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2018 Vol. 23, No. 4
Published: 2018-08-20
Theoretical Research
341
Study on isothermal section of Ti-Al-Nb ternary system at 1 100 ℃
LI Lin, LIU Libin, ZHANG Ligang
Seventeen Ti-Al-Nb alloy samples were prepared by arc melting, annealing at 1 100 ℃ for 1 080 h, quenching in ice water. Isothermal section of Ti-Al-Nb ternary system at 1 100 ℃ were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). Nine single-phase regions, fifteen two-phase regions and seven three-phase regions under the section (0-75%Al composition interval) were identified. The results show that, compared with the isothermal section of 1 100 ℃ obtained from the optimized calculation results of Witusiewicz and Cupid, there is a significant difference between experimental results (30-60%Al composition intervals) and the calculated results. The experimental results show that two three-phase α
2
+β+γ and β+γ+σ regions and a two-phase β+γ region of the isothermal section of 1 100 ℃ are different from the calculated results.
2018 Vol. 23 (4): 341-346 [
Abstract
] (
349
)
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393
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347
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 was fabricated by powder metallurgy and suitable for high speed and heavy load condition. The effects of lead on high-temperature mechanical properties and tribological behavior of materials were investigated. Through investigating 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 are inordinately increased by adding lead in copper graphite material. And adding Lead can 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 (4): 347-353 [
Abstract
] (
351
)
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321
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354
Sintering kinetics and mechanism of nano Al
2
O
3
particles dispersion strengthened copper by spark plasma sintering
JIANG Shaowen, CHENG Lijin, LIU Yao, LIU Shaojun
The effects of nano Al
2
O
3
particles on Al
2
O
3
dispersion strengthened copper prepared by spark plasma sintering (SPS) were studied systematically by using the hot-pressing sintering model. The results show that the densification process is dominated by grain boundary diffusion and sliding in the early stage of sintering, followed by the grain boundary sliding. And the plastic deformation occurs in the last stage of sintering. The density of the copper strengthened by Al
2
O
3
particles decreases. The Al
2
O
3
particles existing along the grain boundaries can inhibit the densification of copper because the particles can block the movement of grain boundaries and dislocation, which indicates that the densification process required higher activation energy. The deformation mode is mainly twinning, which is resulted from co-existence of the shear stress and the pinning of Al
2
O
3
particles.
2018 Vol. 23 (4): 354-360 [
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304
)
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404
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Engineering and Technology
361
Fabrication and mechanical properties of porous Ni wicks
LI Qiang, GAN Xueping, LI Zhiyou, ZHOU Kechao
Porous Ni wicks with high porosity and controllable pore characteristics were fabricated by powder metallurgy method using polymethylmethacrylate (PMMA) as pore-forming agent and carbonyl Ni powder as raw material. The phase composition, micro-structure and mechanical properties of porous Ni were investigated by X-ray diffraction (XRD), scanning electron microscope SEM and mechanical testing instrument. The effects of sintering temperature, the particle size and content of PMMA on pore structures and mechanical properties of porous Ni were investigated. The results show that with the increase of sintering temperature, the porosity and average pore size decrease, mechanical properties increase. With the increase of the particle size and content of PMMA, the porosity and average pore size increase, mechanical properties decrease. The porous Ni wicks with the most excellent comprehensive performance can be fabricated by sintering at the temperature of 800 ℃ with 80% volume fraction addition of PMMA (5 μm). The porosity, average pore size, flexural strength and compressive strength are 71.9%, 2.37 μm, 25.3 MPa and 8.7 MPa, respectively.
2018 Vol. 23 (4): 361-367 [
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] (
436
)
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544
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368
Laser deposition additive/subtractive hybrid manufacturing process for stainless steel powder based on DMG MORI LASERTEC 65 3D
ZHANG Juntao, ZHANG Wei, LI Yujia, HU Songhao, HUANG Songhai, HE Tianyun, LIU Yong
The rapid preparation of the final quality parts using stainless steel powder was performed on the DMG MORI LASERTEC 65 3D, the first additive/subtractive hybrid manufacturing machine tool in China. The effects of laser power, scanning speed and feeding speed on the section shape, size and surface roughness of stainless steel deposits were studied. Optimizing the deposition parameters and determining the mechanical properties of the integrable parts were also performed. The machining capability level and the application space of the DMG MORI LASERTEC 65 3D for the additive/subtractive hybrid manufacturing of the metal alloy components were also investigated. The results show that the ideal equiaxed grain structure can be obtained by powder deposition and lap joint under the optimized laser forming conditions with the laser power of 2 400 W, the scanning speed of 1 000 mm/min, and the powder feeding rate of 14 g/min. The tensile strength and elongation reach 632 MPa and 46.9% respectively, which are comparable with forgings. Using DMG MORI LASERTEC 65 3D composite machining center, the composite machining of stainless steel special type turbocharged shell by powder laser direct metal deposition and 5 axis milling can be completed. On ensuring the precision of the workpiece, the one-time forming of the difficult parts such as the flange drilling and the joint production can be realized, the efficiency is 5-8 times higher than that of the traditional processing method.
