 kW for refining, which could effectively avoid excessive mass loss caused by long-term melting. The increase of the layer mass had little effect on the volatilization of alloying elements during the electron beam smelting layered solidification, but was beneficial to the precise controlling of alloy composition.
  • Testing & Research
    DENG Weitao, LI Wenge, ZHANG Yangyang, ZHANG Bowen, ZHANG Shitao, ZHAO Yuantao
    Materials For Mechanical Engineering. 2022, 46(11): 20-25. https://doi.org/10.11973/jxgccl202211003
    Molybdenum powder, nickel powder and boron powder were mixed by ball milling and press molded, and then Mo2NiB2 cermet was prepared by liquid phase sintering. The effects of powder ball milling time (1,12,24,36,48 h) on microstructure, hardness and electrochemical corrosion resistance of Mo2NiB2 cermet were studied. The results show that under different powder ball milling times, Mo2NiB2 cermets were all mainly composed of Mo2NiB2, MoB and MoNi phases. When the powder ball milling time was 24 h, the raw material powder was most evenly mixed, the content of the Mo2NiB2 phase generated by reaction was the highest, and the relative density of the cermet was the largest. With increasing powder ball milling time, the hardness of the cermet decreased first and increased and then decreased, and the free-corrosion current density increased first and decreased and then increased. When the powder ball milling time was 24 h, the hardness was the highest, and the free-corrosion current density was the smallest, indicating the corrosion resistance was the best. The best corrosion resistance was related to the reduction of diffusion channels of corrosive media due to the fewest pores in the cermet and the promotion of anodic polarization by the high content of Mo2NiB2 phase.
  • Review
    SUN Ruting, MA Ran
    Materials For Mechanical Engineering. 2022, 46(11): 1-8. https://doi.org/10.11973/jxgccl202211001
    Magnetorheological fluids have high controllability and continuity, and are widely used in semi-active shock absorbers, polishing devices and torque transfer devices. The sedimentation stability is an important indicator to ensure their performance. The detection method of the sedimentation stability of magnetorheological fluids is summarized, and the research progress on improving the sedimentation stability of magnetorheological fluids is described from three aspects of magnetic particles, additives and carrier fluid. Considering the problems in the sedimentation stability research of magnetorheological fluids, some points of view are put forward for the future research direction.
  • Failure Analysis
    LAN Haotian, QIN Song, XU Xiaohan, SONG Yifeng, YUE Chongxiang
    Materials For Mechanical Engineering. 2022, 46(10): 113-118. https://doi.org/10.11973/jxgccl202210019
    The tin plate for easy-opening lid produced by a steel factory cracked at the rivet during the lid making process, and the cracking rate was about 0.08%, which was lower than the customer's expected quality requirements. The cracking reasons were analyzed by chemical composition analysis, mechanical property testing, microstructure observation and inclusion analysis, and the improvements were suggested. The results show that the ductile fracture occurred on the rivets of easy-opening lids. The presence of large Al2O3 and CaO inclusions at the edge of the rivets and the obvious thickness thinning were the direct and indirect causes of the lidding cracking of the tin plate, respectively. After the ladle refining furnace (LF) refining process during the smelting process changed to the molten steel vacuum circulating degassing (RH) refining process, the number of inclusions per square millimeter in the finished tin plate was 4.7, and the maximum size was 15.5 μm, which were significantly lower than the 49.8 per square millimeter and 38.9 μm before the process improvement, and no cluster large inclusions were found, indicating that the RH refining process had a better control effect on the inclusions. The chemical composition, hardness, tensile properties and microstructure with the RH refining process were all met the requirements for easy-opening lids, and the cracking rate of lidding was reduced to less than 0.01%.
  • Material Properties & Application
    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
    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.
