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2020 Vol. 25, No. 5
Published: 2020-10-15
Engineering and Technology
Review
Review
363
Preparation technology status and development prospect of high purity ammonium paratungstate product
DAN Ningning, LI Jiangtao
The development of high purity ammonium paratungstate (APT) raw material preparation process to meet the growing demand for high purity tungsten products has important significance. In this paper, the demand status of high purity APT and the raw material of high-end tungsten products are introduced, and the technology status of preparing high purity APT by ammonia dissolution, ion exchange and solvent extraction are analyzed. The development and application prospect of high-purity APT preparation technology are expounded.
2020 Vol. 25 (5): 363-368 [
Abstract
] (
379
)
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(368 KB) (
729
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Engineering and Technology
369
Effect of the speed on current-carrying friction and wear behavior of AuNi9 on AuAg35Cu5 disc
ZHOU Xiong, LUO Bo, KANG Xiao, ZHANG Lei
For the needs of increasing the application speed of space electrical contact materials, the effect of sliding speed on the current-carrying friction and wear behavior of the AuNi9 (HV of 270.3)/AuAg35Cu5 (HV of 202.3) friction pair was investigated. The experimental results show that with increasing sliding speed from 56.5 mm/s to 194.2 mm/s, the average value of friction coefficient and contact voltage drop of the friction pair increase from 1.1 to 2.0 and 71.8 mV to 132.8 mV, respectively. The square root of pressure drop curve (RMS) value of contact voltage drop also increases from 0.16 mV to 0.76 mV. The research findings show that increasing of sliding speed can reduce the contact stability and cause more material transfer between the friction pair, which results in the increasing of both roughness and wear rate of the brush wear surface from 0.41 μm and 4.7×10
-16
m
3
/(N·m) to 1.2 μm and 1.4×10
-14
m
3
/(N·m), respectively. In addition, micro-zone weld pools are clearly observed on the wear surface of disc after the current-carrying friction at the speed of 194.15 mm/s, which decreases the stability of current-carrying friction of the friction pair.
2020 Vol. 25 (5): 369-374 [
Abstract
] (
360
)
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1134
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375
Preparation of ultrafine tungsten powder by nano-tungsten assisting hydrogen reduction of tungsten oxide
ZHANG Yong, ZHANG Guohua
In the temperature range of 900-1 100 ℃, the prepared W powder by hydrogen reduction of pure WO
3
powder will have obvious crystal growth. In order to suppress the growth of W grains, the ultrafine tungsten powders were prepared by 10%-40% (mass fraction) nano-tungsten powder assisting hydrogen reduction of WO
3
. The effects of reaction temperature and the additive amount of nano-tungsten W(
w
(nano-W)) on the morphology and particle sizes of the products were studied, and the reaction mechanism of the two methods was also discussed. The results show that whether nano W is added or not, the particle size of W powder increases with the increase of reduction temperature. Without the addition of nano W powder, it is difficult to control the nucleation and growth of the product due to the chemical vapor transport (CVT) in the reaction process. The particle size of the reduced W powder is 2.10-2.78 μm. However, the addition of nano W can weaken the effect of CVT accompanied with nucleating agent in the reaction process, which makes the particle size of W powder decrease significantly. With the increase of
w
(nano-W) content, the particle size of reduced tungsten powder decreases gradually. When
w
(nano-W) is 40%, the particle size of reduced tungsten powder is 0.32-0.51 μm.
2020 Vol. 25 (5): 375-380 [
Abstract
] (
402
)
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639
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381
Effects of carbon content on the microstructure and performance of WC-TiC-Co cemented carbides
LUO Ren, XIONG Huiwen, CHEN Nan, LI Zhiyou
The powders with main phase of η phase were synthesized via the carbonization of W, Co, C and TiC mixtures firstly, WC-TiC-Co composite powders with different carbon contents were then synthesized by the carbonization of the η phase powder. WC-TiC-Co cemented carbides were prepared by vacuum sintering. The effects of carbon contents on the phase consistent, grain size, morphology and mechanical performance were investigated. The results show that the carbon content is the key factor affecting the phase composition and grain size of the alloy. The η phase with irregular shape remains in carbon-poor alloys and forms a metallurgical bonding with WC phase. Co phase tends to distribute at the interface between WC and (Ti,W)C phases. WC grains in carbon-rich alloys show a more regular shape than that in carbon-poor alloys. The size of WC and (Ti,W)C phase increase and the W content in (Ti,W)C phase and binder phase also increases. The alloy with suitable carbon amount has the hardness (HRA) of 91.7, the transverse rupture strength of 1678 MPa and the fracture toughness of 10.2 MPa∙m
1/2
.
