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2019 Vol. 24, No. 3
Published: 2019-06-15
Engineering and Technology
205
Microstructure and mechanical property of spray forming 7075 aluminum alloy
WU Jianjun, SUI Dashan, ZHU Lingling, LIU Mingxiang, CUI Zhenshan
7075 aluminum alloy ingot was prepared by spray forming process, and the material was sequently processed by forging and peak aging heat treatment. Then the mechanical properties of the material in different conditions were tested, the microstructures and tensile fractures were observed. The test results show that the microstructures of spray-formed 7075 aluminum alloy are equiaxed grains, and the size is fine and uniform. The second phase is distributes not only along the grain boundary but also inside the grains with a large number of acicular and spherical shapes. There are some small pores in the spray-formed material. The distribution of Mg and Zn is more uniform, and the segregation is significantly decreased. In the fracture surface of the spray formed material, a river pattern is fand, and it belongs to brittle fracture. After the densification by plastic deformation, the tensile strength is increased to 529 MPa. Moreover, T6 heat treatment can further improve the mechanical properties of spray-formed 7075 aluminum alloy, the tensile strength can be increased to 642 MPa, and the elongation is improved to 8.36%.
2019 Vol. 24 (3): 205-211 [
Abstract
] (
640
)
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2175
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212
Microstructure and tribological properties of plasma, high velocity oxy-fuel and detonation sprayed iron-based coatings
XIE Lu, XIONG Xiang, WANG Yueming
The microstructure and tribological properties of Fe-based amorphous coatings which fabricated by air plasma spray (APS), high-velocity oxygen-fuel (HVOF) spray and detonation spray (DS) were compared. The relationships between spray technique, amorphous content, porosity and wear resistance behavior were investigated. Coating microstructure, cross-sectional morphology and friction surface morphology were observed by SEM. Amorphous structure of powder and coatings was examined by XRD. Wear resistance of coatings and stainless steel was tested by wear and abrasion equipment. The results show that the microstructures of the coatings are mainly composed of amorphous phase. The amorphous contents of the coatings made by various spray techniques are 79.39%, 85.26% and 88.14%, the porosity are 2.5%, 1.9% and 1.5% respectively. The detonation sprayed coating has the best wear properties, and the wear mechanism is typical fatigue wear. The coatings exhibit better wear resistance than the stainless steel substrate.
2019 Vol. 24 (3): 212-219 [
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] (
444
)
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1094
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220
Effect of heat treatment technology on the mechanical property of 490 MPa grade fire-resistance steel
CHEN Jun, LUO Hengyong, LIN Shenzheng
Taking NSFR490 fire-resistant steel as an example, the changes of its metallographic organization and mechanical properties at different normalizing temperatures were studied. The results show that under the normalizing treatment for 730-820 ℃, the strength decreases with the increase of temperature, but it still meets the engineering application standard. Otherwise, the plasticity is improved (elongation rate increased from 20% to 26%). The tensile test at 600 ℃ satisfy the requirement of high temperature yield strength greater than 2/3 of room temperature yield strength. Further observation of the microstructure of NSFR 490 fire-resistant steel shows that the overall microstructure of the alloy has little change under a high temperature process of 600 ℃, and only the grain size has grown slightly, which is consistent with the mechanical properties of refractory steel at high temperature (yield strength decreased from 315 MPa to 292 MPa). At last, combined with the practical engineering application of the refractory steel, the displacement- temperature curve and failure critical temperature point 600 ℃ of the material are obtained by using ANSYS software.
2019 Vol. 24 (3): 220-225 [
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] (
512
)
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(536 KB) (
708
)
226
Microstructure evolution of Y
2
O
3
powder during mechanical milling
LI Quan, LIU Zuming, PENG Kai, ZHAO Fan, LÜ Xueqian
Y
2
O
3
was mechanical milled by planetary ball mill and its particle size, morphology and the microstructure evolution were systematically investigated by XRD, SEM and TEM. The results show that raw Y
2
O
3
powder has cubic structure, and undergoes crushing, flaky and structure transforming during mechanical milling because of the collision effects of high energy milling balls. Raw Y
2
O
3
powder with bimodal distribution is crushed, refined and dispersed completely, and its particle size shows a single peak and lognormal distribution after mechanical milling for 60 h. The cubic structure Y
2
O
3
powder was destroyed and formed small scaled lattice defects during mechanical milling. The lattice defects region expands to a composite structure which consist of amorphous and nano-grains, and finally completely transformed into amorphous structure. The Y
2
O
3
powders transform to irregular bulk structure and short rod structure after mechanical milling for 60 h. The irregular bulk structure is composite structure which consist of amorphous matrix and a few nano-grains, and the short rod structure is completely amorphous.