  • Testing & Research
    CHENG Binggui, HAN Limei, LI Li, QU Jinbo
    Materials For Mechanical Engineering. 2022, 46(11): 38-42. https://doi.org/10.11973/jxgccl202211006
    The rust layer stabilization treatment was carried out on Q500qENH weathering bridge steel samples by combination of coating rust layer stabilizer and water treatment (84 d). The micromorphology, phase composition and formation mechanism of the surface rust layer of the sample were studied. The results show that the surface corrosion of the weathering bridge steel sample with rust layer stabilizer was uniform in the early stage of water treatment, and the rust layer formed in the later stage had good compactness and no obvious cracks inside. After water treatment for 84 d, the rust layers on the surface of the samples with and without rust layer stabilizer were both mainly composed of α-FeOOH, γ-FeOOH and a small amount of Fe3O4, and the mass ratios of α-FeOOH to γ-FeOOH were 2.77 and 1.85, respectively; the surface of the sample with rust layer stabilizer preferentially formed a stable rust layer. The rust layer stabilizer could make the weathering bridge steel quickly form a uniform rust layer, accelerate the formation and transformation of the initial phase γ-FeOOH in the rust layer, increase the content of the stable phase α-FeOOH in the rust layer, promote the formation of the stable rust layer, and shorten the stabilization period of the rust layer.
  • Testing & Research
    ZHAO Le, LIU Lirong, TIAN Sugui
    Materials For Mechanical Engineering. 2022, 46(11): 33-37. https://doi.org/10.11973/jxgccl202211005
    A new Ni3Al based single crystal superalloy was prepared by liquid metal cooling (LMC) method and treated by 1 290 ℃×4 h solid solution and 1 000 ℃×4 h aging. The microstructure and tensile properties at different temperatures (23-900 ℃) of the alloy were studied. The results show that the γ' phase in the test alloy structure showed a regular cube shape after solid solution and aging treatment, whose average size was about 0.55 μm and volume fraction was about 72%. The tensile strength and yield strength of the alloy increased first and then decreased with increasing temperature, reaching the peak values at 800 ℃, which was 856 MPa and 808 MPa, respectively. The change of elongation after fracture with temperature was opposite to that of strength; the elongation after fracture reached a minimum value of 11% at 800 ℃. The fracture mode of the alloy was pure shear fracture when stretched at 600 ℃ and below. When stretched at 760 ℃, the alloy had a mixed fracture of pure shear fracture and microporous aggregation. When the tensile temperature was between 800-900 ℃, the alloy fractured in a microporous aggregation fracture mode.
  • Review
    CAO Yida, LIU Chengbao, CHEN Feng, QIAN Junchao, XU Xiaojing, MENG Xianrong, CHEN Zhigang
    Materials For Mechanical Engineering. 2022, 46(10): 8-14. https://doi.org/10.11973/jxgccl202210002
    Reducing NOx emission is one of the most critical global environmental problems. At present, the traditional denitrification technology generally has the problems of high reaction temperature, low catalytic efficiency and high cost. Therefore, new photocatalytic NOx removal technologies such as photocatalytic oxidation and photocatalytic selective reduction have attracted great attention. The research progress in NOx removal by photocatalytic materials is reviewed from two aspects including photocatalytic oxidation and photocatalytic selective reduction. The types of photocatalytic materials, the removal principle and the factors affecting the removal efficiency are emphasized. Finally, the prospects for future development of photocatalytic materials used for denitrification are presented.
  • Testing & Research
    WANG Jinhai, YI Chuanming, XIAO Gang, WAN Keqian, WANG Wenyun
    Materials For Mechanical Engineering. 2022, 46(10): 49-55. https://doi.org/10.11973/jxgccl202210009
    The influence of laser power, scanning spacing and scanning speed on the relative density of selective laser melting formed 12Cr9NiAlMo steel was studied by orthogonal experiments, and the optimal process parameters were obtained. The structure and properties of samples formed by the optimal process after solution and aging treatment were studied. The results show that the laser power had the greatest effect on the relative density of the formed samples, followed by the scanning spacing. The optimal process parameters were laser power of 325 W, scanning space of 0.10 mm, and scanning speed of 1 000 mm·s-1, and the relative density was 99.22%. After heat treatment, part of the residual austenite in samples formed by the optimal process was transformed to martensite, and a large number of fine NiAl phase precipitated. The tensile strength, yield strength and hardness increased by 62.1%, 59.6%, 41.2%, and the percentage elongation after fracture and impact absorbing energy decreased by 40.0%, 81.3%, comparing with those without heat-treatment.
