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2024 Vol. 29, No. 2
Published: 2024-04-15
Engineering and Technology
Theoretical Research
Theoretical Research
83
Finite element simulation of the SPTAs bulks preparation process by SPS and its microstructure analysis
LÜ Kuang, TAN Xiaoyue, TU Qingbo, DING Jie, MA Yingqun, LUO Laima, WU Yucheng
DOI: 10.19976/j.cnki.43-1448/TF.2024005
In this paper, the effects of temperature and current fields on the homogeneity of self-passivation tungsten alloys (SPTAs) prepared by spark plasma sintering (SPS) were systematically investigated by combining experiments and simulations, and the relationships between sintering temperature, sintering time, current density, and the microstructure of SPTAs were established. The results show that the temperature of the SPTAs bulks with different sizes during SPS consolidation is unevenly distributed along the radial direction, resulting in the measured temperature being much lower than the actual temperature of the samples. Combined with the microstructure characterization, it is found that increasing the current density during sample sintering can shorten the sintering time, and has a positive effect on obtaining fine-grained and homogeneous microstructure, but it is necessary to consider the difference of grain size caused by radial temperature gradient. This study can provide a reference for the SPS preparation process design of large-sized SPTAs bulks.
2024 Vol. 29 (2): 83-92 [
Abstract
] (
1055
)
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194
)
93
Damage characterization of multiphase refractories under compression based on mesomechanics
HUANG Zhixing, WANG Zhigang, LIU Changming, LI Xianjun
DOI: 10.19976/j.cnki.43-1448/TF.2024013
For the nonlinear mechanical behavior of multiphase composite refractory under compression, on the basis of microscopic damage mechanics, the improved generalized self-consistent model was solved inversely, the damage behavior of multiphase refractory under compression load was investigated, and a method that can characterize the nonlinear damage behavior of multiphase refractory under compression load was proposed. Taking the AMC (aluminum-magnesium-carbon) multiphase refractory as an example, the mechanical behavior under compression was characterized by this method. The results show that the characterization results of this method are in good agreement with the experimental values, which provides an idea and a theoretical basis for the damage characterization of multiphase composite refractory.
2024 Vol. 29 (2): 93-100 [
Abstract
] (
108
)
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(480 KB) (
166
)
Engineering and Technology
101
Effects of Sc and Zr co-addition on structural evolution and mechanical properties of a 7xxx aluminum alloy with high Zn content
ZHANG Xiaoqiang, WANG Feng, HE Junyang, GU Ji, DU Yong, SONG Min
DOI: 10.19976/j.cnki.43-1448/TF.2024003
High Zn content 7xxx aluminum alloy with co-addition of Sc and Zr were prepared by traditional casting and thermomechanical processing technology in this paper. The effects of co-addition of Sc and Zr on the microstructure and mechanical properties of a 7xxx aluminum alloy with high Zn content was investigated by room temperature tensile test, scanning electron microscope, X-ray diffraction, and transmission electron microscope. The results show that the tensile strength of the newly designed and fabricated high Zn content aluminum alloy (
w
(Zn)=10.9%) is 769 MPa, while the elongation is 4.7%. The high Zn content directly leads to the formation of high density nanoscale η' phase, generating superior precipitation hardening effect. The primary Al
3
(Sc,Zr) phase formed by the co-addition of Sc and Zr helps to refine the solidification structures, while the secondary Al
3
(Sc,Zr) phase precipitated during aging effectively inhibits recrystallization and dislocation movements. These two aspects together result in exceptional grain boundary hardening effect.
2024 Vol. 29 (2): 101-108 [
Abstract
] (
116
)
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(951 KB) (
175
)
109
Precipitation phase evolution of a new third-generation Ni-based single crystal superalloy containing osmium
YU Jingyi, ZHANG Lijun, ZHOU Kechao, HUANG Zaiwang
DOI: 10.19976/j.cnki.43-1448/TF.2024007
The application of Re and Ru in Ni-based single crystal superalloys is often limited by their content and phase stability, and it is important to search for new elements that can replace Re and Ru at the same time. In this study, a new type of Ni-based single crystal superalloy with high content of Os was designed, the cast single crystal alloy was prepared by the traditional Bridgman technique, and the alloy was subjected to solution aging treatment, the precipitation phase evolution of the alloy was investigated by optical microscopy and scanning electron microscopy. The results show that Os and W in the as-cast alloy segregate in the dendrite core region, while Al, Ta, and Ti segregate in the inter-dendritic region, even after a long time of solution heat treatment, there is still a slight segregation of Os and W. Due to the elemental segregation in the dendritic region, the γ′ phase in the inter-dendritic region is more likely to be transformed into a cubic shape than that in the dendrite core after the primary aging treatment, and the secondary aging treatment can slightly increase the size and volume fraction of the precipitated phase, and transform the shape from cubic to round.
