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      20 June 2019, Volume 47 Issue 6 Previous Issue    Next Issue
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    Application of carbon materials in perovskite solar cells
    Cheng-zhan YING, Qiu-juan LYU, Chao-hui LIU, Song BI, Gen-liang HOU, Jin TANG
    2019, 47 (6): 1-10.   DOI: 10.11868/j.issn.1001-4381.2018.000224
    Abstract ( 1305 ( PDF (2297KB)( 632 Citation

    Perovskite solar cells have the advantages of low material cost, simple production process and high photoelectric conversion efficiency, and their development prospects are bright. Carbon materials are used in various components of perovskite solar cells due to their low cost, high electrical conductivity, hydrophobicity and chemical stability to improve battery performance and reduce costs. Based on the dimensionality of the carbon materials used in perovskite solar cells, the zero-dimensional C60, carbon quantum dots and graphene quantum dots, one-dimensional carbon nanotubes, two-dimensional graphene and the application of derivatives, graphyne, and three-dimensional graphite in perovskite solar cells were described in this paper, and it is of great importance for the realization of low-cost commercialization and large-scale manufacturing of perovskite solar cells in the future.

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    Research progress in photothermal conversion materials based on full spectrum sunlight utilization
    Jian-ling ZHAO, Chen-yu MA, Jian-qiang LI, Xiao-yu LI
    2019, 47 (6): 11-19.   DOI: 10.11868/j.issn.1001-4381.2018.000539
    Abstract ( 1214 ( PDF (6304KB)( 1384 Citation

    Photothermal conversion materials can effectively improve the utilization and conversion rate of full-spectrum sunlight, which has aroused wide attention of researchers at home and abroad. In this paper, the types and research progress of photothermal conversion materials mainly studied in recent years were reviewed. The methods of increasing the solar steam generation efficiency by using photothermal conversion materials were analyzed. The optimization design model of solar steam generation system was introduced, and the role of low conductive matrix materials in the system was emphasized. Finally, the application prospects of photothermal conversion materials in the field of seawater desalination were prospected, and what was pointed out is that in-depth exploration of the physical mechanism and large-scale preparation of photothermal conversion materials will become important for the future.

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    Research advances in molybdenum dissulfide-based nanomaterials in field of electrochemical sensing/hydrogen evolution
    Gang-bing ZHU, De-peng ZHANG, Jun-juan QIAN
    2019, 47 (6): 20-33.   DOI: 10.11868/j.issn.1001-4381.2018.001306
    Abstract ( 764 ( PDF (7391KB)( 635 Citation

    As an emerging two-dimensional layered transition metal disulfide nanomaterial with typical graphene-like structure, molybdenum disulfide (MoS2) nanosheets have attracted wide attention due to their excellent electrical, optical and thermodynamic properties and their large specific surface area, and it is widely used in the field of electrochemistry. The research status and development trends of MoS2-based hybrid nanomaterials in the fields of electrochemical sensors for life, food, drug, environment and electrochemical hydrogen evolution reaction were reviewed.

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    Research and application progress in casting superalloys for industrial gas turbine blades
    Liang LUO, Cheng-bo XIAO, Jing-yang CHEN, Qing LI, Sheng-long DAI
    2019, 47 (6): 34-41.   DOI: 10.11868/j.issn.1001-4381.2019.000128
    Abstract ( 1285 ( PDF (909KB)( 582 Citation

    Advanced industrial gas turbines are becoming preferred devices for worldwide power generations and large ship power in recent decades due to its outstanding advantages of high thermal efficiency and low pollution. Casting superalloy is the key material for industrial gas turbine blades in hot section components, and to a certain extent their performance and preparation level determine the levels of power, efficiency and service life of the industrial gas turbines. This paper outlines the current research and application status and shows the development trends of manufacturing technology of casting superalloy for industrial gas turbines and turbine blades. In the future, technologies such as advanced directional solidification and "materials genome engineering" will be used in the research and manufacture of casting superalloy for industrial gas turbine blades. Meanwhile, the directional and single crystal superalloy will be used more and more widely in advanced industrial gas turbines.