2018 Vol. 23 (4): 368-374 [
Abstract
] (
406
)
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563
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375
Fabrication and performance of Ni-based alloys coating on Cu matrix sintered by spark plasma sintering
TANG Linjun, LI Ruidi, YUAN Tiechui, ZHANG Mei
Ni-based alloys coating on Cu matrix were fabricated by spark plasma sintering (SPS) using Cu matrix and spherical In718 Ni-based alloys powder as raw materials. The effects of dirrerent sintering parameters on the bonding properties and surface properties of the coating were studied. The results show that a diffusion layer generates between Cu matrix and Ni-based alloys coating after SPS, and the diffusion activation energy of matrix and coating are reduced by the pulse current, which can accelerate the diffusion bonding of Cu matrix and Ni-based alloys coating. The Ni-based alloys coating fabricated at the temperature ranging from 850-1 000 ℃ have more excellent performance than Cu matrix by nanoindentation and microhardness testing. When the sintering temperature reaches 950 ℃, the coating has the optimal properties with the microhardness of 370 HV, and the elastic modulus of 179.163 GPa.
2018 Vol. 23 (4): 375-381 [
Abstract
] (
356
)
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277
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382
Pore diameter adjusting and hydrophobic modification of SiO
2
film
TONG Zhi, JI Liangliang, GAO Tingting, WANG Jiayue, LIU Ting
Using ethyl orthosilicate as precursors, the pore size of the SiO
2
membrane was increased by adding PAA, and the hydrophobicity was modified by the method of polymer solution precipitation phase transformation. The thermal stability, chemical composition, phase composition, specific surface area and pore size distribution, surface morphologies and hydrophobicity of the samples were analyzed by the method of TG-DTG, IR, XRD, AFM, BET and contact angle measurements. The results show that the optimum PAA adding amount is 10% (volume ratio), and the pore size is up to 53.73 nm after sintering at 800 ℃. With increasing the PAA adding amount, the pore size of SiO
2
membrane increases, but when the adding amount reaches 15% (volume fraction), sintering at 800 ℃, the membrane surface begins to appear crack. The contact angle of the SiO
2
membrane after hydrophobicity modification can increase to 113°. The pore size of the modified SiO
2
membrane is obviously smaller after hydrophobically modified, it is because that the DDS coating on the membrane surface blocks the pore. It can be concluded that when the PAA is added in an amount between 10% and 15% and the sintering temperature is 600 ℃, the membrane with good hydrophobicity can be obtained.
2018 Vol. 23 (4): 382-388 [
Abstract
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398
)
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276
)
389
Pore characteristic and performance of sintered copper-based porous wicks
HE Da, WANG Lin, LIU Rutie, WANG Zhubo, XIONG Xiang, ZOU Jianpeng
Copper-based porous wicks were prepared by powder metallurgy using NaCl powders as pore forming agents. The effects of pore forming agent content and particle size on the porosity, pore structure, equivalent pore size, permeability and capillary pumping performance of porous wicks were investigated. The relationships among the pore structure, equivalent-pore-size and performances were discussed. The results show that, with increasing the pore forming agent content, the porosity of the porous wicks increases obviously, the number of prefabricated pores inside wicks increases significantly, which results in the connecting of prefabricated pores. With decreasing the particle size of pore forming agent, the porosity of the porous wicks reduces slightly, and the size of the prefabricated pores becomes smaller and the distribution tends to be uniform. Interstitial pores and prefabricated pores inside the wick can make up different types of pore channels. The equivalent pore size of wick is closely related to the structure and quantity of pore channels. By changing the content and particle size of the pore forming agent, different pore structure can be produced, and the equivalent pore size of the materials can be controlled. The permeability and capillary pumping performance of porous wicks is not only determined by porosity, but also by pore structure and pore size. Porous wicks with high porosity, small average equivalent pores size and concentrated pore size distribution show better capillary pumping performances.
