航空材料学报

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2020, 40(4): 1-2.

[Abstract](3439) [FullText HTML] (1294) [PDF 2329KB](28)

Abstract:

Novel strategy for low-temperature vacuum preparation of high-quality graphene

Xin QI, Xiang CHEN, Bingtian LI, Chen WANG, Xiuhui LI, Shaojiu YAN

2020, 40(4): 1-8.

[Abstract](4117) [FullText HTML] (2130) [PDF 1266KB](45)

Abstract:
Previously, the preparation of graphene often required one or more of strong acid oxidants, reduction temperatures above 1000 ℃,expensive metal catalysts, and accompanied by the problems of low efficiency, high and heavy pollution. Our work provided a novel strategy for low-temperature vacuum preparation of high-quality graphene. Anhydrous AlCl₃ and FeCl₃ were used as bi-intercalants to prepare stage-1 graphite intercalation compounds (AlCl₃-FeCl₃-GICs) with accordion-like structure. Vacuum treatment of stage-1 AlCl₃-FeCl₃-GICs at a relatively low temperature of 180 ℃, low-boiling-point AlCl₃ was heated and vaporized to further stretch the graphite sheet to obtain worm-like expanded graphite. The expanded graphite could maintain a loose structure under atmospheric conditions and was not collapsed. The effect of van der Waals force between the sheets of adjacent graphite layers was greatly weakened, which made the expanded graphite easily to be exfoliated. High-quality graphene was obtained by ultrasonic treatment of expanded graphite in solvent using liquid-phase exfoliation method. The preparation process of expanded graphite did not use strong oxidants, and was carried out in an anhydrous and oxygen-free environment. The reaction temperature was also controlled within 180 ℃. The overall preparation conditions were relatively mild and environmentally friendly. The preparation of graphene by the liquid-phase method could avoid the destruction of the graphene lattice structure as much as possible. The scanning electron microscope (SEM), transmission electron microscope (TEM) and atomic force microscope (AFM) were used to observe the microscopic morphology of graphene, and the X-ray powder diffraction (XRD) instrument, ray photoelectron spectroscopy (XPS) instrument and Raman spectrometer were used to characterize the microstructure of graphene. The results show that the prepared graphene has extremely low defects, the sp² lattice structure still maintains a high degree of regularity, and most graphene layers are within three.

Effect of physical and chemical parameters of graphene on friction and wear properties of PTFE filled with low content graphene

Qiaosi ZHU, Jiongli LI, Jianqiang GUO, Xuerui LI, Jiafeng LIANG, Yue LI, Xudong WANG

2020, 40(4): 9-18.

[Abstract](5109) [FullText HTML] (2318) [PDF 1561KB](167)

Abstract:
4 types of graphene were used to fabricate graphene/polytetrafluoroethylene (PTFE) composites with loadings of 0.5% and 1% respectively. The average size, thickness, specific surface area and carbon/oxygen ratio (C/O ratio) of these graphene were characterized by SEM, AFM, BET and XPS. The friction coefficient was performed on the Controllable Environment Friction and Wear Instrument. The volume wear rate was carried out with the 3D White Light Interferometer. The results show that at the same load, the C/O ratio of graphene is the main factor affecting the friction coefficient of the composites, while the specific surface area of graphene is the main factor affecting the volume wear rate of the composites. With the addition of 1%（mass fraction, the same below） graphene in PTFE, the friction coefficient is reduced by 27.97% when the C/O ratio reaches 45.64 and the carbon content reaches 97.66%. With a specific surface area reaches 466.78 m²/g, graphene can reduce the volume wear rate of the PTFE composite by 76.46%.

Zr₃O-ZrC/graphene strengthened layer directly prepared on the surface of metal Zr by plasma heat treatment

Yifei CHENG, Fei LUO, Dabo LIU, Haitao ZHOU, Ye TIAN, Bingwei LUO

2020, 40(4): 19-24.