  • Materia Testing and Equipment
    ZHANG Bingxian, LEI Longyu, DU Mingke, ZHANG Yunlong, ZHANG Min
    Materials For Mechanical Engineering. 2022, 46(10): 87-91,97. https://doi.org/10.11973/jxgccl202210015
    A laser welding method was used to conduct welding experiments on A286 iron-based superalloy thin plates and the welded joints were subjected to heat heatment with 982℃ solid solution, and 982℃ solid solution+718℃ aging. The influence of heat treatment on the microstructure and mechanical properties of welded joints was studied. The results show that the weld structure of the welded joint was mainly composed of austenite, δ ferrite and γ' phases without heat heatment. After solid solution, the δ ferrite content in the joint weld increased, and the number of γ' phases decreased; the strength and hardness of the joint changed little, compared with those at weld state, but the elongation after the fracture increased from 17.3% at the weld state to 22.7%. After solid solution+aging, most of the δ ferrite in the joint weld structure was converted to austenite, whose grains were coarsened; a large number of diffuse distribution γ' phases were precipitated, and the tensile strength and yield strength of the welded joint increased from 639, 360 MPa at solid solution state to 1 019, 662 MPa; the average hardness reached 200% of solid solution state, but the elongation after the fracture was reduced to 17.1%.
  • Testing & Research
    LIU Weibin, LI Xinmei, JING Zhenyu
    Materials For Mechanical Engineering. 2022, 46(10): 27-33. https://doi.org/10.11973/jxgccl202210005
    WC reinforced Ni35 alloy ladding layers were prepared on 45 steel surface by laser cladding at different laser powers (1.1, 1.3, 1.5 kW). The effect of laser power on the microstructure and performance of the cladding layer was studied by optical microscope, scanning electron microscope, X-ray diffractometer, micro Vickers hardness tester, friction and wear testing machine, electrochemical workstation, etc. The results show that with increasing laser power, the macroscopic cracks on the surface of the cladding layer decreased, and the dilution rate of the cladding layer increased. With increasing laser power, the microhardness of the cladding layer increased, and the wear loss and friction factor decreased. The wear resistance of cladding layers with different laser powers was better than that of the matrix. When the laser power was 1.5 kW, the average hardness of the cladding layer surface was increased by 270%, and the wear loss and friction factor was reduced by 95.2% and 54.93%, comparing with that of the matrix. With increasing laser power, the self-corrosion potential of the cladding layer decreased first and then increased, and the self-corrosion current density increased first and then decreased. When the laser power was 1.5 kW, the self-corrosion current density of the cladding layer was the smallest, the corrosion resistance was relatively good.
  • New Materials & Technology
    ZHAO Yiliang, HUANG Nan, RU Hongqiang, ZHANG Cuiping, YUE Xinyan, LIU Chunming, WANG Wei
    Materials For Mechanical Engineering. 2022, 46(11): 55-59. https://doi.org/10.11973/jxgccl202211009
    TiC ceramics were prepared by pressureless liquid phase sintering at 1 850 ℃. The effect of the mass fraction (0,6%, 8%,10%) of sintering additive Al2O3-Y2O3 (Al2O3 to Y2O3 molar ratio of 1.5) on the microstructure and properties of TiC ceramics was investigated. The results show that TiC phase, YAM (Y4Al2O9) phase and YAG (Y3Al5O12) phase existed in TiC ceramics after adding sintering additive. With increasing mass fraction of sintering additive from 0 to 10%, the relative density of ceramics increased from 94.50% to 97.86%, the open porosity decreased from 0.77% to 0.21%, the YAM and YAG phases increased and gradually aggregated, and the fracture toughness, Vickers hardness and flexural strength all increased first and then decreased. When the mass fraction of sintering additive was 6%, the fracture toughness and Vickers hardness reached the maximum value of 6.2 MPa·m1/2 and 19 GPa, respectively. When the mass fraction of sintering additive was 8%, the flexural strength reached the maximum value of 524 MPa. The resistivity of ceramics was between 1.00×10-6-2.00×10-6 Ω·m, and the addition of sintering additives affected the electrical conductivity little.