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    Study on property model for porous materials 1: mathematical relations
    Pei-sheng LIU, Guang CUI, Wei CHENG
    2019, 47 (6): 42-62.   DOI: 10.11868/j.issn.1001-4381.2018.001407
    Abstract ( 654 ( PDF (7089KB)( 521 Citation

    Three-dimensional reticulated porous materials are excellent engineering materials, and their application cover energy engineering, bioengineering, aerospace, environmental protection, transportation, etc. Author of this paper put forward a simplified structure model of octahedron based on the structural characteristics of these materials. On this basis, serial mathematical relations were obtained for their performance. This model and the related mathematical characterization of the basic physical and mechanical properties of this kind of materials, from unidirectional tension to multidirectional tension and compression, as well as conductivity and specific surface area were comprehensively introduced. The origin and characteristics of the simplified structural model were described comprehensively, and compared with other similar models; different property models and their relationships were explained one by one. Among them, the representative problems including the thin beams assumption of pore struts, the bending of pore struts and the restraint force of bearing units for the loaded porous body, and the correction coefficient and the plastic index value involved in the tension or/and compression relationship. The theoretical results were verified by the experiment of samples prepared in production line, which were well practicable.

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    Research Article
    Preparation and characterization of anti-flooding functional Pt/C catalyst for PEMFC
    Lu LU, Lei WU, Ji-cheng SHI, Hong-feng XU, Tao-quan CONG
    2019, 47 (6): 63-69.   DOI: 10.11868/j.issn.1001-4381.2018.000379
    Abstract ( 907 ( PDF (1968KB)( 423 Citation

    The important reason of the reduction of the catalytic performance of Pt/C catalyst is carbon carrier corrosion. The risk of oxgen flooding in proton-exchange membrane fuel cellsis also increased by hydrophilicity of this catalyst. The Pt/C catalyst was subsequently reduced using hydrazine hydrate to make Pt/C corrosion resistant and anti-flooding. Comparison by infrared spectra of absorption peaks shows the increased number of oxygen-containing functional groups in the XC-72 carbon surface treated with hydrogen peroxide. Its measured contact angle is less than that of untreated XC-72 carbon. Reduction of oxidized XC-72 carbon with hydrazine hydrate shows that the contact angle is increased by 22.4° compared with that of the oxidized XC-72 carbon, indicating anti-flooding enhancement. As shown in the specific surface area measurement, the specific surface area of XC-72 is reduced by the hydrogen peroxide treatment but its mespopore ratio is increased, which favors the carrier load Pt. The anti-flooding of Pt/C catalyst after reduction with hydrazine hydrate is stronger than that before reduction, indicating an increase in contact angle by 6.2°. After 2000 cycles of cyclic voltammetry, the electrochemical specific surface loss is decreased and the durability is improved for the reduced Pt/C catalyst by hydrazine hydrate.

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    Synthesis and catalytic performance of magnetic core-shell structure Fe3O4/P(GMA-DVB)-SH-Au composite catalyst
    Ming-liang MA, Yu-ying YANG, Ping LYU, Li JIA, Xin-cheng JIA, Liu CHEN, Ling-yun KONG, Li-feng CHI
    2019, 47 (6): 70-76.   DOI: 10.11868/j.issn.1001-4381.2018.000856
    Abstract ( 622 ( PDF (3463KB)( 263 Citation

    In this work, monodisperse hollow Fe3O4 magnetic microspheres were synthesized by hydrothermal method. And the P(GMA-DVB) polymer layer was coated on the surface of Fe3O4 microspheres by distillation precipitation polymerization method to form core-shell structure. After adsorption of Au nanoparticles, a magnetic core-shell Fe3O4/P(GMA-DVB)-SH-Au supported catalyst was obtained. The morphologies, structures and catalytic performance of the catalysts were characterized by TEM, SEM, FTIR, XRD, TGA, VSM and UV-vis. Results show that the synthesized materials have uniform particle size, regular microsphere, and obvious core-shell struc-ture. For the catalytic reduction of 4-nitrophenol, the Fe3O4/P(GMA-DVB)-SH-Au exhibits excellent catalytic performance, and the catalytic efficiency still maintains over 80% after 8 successive cycles.