[Abstract](2665) [FullText HTML] (1345) [PDF 781KB](21)

Abstract:
Zr₃O-ZrC/graphene composite layer was directly in-situ grown on the surface of Zr foil by plasma heat treatment method. The microstructure and component of the as-prepared sample were systematically characterized by X-ray diffraction (XRD), Raman spectrum and scanning electron microscopy (SEM). The surface hardness was both characterized by micro hardness tester and nanoindentor. The results show that the composite layer was uniformly distributed on the surface of Zr foil. The surface hardness values of pure Zr foil and Zr/Zr₃O-ZrC/graphene composite were 195 HV and 639 HV, respectively. The surface hardness of the TiC/graphene layer can be signi?cantly increased 3.2 times as that of the pure Zr foil surface. Nanoindentor results showed the signi?cantly improved surface hardness could be attributed to the Zr₃O-ZrC layers. This study provides a particular heat treatment process for significant reinforcement of Zr and its alloys, and showing its great potential application for the future .

Microstructure evolution and comprehensive mechanical properties of β/B2 processed Ti-22Al-23Nb-2（Mo，Zr） alloy

Yi ZHOU, Jingxia CAO, Xu HUANG, Qiming TAN, Nan SUI, Mingda ZHANG

2020, 40(4): 25-35.

[Abstract](2386) [FullText HTML] (1372) [PDF 3273KB](30)

Abstract:
Quinary Ti-22Al-23Nb-2(Mo, Zr) alloy has a broad application prospect in the aeroengine field. The temperature ranges of phase regions, β/B2 processing, heat treatment and the corresponding mechanical properties were investigated by SEM, TEM and multi mechanical testing machines. The results show that the alloy goes through B2, B2+α₂, B2+α₂+O and B2+O four phase regions in the sequence from high temperature to low temperature, the corresponding critical temperatures are 1060 ℃, 950 ℃ and 930 ℃ respectively. The composition and morphology of the grain boundary phase are influenced by the collective effect of distortion degree of B2 grains and heat treatment. Coarse discontinuous α₂ phase is easy to form at the boundaries of original B2 grains with high distortion degree, and is converted into α₂+O_rim structure if heat treated at B2+O phase region; The fine continuous O phase is inclined to form at the boundaries of dynamic recrystallized B2 grains with low distortion degree, which can be completely transformed into α₂ if heat treated at B2+α₂ phase region; no phase is formed at the boundaries of static recrystallized B2 grains. Precipitates within B2 grains are mainly influenced by heat treatment. α₂ and O can directly and independently precipitate from B2, O can also attach α₂ to form an α₂/O_rim core-shell structure. The α₂/O_rim core-shell structure indicates α₂ has good stability at low temperature. After solid solution and aging treated, mixed microstructure with bi-size precipitates emerge within B2 grains, which can be coarse α₂/O_rim+ fine O or coarse O_I+O_II with the corresponding solution treatment at B2+α₂ and B2+O respectively. The size distribution of B2 precipitated phase in grain is the main factor affecting the mechanical properties . Larger size is favorable for the ductility and toughness of alloy, but unfavorable for strength and creep resistance.

High temperature fatigue-creep interactive behavior and life prediction of a TiAl alloy

Chengli DONG, Xiaoan HU

2020, 40(4): 36-44.

[Abstract](2623) [FullText HTML] (1359) [PDF 1255KB](41)

Abstract:
The strain controlled low cycle fatigue (LCF) and creep-fatigue interaction (CFI) tests of a TiAl alloy were conducted at 750 °C in air. The strain ratio, strain amplitude and strain rate were –1, 0.4% and 1 × 10^–3s^–1 respectively. The high temperature LCF and CFI stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life were studied and compared in details. Morrow modified method and unified life model developed in the present study were employed to predict the fatigue life for LCF and CFI life of TiAl alloy. Finally, the failure mechanisms between LCF and CFI specimens were compared, and some interesting conclusions were obtained. The results show that: (1) there are obvious differences on stress-strain stable hysteresis loop, cyclic hardening/softening, mean stress relaxation and life between LCF and CFI tests; (2) Morrow modified method is not able to predict the fatigue life for LCF and CFI life for TiAl alloy, however, the predicted fatigue life by the unified life model is located in the scatter band of ± 1.5; (3) the fatigue cracks are initiated from the surface for all of LCF and CFI specimens, and LCF specimens show more transgranular appearance while CFI specimens show obvious mixed appearance of both transgranular and intergranular.