2020 Vol. 25 (5): 381-388 [
Abstract
] (
306
)
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845
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389
Process research on particle size characteristics of reduced tungsten powder
CHEN Shanshan
The particle size, particle size distribution and agglomeration of tungsten powder are closely related to the properties of subsequent products. In this paper, the reduction process of yellow tungsten oxide and blue tungsten oxide is studied by static reduction test at different temperature and time. The particle size distribution and agglomeration state of the powder were analyzed by scanning electron microscope, the phase change process of the powder was analyzed by X-ray diffraction and oxygen index, and the macroscopic particle size change was characterized by specific surface area. The results show that yellow tungsten (WO
3
) and blue tungsten (WO
2.9
) have the same reaction rate and morphology change process. The particle size, particle size distribution and agglomeration are closely related to reduction temperature. After reduction at a low temperature below 700 ℃, the tungsten powder particles are uniform in size and easy to agglomerate. When the temperature is above 800 ℃, the agglomeration of the powder decreases and the particle size is uneven.
2020 Vol. 25 (5): 389-395 [
Abstract
] (
318
)
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1011
)
396
Effect of binder on properties of iron based mixed powder
SU Fengge, ZHENG Zhuo, CHEN Lushui
Fe-C, Fe-Cr-C, Fe-Ni-Cu-C and other iron-based mixed powders were prepared by bonder-treated process method using self-made binder. Scanning electron microscopy (SEM) was used to observe the morphology and structure of the Fe-Ni-Cu-C mixed powder. The effects of binder content (mass fraction) on the flowability, apparent density, compressibility of Fe-C mixed powder, and on the transverse rupture strength (TRS) of Fe-C greens were studied. The results show that in the Fe-Ni-Cu-C mixed powder prepared by bonder mixing method, most of the small particles are bonded to the surface of the large iron powder, which reduces the segregation of the powder composition. Compared with the Fe-C powder without binder, the flowability of Fe-C mixed powders with 0.02% and 0.03% binder increases, and the required more pressing pressure. But the maximum increase is less than 6%, which is acceptable in actual production. The TRS of Fe-C green without binder is 12.5 MPa, and that with 0.03% binder is 13.7 MPa, and 45.8 MPa after curing. The Fe-Cr-C double row sprocket blank prepared by this process has good machinability, and can keep the integrity of sprocket tooth profile and machining edge under intermittent cutting condition.
2020 Vol. 25 (5): 396-402 [
Abstract
] (
337
)
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(682 KB) (
773
)
403
Effects of B content on microstructure and properties of CrFeCoNiTi
0.6
high-entropy alloy
JIANG Yue, LI Xiuming, ZHOU Guangtai, ZHU Baixiang
High entropy alloy is a new kind of solid solution reinforced metal material with good mechanical properties. CrFeCoNiTi
0.6
B
x
(
x
=0, 0.025, 0.050, 0.075, 0.100, 0.125) high entropy alloy was successfully prepared by mechanical alloying and spark plasma sintering. The microstructure of the high-entropy alloy was analyzed by X-ray diffraction analysis, scanning electron microscope observation and energy spectrum analysis. The properties of the high-entropy alloy were analyzed by Vickers hardness test and compression strength test. The effects of B content on the microstructure and properties of CrFeCoNiTi
0.6
series high-entropy alloy were also investigated. The results show that CrFeCoNiTi
0.6
B high-entropy alloy is composed of FCC structure, simple tetragonal system and boride. When
x
is 0.125, the alloy structure changes from FCC structure to FCC+BCC structure. The mechanical properties of the alloy are significantly improved because of the addition of B. When
x
is 0.1, the alloy has the highest hardness of 207.3 HV and compressive strength of 813.9 MPa.
2020 Vol. 25 (5): 403-409 [
Abstract
] (
312
)
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865
)
410
Microstructure and properties of Al
2
O
3
coating on the surface of hoist piston rod prepared by explosive spraying
FU Li, CHEN Xiaoming, MAO Pengzhan, LIU Wei, ZHANG Lei, ZHANG Kai, LI Yuluo
A composite coating composed of WC-12Co adhesive layer and Al
2
O
3
surface layer was prepared on 40Cr stainless steel surface of hoist piston rod by new type CCDS2000 explosive spraying technology. The microstructure, microhardness, porosity, bonding strength, impact toughness, corrosion resistance and wear resistance of the coating were analyzed and tested. The friction and wear mechanism of the coating was also analyzed. The results show that the porosity of the Al
2
O
3
coating is 0.94%. The hardness is in the range of 1 108-1 316 HV
0.2
. The bonding strength can reachs to 59.4 MPa. The corrosion resistance and wear resistance of the coating are obviously better than that of 40Cr stainless steel, and the impact toughness is slightly improved. The average mass wear loss of 40Cr stainless steel is 99.56 mg, which is 24.5 times of that of Al
2
O
3
coating. The wear mechanism of Al
2
O
3
coating is mainly micro ploughing and adhesive wear.
