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2020 Vol. 25, No. 2
Published: 2020-04-15
Engineering and Technology
Theoretical Research
Theoretical Research
91
Two-phase model calculation of diffraction elastic constant of crystal plane at different temperature
XU Haifeng, ZHU Changjun, CHEN Kanghua, LIU Li
Nickel-based superalloy can be regarded as a two-phase material with matrix phase (Ni phase) and mixed phase (Ni
3
Al phase) (ignoring a few other phases). A two phase model for calculating diffraction elastic constant is established by self-consistent way, combined with Eshelby inclusion theory. The elastic stiffness coefficient of two-phase single crystal at high temperature is obtained by quasi harmonic Debye theory and first principle calculation, and the diffraction elastic constants of related crystal surfaces of nickel base superalloy at different temperatures are calculated by substituting the model. The accuracy of the model is verified by the small error between the calculated results and the experimental measurements reported in the literature.
2020 Vol. 25 (2): 91-97 [
Abstract
] (
342
)
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231
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98
Thermodynamic analysis of Ti
2
AlNb-based alloy in the initial stage of high temperature oxidation
YANG Jiajun, LIU Libin, ZHAO Yun, ZHANG Ligang
The initial oxidation products of Ti-22Al-
x
Nb(
x
=0-30%, mole fraction) alloy at 1 000 ℃ were calculated by phase diagram calculation. The changes of mass fraction and phase composition of Ti-22Al-27Nb and Ti-22Al-15Nb alloys at the initial stage of oxidation at this temperature were predicted. The results show that, with the increase of oxygen partial pressure, Bcc_B2 phase in the matrix changes to Hcp_A3 phase to dissolve the increased O(oxygen). The oxidation order of the elements in the alloy is Al, Ti, Nb. Al
2
O
3
, Halite(TiO) and NbO appear at the oxygen partial pressures of 4.72×10
-32
MPa, 4.11×10
-30
MPa and 5.53×10
-25
MPa, respectively. With the increase of oxygen partial pressure, the oxidation products of Ti and Nb tend to higher oxygen content. Compared with Ti-22Al-27Nb, the mass fractions of NbO and NbO
2
in Ti-22Al-15Nb alloy decrease obviously, while the mass fraction of Al
2
O
3
increases obviously.
2020 Vol. 25 (2): 98-103 [
Abstract
] (
343
)
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223
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Engineering and Technology
104
Structure and mechanical properties of ordered graphene toughened zirconia ceramics prepared by tape casting
CAI Weijin, LI Qing, LIU Yao, LIU Shaojun
Tetragonal zircona polycrysta (TZP) ceramics toughened by graphene nanosheets (GNS) were prepared by tape casting and spark plasma sintering. The effects of graphene content (volume fraction, the same below) on the phase composition, microstructure, hardness and fracture toughness of GNS/TZP ceramics were studied, and the toughening mechanism of ordered arrangement of graphene was further analyzed. The results show that,the addition of a small amount of graphene can significantly improve the fracture toughness of ceramics. The fracture toughness of zirconia ceramics with 0.25% graphene increases from 4.39 MPa·m
0.5
to 7.21 MPa·m
0.5
, increased by 64.1%, and the hardness (HV
20
) decreases to 1 345.3, dcreased by less than 1%. The mechanism of toughening zirconia ceramics is mainly crack deflection and synergistic with various mechanisms.
2020 Vol. 25 (2): 104-111 [
Abstract
] (
397
)
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251
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112
Defect formation mechanism and influence factors of narrow gap multi-pass fiber laser welding of S275 ferritic steel sheets
ZHANG Hong
The narrow gap multi-pass laser welding with filler wire addition of 30-mm-thick S275 ferritic steel was investigated in this paper. The purpose of this paper is to understand the formation mechanism and influencing factors of laser welding defects, in order to optimize the welding process and avoid the formation of cracks, lack of fusion, porosity and other defects. The experimental results show that, properly increasing the heat input can reduce the cooling rate of molten pool and restrain the generation of welding cracks. When the heat input is 0.9 kJ/mm, the longitudinal surface crack is 2.3 mm deep. When the heat input increases to 1.05 kJ/mm, the depth of longitudinal surface crack decreases to 0.8 mm. When the heat input reaches 1.2 kJ/mm, no crack is found in the joint. Choosing a smaller distance between the laser and wire can ensure the contact between the molten metal and the weld pool, and avoid the lack of fusion on the side wall. When the distance between the smooth wires is 1mm, no fusion or splashing is found on the groove side wall. When the distance between the laser and wire is 3 mm, the side wall is not fused. When the distance between the laser and wire 5 mm, the deposited metal is found above the side wall of the welding groove. When a 15 mm diameter pipe is used to transport protective gas at the top of the groove, a large number of air holes can be avoided. The welding joint with better mechanical properties can be obtained by using 6 m/min wire feeding speed.