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    Investigation on tunable ultra-thin radar absorber based on active metamaterial
    Jin-guo HUANG, Yu GUO, Zhi-ya ZHAO, Xue LI, Ming-jun XING, Zhen-kun XIE
    2019, 47 (6): 77-81.   DOI: 10.11868/j.issn.1001-4381.2017.000671
    Abstract ( 846 ( PDF (2697KB)( 288 Citation

    A sort of state-of-the-art metamaterial was introduced to serve as an active ultra-thin RAM. The metamaterial consisted of resistors, varactor diodes and micro-structure array. The effect of resistor, capacitor and electromagnetic polarization on the absorbing properties was investigated in detail. The results indicate that its absorption band can be regulated in 3.7 times frequency-band by actively changing the external voltage. The total thickness of the metamaterial RAM is only 1/181 of the wavelength. Compared with the traditional absorbing materials, the metamaterial RAM shows excellent ultra thin feature under the same wave absorbing performance. In addition, for TE and TM polarized electromagnetic wave, the metamaterial RAM exhibits the same wave absorbing property, i.e., its absorbing property is insensitive to the polarization direction of incident wave.

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    Preparation and ethanol gas sensor properties of SnO2 nanowires
    Li-jun LI, Rui-xia MIAO, Xia ZHANG
    2019, 47 (6): 82-87.   DOI: 10.11868/j.issn.1001-4381.2017.000910
    Abstract ( 637 ( PDF (5739KB)( 271 Citation

    Tin oxide nanowires were successful prepared using thermal evaporation method. The crystal structure and surface morphology of the nanowires were characterized by X-ray diffraction, scanning electron microscope and transmission electron microscope. The as-prepared nanowires are rutile single crystal SnO2 structure, with diameter in 50-200nm, and length of 5-15μm, conforming to the gas-liquid-solid growth mechanism. The heater structure gas sensor was prepared using SnO2 nanowires as the gas sensitive material. The gas sensitive performance of the samples was tested in ethanol gas concentration range of 25×10-6-500×10-6. The results show that the best working temperature of the sensor is about 260℃; in the 25×10-6 and 500×10-6 ethanol gas environment, the sensitivity is 7.54 and 111.01 respectively, response time of the sensor is 2-20s, and recovery time is 5-33s;the sensitivity and the gas concentration has a good linear relationship within the measuring range; the sensor has favourable stability with less than 5% repeated measurement error in 7 days.

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    Reaction mechanism of SiC-TiSi2 by melt infiltration method
    Yi-ran ZHOU, Hu LIU, Jin-hua YANG, Zhuo-yu JIANG, Xiao-xu LYU, Jian JIAO
    2019, 47 (6): 88-93.   DOI: 10.11868/j.issn.1001-4381.2018.001449
    Abstract ( 657 ( PDF (2105KB)( 346 Citation

    The melt infiltration method is one of the main preparation method of SiC matrix composites. Complex reactions and multi-component diffusion are involved in molten-Si infiltration of a C-based preform. In this study, SiC-TiSi2 was fabricated by Si melt infiltration and the TiSi2 was in-situ formed in the matrix of SiC. In order to explore the reaction mechanism of SiC-TiSi2, SEM, EDS and micro-beam XRD were determined to characterize the phase constitute and micro-structure in different regions along the Si melt infiltration direction. The results demonstrate that SiC, TiSi2 and Ti5Si3 which concentrate on the Si/SiC interface are found to be formed through the Si melt infiltration into the C-TiC preform. With the increase of temperature, the liquid phase of Ti-Si appears when exceeding the Si-TiSi2 eutectic temperature. And the liquid Ti-Si eutectic precipitates TiSi2 in the Si region during the cooling period of the sample. Moreover, the isolated SiC grain in Si region is produced by the precipitation from the dissolution of solid C in liquid Si.

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    Effect of milling time on microstructure and mechanical properties of TiC-CoCrFeNi composites prepared by hot pressing sintering
    Gui-fang WANG, Zhong-xia LIU, Guo-peng ZHANG
    2019, 47 (6): 94-100.   DOI: 10.11868/j.issn.1001-4381.2018.000082
    Abstract ( 685 ( PDF (7611KB)( 262 Citation

    TiC-CoCrFeNi composite was fabricated by mechanical alloying and consequently vacuum hot pressing sintering, and the effects of milling time on the microstructure and mechanical properties of the composite was investigated. The results show that a single-phase solid solution with fcc structure is obtained after milled for 10h of Co, Cr, Fe and Ni powders. TiC and Cr7C3 structured carbides are formed and dispersed in the CoCrFeNi solid solution after hot pressing sintered at 1200℃ for 1h. Milling time has a significant effect on the size and amount of TiC and Cr7C3 structured carbides, which can affect the mechanical properties of the composite. When the milling time reaches 10h, the hardness and yield strength of the composite reach the maximum values of 671HV and 1440MPa, respectively, which is probably attributed to the dramatically increasing of nano-sized TiC in sintered bodies.