2020 Vol. 25 (5): 410-416 [
Abstract
] (
280
)
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668
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417
Effect of premix ratio on mechanical properties of silicon nitride ceramics prepared by stereolithography
LIU Yao, HE Yu, XIN Feng, WANG Bin, ZHAN Lina, WEN Ruquan, XIAO Wenfu, LIU Shaojun
Using three diluents of 1,6-hexanediol diacrylate (HDDA), 2-hydroxyethyl acrylate (HEA) and trimethylpropane triacrylate (TMPTA), and four kinds of prepolymers of epoxy acrylate (EA), water-based polyurethane acrylate (PUA), modified acrylate (WUV) and aliphatic epoxy acrylate (APU) as raw materials, Si
3
N
4
ceramic powder modified by silane coupling agent KH560 is added to prepare Si
3
N
4
ceramic slurry. Si
3
N
4
ceramics were prepared by light curing, debinding and sintering. The effects of diluent ratio, prepolymer type and solid content (i.e. the volume fraction of Si
3
N
4
) on the rheological properties of ceramic slurry were studied. The appropriate sintering temperature was determined and the mechanical properties of Si
3
N
4
ceramics were measured. The results show that when HDDA, HEA and TMPTA are mixed in a mass ratio of 3:1:6 as the diluent, the premixed liquid made with prepolymer EA has the lowest relative molecular mass and viscosity. The light cured green body with 45% solid phase content is compact, and there are no holes and cracks after debinding at 160 ℃. The microhardness and fracture toughness of Si
3
N
4
ceramics sintered at 1 750 ℃ and 5 MPa are 14.57 GPa and 5.78 MPa·m
1/2
respectively.
2020 Vol. 25 (5): 417-423 [
Abstract
] (
345
)
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1110
)
424
Ball milling mixing progress for preparation of polycrystalline cubic boron nitride composites
XIE Hui, DENG Fuming, WANG Hao, HAN Shunli, FENG Fei
The operation law of ball mill and the mechanism of ball milling process were studied. The cubic boron nitride powders with different particle sizes were milled, and the particle size distribution and grain refinement rate before and after ball milling were analyzed by laser particle size analyzer. SEM and XRD were used to observe and analyze the powder and sintered samples to study the effect of ball milling process on the preparation of cubic boron nitride polycrystalline materials. The results show that, the horizontal planetary ball mill used for mixing process has a suitable rotation speed range. In this range, the higher the rotating speed is, the stronger the impact and grinding effect the ball will bear. The finer particles tend to agglomerate during ball milling, but the coarser the powder particles are, the higher the refining rate is. The coarse and fine mixed particles appear doping after mixing for 4 h. The longer the milling time, the higher the mixing uniformity and the more doping. The higher the rotating speed, the more significant the doping. The higher the rotation speed, the more significant the ball milling powder doping. The best wet milling mixing process of 2-8 μm fine powder is ball milling at 180 r/min for 12 h.
2020 Vol. 25 (5): 424-432 [
Abstract
] (
380
)
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1522
)
433
Removal process of Mg impurity in AlCl
3
∙6H
2
O
CHAO Xiaoguang, GAO Guimei, WANG Hongbin, CAO Kun, DAI Yin, SONG Litao, ZOU Ping, WANG Yongwang
AlCl
3
·6H
2
O (ACH) is an important intermediate product in the process of extracting Al
2
O
3
from fly ash by hydrochloric acid. The purity of ACH directly determines the purity of the product Al
2
O
3
. Among them, it is an important way to improve the purity of ACH by washing. In this paper, the washing process parameters of ACH were studied from many aspects. It was found that the washing effect of spray washing is slightly better than that of stirring washing when saturated AlCl
3
solution was used as the washing solution, and the washing efficiency of thre-times washing is similar to that of four-times washing. The higher the content of impurity MgO in the raw material, the higher the impurity MgO content in the product after washing. Stimultaneously, the corresponding washing efficiency is also increased. The washing effect of the ratio of 1:1.5 (mass of ACH/ mass of washing solution)is better than that of 1:1. After three times washing, the crystal loss rate is 19.2% and 16.7%, respectively. The loss rate of crystal can be greatly reduced when the washing solution is reused. The washing effect of HCl solution with mass fraction of 29% is slightly lower than that of saturated AlCl
3
solution. After three times washing, the crystal loss rate is more than 50%, and it can be reduced after the washing solution is reused.
2020 Vol. 25 (5): 433-439 [
Abstract
] (
322
)
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929
)
440
Friction and wear properties of PM Zn-W alloy reinforcing copper-based friction material for mining truck clutches
XIE Maoqing, WANG Leigang, PENG Peng, YANG Guosheng, ZHANG Jiahao
The copper baseed friction materials for mine truck clutch were prepared by adding Zn-W alloy into the existing copper base powder metallurgy friction material formulation, with different Zn-W alloy content and different pressing density. The microstructure and friction and wear properties of the materials were analyzed and tested, and the incremental energy/power level test and bench test were carried out. The results show that the surface hardness of Cu based friction materials decreases with the increase of Zn-W alloy content and increases with the increase of density. The friction coefficient increases with the increase of Zn-W alloy content and decreases with the increase of density. The copper based friction plate with mass fraction of 6%Zn-W alloy and 10% higher density has suitable surface hardness, dynamic/static friction coefficient and good wear resistance, and can reduce the noise, vibration and acoustic vibration roughness of automobile. Compared with the friction plate without Zn-W alloy, the energy output of the friction plate can be increased by two levels, and the sixth level energy output (753.16 J/cm
2
) can be sustained. The main performance of the friction plate is slightly higher than that of the imported copper based friction plate.
2020 Vol. 25 (5): 440-448 [
Abstract
] (
268
)
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904
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