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2023 Vol. 28, No. 4
Published: 2023-08-15
Engineering and Technology
Theoretical Research
Theoretical Research
305
Phase field simulation of the effect of doped solute grain boundary segregation and solute dragging on the growth behavior of nano-sized alumina
SHI Jie, TANG Sai, YAO Shuwei, WU Chaozhong, MA Yunzhu, LIU Wensheng
DOI: 10.19976/j.cnki.43-1448/TF.2023020
Phase field simulations combined with sintering experiments were used to study the grain growth behavior and the kinetics of nano alumina under the influence of solute element grain boundary segregation. By introducing the solute dragging effect into the phase field model of alumina polycrystalline grain growth, and relating the solute dragging intensity to the intracrystalline solute atom concentration and atomic equilibrium bias ratio, under various solute atoms equilibrium bias ratios at grain boundaries and initial intracrystalline solute atom concentrations, the growth behavior of alumina grains were investigated, furthermore, the anomalous growth phenomenon of alumina grains with different solute dragging intensity was quantitatively analyzed. By comparing the average size and morphological evolution of the grains, the results of the phase field simulations are consistent with the experimental growth behavior of lanthanum oxide doped nano alumina grains. The results show that the growth of alumina grains is significantly inhibited by the very strong solute dragging effect, leading to a slow growth. While the low solute dragging effect has no significant inhibitory effect on grain growth. From the simulated microstructure evolution results, grain boundary segregation may also trigger the abnormal growth of a few alumina grains, and the specific grains may grow rapidly with overcoming the solute drag effect during the growing process, resulting in the loss of material properties.
2023 Vol. 28 (4): 305-314 [
Abstract
] (
1133
)
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Engineering and Technology
315
High temperature and current-carrying friction and wear properties of resin-coated graphite/copper composites
FANG Huachan, SUN Zhen, XU Yongxiang, ZHANG Zhuo, WANG Jiayu, ZHU Jiamin, CHEN Zhuo
DOI: 10.19976/j.cnki.43-1448/TF.2023025
Resin-coated graphite/copper composites and copper-plated graphite/copper composites were prepared by cold pressing-pressure sintering process using phenolic resin powder, graphite powder, copper-plated graphite powder and electrolytic copper powder as raw materials, respectively, the friction and wear properties of two kinds of graphite/copper composites at room temperature, high temperature and current-carrying were studied, and compared with overseas Roland grounding brush; the effects of resin decomposition on the conductivity, mechanical and friction and wear properties of the composites were analyzed based on the crystal structure of copper matrix and the variation of composite conductivity and mechanical properties at high temperature (200-600 ℃). The results show that the mechanical properties of resin-coated graphite/copper composites at high temperature are better than that of copper-plated graphite/copper composites. When the ambient temperature reaches 600 ℃, the shear strength of resin-coated graphite/copper composites decreases by only 6%, while that of copper-plated graphite/copper composites decreases by 24%. The high temperature (250 ℃) wear resistance and friction stability of resin-coated graphite/copper composites are much better than those of copper-plated graphite/copper composites and Roland brush, the current-carrying friction factor of the resin-coated graphite/copper composites is lower than that of Roland brush. The resin coating of graphite can improve the friction and wear properties of copper matrix composites at high temperature and current-carrying, due to the protection of the resin layer, a continuous and stable graphite lubricating film can be formed even under the conditions of high temperature oxygen and current-carrying, thus reducing the friction contact micro-gap; the carbonized resin breaks into fine hard particles during the friction, which hinder the adhesion and wear between composite and disc; the Cu matrix softening at high temperature is not obvious, so the occurrence of arc decreases.