2024 Vol. 29 (2): 109-117 [
Abstract
] (
90
)
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(2331 KB) (
188
)
118
Microstructure and properties of CoCrFeNiTi
x
high-entropy alloy coating by laser cladding
GONG Shulin, WANG Yongdong, LI Yanchun, SONG Meihui
DOI: 10.19976/j.cnki.43-1448/TF.2024015
In order to study the effects of Ti element on the microstructure and properties of high-entropy alloy coatings, CoCrFeNiTi
x
(
x
=0.4, 0.6, 0.8, 1.0) coatings were prepared on the surface of Q235 substrate using laser cladding technology, and the phase structure and microstructure of the coatings were analysed by XRD, SEM, EDS, etc., and the hardness and wear resistance of the coatings were tested by micro-Vickers hardness tester and friction and wear tester. The results show that the microstructure of the coating changes from cellular crystal to dendritic crystal, and the phase structure consists of BCC and FCC. The increase in microhardness of the coatings is attributed to the combined effect of solid solution strengthening and fine crystal strengthening, and the wear mechanisms of the coatings are mainly abrasive wear and adhesive wear, accompanied by slight oxidation. When
x
=0.8, the hardness (HV) of the coating reaches 524, with relatively flat abrasive marks and excellent wear resistance.
2024 Vol. 29 (2): 118-124 [
Abstract
] (
148
)
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(1163 KB) (
143
)
125
Fabrication of silicon carbide powders prepared from C/C composite processing residues and its microstructure and properties
YU Wenrui, ZHANG Fuqin
DOI: 10.19976/j.cnki.43-1448/TF.2024008
Using C/C composite processing residue as a carbon source and thoroughly mixing with silicon powder, silicon carbide powder for single crystal growth was prepared by high-temperature synthesis method. The microstructure and surface properties of silicon carbide powder were studied. The results indicate that the crystal form of the prepared silicon carbide powder is β-SiC, and the powder partially inherits the tubular and ridge-like structures of C/C composite processing residues. In Raman spectra, the ratio of the full width at half maximum of the folded transverse optic to the folded longitudinal optic of the powder is 0.709, and its relative purity is higher than that of silicon carbide powder prepared by the same process using graphite powder as the carbon source. The silicon carbide powder has porous characteristics with a specific surface area of 25.742 6 m
2
/g, and can be used for physical vapor transport single crystal growth process, furthermore, its feasibility has been preliminarily verified.
2024 Vol. 29 (2): 125-132 [
Abstract
] (
99
)
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(1700 KB) (
172
)
133
Preparation and property of low loss niobate microwave dielectric ceramics
ZHENG Haoran, QIU Rong, YANG Pan, ZHAO Xiaofang, YU Shihui
DOI: 10.19976/j.cnki.43-1448/TF.2024011
In order to obtain niobate-based microwave dielectric ceramics with lower loss, Zn[(Ge
0.5
Mo
0.5
)
x
Nb
1-
x
]
2
O
6
(
x
=0.05, 0.10, 0.15, 0.20) niobate microwave dielectric ceramics were prepared by solid-state reaction method with ZnO, GeO
2
, MoO
3
, and Nb
2
O
5
as main raw materials. XRD, SEM, and vector network analyzer were used to characterize the phase composition, microscopic morphologies, and dielectric properties of materials, respectively. The results show that when the sintering temperature is 1 180 ℃, the surface morphology of microwave dielectric ceramics with
x
=0.05 is the most compact, with the maximum relative density of 94.58%, and has good microwave dielectric properties, dielectric constant
ε
r
is 21.7, quality factor
Q
f
is 64 610 GHz, and temperature coefficient of resonant frequency
τ
f
is -81.2×10
-6
/℃.
2024 Vol. 29 (2): 133-138 [
Abstract
] (
110
)
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(810 KB) (
138
)
139
Preparation and characterization of Cu-Fe alloy by electric co-deposition
CHANG Shuaiqing, GAN Xueping, LIU Chaoqiang
DOI: 10.19976/j.cnki.43-1448/TF.2024014
Cu-Fe alloys have excellent electrical and thermal conductivity and unique electromagnetic shielding property, low cost and wide application, but is prone to component segregation. In order to solve the problem, Cu-Fe alloy coatings were prepared by electric co-deposition with CuSO
4
∙5H
2
O and FeSO
4
∙7H
2
O as raw materials. The coatings were characterized by scanning electron microscopy, energy dispersive spectrometer, and transmission electron microscopy. The effects of current density, main salt ion concentration, and complexing agent concentration on the content and microstructure of the coatings were studied, and the growth process of the coating was explored. The results show that when the concentrations of Fe
2+
, Cu
2+
, and citric acid (complexing agent) are 0.016, 0.04, and 0.2 mol/L, respectively, current density is 2.0 A/dm
2
, the Cu-Fe alloy coating is bright and smooth without cracks, and has a high Fe content (
w
(Fe)=14.87%). The distribution of Cu and Fe in the coating is uniform, and there is no single Fe phase, which proves that metastable alloy is formed during electric co-deposition. Nanocrystals are widely distributed in the coating, with grain sizes ranging from 20 nm to 100 nm. Cu-Fe coating grows densely from small dendrites, and then differentiate into small particles. The particles grow gradually with the extension of time, and there is significant preferential growth and obvious gap between particles. The non-uniform electric field and nucleation position distribution are the main reasons leading to the disordered growth of dendrites.
2024 Vol. 29 (2): 139-150 [
Abstract
] (
172
)
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(3578 KB) (
279
)
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