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2018 Vol. 23, No. 3
Published: 2018-06-20
Theoretical Research
229
A computational fluid dynamics (CFD) research on the atomization mechanism of two-phase flows in ultrasonic gas atomizer
ZHU Lingling, WU Jianjun, LIU Mingxiang, SUI Dashan, CUI Zhenshan
The atomization process of gas-liquid two-phase flows in ultrasonic gas atomizer was analyzed using computational fluid dynamics software. The two kinds of primary-breakup models of liquid metal at different mass flow rates were verified by volume of fluid model, and the effects of atomizing pressure and liquid surface tension on the primary-breakup process were also studied. The simulation results indicate that the transformation of primary-breakup model will occur with decreasing the liquid mass flow rate. When the liquid mass flow rate is 0.053 kg/s, the primary breakup model is melt sheet, but when it is 0.265 kg/s, the primary breakup model is “fountain”. When the atomizing pressure increases from 0.5 MPa to 1.5 MPa, the primary-breakup degree aggravates. However, excessive atomizing pressure will weaken the atomization effect. The smaller-size drop can be formed in the primary-breakup process when the surface tension of liquid metal decreases from 1.2 N/m to 0.4 N/m. Through the following secondary-breakup, more uniform and finer powder particles and high-quality as-spray ingot will be obtained.
2018 Vol. 23 (3): 229-237 [
Abstract
] (
325
)
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776
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238
Lubrication mechanism of copper-based solid self-lubricating materials by lead
GAN Ziyang, LIU Yong, LÜ Xinqun, TAN Yanni, ZOU Jianpeng
Using copper-tin as matrix, graphite and lead as solid lubricant, the new solid self-lubricating material that is suitable for high speed and heavy load condition was fabricated by powder metallurgy. The effects of lead on high-temperature mechanical properties and tribological behavior of materials were investigated. Through the investigation on the friction surface and the subsurface surface, the cooperative lubrication mechanism of lead and graphite was discussed. The results show that the hardness and tensile strength can be markdly increased by adding lead in copper graphite material. Adding lead can also increase high-temperature compression strength below 300 ℃. The compressive strength of the material at 300 ℃ is 215.3 MPa. Meanwhile, the friction stability of copper graphite material under high speed and heavy load condition can be significantly improved by adding lead, and the average friction coefficient is reduced slightly.
2018 Vol. 23 (3): 238-245 [
Abstract
] (
411
)
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737
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Engineering and Technology
246
Preparation of ultrafine Cu-Fe-Sn-Ni Cu-matrixbonded pre-alloyed powder by co-precipitation method and its flexural strength of sintered matrix
XIAO Changjiang, DOU Zhiqiang
Using CuCl
2
·2H
2
O, FeCl
2
·4H
2
O, SnCl
2
·2H
2
O and NiCl
2
·6H
2
O as raw materials, H
2
C
2
O
4
·2H
2
O solution as precipitator, Cu-Fe-Sn-Ni quaternary Cu-based pre-alloyed powder was fabricated by co-precipitation method. The sintered Cu-Fe-Sn-Ni cupric carcass and the carcass/diamond caking were prepared through hot pressing processes. The effects of charging sequence, pH value, aging time, co-precipitation temperature and solution concentration on the particle size of precursor powders were investigated. The phase composition and morphology of the powder were characterized by X-ray diffraction (XRD) and scanning electronic microscope (SEM). Moreover, the flexural strength of Cu-Fe-Sn-Ni quaternary pre-alloyed powder was tested, which was compared with that of the samples that was prepared by mixing the four kinds of elemental powders. The results show the optimal process of Cu-Fe-Sn-Ni pre-alloyed powder is a parallel-flow charging sequence, co-precipitation temperature of 50 ℃, aging time of 40 min and solution concentration of 1 mol/L. The ultrafine Cu-Fe-Sn-Ni pre-alloyed powder with particle size of about 500 nm can be obtained by calcining and hydrogen reducing the precursor powder. The flexural strength of the matrix is 1 302 MPa and the carcass/diamond caking is 853 MPa after hot pressing.