2018 Vol. 23 (4): 389-397 [
Abstract
] (
367
)
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347
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398
Capacitive properties of graphene/MnO
2
nano-composite electrode synthesized by electrodeposition
DENG Gao, HE Hanwei
The electrode graphene/MnO
2
nano-composites were obtained by depositing a layer of reduced graphene on the porous MnO
2
nanoscale which was deposited firstly on the foamed nickel substrate by cyclic voltammetry. The morphology, phase and valence state of the material were analyzed by SEM, XRD and XPS. The specific capacitance, cyclic stability and resistance were characterized by the means of cyclic voltammogram, galvanostatic charge/discharge and electrochemical impedance spectrum. The results show that the MnO
2
nanosheets are mostly coated by graphene. The equivalent series resistance and charge transfer resistance decrease form 0.83 Ω, 9.34 Ω to 0.4 Ω, 6.76 Ω, respeactivly. The specific capacitance of graphene/MnO
2
composites at current density of 2 A/g is 501 F/g which has improved 25% compared to bare MnO
2
, and exhibit an 84% specific capacitance retention after 3 000 cycles.
2018 Vol. 23 (4): 398-406 [
Abstract
] (
367
)
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320
)
407
Effects of carbon content on the original particle boundary and mechanical properties of HIP FGH4169 alloy
YAO Caogen, YANG Wenhao, MENG Shuo, YI Danqing, LÜ Hongjun, WANG Bin
Three types of FGH4169 alloy with carbon mass fraction of 0.026%, 0.045% and 0.078% were prepared by hot-isostatic pressing (As-HIP) and heat treatment. The effects of carbon content on the original particle boundary (PPB) and mechanical properties of FGH4169 alloy were investigated. The results show that, with the carbon content increases from 0.026% to 0.078%, the precipitated carbide of FGH4169 alloy increases, and when the carbon content exceeds 0.078%, the PPB formed. The carbides in FGH4169 alloy are mainly MC type carbides rich in Ti and Nb, and the carbon content has no obvious effect on the type and morphology of carbides in FGH4169 alloy; Within a certain range of the C content, as the C content increases, the amount of γ″ phase precipitated in the FGH4169 alloy matrix decreases, and the carbides tend to aggregate at the PPB, resulting in the strength and plasticity gradually decreasing under room temperature and 650 ℃.
2018 Vol. 23 (4): 407-413 [
Abstract
] (
312
)
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193
)
414
Effects of compacting pressure on the microstructure and properties of resin carbon-coated graphite/copper composites
JIANG Xu, XIAO Peng, FANG Huachan, LU Yuhai, LIU Tan, LIU Zeyan
Resin carbon-coated graphite/copper composites were fabricated by power metallurgy method using electrolytic copper powder, natural flake-graphite, resin, silica, et al as raw materials. The effects of compacting pressure on microstructures, electrical conductivity, mechanical and tribological properties of resin carbon-coated graphite/copper composites were investigated. The results indicate that, with increasing the compacting pressure, the connectivity of Cu phase in the composite is better, the distribution of graphite is more uniform, the shape of the graphite is seriously deformed to slender strip, and silicon dioxide is better sandwiched between the copper matrix. Meanwhile, the density and mechanical properties of the composites increase but the conductivity and tribological properties decrease. With increasing the compacting pressure, the electrical conductivity of resin carbon-coated graphite/copper composites decrease from 12.23 MS/m to 6.67 MS/m, the bend strength and hardness (HV) increase from 57.40 MPa to 73.95 MPa and 22.8 to 35.22, respectively. The volume wear rate of resin carbon-coated graphite/copper composites for 10 h increase from 2.49×10
-7
m
3
/(m·N) to 3.04×10
-7
m
3
/(m·N).
2018 Vol. 23 (4): 414-421 [
Abstract
] (
297
)
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714
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422
Anti-oxidation property of 88WC-12Co coating prepared by high velocity oxy-fuel spraying
LIU Baogang, MA Qilin, LIU Chao, PENG Xinke, ZHU Xiaoyun, JI Qing
A high density 88WC-12Co coating was prepared on the surface of 45
#
steel by high velocity oxy-fuel (HVOF). The microstructures, phases, and micro-hardness of the coatings after spraying and oxidation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and micro-hardness tester respectively. The oxidation mechanism of the coating material was also discussed. The results show that 88WC-12Co coating has excellent oxidation resistance under 500 ℃, and the micro-hardness of the coating changes little after oxidation. However, the WO
3
and CoWO
4
phases significantly increased above 500 ℃, and the oxidation resistance and micro-hardness of the coating decreased obviously. The oxidation mechanism of the coating materials is that WC, W
2
C and Co in the coating react with O
2
in the air to form WO
3
and CoWO
4
under high temperature.