2020 Vol. 25 (2): 112-117 [
Abstract
] (
299
)
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168
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118
Preparation and properties of HfB
2
-ZrB
2
-SiC modified C/C composites
XIANG Qiuling, TANG Zhenxiao, PENG Ke, YI Maozhong
C/C-HfB
2
-ZrB
2
-SiC composites with a density of 3.37 g/cm
3
were prepared by high-solid-loading slurry impregnation and densified by polycarbosilane precursor infiltration and pyrolysis process, and the high-solid-loading slurry consist of HfB
2
and ZrB
2
ceramic powders with a volume fraction of 1:1. The microstructure, mechanical properties and ablation resistance of the composites were investigated. The results show that HfB
2
and ZrB
2
ceramic particles introduced by slurry impregnation method are mainly distributed in short cut fiber web layer and needle-punched area of C/C composites. SiC obtained by polycarbosilane precursor infiltration and pyrolysis process mainly distributes between ceramic particles and fiber bundles. HfB
2
, ZrB
2
and SiC are uniformly filled in the materials. The bending strength and fracture toughnes of the C/C-HfB
2
-ZrB
2
-SiC composites are 382.6 MPa and 11.2 MPa∙m
1/2
respectively, showing obvious pseudoplastic fracture characteristics. In the process of ablation, the formation of HfO
2
-ZrO
2
mixed layer preventes oxygen from entering into the composites, which improves the ablation resistance of the material. C/C-HfB
2
-ZrB
2
-SiC composites exhibit good ablation resistance at 2 500 ℃. The linear and mass ablation rates after ablation for 120 s are 0.71 μm/s and 0.53 mg/s.
2020 Vol. 25 (2): 118-124 [
Abstract
] (
533
)
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382
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125
Microstructure and flow stress behavior of 2055 Al-Li alloy under hot tension
LIU Ning, XIAO Daihong, LIU Wensheng
The hot deformation behavior and microstructure evolution of 2055 Al-Li alloy have been investigated by subjecting the alloy to hot tensile tests carried out on Gleeble-1500 thermal simulator at the temperatures varied from 480-540 ℃ and strain rates 0.000 1-0.1 s
-1
. The microstructures of the alloy during deformation was studied by OM, TEM and EBSD. The results show that there are three stages in the hot stretching process and the deformation mechanism is different in each stage. In the process of hot stretching, it shows obvious rheological stability, the change from dynamic recovery to dynamic recrystallization is the main mechanism. When strain rate is 0.001 s
-1
and deformation temperature is 480 ℃, the recrystallization nucleus are difficult observed. When the temperature are 510 ℃ and 540 ℃, serrated grain boundary appears. The higher the temperature is, the more obvious phenomenon of serrated grain boundary appears, which belongs to typical geometric dynamic recrystallization. At a certain temperature, the lower the strain rate is, the smaller the peak stress of the alloy is, which indicates that 2055 Al-Li alloy has the sensitivity of normal strain rate. The constitutive equation of hyperbolic sine function including deformation activation energy Q and temperature T proposed by Sellars and Tegart are used to describe the thermal activation behavior of the alloy. The activation energy of thermal deformation is 226.783 kJ/mol.