2018 Vol. 23 (3): 246-251 [
Abstract
] (
370
)
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570
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252
Infiltration kinetics, microstructure and mechanical properties of B
4
C-MgSi composite fabricated by melt infiltration
ZOU Zhihuan, ZENG Fanhao, LIU Ji’an, LI Yi, GU Yi, ZHANG Fuqin
B
4
C-MgSi composites were prepared by vacuum perpetration with infiltrating porous B
4
C substrates at 1 000 ℃ with a Mg-Si eutectic alloy. The theoretical calculation shows that at the temperature of 1 000 ℃, the infiltration depth of molten Mg in porous B
4
C increases with increasing time, and the penetration rate is faster first and then tends to be stable. The infiltration depth can reach more than 2.2 cm after 60 min for Mg, while MgSi alloy, under the same conditions, has a greater depth. The phase composition was tested by XRD. The microstructures of B
4
C substrates and B
4
C-MgSi composites were analyzed by scanning electron microscope (SEM). The mechanical properties were also studied. The results show that the porosity of B
4
C-MgSi composites have many connected pores, and the density is more than 98% after the melting. The composites displays high rockwell hardness (71.3±3.3 HRA), good bending strength (285.81±11.2 MPa) and high fracture toughness (5.27±0.53 MPa·m
1/2
). A mixed fracture morphology of B
4
C-MgSi composite is indicated. It is different from the brittle fracture of B
4
C substrates.
2018 Vol. 23 (3): 252-260 [
Abstract
] (
312
)
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586
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261
Effect of layer thickness on hydrogen reduction of iron powder in powder metallurgy
GUO Peimin, ZHAO Pei, KONG Lingbing, WANG Lei
To investigate the influence of layer thickness of iron powder on reducing efficiency in reducing furnace with H
2
as reducing agent, the diffusion kinetic model of iron powder reduction was established using coupling kinetic model of FeO reduction and reducing gas oxidation. For 0.2 mm sponge iron powder with 0.74% remaining oxygen, the reduction condition is as follows: layer depth of 30 mm, heating time of 1 h,temperature of 850-900 ℃ and hydrogen flow of 30 Nm
3
/(t∙h). The remaining oxygen of product is 0.25%, which is coincidence with the calculation result (0.27%). The remaining oxygen in iron powder can be reduced easily. The hydrogen in the hydrogen reduction furnace penetrates into the iron powder layer, and the iron powder is reduced layer by layer from top to bottom. For 30 mm layer thickness, penetrating depth of hydrogen is about 25 mm, and another 5 mm thickness iron powder near the bottom can not be reduced. The remaining oxygen increases, the utilization rate of hydrogen and the yield decease with increasing layer thickness. When layer thickness decreases from 3 cm to 2 cm, reducing time will shorten 50%, yield will improve 33%, and consumption of H
2
will decrease 50%.
2018 Vol. 23 (3): 261-265 [
Abstract
] (
359
)
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929
)
266
Effects of acid mixture treatment during oxidation process on the electroless copper plating for multi-walled carbon tubes
WANG Xinhua, GUO Baisong, NI Song, YI Jianhong, SONG Min
In this work, the nano-copper particles were coated on the multi-walled carbon nanotubes (MWCNTs) by electroless plating, and the effects of acid mixture time and pretreatment of acid mixture on the nano-Cu particles coated on MWCNTs were also investigated. The results show that the acid treatment time mainly affects the removing content of amorphous carbon layer that attached on the surface of the CNTs. The amorphous carbon layer can be partially corroded by appropriate acid treatment time and acquire perfect electroless plating results. Pretreatment of acid mixture has a corrosive influence on the C walls. When only the sulfuric acid concentration reaches the critical value, the C wall can be corroded seriously and notably. The critical value of HNO
3
:H
2
SO
4
is 1:3. If the concentration value of sulfuric acid is lower than the critical value, pretreatment of acid mixture can only corrode the amorphous carbon layer on the surface of MWCNTs, but cannot corrode the C wall obviously. This study demonstrated that the good dispersed nano-Cu particles coated on MWCNTs can be obtained after treated by sulfuric acid and nitric acid in ratio 1:3 for 5 h.