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    Effect of two-dimensional layered material/zinc borate compounds on flame retardancy of expandable polystyrene foams
    Xi-shan LIU, Bo CAO, Wen-fei JI, Jun SUN, Sheng ZHANG
    2019, 47 (6): 101-107.   DOI: 10.11868/j.issn.1001-4381.2017.001570
    Abstract ( 619 ( PDF (8477KB)( 257 Citation

    Flame retardant expandable polystyrene foams were prepared by coating with melamine modified urea formaldehyde resin. The flame retardant system was based on ammonium polyphosphate, and the combination of three kinds of two-dimensional layered material and zinc borate was used as synergist. The influence of different flame retardants on fire resistance, smoke suppression and thermal stability was discussed. The experimental results show that the flame retardancy is significantly improved by the presence of expandable graphite and zinc borate with mass ratio of 2:1 and total additive amount of 24 phr. The limiting oxygen index of EPS foams is increased to 32.6%, with V-0 rating in UL-94 vertical burning test. The smoke density grade is decreased to 27.31. Compared with the sample containing only expandable graphite, the introduction of zinc borate enhances the strength of residue char from 14.3 to 86.1. Thermal analysis suggests that the thermal stability and char formation are improved by the presence of synergist. The residual char observation reveals that zinc borate is beneficial to form complete and integrated char layers with less crack and breakage.

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    Tribological properties of modified phenolic resin ceramic friction materials
    Hai-long CHEN, Xue-feng YANG, Shou-ren WANG, Chong-yang LU, Yuan-bo WU
    2019, 47 (6): 108-113.   DOI: 10.11868/j.issn.1001-4381.2018.000038
    Abstract ( 832 ( PDF (6141KB)( 340 Citation

    Three kinds of phenolic resin ceramic brake pads were prepared with phenolic resin, boron modified phenolic resin, melamine modified phenolic resin as binder, and ceramic fiber as reinforcing fiber. The impact toughness and hardness of the material were tested. The friction and wear properties were investigated by friction and wear tester. The worn surface morphology and its composition were analyzed by scanning electron microscope (SEM) and X-ray energy spectrometer, and the wear mechanism was also discussed. The experimental results show that boron modified phenolic resin binder can improve the hardness of friction materials, melamine modified phenolic resin can improve the impact toughness of materials, reducing material hardness; in the friction process, melamine modified phenolic resin carbonized at high temperature, forming a dense layer of friction on the surface of friction material. The existence of friction layer makes the friction coefficient of the friction material become relatively stable, and reduces the wear rate of the friction material.

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    Tribological properties of surface modified Cu nanoflakes prepared by plasma assisted ball milling
    Guang-pu JI, Xiu-fang HE, Hai-feng LIAO, Le-yang DAI, Di SUN, Gu-chang CAI
    2019, 47 (6): 114-120.   DOI: 10.11868/j.issn.1001-4381.2018.000277
    Abstract ( 605 ( PDF (10215KB)( 204 Citation

    Surface modified nano-flake Cu powder was prepared by plasma assisted ball milling by adding stearic acid as a process agent and its tribological properties were tested. The results indicate that the Cu particle exhibiting an excellent superplasticity has severe plastic deformation induced by a synergistic effect of plasma high-rate heating and electroplasticity, and the 20nm-thick flake-like Cu particles are obtained after 5h milling time of plasma milling. These nano-flake Cu particles owning oleophobicity characteristics exhibit good dispersion in the 40CA marine lubricating oil due to that the surface of Cu nano-flake adsorbs and chemically bonds with some non-polar groups under the plasma assisted ball milling with stearic acid. The severe deformation of the nano-flake Cu particles displaying high activation are easily adsorbed and spread on the surface of the friction counterpart in the process of sliding, which promotes a better wear resistance for compound lubricant with nano-flake Cu addition. Under a high rotating speed and excessive load, the nano-flake Cu powder provides excellent friction-reducing and self-repairing characters and improves the anti-wear performance under an extreme pressure condition.

