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2024 Vol. 29, No. 1
Published: 2024-02-15
Engineering and Technology
Theoretical Research
Theoretical Research
1
Numerical simulation of process parameters for selective laser sintering of coal gangue/PES composite materials
QU Fang, ZHAI Qin, YUAN Kai, WANG Pingshan, SU Dan
DOI: 10.19976/j.cnki.43-1448/TF.2024004
Based on the Gaussian heat source model, thermal conductivity model, and Flow-3D software, a powder particle model of coal gangue and polyethersulfone (PES) powder, as well as a three-dimensional model of coal gangue/PES (CPES) composite material powder bed, were established to numerically simulate the temperature field during the selected laser sintering process of CPES composites. The influences of laser power, scanning speed, and scanning space on the formation of single and double pass sintered layers were studed, the values of sintering process parameters was predicted and verified through experiments. The results show that when the laser power is 15 W, the average temperature of the melten pool is 596 K, the impact strength of the sintered part is 179.4 MPa, the melt path is relatively straight, the spheroidization phenomenon disappears, and the bonding with the powder is good, forming a high-quality melt path; When the scanning speed is 1 800 mm/s, the average depth of the molten pool is 99 um, the average width is 200 μm, and the impact strength of the sintered part is 173.5 MPa, the melting area is almost circular, the length of the melten pool is the shortest, the heat accumulation in the melt path is significant, and no deflection phenomenon is found; When the scanning space is 100 μm, the overlap rate of the melt path is 60.8%, and the impact strength of the sintered part is 176.2 MPa, the surface transition of the overlap area between two melt paths is smooth and continuous, without any holes or spheroidization phenomenon.
2024 Vol. 29 (1): 1-10 [
Abstract
] (
540
)
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(651 KB) (
84
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11
Hot deformation behavior of Co8W6Mo5Cr4V3 powder high speed steel
YANG Lilin, CHEN Xuemin, CHEN Shuo, ZHAO Liping
DOI: 10.19976/j.cnki.43-1448/TF.2023064
Co8W6Mo5Cr4V3 powder was prepared by melting, electroslag remelting, and gas atomization method, then Co8W6Mo5Cr4V3 powder high speed steel was prepared by hot isostatic pressing. Its thermal deformation behavior was studied through hot compression experiments that were conducted on the powder high speed steel under different deformation conditions. Based on the obtained stress-strain curves, a thermal deformation constitutive equation was established and a hot processing map was drawn. The results show that the flow stress of Co8W6Mo5Cr4V3 powder high speed steel decreases with the increase of deformation temperature or the decrease of strain rate. The correlation coefficient between the predicted flow stress through the constitutive equation and the experimental flow stress is 0.995, which can be used to predict the stress of powder high speed steel under different deformation conditions. According to the hot processing map, the optimal deformation temperature and strain rate of powder high speed steel are 1 100-1 150 ℃ and 0.1-1.0 s
-1
, respectively.
2024 Vol. 29 (1): 11-19 [
Abstract
] (
46
)
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(1040 KB) (
85
)
Engineering and Technology
20
Effects of low temperature annealing on microstructure and residual stress of René104Sc nickel-base superalloy fabricated by laser powder bed fusion
ZHOU Huan, LIU Zuming, LI Jian, ZHANG Yazhou, JIANG Daoyan
DOI: 10.19976/j.cnki.43-1448/TF.2023016
Residual stress in additive manufacturing can cause deformation or even cracking of as-built parts, seriously reducing mechanical properties. In this paper, the microstructure evolution and its effect on residual stress of laser powder bed fusion fabricated René104Sc nickel-base superalloy during low temperature annealing were systematically observed. The results show that after annealing treatment, the cellular structure disappears, the texture strength decreases, the microstructure becomes more uniform and the residual stress is released. After annealing at 500 and 600 ℃, the microstructure has no obvious change and the residual stress decreases slightly. After annealing at 800 ℃, the residual stress in sample center decreases from 63 MPa to 21 MPa, and a large amount of γ′ phase precipitates in the alloy, resulting in brittle fracture and elongation decreases from (25.2±2.6)% to (4.7±1.6)%. After annealing at 700 ℃, the alloy undergoes partial recrystallization, the residual compressive in sample center decreases from 63 MPa to 29 MPa, and its comprehensive mechanical properties are the best with hardness (HV
0.3
) and tensile strength of 499±4 and (1 461±7) MPa, respectively, which are 18% and 56% higher than that as-built one (423±9, (935±25) MPa). The results provide an effective way to eliminate the residual stress in the additive manufacturing nickel-base superalloy parts and prevent cracking in the storage or post heat treatment process.