2018 Vol. 23 (3): 266-273 [
Abstract
] (
265
)
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647
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274
Microstructure and mechanical properties of Al-18Si alloy modified by Al-3P master alloy
YANG Wei, LU Xiaowang, LIU Ya, WU Changjun, WANG Jianhua, SU Xuping
Al-18Si alloy was modified by Al-3P master alloy. The effects of adding amount of alterant
w
(Al-3P)(0-1.0%) and modification temperature (750-850 ℃) on microstructures and tensile properties of the alloy were investigated by optical microscope (OP), Image Pro Plus 6.0, scanning electron microscopy (SEM) and universal testing machine. The results show that the size of primary Si decreases and its area fraction increases after modification. With the increase of
w
(Al-3P), the size of primary Si first decreases and then increases, and the area fraction of primary Si first increases and then decreases when Al-18Si alloy was modified at 800 ℃.When the adding amount of alterant
w
(Al-3P) is 0.6%, the size of primary Si is the smallest, and the average size is 14 μm. When the adding amount of
w
(Al-3P) is 0.8%, the area fraction of primary Si reaches the maximum of 14.4%. When the adding amount of
w
(Al-3P) is 0.8%, the area fraction of primary Si in Al-18Si alloy decreases with the increase of modification temperature. The size of primary Si decreases first and then increases. The size of primary Si is the smallest of 15 μm when the alloy is modified at 800 ℃. Compared with unmodified Al-18Si alloy, the tensile strength and elongation of Al-18Si alloy increase by 17.6% and 109% respectively after modified with
w
(Al-3P)0.8% at 800 ℃. The fracture mode of the modified Al-18Si alloy is ductile fracture.
2018 Vol. 23 (3): 274-280 [
Abstract
] (
427
)
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432
)
281
Effects of ball milling time on microstructures and properties of graphene/ODS copper composite materials
YANG Changyi, LIU Yunzhong, YU Kaibin
A mixture of 0.1% graphene oxide and 0.5% ultrafine alumina particles (both mass fraction) were added to the copper powder for a mixed mechanical milling. Then the powders mixture was densified by vacuum hot pressing sintering technique and the thermal reduction of graphene oxide was realized at the same time. Graphene/ODS (G/ODS) copper matrix composites were prepared using graphene as the second reinforcement phase in the copper matrix composite. The effects of milling time on the microstructures and properties of Cu-0.5Al
2
O
3
-0.1GO composite before and after sintering were studied by SEM, XRD, Raman spectrum, mechanical properties test and physical properties test. The results show that the mechanical and physics properties both increase by increasing ball milling time (0-8 h). Graphene has a better combination and distribution in copper matrix with the 8-hour ball milling, which result in optimal comprehensive properties of sintered composites. The compression yield strength of G/ODS copper composite is 324MPa, 29.6% higher than that of ODS copper (250 MPa).The bending strength is 621 MPa, which is very near to that of ODS copper (629 MPa). The fracture mechanism of the composite is ductile fracture. The hardness, electric conductivity and thermal conductivity are 100 HV, 87.23%IACS and 385 W/(m∙K), respectively.
2018 Vol. 23 (3): 281-291 [
Abstract
] (
352
)
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1097
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292
Numerical simulation research on the effect of gate patterns on powder volume fraction variation of MIM milling cutter
LIU Fei, LI Wenming
In this paper, milling cutter was prepared, by metal injection molding (MIM) process under four gate patterns with different numbers and locations. Combined with Cross-WLF viscosity model, the influence of the gate patterns on powder concentration was analyzed using Moldflow2017 software. The results show that the position and the number of the gates can affect the distributions of the powder in the milling cutter. While filling, the pressure has little effect on the distribution of powder concentration. For, different gate patterns, the change of shear rate of the feeding is different during the filling process, thus the distribution of powder concentration appears obvious difference. Using two gates in the end of handle plane, while filling, the distribution of powder concentration is in the range of ±0.5%. The powder distribution is evenly distributed, which meets the requirements of injection molding process. It is the optimal gate patterns when milling cutter is prepared by MIM.
