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2020 Vol. 25, No. 6
Published: 2020-12-15
Engineering and Technology
Engineering and Technology
449
Characterization of Y
2
O
3
reinforced Ti-6Al-4V composite powder prepared by electrode induced gas atomization
LIU Lianping, CHEN Shiqi
Y
2
O
3
reinforced Ti-6Al-4V (TC4 alloy) composite powders were prepared by electrode induced gas atomization (EIGA). The flowability and apparent density of the powders were measured. The morphology and distribution of Y
2
O
3
were observed by optical microscope (OM) and scanning election microscope (SEM). The phase and element composition of Y
2
O
3
/TC4 composite powders were analyzed using X-ray diffraction (XRD) and plasma emission spectrometer (PES). The results show that the Y
2
O
3
/TC4 composite powders prepared by EIGA have good sphericity with a small amount of non-spherical powders. Satellite powders and Y
2
O
3
particles are adhered on the surface. The flowability of the composite powders is poor, ranging from 33.9-45.6 s/50 g, which is greatly affected by Y
2
O
3
original particle size. The apparent density is mainly affected by the Y
2
O
3
content (
w
(Y
2
O
3
)), which increases with the increase of Y
2
O
3
content. Y
2
O
3
particles maintain the original shape and size, which are distributed in TC4 matrix uniformly. The interface with matrix is smooth and flat. Y
2
O
3
particles are easy to agglomerate, and the micromorphology is mainly influenced by the original particle size. Y
2
O
3
with ring distribution are found in large-size composite powders. The Y
2
O
3
content in small-sized composite powders is less, and the distribution is uniform.
2020 Vol. 25 (6): 449-457 [
Abstract
] (
359
)
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(1 KB)
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504
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458
Effects of SiC content on the composite membrane structure and friction properties of Ti-6Al-4V alloy for internal combustion engine
WANG Xue, YU Xiutao
Ti-6Al-4V alloy composite membrane for internal combustion engine was prepared by adding SiC particles into micro arc oxidation electrolyte. The microstructure and friction properties of the composite film were studied by SEM and friction-wear test. The results show that many net micropores form on the surface of the sample without SiC. When the SiC content is lower than 5.0 g/L, uniform microporous structure forms on the membrane surface. With the increase of SiC content to 7.5 g/L, the number of pores in the membrane layer decreases. The membrane layer and the substrate of Ti-6Al-4V alloy is bonded well and almost no crack is found. Moreover, partial pore structure forms in the interface area of the membrane layer. The film thickness decreases with the increase of SiC content. The friction coefficient decreases first and then increases with increasing SiC content, many grooves with larger width and depth form in the alloy matrix. The wear mechanism is abrasive wear.
2020 Vol. 25 (6): 458-464 [
Abstract
] (
260
)
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(1 KB)
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(1053 KB) (
303
)
465
Quantitative characterization of Inconel 718 alloy powder particle shape and optimization of its SLM forming process
XU Yang, ZHANG Rong, XIAO Zhiyu
The grain shape of Inconel 718 alloy powder for selective laser melting (SLM) was quantitatively characterized by integrating grain shape parameters. The surface quality, densification behavior, microstructure and mechanical properties of Inconel 718 alloy formed by selective laser melting (SLM) were studied as well. The results show that the overall sphericity of Inconel 718 alloy powder is relatively high. Excessive or deficient volume energy density will lead to obvious nodularization and porosity on the surface of SLM alloy. When the volume energy density is in the range of 120-140 J/mm
3
, the forming effect of the sample is better. After processed with optimized forming parameters, a large number of directional dendrites form in the deposited sample and the dendrites in molten pool on the side of the sample grow centripetally perpendicular to the boundary. The elongations of specimen at 650 ℃ and room temperature are 1.7 times and 2.6 times higher than these of the standard forging respectively. Although the tensile strength at 650 ℃ is lower than that at room temperature, the elongation of high temperature stretching is 1.5 times that at room temperature.