Formation of abnormal structure in ZTA15 titanium alloy casting and its impact mechanism on tensile behavior

Gaoyang LIU, Wenxia ZHAO, Xi WANG

2020, 40(4): 45-51.

[Abstract](2766) [FullText HTML] (1356) [PDF 1471KB](25)

Abstract:
Partial block-dropping phenomenon was existed during the precision process of TA15 titanium alloy casting. In view of multiple means of microscopic physical characterization analysis such as OM/SEM/EDS/XRD and by considering the tensile performance results, the microstructure and mechanical properties between block-dropping area and the regular areahad been investigated. This article focused on the impact mechanism on tensile behavior that generated from the abnormal structure of block-dropping area. The results reveal that both the block-dropping area and the regular area show bi-modal microstructure, whereas the β phase concentration of the block-dropping area is far beyond the regular area and emerges as β spot. Microanalysis shows that the segregation of Fe is the major factor causing the abnormal structure and β spot, as well as the sharp plasticity decreases of alloy. The segregated Fe alters the microstructure and properties of the alloy, mainly because the saturation of Fe in α-Ti is only 0.1%, which leads to the formation of brittle TiFe eutectic phase. The increase of strength reduces the plasticity of the alloy casting, and further lead to the block-dropping during the process.

Microstructure and mechanical properties of TiZrHfNbMo high-entropy alloy and Ti-based composites brazed joint

Peng HUANG, Dongdong ZHU, Gang WANG, Duo DONG, Xiaohong WANG

2020, 40(4): 52-61.

[Abstract](3497) [FullText HTML] (1436) [PDF 1782KB](33)

Abstract:
TiZrHfNbMo high-entropy alloy and titanium matrix composite were vacuum brazed using carbon nanotubes reinforced AgCuTi composite filler. Microstructure and mechanical properties of the joints were systematically studied by X-ray diffractometer, scanning electron microscopy, energy spectrum and universal testing machine. The results show that the joints brazed at different temperatures from 820 °C to 910 °C for 15 min are successfully connected. The microstructure of the joint is composed of Ag(s,s), Cu(s,s), Ti(s,s), CuTi, ZrCu and CuTi2, the base material elements are fully diffused in the joint. When the brazing holding time is fixed, the shear strength of the joint at room temperature increases first and then decreases with the increase of brazing temperature. The formation of a certain amount of Ti-Cu intermetallic compounds widens the thickness of the reaction layer and improves the strength of the joint, while the formation of excessive Ti-Cu intermetallic compounds weakens the joint ability to relieve stress through plastic deformation, leading to a significant reduction in the joint strength. The best welded joint is obtained when the brazing temperature is 850 ℃ and the holding time is 15 min. The shear strength is up to 146 MPa, and the fracture mode of the shear fracture of the joint is brittle fracture.

Microstructure and mechanical behavior of CrCoNi medium entropy alloys in 1000 MPa grade

Lingyun SONG, Yanfei WANG, Mingsai WANG, Fengjiao GUO, Qiong HE, Hao RAN, Yong WEN, Chongxiang HUANG

2020, 40(4): 62-70.

[Abstract](2821) [FullText HTML] (1361) [PDF 986KB](44)

Abstract:
The ultrafine-grained (UFG) CrCoNi medium entropy alloys (MEAs) with excellent mechanical and tribological performances were fabricated by combining rolling deformation and annealing treatment. The microstructures of CrCoNi MEAs were characterized by electron backscatter diffraction (EBSD) and transmission electron microscope (TEM). The results show that the materials annealed at 650 ℃ for 10 min after cryogenic rolling display a yield strength as high as 1135 MPa and a graceful uniform ductility of 14.1%. Another group of materials rolled at room temperature followed by annealing at 650 ℃ for 20 min exhibit a yield strength of 987 MPa and an improved ductility of 18.6%. In addition, the grains of CrCoNi medium entropy alloys after above treatment are greatly refined to an average grain size of 0.81 μm and 0.92 μm respectively. The ultra-high strength is due to the grain boundary strengthening of high angle boundaries and dislocation strengthening of low angle boundaries. Remarkably, such UFG MEAs exhibit high wear resistance.

