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2020 Vol. 25, No. 3
Published: 2020-06-15
Engineering and Technology
Engineering and Technology
185
Densification behavior of GH4169 ultra-fine curved surface irregular structures formed by high temperature and high pressure flexible media
MA Ding, LANG Lihui, XIAO Yi, MENG Fandi, LI Shiyue
The ceramic mold was used to control the shape and the GH4169 ultra-fine irregular curved surface was prepared under the high temperature and high pressure flexible medium, the thickness of the curved surface was 0.5 mm. The densification degree of the irregular curved surface was observed and analyzed by SEM. The results show that the densification degree of the curved surface is the densest at both ends, followed by the middle center, and the lowest at the middle edge. At the same time, the Shima-Oyane constitutive equation modified by the uniaxial tension experiment was used to simulate the numerical simulation. The distribution nephogram of density, equivalent Cauchy stress and displacement vector of the neutral surface of the irregular curved surface were obtained. The densification behavior of GH4169 powder in the rigid mold was described from the point of node displacement. The results show that in the process of hot isostatic pressing, the irregular surface shrinks inward along the thickness direction. The displacement of the two ends is the largest, and the density is the highest. The center position in the middle is lower, and the edge in the middle is the lowest. The simulation results are consistent with the experimental results.
2020 Vol. 25 (3): 185-190 [
Abstract
] (
537
)
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191
Densification process of pressureless sintered silicon nitride ceramics
LIU Wenyong, LI Jianbin, SUN Zhenfei, JIANG Qiangguo
Silicon nitride ceramics were prepared by pressureless sintering, with Al
2
O
3
-Y
2
O
3
as sintering aids, after dry pressing and cold isostatic pressing. The shrinkage and densification of Si
3
N
4
ceramics was observed in real time with TOM-AC high temperature sintering equipment. Meanwhile, the densification process of Si
3
N
4
ceramics was studied by analyzing the structure and morphology of ceramics sintered at different temperatures. The results show that α-Si
3
N
4
begins to transform into β-Si
3
N
4
at 1 400 ℃. The density increases rapidly in the range of 1 400-1 600 ℃, and the higher the density of compact, the faster the densification rate. When the sintering temperature is higher than 1 600 ℃, α-Si
3
N
4
transforms into β-Si
3
N
4
columnar crystal completely, and the crystal grain grows obviously, while the densification rate decreases. The compacts density has little effect on the final sintering density. The optimal sintering process is sintering at 1 650 ℃ and 1 800 ℃ for 2 h respectively. The density of Si
3
N
4
ceramics is 98.4%, and the hardness (HV
10
) is 15.7±0.5 GPa. The bending strength and fracture toughness are 1037.3±48.9 MPa and 5.8±0.2 MPa∙m1/2, respectively.
2020 Vol. 25 (3): 191-196 [
Abstract
] (
604
)
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1471
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197
Microstructure and mechanical properties of selective laser melting of (TiH
2
+TiB
2
)/AA7075 composite powders
OUYANG Sheng, LIU Yunzhong, SHEN Junjian, XIAO Xiaojun
0.6%-1.4% submicron TiH
2
and 0.8% nano-TiB
2
particles (mass fraction, the same as below) were added into AA7075 powders, low-energy ball milled (TiH
2
+TiB
2
)/AA7075 composite powders were used to fabricate composites by selective laser melting (SLM). Microstructures and mechanical properties of SLMed composites with different TiH
2
additive amounts were studied. The results show that the addition of submicron TiH
2
and nano-TiB
2
particles can significantly inhibit the cracks of SLMed AA7075 composites. The cracks can be completely eliminated when 1.4%TiH
2
and 0.8%TiB
2
are added. When the TiH
2
additive amount increases from 0.6% to 1.4%, columnar grains in the microstructure are all transformed into equiaxed grains, and the average grain size is refined to 1.38 μm from 2.33 μm. When the TiH
2
additive amount is 1.4%, the tensile strength, yield strength and elongation of the AA7075 composites are 360 MPa, 328 MPa and 12.0%, respectively. After T6 heat treatment, the properties are further improved. The tensile strength and yield strength increase to 461 MPa and 394 MPa, respectively, and the elongation increases to 15.3%.