  • Testing & Research
    CHANG Xubing, WANG Yong, LIN Lin, JI Dongmei
    Materials For Mechanical Engineering. 2023, 47(1): 34-41,47. https://doi.org/10.11973/jxgccl202301005
    The creep-fatigue tests with load holding at maximum stress controlled by load with different stress ratios (0.2-0.4) and holding times (0.3-1.5 h) of X12CrMoWVNbN10-1-1 steel at 620℃ were carried out, and the creep-fatigue interaction and fracture mechanism of the steel were analyzed. The results show that the creep-fatigue life of the test steel had exponent relation with the holding time. The longer the loading time, the less the influence of stress ratio on creep-fatigue life. The creep fatigue interaction factor defined from the view of strain could well reflect the interaction between the true stress-true strain hysteretic curve and the creep fatigue life in the stable stage. The creep-fatigue fracture mode of the test steel was ductile fracture. When the holding time was short of 0.3, 0.5 h, the fatigue damage suppressed creep damage, and the damage was mainly controlled by cyclic fatigue load; the dimples on the fracture were caused by crystal boundary slide controlled by fatigue. When the holding time was long enough of 1.0, 1.5 h, the fatigue damage promoted creep damage, and the damage was mainly controlled by time-related creep load; the dimples on the fracture were caused by detachment of inclusions or second phase particles.
  • Material Properties & Application
    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
    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.
  • Testing & Research
    YANG Conghui, CAO Tieshan, CHEN Xiangang, CHENG Congqian, ZHAO Jie
    Materials For Mechanical Engineering. 2023, 47(2): 26-32,66. https://doi.org/10.11973/jxgccl202302005
    On the basis of the chemical composition of HR3C steel, the mass fractions of niobium element were adjusted to 0.5%, 0.8% and 1.1%, respectively. The ingot samples with the three components were obtained by melting, and then subjected to hot rolling, homogenization annealing at 1 200℃, solid solution at 1 200℃, and aging at 750℃ for different times (0-2 000 h). The effects of niobium content on the microstructure, grain size and hardness of the test steel were studied. The results show that increasing the niobium content could increase the content of undissolved MX phase in the solid solution test steel and reduce the grain size. During aging at 750℃, increasing the niobium content could promote the precipitation and coarsening of σ phase at grain boundaries and inside grains, and improve the hardness. When aging for 2 000 h, the niobium content had little effect on the size and distribution of grain boundary precipitates, but had some influence on the size and shape of intragranular precipitates; the test steel containing 1.1wt% niobium had a relatively small number of strip-like intragranular precipitates.
  • New Materials & Technology
    HUANG Yuntao, ZHANG Jin, YUE Xinyan, ZHANG Cuiping, RU Hongqiang
    Materials For Mechanical Engineering. 2022, 46(11): 43-48. https://doi.org/10.11973/jxgccl202211007
    TiC/ZrO2 conductive ceramic composites were prepared by pressureless sintering with ZrO2, TiC, TiO2 and phenolic resin as raw materials and combining with in-situ synthesized TiC by carbothermal reduction reaction. The effect of TiC mass fraction (25%-40%) on the relative density, microstructure, mechanical properties and conducivity of the ceramic composites were investigated. The results show that the ceramic composites consisted of TiC and t-ZrO2 phases. With increasing TiC content, the TiC particles in ZrO2 matrix gradually connected with each other and then formed a continuous network structure, the bending strength of the ceramic composites increased first and then decreased, the hardness decreased first and then increased, and the relative density, fracture toughness and resistivity decreased constantly. When the mass fraction of TiC was 30%, the ceramic composite had the best comprehensive properties, whose relative density, bending strength, Vickers hardness, fracture toughness and resistivity were 97.42%, 571 MPa, 12.1 GPa, 3.43 MPa·m1/2 and 3.10×10-5 Ω·m, respectively.