2018 Vol. 23 (3): 292-297 [
Abstract
] (
281
)
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(516 KB) (
398
)
298
Effects of heat treatment on microstructures and mechanical properties of AlSi10Mg alloy produced by selective laser melting
YU Kaibin, LIU Yunzhong, YANG Changyi
AlSi10Mg alloy was prepared by selective laser melting (SLM) process, and then treated by annealing, solid solution and T6 treatment, respectively. The effects of heat treatment on microstructures and mechanical properties of AlSi10Mg alloy produced by SLM were investigated in order to improve heat treatment process of the alloy. The results show that the phases in as-built AlSi10Mg SLM products are α-Al matrix and eutectic Si. The eutectic structure [α-Al+Si] is continuous network distribution on the matrix of α-Al. The sections of both XOY and XOZ have coarse grain, fine crystal and heat affected zones. After annealing treatment, the eutectic Si network is partial dissolution and fracture, the strength decreases and the hardness increases slightly. While after T6 treatment, the eutectic Si appears with scattered and regular geometry inlays in the α-Al matrix, the tensile strength of the alloy decreases, yield strength slightly increases, and ductility significantly increases. In a comprehensive comparison with respect to strength and ductility, the T6 treatment is more suitable for the AlSi10Mg SLM products.
2018 Vol. 23 (3): 298-305 [
Abstract
] (
507
)
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2707
)
306
Effect of microstructure on nanoindentation behavior of beryllium materials
YU Yongxin, XIAO Daihong, LIU Wensheng, MA Yunzhu
In this paper, optical microscopy (OM), scanning electron microscopy (SEM) and nanoindentation test has been performed on the beryllium materials prepared by HIP with different microstructures. The creep properties of the beryllium were studied by measuring load-depth (
P
-
h
) curves with different loading rates. The results show that the creep behavior of beryllium is loading rate dependent, and the creep increases with increasing the loading rate. In addition, further analysis the load-depth (
P
-
h
) curves found that the microstructures of beryllium, including the pores and the content of BeO, have certain effects on the nanoindentation behavior of the beryllium metal. It’s due to the pores and BeO that changed the interaction between dislocations and particles.
2018 Vol. 23 (3): 306-311 [
Abstract
] (
274
)
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(564 KB) (
529
)
312
Effects of gas-atomized pressure on morphology and properties of TC4 powder prepared by electrode-induced gas atomization
JIN Ying, LIU Ping, SHI Jinguang, WENG Ziqing, GU Xiaolong
TC4 powder was fabricated by electrode-induced melting gas atomization. The properties of TC4 powder were characterized by laser particle size analyzer, scanning electron microscopy (SEM), powder comprehensive-performance analyzer and true density analyzer. The effects of atomization pressure on the yield of powders with particle size <53 μm, mean size, morphology, hollow powder, apparent density and fluidity were studied. The results show that the mean size of TC4 powder and the fine-powder yield increases with increasing gas-atomized pressure (3.5-6.0 MPa). The powder with more spherical and less satellite-ball, mean size of 69.4 μm, fine particle yield of 23.0%, the relative density of 99.1%, the apparent density of 2.40 g/cm
3
, the flow ability of 22.4 s/50 g can be obtained when the gas-atomized pressure is 3.5 MPa. When the gas-atomized pressure is 6.0 MPa, the mean size of TC4 powder is 48.6 μm and the yield of powder ranging from 0 to 53 μm is 40.8%. With further increasing the gas-atomized pressure, the mean size of the powder increases, the yield of fine powder decreases, the number of satellite-ball powder increases, the degree of sphericity becomes worse. The apparent density and fluidity decrease with increasing gas-atomized pressure.