2020 Vol. 25 (3): 197-205 [
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] (
447
)
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206
Preparation and properties of SiC coating on inner surface of Zr-cladding by PECVD at low temperature
TAN Ruixuan, WANG Honglei, YU Jinshan, LI Huailin, LIU Yanhong, FAN Zheqiong, LU Leiwen, ZHOU Xingui
A new and convenient plasma enhanced chemical vapor deposition (PECVD) method was proposed for the preparation of SiC coating with thickness of 3 μm and 5 μm respectively on the inner wall of slender Zr-alloy clad tube (outer diameter 9.5 mm, wall thickness 0.57 mm, length 200 mm). The microstructure of the coating was characterized by SEM and the properties of resistance to thermal shock and high temperature water vapor were tested. The results show that SiC can be deposited on inner surface of clad tube rapidly and effectively by PECVD. The prepared SiC coating is smooth, flat and dense, and the thickness of the coating is uniform no matter in the axial or radial direction of clad tube. The bonding between the SiC coating and Zr-alloy substrate is good enough to withstand high temperature quenching and water vapor oxidation at 1 200 ℃ without exfoliation. The SiC coating can effectively insulate Zr-alloy from high temperature water vapor, and protect Zr-alloy clad tube from oxidation.
2020 Vol. 25 (3): 206-212 [
Abstract
] (
602
)
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956
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213
Thermoelectric properties of Bi
x
Sb
2-
x
Te
3
alloy with layered microstructure optimized by microwave hot pressing
LIU Peihai, FENG Bo, HU Xiaoming, LI Rusong, ZHANG Yanglin, FAN Xi'an
The
p
-type Bi
x
Sb
2-x
Te
3
alloys with hierarchical microstructures were prepared by mechanical alloying and a new sintering technique of microwave activated hot pressing (MAHP). The effects of Bi content on the microstructure and thermoelectric properties of Bi
x
Sb
2-
x
Te
3
alloy were studied. The results show that there are irregular nanoparticles, which are in-situ nanostructures caused by microwave arc effect. With increasing Bi content, the electrical resistivity and Seebeck coefficient increase due to the obvious decrease of carrier concentration. At the same time, the lattice thermal conductivity increases due to the decrease in the amount of irregular nanograins. Bi
x
Sb
2-
x
Te
3
has a maximum power factor of 3.81 mW/(m·K
2
) and a minimum lattice thermal conductivity of 0.33 W/(m·K), so as to obtain the maximum dimensionless figure of merit value of 1.23 at 70 ℃. The MAHP technique introduced in this work has achieved a significant improvement in the thermoelectric properties of the Bi
x
Sb
2-
x
Te
3
alloy.
2020 Vol. 25 (3): 213-220 [
Abstract
] (
334
)
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697
)
221
Effect of B-site Hf doping on the structure and properties of 0.94Bi
0.5
Na
0.5
TiO
3
-0.06BaTiO
3
ceramics
PENG Congfei, HUANG Rongxia, LI Jiajiu, XIONG Shunjin, LIN Huatai
A series of HfO
2
-modified (Bi
0.5
Na
0.5
)
0.94
Ba
0.06
Ti
1-
x
Hf
x
O
3
(100BNBT-
x
Hf,
x
=0-2.0, mole fraction) ceramics were prepared by solid state sintering method, and Hf element was doped into BNBT ceramics in the form of HfO
2
. The effects of Hf element on crystal structure, microstructure and electrical properties of 100BNBT-
x
Hf samples were analyzed systematically. The results show that all 100BNBT-
x
Hf ceramics with pure perovskite structure were near the morphotropic phase boundary. The addition of Hf can promote the grain growth of 100BNBT-
x
Hf, and the average grain size of 100BNBT-1.0Hf were reached 2.30 μm. With the increase of Hf
4+
content, the ceramic changed from normal ferroelectric phase to relaxor ferroelectric phase and then to paraelectric phase at room temperature. The 100BNBT-1.0Hf showed the best excellent ferroelectricity, while the 100BNBT-2.0Hf ceramics displayed the best energy storage characteristics, and the energy storage efficiency reached 38.23%. In terms of field-induced strain, a large electro-strain of 0.35% and a large piezoelectric coefficient of 583 pm/V were obtained at
x
=1.0.
2020 Vol. 25 (3): 221-226 [
Abstract
] (
425
)
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(607 KB) (
952
)
227
Deoxygenation process of high oxygen niobium powders by magnesium reduction
LIU Fang, LI Qingkui, LUO Junfeng, XU Guojin, ZHANG Qiaoxia
Hydrogen-dehydrogenation and oxygen reduction equipment was used to reduce the oxygen content of the industrial niobium powder with an original oxygen content of 4.1×10
-3
by magnesium reduction. The effects of reduction temperature, reduction time and magnesium powder amount on the oxygen content of niobium powder were studied. The magnesium reduction and oxygen reduction process of niobium powder was optimized. The results show that when the reduction temperature is 1 133 K and the amount of magnesium is enough, the oxygen content of niobium powder decreases first and then tends to be stable with the increase of reduction time. The oxygen content of deoxidized niobium powder decreases from 8.90×10
-4
to 3.56×10
-4
with the increase of reduction temperature from 953 K to 1 133 K at 4 times of theoretical magnesium addition and 4 h of reduction time. With increasing the temperature to 1 203 K, the oxygen content of niobium powder increases instead. The best magnesium reduction process of niobium powder is that the reduction temperature is 1 133 k, the amount of magnesium is 4 times of the theoretical amount, the reduction time is 4 h, and the oxygen content of niobium powder after deoxidization is 3.56×10
-4
. The morphology of niobium powder is basically unchanged.