2020 Vol. 25 (2): 125-132 [
Abstract
] (
389
)
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268
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133
Structure and properties of SiC ceramics prepared by dip cracking method based on oriented porous SiC
HUANG Yujuan, XIONG Huiwen, ZOU Jinzhu, ZHOU Kechao, ZHANG Dou
The porous SiC scaffolds were prepared by freeze casting, and then the porous scaffolds were impregnated and cracked by liquid polycarbosilane (LPVCS) to prepared SiC ceramics. The effects of the number of immersion cracking cycles on the density, porosity, microstructure and bending strength of SiC flexural were studied. The results show that, the porous SiC scaffolds formed by freeze casting are oriented porous dendrites. The density, porosity and flexural strength of the scaffolds are 0.45 g/cm
3
, 87.7% and 8.53 MPa, respectively. The density, porosity and flexural strength of SiC composites are 2.08 g/cm
3
, 5.9%, and 157.43 MPa, respectively. SiC ceramic material with lower density and good flexural strength can be otained by this method.
2020 Vol. 25 (2): 133-139 [
Abstract
] (
354
)
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194
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140
Effect of powder surface modification on the stereolithography of zirconia
LI Qing, LIU Yao, CAI Weijin, SHI Yuan, LIU Shaojun
The surface of ZrO
2
powder was modified by MAA, 3-(isobutyryloxy) propyltrimethoxysilane (γ-MPS) and stearic acid (SA), and then the stereolithography slurry was prepared. By means of infrared spectrum, particle size analysis, sedimentation experiment and rheological test, the effect and mechanism of modifier on particle size distribution, stability and viscosity of slurry were studied. The results show that the modifier exists on the surface of ZrO
2
powder in the form of chemical adsorption, which can effectively reduce the agglomeration of powder. The surface modification of ZrO
2
powder can improve the stability and reduce the viscosity of the stereolithography slurry. Adding 0.5%MAA (mass fraction) has the best modification effect. The viscosity of the slurry decreases from 156.2 Pa·s to 47.1 Pa·s at the shear rate of 1 s
-1
. ZrO
2
green bodies are formed via stereolithography with slurry of 75% solid content and sintered at 1 500 ℃ for 3 h. ZrO
2
ceramics with density of 6.02 g/cm
3
and hardness (HV
10
) of 1 290 are obtained.
2020 Vol. 25 (2): 140-147 [
Abstract
] (
378
)
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238
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148
Microstructure and mechanical property of aluminum matrix composite strengthened by short carbon fiber with Ni-coating (SCF-Ni)
JIANG Wenting, LI Guodong, YANG Juan, LIU Yang, YU Shijie
The short carbon fiber that completely coated with nickel layer by electroless was prepared. The nickel-plated short carbon fibers (SCF-Ni) and the aluminum silicon alloy powder (Al-Si) were uniformly mixed by wet mixing method. The aluminum matrix composites strengthened by SCF-Ni were prepared by the plasma sintering technique (SPS). The surface of the carbon fibers and the morphology of the composites were observed by SEM and the interface of the composites was analyzed by XRD. The effects of the content of SCF-Ni on the microstructure and mechanical properties of the composites were investigated. The experimental results show that with the increase of the mass fraction of SCF-Ni, the density of the composites decreases, the hardness increases, and the room temperature tensile strength increases first and then decreases. When the mass fraction of SCF-Ni reaches 9%, the tensile strength reaches a maximum value (152 MPa), which is 68% higher than the tensile strength (90 MPa) of the substrate.
2020 Vol. 25 (2): 148-156 [
Abstract
] (
389
)
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201
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157
Effect of ZrB
2
content and sintering temperature on the microstructure and properties of ZrC-ZrB
2
composites
WANG Yuanyuan, FAN Jinglian, LU Qiong, HAO Ya’nan, GAO Yin
Using ZrC and ZrB
2
powders as raw materials, ZrC-ZrB
2
composite ceramic bulk materials with ZrB
2
content (mass fraction) of 5%, 10%, and 15% were prepared at 1 750 ℃ and 1 850 ℃ respectively by spark plasma sintering. The effects of ZrB
2
content on the microstructure and properties of the composites were studied. The results show that the surface morphology of ZrC-ZrB
2
composite is scaly, with the increase of ZrB
2
content, the grain becomes finer. When the sintering temperature is 1 750 ℃, with the increase of ZrB
2
content, the material density decreases, but the fracture toughness increases. When the content of ZrB
2
is 15%, the fracture toughness reaches 11.972 MPa·m
1/2
, while when the content of ZrB
2
is 10%, the hardness is the highest of 16.868 GPa. Compared with the ZrC-ZrB
2
composites sintered at 1 750 ℃, when the sintering temperature is 1 850 ℃, recrystallization and grain growth occur, and the overall mechanical properties decrease. With the increase of ZrB
2
content, the density of the composites decreases, but the size of grain decreases and mechanical properties increases.