2024 Vol. 29 (1): 20-34 [
Abstract
] (
47
)
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(2350 KB) (
80
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35
High-performance B
4
C-LaB
6
composite ceramics fabricated via rapid hot press sintering
XU Zhiwei, PENG Ke, YUAN Tiechui
DOI: 10.19976/j.cnki.43-1448/TF.2023075
In order to solve the problem that boron carbide (B
4
C) is difficult for sintering densification and poor toughness, the B
4
C-LaB
6
composite ceramics were fabricated via rapid hot press sintering at 2 000 ℃ and 30 MPa with B
4
C and lanthana (La
2
O
3
) as raw materials. The effects of additive La
2
O
3
content on the microstructures and mechanical properties of B
4
C-LaB
6
composite ceramics were investigated, and the toughening mechanism of LaB
6
was studied. The results show that the B
4
C-LaB
6
composite ceramics with
w
(La
2
O
3
)=3% have better comprehensive mechanical properties, the relative density, Vickers hardness, bending strength, and fracture toughness reach 99.51%, 36.56 GPa, 547.43 MPa, and 4.18 MPa∙m
1/2
, respectively. LaB
6
refines the grain, and improves the relative density and fracture toughness of the B
4
C-LaB
6
composite ceramics. The toughening mechanism of LaB
6
is related to crack deflection and grain cracking.
2024 Vol. 29 (1): 35-44 [
Abstract
] (
41
)
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(1402 KB) (
80
)
45
Ti plate embedding diamond particles boron-doped diamond electrode and its properties
DOU Jinjie, LIU Dianhong, JIANG Luan, LI Jing, MA Li, WEI Qiuping
DOI: 10.19976/j.cnki.43-1448/TF.2023077
Diamond particles were embeded on the surface of Ti plate by a powder pellet mill, boron-doped diamond (BDD) films were deposited on this substrate by hot filament chemical vapor deposition to prepare a new Ti/D/BDD electrode, and Ti/BDD electrode was prepared for comparision. The morphology, B doping level, and electrochemical performance of the electrode were characterized by scanning electron microscope, Raman spectrometer, and electrochemical workstation, the degradation effect of the electrode simulated wastewater was tested by ultraviolet-visible spectrophotometer. The results show that the Ti/D/BDD electrode has a larger electrochemical active area and lower film impedance than the Ti/BDD electrode at the same deposition time, which makes the electrode show higher degradation rate and lower degradation energy consumption for acid orange G. When deposited for 10 h, Ti/D/BDD electrode has the highest electrical double layer capacitance (1.87 mF) and the lowest film resistance (0.4 Ω); after 120 min of degradation, the chromaticity removal rate of Ti/D/BDD electrode is 53.1% higher than that of Ti/BDD electrode, and the energy consumption is reduced by 14.2%.