2020 Vol. 25 (3): 227-233 [
Abstract
] (
455
)
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(530 KB) (
621
)
234
Seawater cavitation resistance of supersonic sprayed nano-WC-10Co4Cr and WC-12Co coatings
FU Li, LIU Wei, CHEN Xiaoming, ZHAO Jian, LI Yuluo, ZHANG Lei
In order to improve the seawater resistance of marine equipment, WC-10Co4Cr coating and WC12-Co coating were prepared on the 45
#
steel matrixes using supersonic flame spraying technology (HVOF). The microstructures of WC-10Co4Cr, WC12-Co powders and coatings were analyzed by scanning electron microscope (SEM), and the porosity, microhardness, and electrochemical properties of the coating were tested. The coatings and substrate were subjected to a seawater cavitation resistance comparison experiment under 3.5%NaCl solution. The mechanism of coating seawater cavitation was discussed. The results show that the porosity of WC-10Co4Cr coating prepared by HVOF is 0.42%, the microhardness of the coating is 1 317 HV
0.2
. The porosity of the WC-12Co coating is 0.54%, and the microhardness of the coating is 1 253 HV
0.2
. The corrosion resistance of WC-10Co4Cr coating is better than that of WC-12Co coating. The impact toughness of WC-10Co4Cr coating is slightly better than that of WC-12Co coating. For seawater cavitation resistance, WC-10Co4Cr coating is better than WC-12Co coating, and WC-12Co coating is better than 45
#
steel. The micro--holes and cracks of WC-10Co4Cr coating and WC-12Co coating were expanded and fallen off under the action of cavitation impact force, internal stress, and Cl− in seawater.
2020 Vol. 25 (3): 234-238 [
Abstract
] (
309
)
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(1 KB)
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959
)
239
Effect of Er
2
O
3
on properties of 3D printed zirconia ceramic jewelry
WANG Shengliang, LI Lian, WANG Minglang, HE Fupo, LI Yanhui, WU Shanghua
Er
2
O
3
was added to ZrO
2
ceramic powder as a colorant, and digital light processing (DLP) 3D printing molding and 1 500 ℃ sintering are used to prepare magenta ZrO
2
ceramic jewelry. The effects of Er
2
O
3
on the mechanical properties, microstructure and color values (Lightness
L
*, red-greenness
a
* and yellow-blueness
b
*) of ZrO
2
ceramic jewelry were studied. The results show that with the increase of Er
2
O
3
content, ZrO
2
changes from tetragonal phase to cubic phase. The porosity increases slightly, and the relative density, hardness and fracture toughness decrease. Lightness
L
* decreases, and red-greenness
a
* increases. When the amount of Er
2
O
3
is 5%, the relative density of the ceramic is 93.16%; the Vickers hardness is 9.8±0.3 GPa; the fracture toughness is 5.0±0.4 MPa∙m
1/2
. The color values are
L
*=84.49,
a
*=14.57,
b
*=-2.54. The color is beautiful, and the magenta color is pure, which meets the aesthetic requirements.
2020 Vol. 25 (3): 239-244 [
Abstract
] (
487
)
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(0 KB)
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(533 KB) (
891
)
245
Crystallization mechanism and morphology of high purity titanium prepared by molten salt electrolysis
FENG Xiao, JIANG Yuanyuan, MA Xin, WENG Qigang, YUAN Tiechui, ZHOU Zhihui
Sodium chloride and potassium chloride were used as molten salt, and sponge titanium cathode was purified by molten salt electrolysis. According to the theoretical deduction of nucleation rate in the electrolysis process, the effects of electrolysis temperature and different proportion of molten salt on the crystal morphology of high purity titanium were analyzed, and the crystallization mechanism in the electrolysis process was studied. The results show that the size of crystalline Ti particles gradually increases with the increase of electrolytic temperature, and the crystalline particles gradually change from long strip or elliptic to dendritic. The increase of KCl content in molten salt will lead to the increase of molten salt resistance and the decrease of current efficiency, resulting in the decrease of crystalline Ti particle size, the loose of crystalline Ti and high salt inclusion rate. The microscopic characterization of crystalline Ti particles revealed that during the molten salt electrolysis process, the titanium crystals grew in steps, corresponding to two-dimensional nucleation. The electrolytic titanium powder is not a single crystal, but a polycrystal containing many nanocrystals and subcrystals, with a grain size range of 100-500 nm.