  • Materia Testing and Equipment
    WANG Haomin, WANG Guoqing, XIONG Yangkai, JIANG Hao, ZHAO Yuantao, FANG Zhiqiang, LI Wenge
    Materials For Mechanical Engineering. 2022, 46(10): 98-105. https://doi.org/10.11973/jxgccl202210017
    Taking chromium powder, tungsten powder, graphite powder and iron powder as cladding layer raw materials, and Ni60 alloy powder as bonding layer raw material, WC-Cr7C3 composite reinforced iron-based cladding layer was prepared on the surface of 45 steel substrate by laser cladding technique. The macroscopic morphology of the cladding layer under different laser power (2 500-3 500 W) and scanning speed (2-5 mm·s-1) was studied to determine the optimal process parameters, and the microstructure and properties of the cladding layer under the optimal process were analyzed. The results show that the optimal laser cladding process parameters were the laser power of 3 500 W and the scanning speed of 2 mm·s-1. The WC-Cr7C3 composite carbides with network structure were in situ spontaneously generated in the cladding layer. From the surface to the interior of the cladding layer, the microstructure gradually changed from equiaxed and dendrite to columnar and plane crystal. The average hardness of the cladding layer was 507.6 HV, which was about 63.8% higher than that of the matrix. The average stable friction coefficient was 0.128, which was only one forth of the matrix, and the wear rate was 4.9×105 cm3·N-1·m-1, which was only one ninth of the matrix; the wear form was slight abrasive wear and slight adhesive wear.
  • Testing & Research
    ZHAI Chuantian, SUN Youping, LI Wangzhen, HE Jiangmei, WAN Siyu
    Materials For Mechanical Engineering. 2023, 47(1): 26-33. https://doi.org/10.11973/jxgccl202301004
    As-cast Mg-4Zn-4Y alloy was treated by homogenization annealing at different temperatures (440,460,480℃) for different holding times (4-24 h), and the effects of homogenization annealing on the microstructure and properties of the alloy were studied. The results show that there were α-Mg phase, W phase Mg3Zn3Y2, LPSO phase Mg12ZnY and yttrium-rich phase in the as-cast alloy. With increasing annealing temperature, most of the LPSO phase gradually dissolved into the matrix. With increasing annealing temperature and holding time, the content of yttrium-rich phase decreased, and the dendrite segregation was reduced. Compared with the as-cast alloy, the tensile strength of the alloy after homogenization annealing at 440℃ and 460℃ decreased slightly, and the percentage elongation after fracture changed slightly. The tensile strength and percentage elongation after fracture after homogenization annealing at 480℃ were relatively high, but the burning loss occurred. The best homogenization annealing of the alloy was 440℃×12 h.
  • Testing & Research
    WANG Zixuan, XUE Rong, ZHU Congzhen, LIN Haoran, WANG Jiping
    Materials For Mechanical Engineering. 2022, 46(10): 21-26. https://doi.org/10.11973/jxgccl202210004
    Taking two kinds of constituent siliconized graphite composites prepared by reactive molten infiltration with different isostatic pressures (40 MPa and 70 MPa) and commercially purchased Russian-made siliconized graphite composites as research objects, the phase composition, microstructure and friction and wear properties under water lubrication conditions of three kinds of constituent siliconized graphite composites were studied. The results show that the phases of the siliconized graphite composites were composed of carbon phase, silicon carbide phase and silicon phase, which were distributed as a three-dimensional network embedded. When the carbon phase content was relatively low and the silicon graphite content was relatively high, friction coefficient of siliconized graphite composites increased with the load; when the carbon phase content was relatively high and silicon carbide content was relatively low, the friction coefficient increased first and then decreased with the load. The wear loss of different constituent siliconized graphite composites was extremely low, and the siliconized graphite composites had excellent wear resistance. The wear mechanism was mainly abrasive wear.
  • Testing & Research
    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
    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.
  • Testing & Research
    YU Qingping, ZHANG Guangsheng, XIA Liansen, FANG Huimin
    Materials For Mechanical Engineering. 2023, 47(4): 18-22,32. https://doi.org/10.11973/jxgccl202304004
    Fe-2%Cu-0.4%C iron-based powder metallurgy material was boronized at 950 ℃ for 5 h by solid powder boronizing method with a boronizing agent containing CeO2. The effects of CeO2 addition (0,2%, 4%, mass fraction) on the microstructure and friction and wear properties of the boronizing layer were studied. The results show that the boronizing layer with different addition amounts of CeO2 had a single Fe2B phase. With the increase of CeO2 addition, the surface roughness of the boronizing layer increased, and the thickness, hardness and wear resistance increased first and then decreased. When the mass fraction of CeO2 was 2%, the thickness and hardness of the boronizing layer were the largest, about 144 μm and 58.0 HRC, respectively. At this time, the surface integrity of the boronizing layer was relatively good, the amount of wear was the smallest, about 0.008 g, and the wear resistance was the best.