2018 Vol. 23 (3): 312-317 [
Abstract
] (
304
)
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(645 KB) (
1145
)
318
Effects of reflow number and Ag content on microstructure and shear strength of (Au-20Sn)-
x
Ag/Cu joints
LIU Wensheng, CHEN Baishan, MA Yunzhu, TANG Siwei, HUANG Yufeng
Two pure Cu plates were bonded using (Au-20Sn)-
x
Ag(
x
=0.5, 1, 2) as solder. The effects of reflow number and Ag content on the microstructure and shear strength of (Au-20Sn)-Ag/Cu solder joint were studied. The results show that IMC (intermetallic compound) in the joint line is composed of (Au,Ag,Cu)
5
Sn after one reflow. The CuAu layer appears after 50 reflows. Lastly, Cu
3
Au layer appears beside the Cu substrate after 100 reflows. The addition of Ag can suppress the growth speed of the IMC. When reflow number is one, the shear strength of solder joint increases with increasing Ag content. The shear strength of (Au-20Sn)-
x
Ag/Cu (
x
=0, 0.5, 1, 2) are 92.14, 93.59 and 98.43 MPa, respectively. The shear strength decreases with increasing reflow number, and the decreasing rate decreases with increasing Ag content.
2018 Vol. 23 (3): 318-327 [
Abstract
] (
307
)
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1207
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328
Effect of duty ratio on surface morphology and performance of TiAlN coatings deposited by multi-arc ion plating
ZHOU Jun, LI Tao, FAN Xiangfang, LI Huailin
TiAlN coatings were deposited on the surface of zirconium alloys by multi-arc ion plating with different duty ratio. The surface and cross-sectional micro-morphologies were observed by scanning electron microscopy (SEM), the elemental composition of the coatings was analyzed by an energy dispersive spectroscopy (EDS). The high temperature oxidation resistance performance of coatings was tested by a box-type resistance furnace in air at 800 ℃ for 3 h. The adhesion strength of the coating to the substrate was tested by an automatic scratch tester. The phase composition was analyzed by X-ray diffractometer (XRD). The results show that the change of duty ratio can significantly affect the micro-morphology, high temperature oxidation resistance performance, adhesion strength and elemental composition of TiAlN coatings. With the duty ratio increasing, the quantity of large particles on TiAlN coatings decreases gradually, and the quality of surface morphology improves. The deposition rate increases first and then decreases, and the density keeps increasing. EDS analyses show that the mass ratio of Ti and Al elements is gradually reduced, the biggest value is 2.437. With the duty ratio of 50%, the coating has better high temperature oxidation resistance and the higher adhesion strength of 26 N. With the duty ratio of 30%, TiAlN coatings contain Ti
3
AlN and AlN phases, and the (111) plane of Ti
3
AlN and (100) plane of AlN are the preferred planes. With increasing duty ratio, there are no preferred orientation behavior. As the duty ratio is 50%, the TiAlN coating has better surface, quality higher adhesion strength between the coating and substrate and high temperature oxidation resistance performance.
2018 Vol. 23 (3): 328-334 [
Abstract
] (
481
)
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1138
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335
Effect of magnetron sputtering power on composition and microstructure of NiAl coating
HE Dianmin
In order to study the chemical composition variation, microstructure evolution and related properties of the coatings caused by sputtering power modulation, the binary Ni-Al alloy coating were prepared by magnetron co-sputtering on the surface of Si(100). The XRD, SEM and TEM were used to study the phase composition and microstructure of the coatings. The result show that the microstructure consisted of a significant crystallization feature of a metastable (Ni,Al) matrix and Ni
3
Al precipitations is observed for the coatings under high sputtering powers, the coatings deposited at lower sputtering powers exhibit a (Ni,Al) solid solution polycrystalline structure with preferred orientation. The coatings with (Ni,Al) matrix and Ni
3
Al precipitations exhibit a higher hardness than those on the single (Ni,Al) phase. The variation in hardness of the magnetron co-sputtered Ni-Al coatings could be attributed to the grain size and microstructure evolution. The nano-crystallites of (Ni,Al) and Ni
3
Al phases in the Ni-Al coatings are obtained under the higher energy input during sputtering. With increasing Al sputtering power, a slight decrease of grain size is observed due to the increase of the Al concentration in the Ni-Al coatings. The change of the hardness of Ni-Al coating can be attributed to the evaluation of the grain size and microstructure.
2018 Vol. 23 (3): 335-340 [
Abstract
] (
384
)
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(674 KB) (
810
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