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    Hot deformation behavior of new type of near β type Ti-5.5Mo-6V-7Cr-4Al-2Sn-1Fe alloy
    Qiang ZHOU, Jun CHENG, Zhen-tao YU, Wen-fang CUI
    2019, 47 (6): 121-128.   DOI: 10.11868/j.issn.1001-4381.2018.000273
    Abstract ( 577 ( PDF (6412KB)( 168 Citation

    The isothermal constant strain rate compression tests of Ti-5.5Mo-6V-7Cr-4Al-2Sn-1Fe alloy were conducted by Gleeble-3800 simulator. The hot deformation temperature range is from 655℃ to 855℃ and the strain rate range is from 0.001s-1 to 10s-1 and the maximum true strain is 0.8. A high temperature flow stress model was built with activation energy of 255kJ/mol according to the experimental results for the alloy and the processing map of alloy was constructed according to DMM model. The metallographic analysis of alloy shows that the alloy exhibits domain of flow localization and adiabatic shear bands and low power dissipation efficiency in the high strain rate(1-10s-1). The alloy undergoes dynamic recovery in the temperature region of 655-755℃ and the strain rate below 0.01s-1. The dynamic recrystallization takes place at the strain rate below 0.01s-1 and in the temperature region of 755-855℃, the original deformed grains and recrystallized grains gradually grow with the increase of temperature. When the temperature is 755-770℃ and the strain rate is 0.001-0.003s-1, the alloy's power dissipation efficiency reaches the maximum and the recrystallized grain is uniform and fine. These regions can be considered as the optimal parameter range of isothermal compression for the alloy.

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    Effect of rare earth element Gd on microstructure and mechanical properties of Al-Si-Mg cast alloy
    Wen-yi LIU, Cong XU, Mao-wen LIU, Wen-long XIAO, Chao-li MA
    2019, 47 (6): 129-135.   DOI: 10.11868/j.issn.1001-4381.2017.000076
    Abstract ( 728 ( PDF (9381KB)( 303 Citation

    To systematically investigate the effect of rare earth element Gd on microstructure and mechanical properties of Al-Si-Mg(A357) cast alloy, A357 alloys with different Gd additions were investigated by OM, SEM, EPMA, XRD, DSC, TEM and tensile test. The results show that the addition of Gd can refine the grain and secondary dendrite arm spacing of the alloy. Besides, Gd refines eutectic Si, instead of transforming its morphology. The mechanical properties are improved by Gd addition due to obvious refinement of the grain and eutectic Si, the reduction of secondary dendrite arm spacing. For the A357-0.5Gd(mass fraction/%) alloy, the ultimate tensile strength(UTS) is 355MPa, which is 37MPa higher than that of the alloy without Gd. However, when increasing the Gd mass fraction to 1.0%, the formation of a high number of coarse Al2Si2 Gd results in the decrease of the mechanical properties of the alloy.The refinement mechanism of Gd was investigated.Combined with the TEM observation, it can be inferred that the Gd addition produces fewer twins but some nanosized particles within eutectic Si. The density of twins is not high enough to cause the morphology transition of eutectic Si. The refinement effect of Gd on eutectic Si may be attributed to the increase of constitutional overcooling and the formation of nanosized particles, inhibiting the growth of eutectic Si during solidification.

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    Influence of multi-stage aging heat treatment on precipitation microstructure and corrosion resistance of 7056 aluminum alloy
    Shu-min FAN, Song-yi CHEN, Xing-lin ZHANG, Liang ZHOU, Lan-ping HUANG, Kang-hua CHEN
    2019, 47 (6): 136-143.   DOI: 10.11868/j.issn.1001-4381.2017.001061
    Abstract ( 619 ( PDF (12613KB)( 464 Citation

    The influence of different multi-stage aging heat treatment on microstructure and corrosion resistance of 7056 alloy was investigated by the measurements of transmission electron microscope(TEM), scanning electron microscope(SEM), mechanical properties and electrical conductivity, exfoliation corrosion, slow strain rate testing(SSRT), Tafel cyclic polarization. The results show that after over-aging and re-aging heat treatment, the solute atoms precipitate again, and the volume fraction of the precipitate in the matrix increases, the grain boundary precipitates coarsen and become discontinuous, the precipitate-free zone becomes wider. Compared with 120℃/24h pre-aging, 120℃/6h has advantage in terms of dissolution of finer precipitates and the growth of large coarse phase. Re-aging heat treatment can improve the strength and conductivity of over-aging alloys; compared with peak aging and retrogression and re-aging, the loss of tensile strength of the alloy is not significant, while the conductivity increases obviously. After over-aging and re-aging heat treatment, continuous anodic dissolution is avoided effectively, and the exfoliation corrosion resistance and stress corrosion cracking is enhanced.