2023 Vol. 28 (4): 315-328 [
Abstract
] (
270
)
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545
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329
Effects of trace Y and Si doping on the microstructure and mechanical properties of MoAlB ceramics
LIU Yakun, JIAN Yongxin, KONG Hanbing, QI Hongjun, HUANG Guosheng, HE Peipei
DOI: 10.19976/j.cnki.43-1448/TF.2023024
MoB, Al, Y and Si powders were used as raw materials to prepare MoAlB ceramics with trace Y and Si doping by dry milling and vacuum hot pressing methods. The phase composition and microstructure of the sample were characterized and analyzed by X-Ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The hardness, fracture toughness, bending strength and compressive strength of the ceramic were tested to study the effects of different doping elements on the microstructure and comprehensive mechanical properties of MoAlB ceramics. The results show that the MoAlB ceramics are mainly composed of MoAlB, Al
8
Mo
3
and Al
2
O
3
phases, and new phases are produced after doping with trace Si and Y. The doping of Si element can effectively refine the MoAlB grains, while the MoAlB grain size slightly increases after doping with Y element. MoAlB ceramics have good tolerance to damage. The hardness of MoAlB ceramics increases by doping Si and decrease by doping Y. The fracture toughness and bending strength of MoAlB ceramics increase by doping Si, while the bending strength and fracture toughness of ceramics decrease slightly by doping Y. Both Y and Si doping have a positive effect on improving the compressive strength of MoAlB ceramics, and Si doping has a better strengthening effect.
2023 Vol. 28 (4): 329-337 [
Abstract
] (
282
)
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608
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338
Effects of powder mixing process by ultrasonic freeze-drying method on the microstructure and properties of WC-6Co-Go/Al
2
O
3
cemented carbide
ZHANG Zhen, SU Wuli, SUN Lan
DOI: 10.19976/j.cnki.43-1448/TF.2023030
The mixed powders of WC-6Co-GO/Al
2
O
3
were prepared by mechanical ball milling method and ball milling-ultrasonic-freeze-drying method, respectively, and the bulk cemented carbide was prepared by cold press forming-sintering. The effects of the mixing process and the content of GO/Al
2
O
3
composite particles on the dispersion of the mixed powders and the microscopic morphology, density and mechanical properties of the alloy were studied. The results show that ultrasonic freeze-drying can effectively solve the agglomeration problem of GO/Al
2
O
3
composite particles and obtain fine uniform powder particles. In the prepared cemented carbide with the mass fraction of GO/Al
2
O
3
composite particles of 0.15% when mixing powder by ball milling-ultrasonic- freeze-drying method, the composite particles are uniformly distributed among the WC grains to make the effect of refining the grains more significant, and the relative density of the alloy is higher, and the strength of the alloy increases to 2 723.6 MPa, which is about 600 MPa higher than that of the alloy with ordinary mechanical ball milling, and the hardness (HV
30
) and toughness also increase by about 200.0 and 1.0 MPa∙m
1/2
, respectively.
2023 Vol. 28 (4): 338-346 [
Abstract
] (
213
)
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518
)
347
Effects of magnesium oxide and calcium carbonate mineralizers on the performance of porous alumina ceramic
CHEN Guang, WANG Wei, LIANG Lixing, PENG Yonghui, ZHOU Wentao, OUYANG Jing, WANG Zhiguo
DOI: 10.19976/j.cnki.43-1448/TF.2023028
TiO
2
, MgO and CaCO
3
were selected as mineralizing agents for porous alumina ceramics, which were prepared by atmospheric sintering under air atmosphere. The effects of different contents of MgO, CaCO
3
and holding time on the bending strength at room temperature, sintering shrinkage rate, apparent porosity and dissolving efficiency were studied. The results show that the addition of mineralizing agents MgO and CaCO
3
can decrease the shrinkage rate, bending strength at room temperature and density, and increase the apparent porosity and the dissolving efficiency. The shrinkage rate of the samples containing MgO decreases from 1.75% to 0.21% after 1 320 ℃/3 h sintering, and the apparent porosity increases from 33.49% to 36.86%. The shrinkage of the samples containing MaO decreases from 1.88% to 0.38% after 1 320 ℃/6 h sintering, and the apparent porosity increases from 32.94% to 35.46%. The shrinkage rate of the samples containing CaCO
3
decreases from 0.55% to -0.50% after 1 320 ℃/3 h sintering, and the porosity increases from 35.47% to 41.26%. The shrinkage of the samples containing CaCo
3
decreases from 1.16% to -0.21% after 1 320 ℃/6 h sintering, and the apparent porosity increases from 35.96% to 42.44%. When the holding time of heating treatment is extended from 3 h to 6 h, the shrinkage rate of the samples containing mineralizing agent MgO and CaCO
3
increases, while the bending strength at room temperature do not change significantly. The apparent porosity of the samples containing MgO decreases and that of the sample containing CaCO
3
increases. MgO and CaCO
3
can significantly improve the dissolving efficiency. The quality of the samples containing only mineralizing agent TiO
2
is almost unchanged after 72 h of boiling in alkaline liquid (adding cosolvent LiF), the samples containing MgO can be completely dissolved after 24 h of boiling in alkaline liquid (no cosolvent added), and the samples containing CaCO
3
can be completely dissolved after 72 h of boiling in alkaline liquid (adding cosolvent).