2020 Vol. 25 (2): 157-163 [
Abstract
] (
396
)
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224
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164
Morphology and electrochemical performance of high temperature etching boron doped diamond electrode materials
LIU Ting, MIAO Dongtian, WEI Qiuping, MA Li
The boron doped diamond electrode was prepared by hot filament chemical vapor deposition, and then heat- treated at 800 ℃ for oxidation to obtain the boron doped diamond electrode with irregular pore structure. The effects of heat-treatment etching time on the surface morphology and the ratio of Sp
3
carbon and Sp
2
carbon (Sp
3
/Sp
2
) of the electrode were studied. The results show that the best time of heat treatment is 30 minutes, and the electrochemical active area of the electrode after heat treatment is 2.14 times of that without heat treatment. Boron doped diamond electrode is used to degrade the organic wastewater with Reactive Blue 19 as the target, the color removal rate of Reactive Blue 19 from the treated electrode is 2.43 times than that from the untreated electrode, the removal rate of chemical oxygen demand from the electrode after heat treatment is 1.89 times than that from the electrode without heat treatment, and the energy consumption to achieve the same chemical oxygen demand removal rate is lower than that of untreated electrode. This etching technology does not pollute the surface of boron doped diamond electrode. It is suitable for large area etching to improve the specific surface area of the electrode, and has a broad application prospect in the field of water treatment.
2020 Vol. 25 (2): 164-170 [
Abstract
] (
489
)
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227
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171
Microstructure and mechanical properties of C/C composites prepared by a novel slurry injection technique
HU Jiao, LI Guodong, ZHANG Yang, HAN Qianwu, JIANG Yi
C/C composites were fabricated by novel slurry injection and chemical vapor infiltration (CVI). In the slurry injection step, natural flake graphite was introduced to carbon fiber preform. Microstructure and mechanical properties of the as-fabricated C/C composites were analysed by X-ray nondestructive test, scanning electron microscope (SEM) polarizing microscope (PLM), and mechanical properties test. The results show that the flake graphite which replaces part of pyrolytic carbon can be introduced by slurry injection. This injected flake graphite can provide additional nucleation sites thereby greatly promoting densification rate of CVI process. The addition of natural flake graphite is beneficial to the formation of rough lamina (RL) pyrolytic carbon (PyC) and increases the degree of graphitization of the composites. After 80 h CVI, C/C composites with a density of 1.68 g/cm
3
and a flexural strength of 69.07 MPa are obtained. Compared with the C/C composites fabricated by traditional CVI process, the flexural strength is close while the average densification rate is nearly tripled. Moreover, carbon fibers and flake graphite are well connected by PyC and the obtained C/C composites shows pseudo-plasticity fracture.
2020 Vol. 25 (2): 171-178 [
Abstract
] (
437
)
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251
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179
Effect of carbon nanotube on thermal properties of copper foam/paraffin composite phase change materials
BAO Shengyou, AN Junjie, MA Li, WEI Qiuping, BO Zhenhai, ZHOU Kechao
Copper foam (CF), carbon nanotubes (CNT) and paraffin were used to prepare CF/mixed CNT/paraffin and CF/catalyzed CNT/paraffin composite phase change materials (PCM). The mass ratio of CNT and paraffin was 1:99. SEM and Raman spectra were used to characterize the morphology and quality of the samples. The thermal conductivity and phase change behavior of phase change materials were measured by laser thermal conductivity tester and differential scanning calorimeter. The results show that the composite PCM is well compounded, and the thermal conductivity of paraffin can be improved by introducing two kinds of CNT. Even though the quality of mixed CNT is better than that of catalytic CNT, compared with the thermal conductivity of CF/mixed CNT/paraffin composite (3.28 W/(m∙K)), the thermal conductivity of CF/catalytic CNT/paraffin sample increases to 3.94 W/(m∙K). In addition, two kinds of CNT can effectively improve the influence of supercooling degree and shape stability of the paraffin.
2020 Vol. 25 (2): 179-184 [
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425
)
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220
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