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    Flow stress curve correction and phenomenological constitutive relationship of A100 ultra-high strength steel
    Shu-jie REN, Fei LUO, Ye TIAN, Da-bo LIU, Ke-lu WANG, Shi-qiang LU
    2019, 47 (6): 144-151.   DOI: 10.11868/j.issn.1001-4381.2017.000853
    Abstract ( 693 ( PDF (1616KB)( 292 Citation

    The flow stress curves in the deformation temperature range of 850-1200℃, the strain rate of 0.001-10s-1 and the deformation degree of 60% were obtained by hot compression test of A100 ultra-high strength steel on Gleeble-3500 thermal mechanical simulator. The effect of friction and temperature rise on the flow stress during the hot compression process was analyzed, and the flow stress curves were corrected. Phenomenological constitutive model based on introducing the strain parameter was established by the Arrhenius hyperbolic sine function equation. The results show that the influence of friction and temperature rise on the flow stress is gradually obvious with the decrease of deformation temperature or the increase of strain rate. Through comparison between experimental and predicted values, the absolute average relative error is 4.902% and the correlation coefficient is 0.99. It is revealed that the established constitutive model can accurately predict the flow stress under different strains.

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    Effect of heat treatment temperature on microstructure and properties of new maraging stainless steel
    Fei-yun WANG, Jian-jun JIN, Zhi-hua JIANG, Xiao-zhen WANG, Chun-wen HU
    2019, 47 (6): 152-160.   DOI: 10.11868/j.issn.1001-4381.2017.000993
    Abstract ( 752 ( PDF (13950KB)( 306 Citation

    The mechanical properties and microstructure of tested steel strengthened via Al at different solution and aging temperatures were studied by mechanical property test, optical microscope and transmission electron microscope. The results show that the tensile strength and yield strength of tested steel reach up to 1876MPa and 1762MPa respectively, with the higher strength and better match of toughness. Fine lath martensite with high-density dislocations is formed after solution and the precipitation of dispersive NiAl phase from matrix makes the strength greatly improved during the aging. The strength of tested steel decreases rapidly after reaching peak due to the coarsening of particles, namely, overaging phenomenon occurs. The optimum comprehensive mechanical properties of tested steel can be obtained after solution treatment at 820℃, cold treatment at -70℃ and aging treatment at 540℃.

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    Effect of recrystallization on axial high cycle fatigue properties of DD6 single crystal superalloy
    Mei HAN, Hong-ji XIE, Jia-rong LI, Jian-min DONG, Xiao-dai YUE, Jian YU, Liang YANG
    2019, 47 (6): 161-168.   DOI: 10.11868/j.issn.1001-4381.2019.000089
    Abstract ( 753 ( PDF (20497KB)( 261 Citation

    In order to study the effect of recrystallization on the high cycle fatigue (HCF) properties of DD6 single crystal superalloy, the specimens of DD6 alloy after standard heat treatment were grit blasted and heat treated at 1120℃ and 1315℃ for 4h at vacuum atmosphere, respectively. Axial HCF tests on both raw and recrystallized samples were carried out, and then the recrystallization microstructures and fatigue fracture morphology of DD6 alloy were observed by SEM. The results show that cellular recrystallization and equiaxed recrystallization reduce the axial HCF properties of the alloy, and the effect of cellular recrystallization on the axial HCF properties is less than that of the equiaxed recrystallization. The axial HCF fracture mechanism of DD6 alloy with recrystallization is the maxed fracture of dimple fracture distributed in interdendritic region and cleavage-like fracture. Also, it is emphasized that DD6 alloy with recrystallization is a multiple fatigue crack initiation mechanism. Under high temperature conditions, the presence of recrystallization significantly promotes oxidative damage of alloy specimens, thereby accelerating the earlier crack initiation and propagation, which is responsible for fatigue degradation.

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