2024 Vol. 29 (1): 45-52 [
Abstract
] (
53
)
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(704 KB) (
73
)
53
Preparation, physical and mechanical properties of La
2
O
3
second-phase reinforced tungsten alloys
FU Kaichao, XU Dang, SANG Changcheng, CHEN Ruizhi, CHEN Pengqi, CHENG Jigui
DOI: 10.19976/j.cnki.43-1448/TF.2023082
Second-phase reinforced tungsten (W) alloy has excellent properties such as high strength, great creep resistance, and irradiation resistance, it is a highly promising plasma facing material for fusion reactor. In this paper, W-La
2
O
3
composite powders with different La
2
O
3
contents (
w
(La
2
O
3
)=0-1.5%) were prepared by solution combustion synthesis (SCS) using ammonium metatungstate and lanthanum nitrate (La(NO
3
)
3
) as the main raw materials. Then the La
2
O
3
second-phase reinforced W alloys were further prepared by spark plasma sintering, and the effects of La
2
O
3
content on the microstructures and mechanical properties of the W alloys were investigated. The results show that W-La
2
O
3
composite powders with average particle size of approximately 200 nm, well dispersion, and uniform distribution of La
2
O
3
can be successfully synthesized using SCS. The addition of appropriate amount of La
2
O
3
can effectively improve the physical and mechanical properties of W alloys. With the increase of La
2
O
3
contents, the microhardness and tensile strength of the La
2
O
3
second-phase reinforced W alloys show a tendency that increases first and then decreases, while the relative density gradually decreases. The microhardness (HV) of W5La alloy reaches the maximum value of 524.10 at
w
(La
2
O
3
)=0.5%. After the addition of the second-phase of La
2
O
3
, the fracture mode of the W matrix is changed from W grain fracture predominantly to a mixed fracture with the co-existence of intergranular fracture and transgranular fracture, and the grain size is reduced with an average grain size of 4.1 μm. Compared with pure W, W5La alloy has higher tensile strength and lower ductile-brittle transition temperature (DBTT), and its tensile strength at room temperature and 500 ℃ is 279.6 MPa and 498.9 MPa, respectively, and DBTT is 200-300 ℃.
2024 Vol. 29 (1): 53-62 [
Abstract
] (
42
)
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(1085 KB) (
61
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63
Effect of texture on the superelasticity of Ni
50.8
Ti shape memory alloy for laser directed energy deposition
WU Huiting, LI Ruidi, KANG Jingtao, ZHENG Dan
DOI: 10.19976/j.cnki.43-1448/TF.2023081
NiTi shape memory alloy exhibits excellent superelasticity and shape memory effect due to thermoelastic martensitic phase transformation, and is widely used in medical devices, aerospace and other fields. Ni
50.8
Ti shape memory alloy was prepared by laser directed energy deposition, the influences of forming angle on the superelasticity and stability of the alloy were analyzed by room temperature compression and cyclic compression experiments, the microstructure and texture characteristics of alloys with different forming angles were analyzed by X-ray diffraction analysis, electron backscatter diffraction and other characterization methods, and the influences of microstructure and texture on the superelasticity and stability of Ni
50.8
Ti shape memory alloy were further studied. The results show that the Ni
50.8
Ti shape memory alloy prepared by laser directed energy deposition is composed of B2 austenitic phase with uniform matrix composition and no cracking phenomenon. Alloy at 90°
Y
-axis shows the best superelasticity at room temperature, and the worst superelasticity at 0°. At the same time, the 45° alloy shows a strong 〈112〉 texture and the 90° alloy shows a strong 〈110〉 texture, the superelasticity of the strong texture alloy is better than that of the weak texture (60°) and the unfavorable orientation (0°) alloy, the texture has a significant influence on the microstructure and superelasticity of the Ni
50.8
Ti shape memory alloy.
2024 Vol. 29 (1): 63-73 [
Abstract
] (
51
)
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74
Microstructure and properties of silver-graphite composites prepared with silver-coated graphite powders
ZHANG Yihuan, GAN Xueping, LIU Chaoqiang
DOI: 10.19976/j.cnki.43-1448/TF.2024002
Silver-graphite composites are electrical contact materials with ideal comprehensive properties. In order to solve the problem of uneven distribution of graphite and weak interfacial bonding in the composites, the dense and uniform pre-copper-silver-coated graphite powder was prepared by the two-step electroless plating method of copper plating first and then silver plating on the surface of graphite, and the high performance silver-graphite composites were prepared by hot press sintering. The results show that the introduction of pre-copper plating technology can improve the distribution uniformity of graphite in the composites, reduce the pores and cracks at the interface, improve the density of the composites, furthermore, make the silver matrix form a continuous three-dimensional network structure around the graphite particles, and effectively improve the mechanical properties and electrical conductivity of the composites. Compared with the activation-silver-coated graphite composite, the hardness (HV) of the pre-copper-silver-coated graphite composite increases from 22.9 to 33.0 by 44.1%; the bending strength increases from 70.4 MPa to 97.2 MPa by 38.1%; the resistivity decreases from 0.11 μΩ·m to 0.08 μΩ·m.
2024 Vol. 29 (1): 74-82 [
Abstract
] (
41
)
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(1337 KB) (
72
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