2020 Vol. 25 (6): 465-474 [
Abstract
] (
312
)
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843
)
475
Microstructure and corrosion properties of laser cladding CoCrW coating on 37Mn5 steel surface of oil and gas pipeline
WANG Rongjian, LIANG Jinlu, HUANG Xiaoyu, SHI Haixin
The CoCrW coating was prepared on the surface of 37Mn5 steel in oil and gas pipeline by laser cladding method. The microstructure and hardness of the coating were studied, and the corrosion tests of CoCrW coating and 37Mn5 steel were conducted with 3.5%NaCl solution. The results show that γ-Co and some Cr
7
C
3
phases were formed in CoCrW coating. A good interface with metallurgical bonding is formed between the coating and the substrate. Oriented dendrites were formed in the coating and layered dendrites were formed in the cladding structure. The mean hardness of CoCrW coating was 476 HV, and the hardness of CoCrW coating was lower in the area close to the interface. The coating has a larger arc resistance and better corrosion resistance than the substrate. The coating can insulate the matrix from the corrosive solution and avoid the corrosion of the matrix. CoCrW coating has higher corrosion potential and resistance than 37Mn5 steel, which is 1.137 V and 20 208 Ω∙cm
2
respectively, CoCrW coating has stronger corrosion resistance than 37Mn5 steel.
2020 Vol. 25 (6): 475-479 [
Abstract
] (
372
)
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(1 KB)
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(502 KB) (
655
)
480
Microstructure and nano-indentation behavior of detonation sprayed iron-based amorphous coating
OUYANG Sheng, CHU Zhiqiang, TANG Qiuhao, XIE Lu
The iron-based amorphous coatings were prepared by detonation spray under three kinds of oxygen fuel ratios. The microstructure and nanoindentation behavior were examined by XRD, SEM and nanoindenter. The results show that the amorphous phase contents of coatings under 1:1, 1.2:1 and 1.5:1 are calculated to be 88.71%, 86.18% and 81.36%, respectively. The variation speeds of indentation depth are similar under different load, indicating the homogenous coating structure. In similar position, the coatings under oxygen fuel ratios of 1:1 and 1.2:1 have higher hardness, exhibiting smaller maximum indentation depth. In the longitudinal direction, the variation of nanohardness is very small. In the transverse direction, the nanohardness value decreases from 16.75 GPa to 10.25 GPa with increasing the distance from the coating to the substrate.
2020 Vol. 25 (6): 480-485 [
Abstract
] (
329
)
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(536 KB) (
592
)
486
Microstructure and properties of bindeless Ti(C,N)-based cermets prepared by spark plasma sintering
LU Saijun, KANG Xiyue, ZHANG Meimei, HE Yuehui
The binderless Ti(C,N)-based cermets were fabricated by spark plasma sintering using Ti(C,N) powder as raw materials. The microstructure, mechanical properties, wear resistance of the materials were studied. Effects of sintering temperature, carbon black addition, carbides additives and solid solution raw powders on the relative density and mechanical properties were investigated. Furthermore, the (Ti,W,Mo,Ta) (C,N) solid solution powder fabricated by the dissolving of other alloying elements in the lattice of Ti(C,N) was also used to prepare the binderless cermets. The experimental results show that the relative density and mechanical properties of binderless cermets increase with increasing sintering temperature. With increasing carbon black content, the relative density and mechanical properties increase firstly and then decrease. After adding WC, Mo
2
C and TaC carbides into Ti(C,N) powder, or using (Ti,W,Mo,Ta) (C,N) solid solution powder as raw materials, the oxygen content of Ti(C,N)-based cermets with bindeless phase is obviously reduced. The density and mechanical properties of the materials are greatly improved, and the friction coefficient and wear resistance of the materials are lower. The binderless Ti(C,N)-based cermet prepared by (Ti,W,Mo,Ta) (C,N) solid solution powders exhibits hardness (HV
30
) of 19.9 GPa, transverse rupture strength of 1 030 MPa and fracture toughness of 7.8 MPa·m
1/2
.