2018 Vol. 23 (4): 422-426 [
Abstract
] (
434
)
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221
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427
Preparation and methanol electro-catalysis property of concave hexahedron CuPt nanoparticle
ZHANG Yufang, WANG Qi, WANG Mingpu, JIA Yanlin, LI Zhou
Compared to regular octahedron and tetrahedron Pt-alloy nanoparticles, concave hexahedron CuPt alloy nanoparticles have larger surface area. Moreover, the incorporation of Cu atoms allows it exhibits higher stability under harsh environment. In this paper, unique concave hexahedron CuPt alloy nanoparticles were prepared through a facial hydrothermal method. The structures were characterized by scanning electron microscope (SEM), transmission electron microscope (TEM), scanning transmission electron microscopy-high angle annular dark field (STEM-HAADF), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The results show that the sample is concave hexahedron uniform particles with size of about 30 nm. The as-prepared CuPt/C catalyst exhibits 12 times catalytic activity than commercial Pt/C towards methanol oxidation and presents excellent poison resistance which can prove it to be a potential anode catalyst for fuel cell.
2018 Vol. 23 (4): 427-432 [
Abstract
] (
285
)
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207
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433
Fabrication and electrical properties of nano-silver/graphene composite powders prepared in-situ by chemical reduction
ZHI Ying, GAN Weiping, ZHOU Jian, WANG Xiaoqing
Nano-silver/graphene composite powders were prepared by chemical reduction method using hydrazine hydrate as reducing agent, PVP as dispersant, graphene oxide and silver nitrate as precursor at the reaction temperature of 60 ℃ and the pH of 6. The effects of silver nitrate concentration in solution on the morphology and structure of nano-silver/graphene composite powders were investigated by SEM, XRD, IR and RAMAN. Low temperature curing conductive silver paste was prepared by using graphene/nano-silver composite powder instead of some micron silver powder, and its conductive properties were studied. The results indicate that Ag nanoparticles uniformly distribute in the graphene sheets. Pherical silver particles with better dispersibility and uniform particle size can be obtained by using 0.75 g/L of silver nitrate, 0.25 g/L of graphene oxide. The size of Ag nanoparticles on the graphene sheets centralizes at 100 nm. When using graphene/nano-silver composite powder instead of 4% micron silver powder to prepare conductive paste, the volume resistivity of conductive paste is 1.8×10
-5
Ω·cm. Compared with the conductive paste without graphene/nano-silver composite powder, the resistivity decreases by 61.7%.
2018 Vol. 23 (4): 433-438 [
Abstract
] (
347
)
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217
)
439
Two step synthesis and characterization of high purer PMN-PT composite powder
YU Qiushan, SU Yuchang, RABIGUL•Tursun, TAN Jiang, ZHANG Jing
High purity PMN-PT composite powders was synthesized by two step method at lower temperature, two step synthesis method was used. Firstly, MgO or 4MgCO
3
·Mg(OH)
2
·4H
2
O were mixed with Nb
2
O
5
to get MgNb
2
O
6
. Secondly, 2PbCO
3
·Pb(OH)
2
and TiO
2
were put into MgNb
2
O
6
, or Pb(Ac)
2
·3H
2
O and TiO
2
were put into MgNb
2
O
6
, to synthesize PMN-PT powder. The phase composition of the product was qualitatively analyzed by XRD. The morphologies of the powders and the thermal behavior of precursor were analyzed by SEM and TG-DSC. The effects of raw material system, synthesis temperature and milling time on the purity of product were investigated. The results show that under the same technological conditions, the purity of MgNb
2
O
6
prepared by 4MgCO
3
·Mg(OH)
2
·4H
2
O is higher. Using Pb(Ac)
2
·3H
2
O as Mg source is benefit to improve the purity of PMN-PT. The lower synthesis temperature and higher product purity of PMN-PT powders can be obtained by using Pb(Ac)
2
·3H
2
O crystal with lower melting point and gradually thermal decomposition as raw materials.
2018 Vol. 23 (4): 439-444 [
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] (
265
)
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312
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