Development and experimental study on linear friction welding titanium alloy blisk

Zuojun LI, Wei TIAN, Tiancang ZHANG, Yajuan JI, Yan ZHONG

2020, 40(4): 71-76.

[Abstract](2307) [FullText HTML] (1262) [PDF 828KB](34)

Abstract:
Taking the advanced aeroengine compressor blisk as the application object, the development and experimental study on the TC11/TC17 different materials linear friction welding integral blisk was carried out. The microstructure of welded joint was analyzed, the tensile and stress rupture properties of base metal and welded joint were compared, the vibration fatigue test on welded blade test pieces, and the overrunning test and low-cycle fatigue test on welding blisk were developed. The results show that the TC11/TC17 linear friction welding joint consists of five typical zones, they are TC11 base metal zone, TC11 thermal influence zone, weld zone, TC17 thermal influence zone and TC17 base metal zone. The tensile strength of the welded joint is basically equivalent to that of the TC11 base metal, elongation is equivalent to TC17 base metal; endurance strength lower than TC17 base metal, but less higher than TC11 base metal. The median fatigue life of welded blade test pieces with three weld positions is respectively 1.501 × 10⁶, 0.344 × 10⁶, and 0.132 × 10⁶ cycles, the fatigue crack isn’t at welding seam and thermal influence zone. The welding blisk pass the 115% overrunning test and 1000 cycles low-cycle fatigue test, the experiment results meet the requirement.

SUS304 stainless steel sheet adhesive spot welding and joint fatigue strength

Long ZHANG

2020, 40(4): 77-84.

[Abstract](3043) [FullText HTML] (1461) [PDF 926KB](25)

Abstract:
1.5 mm thick SUS304 austenitic steel sheet was used as the test material to study the spot weld bonding process and fatigue performance. The joint performance was analyzed by the process, strength distribution, fatigue life and F-N curve. The effectiveness of experimental data was analyzed by t distribution, pivot method and Weibull distribution. Results show that under the same parameters, the nugget diameter of the spot weld bonding joint is larger than the resistance spot welding joint. The static strength of the spot weld bonding joint is decreased by 25% compared with the spot weld, and it is increased by 33% compared with the adhesive joint. At the same loading level, the fatigue life of the spot weld bonding joint is increased by 60%-100% compared with the spot weld.

Comparative study of several different modeling methods for clossed- cell metal foam

Yazhou GUO, Xiaochuan LIU, Chunyu BAI, Zhijun ZHENG, Jizhen WANG

2020, 40(4): 85-91.

[Abstract](2739) [FullText HTML] (1320) [PDF 1015KB](30)

Abstract:
In order to study the uniaxial compression properties of closed-cell metal foam, three different modeling methods were used in this paper to establish 2D random cell, 3D Kelvin and 3D voronoi metal foam model. Based on the LS-DYNA software, the differences of the compressive mechanical properties of the closed-cell metal foam under three different models were analyzed. The deformation mode and the stress strain response of the metal foam under three models were studied. The results show that 2D random cell model is more suitable for the study of the compression regularity of metal foam, and the 3D model is more suitable for the prediction and optimization of the compression response of metal foam. The 2D random cell model is restricted by its plane geometry, it can only simulate the closed-cell metal foam with low porosity in most cases. The Kelvin model and Voronoi model can simulate the closed- cell metal foam with high porosity. Compared with the Kelvin model and 2D random cell model, the voronoi model is more realistic and reasonable, and it is able to better characterize the compressive mechanical properties of closed-cell metal foam.

Comparative study on absorbing characteristics of aperture-type and patch-type FSS

Xujiong YUAN, Wenyan LIU, Yan WANG, Zetao LU, Youwei ZHANG, Muchou HAN, Xiao LI, Min LIU

2020, 40(4): 92-98.