2023 Vol. 28 (4): 347-360 [
Abstract
] (
445
)
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695
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361
Effects of pressing pressure on the pore structure and performance of tungsten cathode skeleton for discharge lamps
ZHANG Yuning, WANG Dezhi, WU Zhuangzhi, LIU Xinli, DUAN Bohua
DOI: 10.19976/j.cnki.43-1448/TF.2023036
Tungsten skeleton with uniformly distributed pores is the key material for producing high-performance electronic cathodes and discharge lamps. This study systematically investigated the effects of pressing pressure on the pore structure, mechanical properties of the tungsten skeleton and the performance of discharge lamp. The results show that with the increase of pressing pressure, the porosity and average pore size of the tungsten skeleton decrease, the microhardness and compressive strength increase, and the uniformity index of pore distribution first increases and then decreases. When the pressing presure is 500 MPa, the pore structure and mechanical properties of the tungsten skeleton are the best, the porosity is 26.29%, the average pore size is 1.24 μm, the uniformity index of pore distribution is 4.17, the microhardness is 1 506 MPa, and the compressive strength is 810 MPa. The xenon lamp prepared by the tungsten skeleton as the cathode substrate do not show any flashovers after continuous flashing for 500 000 times, and its cathode emission performance is stable, and the tungsten cathode has not reach its lifespan limit yet, which shows a significant improvement in lifespan compared to existing cathodes.
2023 Vol. 28 (4): 361-367 [
Abstract
] (
336
)
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460
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368
Effects of rare earth Y on the microstructure and properties of recycled 6061 aluminium alloy
QUAN Xiang, WEI Qirong, LI Jiabin, WANG Bin
DOI: 10.19976/j.cnki.43-1448/TF.2023041
The promotion of recycled aluminium alloys can reduce energy consumption and carbon pollution, but the excess of Fe impurities is not conducive to efficient recycling of the alloy. In this paper, recycled 6061 aluminium alloys with different Y contents (0, 0.15%, 0.30% and 0.60% by mass fraction) were prepared by melting and casting. The microstructure and phase composition of the alloys were analysed by metallographic microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD), and the tensile and corrosion resistance were tested. The results show that ternary Al
2
Si
2
Y phases are formed in Y-containing alumium alloys, with significant refinement of the α-Al dendrites and α-Al
15
(Fe,Mn)
3
Si
2
(α-Fe) phases, with the best refinement achieve in alloys with a
w
(Y) of 0.30%. Y addition can significantly enhance the mechanical properties of the alloy, with the highest tensile strength (199.2 MPa) for a
w
(Y) of 0.30% and the highest elongation (14.5%) for a
w
(Y) of 0.60%. In addition, Y addition can also increase the corrosion potential of the 6061 alumium alloy and reduce the corrosion current density, improve the corrosion resistance property of the alloy. In the intergranular corrosion experiments, the alloy with a
w
(Y) of 0.60% possesses the smallest corrosion depth for the same time. Overall, the recycled alumium alloy with a
w
(Y) of 0.60% exhibits both good mechanical and corrosion resistance properties, achieving effective recycling of high iron content 6061 aluminium alloys.
2023 Vol. 28 (4): 368-378 [
Abstract
] (
284
)
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572
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379
Hydrogen evolution performance of amorphous NiCoSe electrode for alkaline electrolysis of water
PENG Zhenxin, HE Hanwei
DOI: 10.19976/j.cnki.43-1448/TF.2023045
Ni and Co co-doped amorphous selenide was synthesized on nickel mesh as hydrogen evolution catalyst electrode by electrode position method, and the morphology and microstructure of NiCoSe electrode were observed and analyzed by scanning electron microscopy, X-ray diffractometer, transmission electron microscopy and X-ray photoelectron spectrometer, and the electrocatalytic hydrogen evolution performance of the electrode was tested by electrochemical experiments. The results show that the NiCoSe electrode surface is embedded with NiCoSe spherical particles, and no obvious cracks. NiCoSe compound is amorphous and can provide more low-energy barrier cavities. The appropriate ratio of Ni and Co co-doping can modulate the electronic structure of Se to shift the electronic binding energy of the catalyst, which in turn enhances the adsorption ability of the catalyst to H atoms, resulting in a higher intrinsic catalytic activity of the NiCoSe hydrogen evolution catalyst electrode. At a current density of 10 mA/cm
2
in 1 mol/L KOH solution, the overpotential of the NiCoSe cathode is 83 mV, and the Tafel slope is 108.98 mV/dec. The step controlling the reaction rate is the adsorption process of the catalyst on H atoms. The current density decay rate is less than 5% after 60 h electrolysis.