2020 Vol. 25 (6): 486-496 [
Abstract
] (
429
)
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(1 KB)
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(1060 KB) (
465
)
497
Microstructure and properties of pure molybdenum block prepared by selective electron beam melting
LI Huixia, ZHU Jilei, TAN Yannni, LIU Bin, CHEN Rui, ZHAO Pei, YI Yang
The block of pure molybdenum was fabricated for the first time by selective electron beam melting. Its impurities, microstructure, density and micro-hardness were tested using chemical analysis, metallurgical microscopy, chemical balance and microhardness tester. The results show that the impurity increments of the as-build pure molybdenum such as C, N, O and H are not more than 0.001%. Using a single-melting process, the microstructure of pure molybdenum along the deposition direction present scoarse columnar crystal characteristics, and there are a few microcracks along the columnar grain boundary. Using a double-melting process, the grain size is refined and the microcrack phenomenon is suppressed. The better selective electron beam double-melting process is as follows: the primary melting current is 12 mA, and the velocity is 0.6 m/s; the secondary melting current is 12 mA, and the velocity is 0.89 m/s. Under the better process, the relative density of the as-build pure molybdenumblock is higher than 99% with a density of (10.15±0.13) g/cm
3
. The microhardness (HV
0.2
) is 185-200 and shows no anisotropy.
2020 Vol. 25 (6): 497-504 [
Abstract
] (
305
)
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(1 KB)
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(1586 KB) (
761
)
505
Effects of SPS process parameters on microstructure and high-temperature oxidation resistance of ZrB
2
-MoSi
2
-SiC composite ceramics
ZHANG Yudong, LI Jiwen, WANG Nannan, PAN Kunming, ZHANG Liangliang
ZrB
2
-MoSi
2
-SiC composite ceramics (ZMS15 ceramics) were prepared by spark plasma sintering (SPS) at the sintering temperature of 1 700-2 000 ℃, heating rate of 75-150 ℃/min and holding time of 3-10 min. The effects of sintering temperature, heating rate and holding time on the relative density and the oxidation resistance at 1 200 ℃ of the composite ceramics were studied. The results show that the relative density of ZrB
2
-MoSi
2
-SiC composite ceramics increases with the increase of sintering temperature and heating rate, and the relative density reaches the maximum value when the holding time is 7 min. ZMS15 ceramic forms a double-layer structure during oxidation. The outer layer is glassy SiO
2
layer, and the inner layer is granular ZrO
2
layer. With increasing sintering temperature, the high temperture oxidation resistance of the material increases. The optimal SPS process for ZrB
2
-MoSi
2
-SiC composite ceramics is sintering temperature of 2 000 ℃, heating rate of 125 ℃/min, and holding time of 7 min. The relative density of the ceramics is greater than 98.5%, and the mass change is less than 8 mg/cm
2
after oxidation at 1 200 ℃ for 72 h.
2020 Vol. 25 (6): 505-512 [
Abstract
] (
302
)
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(1 KB)
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(850 KB) (
787
)
513
Effects of ball milling time on microstructure and properties of NbMoTaWVCr refractory high entropy alloy
PENG Haiyan, KANG Zhixin, LI Xiaozhen, ZHOU Li, LONG Yan
Refractory NbMoTaWVCr high entropy alloy (HEA) was fabricated by combination of mechanically alloying (MA) and spark plasma sintering (SPS) using powders of Nb, Mo, Ta, W and V as raw materials. The effects of milling time on phase composition, microstructure evolution and mechanical properties were investigated. The results show that mechanical alloying can be achieved after 40 h ball milling, and the single-phase BCC NbMoTaWVCr high entropy alloy powder is obtained. With the increase of milling time, the grain size is refined and the micro strain increases.The bulk alloy sintered by SPS at 1 500 ℃ consists of BCC matrix, Laves phase and oxide phase. The content of precipitated phase increases with the increase of milling time. With the increase of milling time, the compressive yield strength increases first and then decreases and the plasticity decreases gradually. The NbMoTaWVCr refractory high entropy alloy sintered from powders milled for 40 h exhibits an excellent yield strength of 3416 MPa and plastic strain of 5.3%.