2020 Vol. 25 (3): 245-250 [
Abstract
] (
920
)
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(1217 KB) (
1920
)
251
Microstructures and mechanical properties of aluminum matrix composites reinforced with hybrid TiB
2
and SiC prepared by selective laser melting
SHEN Junjian, LIU Yunzhong, OUYANG Sheng, HONG Xuchao, LIU Xiaohui
The (TiB
2
+SiC)/AlSi10Mg composite powders, with 2% nano-TiB
2
particles and 1% submicron-SiC particles were prepared by low-energy ball milling and used for selective laser melting (SLM) process. The microstructures and mechanical properties of aluminum matrix composites (AMCs) reinforced with hybrid TiB
2
and SiC and AlSi10Mg alloy were studied by XRD, EBSD and SEM. The results show that the laser reflectivity of the composite powders reduces from 46% to 31% compared to that of AlSi10Mg alloy powders. AMCs reinforced with TiB
2
and SiC, with excellent properties, were successfully prepared by SLM at a low laser power of 240 W. Nano-TiB
2
particles and submicron-SiC particles are uniformly distributed inside the grains, but a few nano-TiB
2
particle sagglomerate and growup tomicron-scale. With the addition of nano-TiB
2
particles and submicron-SiC particles, the coarse columnar grains are transformed into equiaxed grains and the average grain size decreases from 7.88 μm to 2.48 μm. The tensile strength, ductility increase to 509.8 MPa, 10.6%, respectively.
2020 Vol. 25 (3): 251-259 [
Abstract
] (
427
)
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1284
)
260
Preparation of Ni
10
Mo/CF composite as an electrocatalyst for hydrogen evolution reaction in alkali solution
PU Jiaxuan, CAO Jun, WEI Qiuping, YIN Dengfeng, MA Li, ZHOU Kechao
Ni
10
Mo/Cu foam (CF) electrode was prepared by electrochemical depositing the Ni
10
Mo film on CF. Ni
10
Mo/CF electrodes with different Ni
10
Mo contents and particle sizes were obtained by changing the deposition time, the surface morphology and electrochemical hydrogen evolution reaction (HER) performance of Ni
10
Mo/CF electrodes were also explored. The morphology of Ni
10
Mo alloy nanoparticles was studied by SEM analysis, and the composition of Ni
10
Mo was studied by EDS and XRD analysis. The electrochemical activity of the electrodes was comprehensively evaluated by linear scanning voltammetry (LSV), testing electrochemical double-layer capacitance, and stability tests. The results show that the morphology of the catalysts depends on the deposition time. With the increase of the deposition time, the HER catalytic activity of Ni
10
Mo alloy nanoparticles in 1 M KOH increases first and then decreases, when the current density remain the same. Among them, when the deposition time is 6 min, the electrode shows an overpotential of 227 mV at 10 mA/cm
2
and exhibits excellent stability.
2020 Vol. 25 (3): 260-266 [
Abstract
] (
451
)
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723
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267
Microstructure and properties of FeCr and CoCr laser cladding coatings
LIU Wei, FU Li, CHEN Xiaoming, ZHANG Lei, LI Yuluo, ZHANG Kai
FeCr and CoCr cladding coatings were prepared by laser cladding technology on 40Cr steel substrate for hoist piston rod. The microstructure, microhardness, porosity and wear resistance of cobalt based and iron-based alloys were characterized and analyzed. The results show that the porosity of FeCr and CoCr alloy cladding coatings obtained by laser cladding technology approaches to zero. The average microhardness of FeCr and CoCr alloy cladding layer are 718.6 HV
0.2
and 541.4 HV
0.2
, respectively. The impact toughness of FeCr alloy cladding layer is better than that of CoCr alloy cladding layer. After 180 min friction and wear test, the mass loss of FeCr alloy cladding layer is 0.002 01 g, the mass loss the CoCr alloy cladding layer is 0.003 47 g, and the mass loss of the matrix 40Cr is 0.081 08 g. The wear resistance of FeCr alloy cladding layer is better than that of CoCr alloy cladding layer and also better than 40Cr stainless steel. The wear mechanism of 40Cr steel, FeCr alloy and CoCr alloy cladding layer is mainly micro ploughing and adhesive wear.
2020 Vol. 25 (3): 267-272 [
Abstract
] (
398
)
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(860 KB) (
519
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