2023 Vol. 28 (4): 379-389 [
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291
)
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967
)
390
Microstructures and properties of carbon fiber powders modified iron-based powder metallurgy materials
WANG Jiayu, FANG Huachan, ZHANG Qianqian, DUAN Zhiying, FANG Zhou, ZHANG Zhuo, CHEN Zhuo, XU Yongxiang, REN Zian
DOI: 10.19976/j.cnki.43-1448/TF.2023047
MC
sf
/Fe and C
fp
/Fe powder metallurgy materials were prepared by pressing-vacuum sintering using reduced Fe powder as the matrix, micron short carbon fibers (MC
sf
) with a length of about 20 μm and carbon fiber particles (C
fp
) with a particle size of 1-4 μm as the dispersoid, respectively. Natural graphite (NG) with an average particle size of 10 μm as the raw material was used to prepare NG/Fe powder materials for comparison. The effects of micronshort carbon fibers and carbon fiber particles on the microstructure, physical properties, mechanical properties and dimensional changes were investigated. The results show that the activity of carbon fiber particles is much higher than that of graphite and degummed short carbon fibers (DC
sf
), and the maximum mass loss rate at 800 ℃ in air atmosphere is 3.75 times that of graphite and 16.6 times that of degummed short carbon fibers. Compare with NG/Fe and MC
sf
/Fe powder metallurgy materials, the dimensional stability of C
fp
/Fe powder metallurgy materials during sintering is greatly improved, with the maximum radial expansion and shrinkage rates of 0.39% and 0.14%, respectively; the strength and toughness are the highest, with the density, flexural strength, shear strength and tensile strength of 6.91 g/cm
3
, 736.9 MPa, 205.7 MPa and 334.8 MPa, respectively. The elongation reach 10.5%, and the fracture mode of the materials change from a brittle along-crystal fracture to a completely severe nest fracture.
2023 Vol. 28 (4): 390-403 [
Abstract
] (
286
)
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404
Effects of seeding and boron-doped nucleation on diamond coating of cemented carbide surface
YU Han, XIA Xin, ZHU Junkui, WANG Run, ZHANG Long, DOU Jinjie, LI Jing, MA Li, WEI Qiuping
DOI: 10.19976/j.cnki.43-1448/TF.2023035
In order to improve the quality of diamond coating on cemented carbide tools and increase the nucleation density to enhance the uniformity of the coating, the hot filament chemical vapor deposition was used to deposit nanodiamonds (NDs) onto the surface of YG8 cemented carbide substrate, the effects of seed crystal planting and boron doping in the nucleation stage on the nucleation and growth of diamond coatings were studied. The results show that when hydrogen-terminated nano-diamond suspension with a mass concentration of 1.0% is used for seed crystal plant, the seed density on the sample surface is the highest, the distribution is the most uniform, and the subsequent growing diamond grain size is finer and more uniform, which can improve the uniformity and flatness of the coating. Boron-doped nucleation can inhibit the formation of graphite phase in the diamond coating and improve the purity of the diamond coating, but increase the full width at half maximum (FWHM) of the diamond peak, which will have an adverse effect on diamond crystallization. Seed crystal planting can reduce the FWHM of diamond peak from 17.43 cm
-1
to 10.91 cm
-1
, improve the quality of boron-doped nucleation crystallization, and weaken the adverse effects of boron-doped. By combining boron doping and seed crystal planting, the minimum diamond grain size is about 1-3 μm, the
I
D
/I
G
value is as high as 12.83, and the coating quality is good. In addition, under the joint action of seed crystal planting and boron-doped nucleation, the bonding performance of the diamond coating is significantly improved, and it can reach the HF1 level at 600 N.
2023 Vol. 28 (4): 404-412 [
Abstract
] (
260
)
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521
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