[Abstract](2995) [FullText HTML] (1702) [PDF 776KB](46)

Abstract:
Aperture-type and patch-type frequency selective surfaces (FSS) were prepared by using carbon fiber paper containing carbon fiber. Using honeycomb as the matching dielectric layer, microscopic characterization of carbon fiber distribution in carbon fiber paper was performed by stereo microscope, the reflectivity of the composite FSS structure was tested by a vector network analyzer. The influences of unit shape, carbon fiber content in carbon fibre paper and carbon fiber length on the wave absorbing performance of aperture type FSS and patch type FSS were studied with the same matrix area ratio of carbon fiber paper. The results show that in the range of 2-18 GHz, the absorbing properties of aperture-type FSS and patch-type FSS are related to the content and length of carbon fiber in carbon fiber paper, and has nothing to do with the shape of the unit. At 6-18 GHz, with the same the ratio of the matrix area of carbon fiber paper, the shape of unit, the length and content of carbon fiber in the carbon fiber paper, the absorbing properties of aperture-type FSS are better than that of patch-type FSS.

Research on stepped cohesive joint repair slope of composite laminates based on finite element numerical simulation

Fen YU, Tuo GUO, Wushuai LIU, Boning AN, Diankai DENG, Zhenpeng HE

2020, 40(4): 99-108.

[Abstract](2576) [FullText HTML] (1474) [PDF 1414KB](28)

Abstract:
The progressive damage analysis model of stepped adhesive repairing structure was established to study the ultimate load-bearing strength and failure mode of laminates under axial tensile load after stepped adhesive repairing, and the effect of different slope repairing technology on the strength of repaired laminate was further studied. By compiling VUMAT subroutine, failure criteria and stiffness degradation models of laminate and patch were set respectively, and cohesive element was selected to simulate the adhesive layer to complete progressive damage analysis of composite laminates with stepped adhesive repair structure. The results show that the ultimate tensile strength increases with the decrease of slope, but the strength recovery rate does not change much when the slope is 1:20 or less. The adhesive layer at the 0° laminate connection first occurs damage and extends along the direction perpendicular to the loading until failure, and then causes the damage of laminate and patch. The effective adhesive area of the cohesive layer increases with the decrease of the slope, which can effectively alleviate the stress concentration phenomenon; The tensile failure of laminate first occurs at the minimum radius of the damage area, and the tensile failure of fibers first occurs at the 0° laminate and then extends perpendicular to the loading direction.

Dielectric properties of multi-phase carbon nanofiber/polyethylene composites

Lili SUN, Nan WU, Rui PENG

2020, 40(4): 109-115.

[Abstract](2736) [FullText HTML] (1468) [PDF 1123KB](23)

Abstract:
An attractive type of nanofiller-carbon nanofiber (CNF) was used to modify High-density Polyethylene (HDPE) and polymer blends (UH-HDPE) of HDPE and ultra-high molecular weight polyethylene (UHMWPE), and two-phase and three-phase nanocomposites were prepared via a two-step process including melt mixing and hot press. The effects of CNF addition and their dispersion on the dielectric properties of nanocomposites were investigated. The results show that CNFs are well dispersed in HDPE matrix, while they are not permeated into the UHMWPE. It is demonstrated that CNFs are distributed homogenously in two-phase CNF/HDPE composites and heterogeneously in three-phase CNF/UH-HDPE composites. The dielectric constant of nanocomposites is dramatically improved with higher CNF content. The highest dielectric constant in CNF/HDPE composites, 190 at 102 Hz, is achieved with CNFs above 10% (mass fraction, the same as below), which is about 50 times higher than that of pure HDPE. Simultaneously, the dielectric constant of CNF/HDPE composites shows high dependence on the frequency due to the existence of CNFs, compared with the independent dielectric constant of pure HDPE. The influence of CNFs on the dielectric constant of CNF/UH-HDPE composites is similar to that of CNF/HDPE composites. However, the dielectric constant of three-phase composites is higher than that of two-phase counterparts with the same CNF addition. Additionally, no obvious dielectric loss is exhibited in both nanocomposites with CNF concentration under 5%.

2020 Vol. 40, No. 4