  • New Materials & Technology
    GUO Guanghan, LIU Jiaqi, HUANG Yuntao, YUE Xinyan, ZHANG Cuiping, RU Hongqiang
    Materials For Mechanical Engineering. 2022, 46(11): 49-54. https://doi.org/10.11973/jxgccl202211008
    Ti(C, N)/ZrO2 ceramic composites were prepared by pressureless sintering with Y2O3 stabilized nano ZrO2 powder, TiO2 powder, TiN powder, carbon black and water-soluble phenolic resin as raw materials. The effects of Ti(C, N) mass fraction (25%-40%) on the microstructure and properties were studied. The results show that the Ti(C, N)/ZrO2 ceramic composites consisted of t-ZrO2 and Ti(C,N) phases. The Ti(C, N) particles agglomerated gradually with increasing Ti(C,N) content, while distributed relatively evenly when the Ti(C, N) mass fraction increased to 40%. With increasing Ti(C, N) phase content, the open porosity of the ceramic composites increased first and then decreased, and the hardness, flexural strength and fracture toughness decreased first and then increased. When the mass fraction of Ti(C, N) was 40%, the ceramic composites had the best comprehensive performance with the open porosity of 0.73%, the hardness of 14.4 GPa, the flexural strength of 354 MPa and the fracture toughness of 5.8 MPa·m1/2.
  • Testing & Research
    LI Cong, DING Zhili, HUANG Can, ZHOU Libo, CHEN Wei, CHEN Jian
    Materials For Mechanical Engineering. 2023, 47(1): 48-55,64. https://doi.org/10.11973/jxgccl202301007
    SP-700 titanium alloy was treated by solid solution in β phase region at 1 000℃ for 15 min, and then was cooled to (α+β) phase region for solid solution at different temperatures (650-900℃) for different times (3-10 min) or was treated by single stage aging and or double stage aging including 280℃ low temperature pre-aging and the second aging at different temperatures (370-650℃) for different times (15, 90 min). The microstructure and properties of the alloy under different processes were studied. The results show that the volume fraction of α phase in the alloy after 850℃ solid solution increased with the solid solution time; when the solid solution time was 5 min, the alloy had good strong plastic matching. Under solid solution time of 5 min, the volume fraction of α phase decreased with increasing solid solution temperature; when the solid solution temperature was 650℃, the alloy had good strong-plastic matching. After β phase region solid solution and single/double stage aging, the alloy was basically composed of β grain, α phase and acicular martensite. After single stage aging at aging temperature of 650℃ for 90 min or double stage aging at aging temperature of 650℃ for 15 min, the alloy showed good strong-plastic matching.
  • Testing & Research
    YAO Shangjun, MIAO Xin, CHEN Sijie, HAO Lili, LI Zhenhao
    Materials For Mechanical Engineering. 2023, 47(2): 33-38. https://doi.org/10.11973/jxgccl202302006
    Taking composite steel pipe with TA2 industrial pure titanium lining and 20 steel coating as the research object, and BNi2 amorphous alloy foil as the interlayer, the titanium/steel composite pipe was welded by transient liquid phase diffusion bonding at bonding temperatures of 1 130-1 200℃ under argon protection. The effect of bonding temperature on the microstructure and properties of titanium/steel composite pipe joints was investigated. The results show that the joints at different bonding temperatures were formed well without macroscopic defects such as holes and cracks. With increasing bonding temperature, the equiaxed microstructure of weld at the titanium side grew up, α→α'+β phase transition occurred, and the weld boundary became blurred gradually. The acicular ferrite and pearlite in the weld at the steel side became thicker, the black brittle phase gradually disappeared, and the diffusion distance of elements of interlayer and base material increased. The joints welded at different bonding temperatures all fractured in the weld at the titanium side. With increasing bonding temperature, the tensile strength of the joint increased first and then decreased. When the bonding temperature was 1 180℃, the tensile strength was the biggest of 460 MP, and the fracture form was ductile-brittle mixed fracture.