2019 Vol. 24 (3): 226-231 [
Abstract
] (
411
)
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(1592 KB) (
578
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232
Fabrication and mechanical properties of silicon carbide fiber reinforced AlN-SiC composites
WANG Hongfei, LI Guodong, SUN Yehua, LI Dan, XIONG Wei
Silicon carbide fiber reinforced AlN-SiC ceramic composite was fabricated by spark plasma sintering (SPS), using AlN, SiC and SiC fibers as main raw materials. By means of metallographic analysis,scanning electron microscopy (SEM) and mechanical properties test, the effects of sintering temperature and content of SiC fibers on the microstructure,phase composition,mechanical properties and thermal conductivity of the composites were studied. The results show that the optimum temperature for preparing AlN-SiC ceramic matrix composites with domestic SiC fibers by SPS method is 1 650 ℃. Adding a small amount of SiC fibers can effectively improve the comprehensive properties of AlN-SiC composite ceramics. When the content of SiC fibers is 5%, the comprehensive property of AlN-SiC composite ceramics is the best, the bending strength is 241.36 MPa, the hardness is 569.48 N, and the fracture toughness is 11.66 MPa·m
1/2
.
2019 Vol. 24 (3): 232-238 [
Abstract
] (
483
)
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(851 KB) (
883
)
239
Effect of synergistic adjustment of Ba-Pb doping and grain refinement on thermoelectric property of BiCuSeO semiconductor ceramics
SU Yisi, FENG Bo, HU Xiaoming, LIU Peihai, LI Guangqiang, FAN Xi’an
The bulk Bi
1-2
x
Ba
x
Pb
x
CuSeO (
x
=0, 0.06) oxide semiconductor ceramics doping Ba/Pb in BiCuSeO were prepared by mechanical alloying (MA) and spark plasma sintering (SPS). The effects of Ba/Pb doping and ball milling (BM) time on the microstructure, thermoelectric properties, and hardness were investigated systematically. The results show that partial substitution of Bi in BiCuSeO with a small amount of Ba/Pb can significantly improve the conductivity and power factor of the material, while ball milling can reduce the grain size of the material to about 350 mm, thus reducing the thermal conductivity of the material and improving its electrical conductivity. The maximum power factor of Bi
0.88
Ba
0.06
Pb
0.06
CuSeO ceramics prepared by ball milling for 16 h is 0.76 mW/(m∙K
2
) at 873 K, and the maximum ZT value is 1.18, which is 2.71 times and 2.19 times higher than that of undoped BiCuSeO ceramics, respectively.
2019 Vol. 24 (3): 239-247 [
Abstract
] (
393
)
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(1 KB)
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(692 KB) (
831
)
248
Effect of carbon fiber coating modification on mechanical properties of rapidly prepared C
f
/SiC composite
SUN Yehua, LI Guodong, YE Guozhu, SHI Qi, ZHANG Yang, HE Anqing
C
f
/SiC composites were fabricated by new rapid forming process and reactive melt infiltration, using SiC powder, phenolic resin powder and coated as well as uncoated carbon fiber felt/cloth as raw materials. Then the surface of C
f
/SiC composites were coated by chemical vapor deposition (CVD) SiC coating. The effects of coating modification of the carbon fiber and surface coating on the mechanical properties of C
f
/SiC composite were studied by XRD phase analysis, scanning electron microscopy (SEM) and mechanical properties test of composite. The results show that CVD PyC/SiC composite interface coating can improve the mechanical properties of the composite materials by protecting carbon fibers from liquid Si corrosion during reactive melt infiltration. CVD SiC surface coating can improve the bending strength of C
f
/SiC composite by filling surface defects, cladding fragile parts, coating debonding and remedying internal defects. The bending strength of carbon fiber with PyC/SiC composites coating increases from 150.90 MPa to 217.96 MPa. By means of CVD SiC surface coating, the bending strength is further improved to 266.94 MPa.