2020 Vol. 25 (6): 513-519 [
Abstract
] (
367
)
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(1 KB)
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1110
)
520
Thermal degradation and judder characteristics of the friction facing for automobile dry clutch enhanced by potassium hexatitanate whisker
XIE Maoqing, WANG Leigang
Friction facings for automobile clutches are the key parts that affect the service life, power transmission efficiency and comfort of the clutch. Improving the stability of the friction factor and the attenuation characteristics of judder during the sliding process is an important technical mean to avoid the unstable transmission torque and vehicle judder. In this paper, a kind of potassium hexatitanate whisker reinforced clutch friction facing was prepared. The thermal decay characteristics of the modified materials were studied and the judder bench test was carried out. The results show that the addition of 8% (mass fraction) potassium hexatitanate whiskers to enhance the friction coefficient of the automobile clutch friction facing at 400 ℃ is greater than or equal to 0.2, which is better than the requirement of the German Volkswagen 3101 program thermal decay test standard at 350 ℃. Its average damping factor at 500 r/min and 800 r/min after 20 000 cycles is less than or equal to 0.05 N∙m∙s, which meets the German 3102 procedure judder test regulations. After 20 000 cycles, the maximum damping factor of 500 r/min is less than or equal to the specified standard of 0.1 N∙m∙s, which has a significant damping effect on judder.
2020 Vol. 25 (6): 520-526 [
Abstract
] (
283
)
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(1 KB)
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(556 KB) (
981
)
527
Effect of nozzle inlet angle on the atomization process of Si
3
N
4
particles prepared by dry granulation
LIAO Dahai, FANG Yongzhen, ZHOU Jiangen, GAN Zhenhua, FANG Changfu, WU Nanxing
In the process of preparing Si
3
N
4
particles by dry granulation, volume of fluid (VOF) method and realizable
k-ε
model (
k
is turbulent kinetic energy,
ε
is dissipation rate) in turbulence model were used to simulate and calculate the influence of the deflection angle α of the nozzle inlets on air core, atomization cone angle and adhesive velocity at nozzle outlet. The experimental verification of Si
3
N
4
ceramic particles prepared by dry granulation was carried out. The results show that when the deflection angle
α
increases from 0° to 30°, the area of air core in nozzle increases from about 18% to 25%. The mean diameter of air core increases, and the velocity gradient of binder at nozzle outlet increases from 4.43-5.06 m/s to 5.69-6.32 m/s. The spray cone angle increases from 63° to 74° and then the breakup process of the liquid film can be accelerated. When the deflection angle increases to 45°, the average diameter of the air core, the velocity of adhesive at the nozzle outlet and the atomization cone angle are the minimum. The experimental results show that the particle size of Si
3
N
4
is the smallest when the deflection angle of atomizer is 30°. The numerical results are in good agreement with the experimental results.
2020 Vol. 25 (6): 527-537 [
Abstract
] (
286
)
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(1 KB)
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(943 KB) (
478
)
538
Effect of coating on steel back of Cu-based powder metallurgy brake materials on carburizing resistance
CAO Wenming, YAO Pingping, ZHOU Haibin, ZHAO Lin, XU Liang, XIAO Yelong
Three kinds of steel back (45
#
steel) with different surface coatings were used to prepare Cu-based powder metallurgy brake materials. The effects of surface coatings on the anti carburizing and thermal fatigue resistance of the steel back and the bonding properties between the steel back and friction materials were studied. The results show that Ni coating on the surface can not prevent the carburization of the graphite backing plate to the steel back during pressure sintering, while the surface plating of Cu or Cu + Ni can effectively prevent the carburization of the steel back. Under the condition of thermal fatigue, the strength and hardness of the steel back coated with Ni are improved by carburizing, and the bonding strength with friction material is good, but it is easy to warp and crack. The back plates coated with Cu and Cu + Ni are not easy to warp, deform and crack. The bonding strength between Cu plated back plate and friction materials is poor. The bonding strength between the steel back coated with Cu + Ni and the friction material is good.
2020 Vol. 25 (6): 538-544 [
Abstract
] (
276
)
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(1 KB)
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(677 KB) (
573
)
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