2019 Vol. 24 (3): 248-254 [
Abstract
] (
381
)
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(1367 KB) (
741
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255
Effect of pore-forming agent (NH
4
)
2
CO
3
and urea on properties of porous TiAl intermetallics
LIU Yuzuo, LI Xide, LI Juying, PEI Houchang, YANG Junsheng, HE Yuehui
Ti and Al intermetallic compound porous materials with high porosity and controllable pore characteristics were prepared by partial diffusion reaction using Ti and Al powders as raw materials and (NH
4
)
2
CO
3
and urea as pore formation agent. By means of XRD, SEM and metallographic microscopy, the effects of pore-forming agent content on the phase structure, pore size, total porosity, permeability, expansion rate and mechanical properties of TiAl intermetallic compound porous materials were studied. The results show that the pore-forming agent has no effect on the phase composition of porous materials, and the average pore diameters are 30.6 μm and 28.8 μm respectively with adding 7% ammonium carbonate and urea, the volume expansion rate increases to 45.6% and 44.4%, the total porosity is 49.9% and 48.3%, the permeability is 307.3 m
3
/(m
2
·kPa
1
·h
1
) and 302.1 m
3
/(m
2
·kPa
1
·h
1
), and the ultimate tensile strength are 27.85 MPa and 32.49 MPa respectively.
2019 Vol. 24 (3): 255-260 [
Abstract
] (
475
)
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(486 KB) (
1419
)
261
Effects of oxygen fuel rate on microstructure and wear properties of detonation sprayed iron-based amorphous coatings
XIE Lu, XIONG Xiang, WANG Yueming
The Fe-based amorphous coatings were prepared by detonation spray at various oxygen fuel rates (oxygen flow m
3
/h to acetylene flow m
3
/h ratio). The effects of oxygen fuel rate on coating microstructure and wear properties were examined. The effects of microhardness and porosity on the wear properties are also studied. The results show, the amorphous phase contents of coatings were calculated to be 89.73%, 86.23% and 81.46%, respectively, which were higher than those fabricated by other thermal spray techniques. The porosity was tested to be 2.1%, 1.4% and 0.8%, respectively. The wear resistance of Fe-based amorphous coatings was four times better than the stainless steel substrate. The oxygen fuel rate of 1.2:1.0 was proved to be the optimal parameter of fabricating Fe-based amorphous coating. Amorphous coatings with moderate hardness and porosity have the best wear resistance, and the effect of hardness on wear resistance is greater than that of porosity.
2019 Vol. 24 (3): 261-266 [
Abstract
] (
358
)
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(1 KB)
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(597 KB) (
552
)
267
Effect of ultrasonic impact treatment on corrosion fatigue behavior of A106-B steel welded pipes
ZHANG Dehong
Tensile residual stresses caused in manufacturing processes are the main reason of decreasing in corrosion fatigue property of structures. Applying ultrasonic impact treatment is one of the promising and effective methods for enhancing corrosion fatigue properties of materials. In this work, effect of ultrasonic impact treatment on corrosion fatigue behavior of A106-B welded steel pipe, provided by a gas refinery, has been investigated. The results indicated that ultrasonic impact treatment modified the weld toe geometry obviously, weld toe angle is reduced by 50% and weld toe radius is increased by 15.5 times, the stress concentration decreases significantly. Meanwhile, the surface tensile residual stress releases effectively. And the compressive stress is introduced in the sub-surface region. In addition, grain refinement is observed in the surface region of the material. Hence, after ultrasonic impact treatment, both corrosion resistance and fatigue resistance of the specimens are improved, the corrosion fatigue life is increased by 99.4%.
2019 Vol. 24 (3): 267-272 [
Abstract
] (
347
)
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(1 KB)
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(731 KB) (
709
)
273
Effects of carbon content on microstructure and properties of M2 high speed steel prepared by elemental powder method
WU Wendeng, XIONG Xiang, LIU Rutie, LUAN Huaizhuang, HAO Yanrong
The element powder was used as the raw material, the uniformly distributed mixed powder was obtained by two steps ball-milling, and M2 high speed steel was obtained by compression molding and vacuum sintering. The effects of carbon contents on the phase composition, microstructure, density, bending strength and hardness of high speed steel were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and mechanical property testing. The results show that increasing the carbon contents can decrease the sintering temperature and achieve densification at lower temperature. The main components of the sintered samples are α-Fe, M
6
C carbides, MC carbides, and austenite. With the increase of carbon contents, the porosity of M2 high-speed steel decreases and the amount of granular carbides with regular shape increases, which is beneficial to the improvement of bending strength and hardness of the material. However, excessive carbon contents will lead to the precipitation and growth of carbides at grain boundaries and reduce the strength of high-speed steel.
2019 Vol. 24 (3): 273-281 [
Abstract
] (
514
)
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(1 KB)
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(1327 KB) (
1171
)
282
Low temperature combustion synthesis and luminescence properties of CaYAlO
4
: Tb
3+
green phosphors
WANG Shuxue, DENG Jingyu, YU Long, LUO Hu, GAO Xiaofeng, ZHU Desheng
The CaYAlO
4
: Tb
3+
green luminescent phosphors were synthesized by low temperature combustion using urea as fuel and ethylene glycol as complexing agent. The structures of the phosphors were analyzed by XRD to determine the optimum synthesis temperature and urea dosage. The morphology and luminescent effect of phosphors were observed and tested, the effects of the amount of Tb
3+
doping on the luminescence properties of the phosphor were investigated. The results show that the optimum ratio of urea to CaYAlO
4
is
n
(CH4N
2
O):
n
(Ca)=3:1, and the optimum synthesis temperature is 800 ℃. The synthesized samples are spherical particles with a diameter of about 15 nm. The excitation spectra of the phosphors is mainly composed of a broadband excitation band of O
2-
→Y
3+
, O
2-
→Tb
3+
, the excitation peak wavelength is 265 nm. The emission spectra consists of excitation peaks at 490, 545, 586 and 620 nm, which are derived from the
5
D
4
to
7
F
J
(
J
=6, 5, 4, 3) transition of Tb
3+
, respectively. The 545 nm transition intensity is the largest and the phosphor glows green. The optimum doping concentration of Tb
3+
is 0.06%. The concentration quenching is caused by exchange interaction. Under the excitation of UV 265 nm, the color coordinate of the emission spectrum of CaY
0.96
AlO
4
: 0.06Tb
3+
phosphor is (0.320, 0.363), which is located at the junction of green-yellow-white light on the CIE1931 chromaticity diagram, and it is a potential single-doped green luminescent material for LED.
2019 Vol. 24 (3): 282-288 [
Abstract
] (
361
)
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(1 KB)
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(504 KB) (
1898
)
289
Structure of Cu@Pt/C catalyst derived from HKUST-1 and its catalytic activity for methanol oxidation
LONG Xiangyu, LEI Ting, WANG Kunchan, ZHAN Zhenxiang
Copper nitrate and trimesic acid were used as raw materials to fabricate octahedral HKUST-1 by hydrothermal method. HKUST-1 was calcined in Ar protective atmosphere and Cu/C nanoparticles were derived through carbothermal reduction reaction. The Cu@Pt/C catalyst was obtained by soaking Cu/C in potassium chloroplatinic acid solution by galvanic displacement. The morphology and microstructure of Cu@Pt/C catalyst as well as its electrocatalytic activity towards methanol were further characterized by SEM, XRD, XPS and cyclic voltammetry (CV). The results show that the as-prepared Cu@Pt/C catalyst retains special octahedral structure of HKUST-1 and has a core-shell structure formed by Pt coating on the surface of Cu. The electrochemically active surface areas (ECSA) measured by cyclic voltammetry curves in H
2
SO
4
solution is 74.3 m
2
/g, about 1.47 times as much as that of commercial Pt/C. The cyclic voltammetry curves in H
2
SO
4
+CH
3
OH solution shows the ratio of positive sweep peak current density to reverse sweep peak current density
J
f
/
J
b
is 2.18, which is much higher than that of commercial Pt/C. Thus Cu@Pt/C catalyst has better electrocatalytic activity to methanol oxidation and better CO tolerance.
2019 Vol. 24 (3): 289-295 [
Abstract
] (
585
)
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(1 KB)
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(514 KB) (
2055
)
296
Physicochemical properties of activated carbon for sintering flue gas desulfurization and denitrification
ZHAO Hongwei, HUANG Bangfu, LIU Lanpeng, LIU Weisai, ZHAO Simeng
Activated carbon flue gas purification technology is an advanced technology suitable for sintering flue gas treatment and enabling waste resource utilization. SO
2
, NO
x
and other pollutants are adsorbed and catalyzed in the activated carbon tunnel. The adsorption and catalytic properties are mainly depended on the activated carbon physical structure and chemical property. In this study, the physical and chemical properties of coconut shell, nut shell and coal-based activated carbon, such as specific surface area, pore structure, surface morphology, phase composition, constituent elements and surface functional groups were characterized. The results show that the three activated carbons have large specific surface area and are amorphous carbon materials mainly composed of micropores. The main elements are carbon and oxygen, and also contain a small amount of sulfur and chlorine. The coconut shell activated carbon channels are arranged neatly and clearly. It can be seen that the surface of the shell and coal-based activated carbon is uneven, and it is difficult to clearly observe the microporous structure; the surface contains oxygen-containing functional groups closely related to adsorption and catalytic properties. The research results as a basic research on the modification of activated carbon can provide reference for optimizing the modification technology.
2019 Vol. 24 (3): 296-302 [
Abstract
] (
411
)
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(1 KB)
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(717 KB) (
510
)
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