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2019 Vol. 24, No. 4
Published: 2019-08-15
Theoretical Research
303
Thermodynamic optimization of the Sm-Sn binary system
JIANG Yun, HUANG Guoxing, ZHENG Linghong, LIU Libin, ZHANG Ligang
Based on the comprehensive evaluation of experimental data of Sm-Sn system, the equilibrium phase diagram of the binary alloy system was optimized and calculated by CALPHAD method. The liquid phase was described by the substitutional solution model, and the thermodynamic functions of stoichiometric intermediate compounds were explained by the Neumann-Kopp rule. Through optimization, a set of thermodynamic parameters with self-consistency are obtained. The phase diagrams calculated by the thermodynamic parameters coincide with the experimental information reported in the literature. The calculated liquid mixing enthalpy in 1 203 K and solid phase formation enthalpy in 295 K are also in good agreement with the existing thermochemical data.
2019 Vol. 24 (4): 303-307 [
Abstract
] (
423
)
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816
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Engineering and Technology
308
Research progress of wear-resistant and corrosion-resistant coatings prepared by laser cladding
ZHANG Kai, CHEN Xiaoming, ZHANG Lei, FU Li, LIU Wei, JIANG Zhipeng
Wear-resistant and corrosion-resistant coatings manufactured by laser cladding technology is used to solve the wear and corrosion problems of parts in harsh environments. It has good prospects for development. In this paper, the development history of laser cladding technology is briefly introduced, and the research progress of the influence of laser cladding technology on the preparation of wear-resistant and corrosion-resistant coatings is summarized emphatically at home and abroad, as well as the relationship between the change of molten pool and laser cladding process parameters and the structure properties of the cladding layer. The research progress of laser cladding technology for wear-resistant and corrosion-resistant coatings in specific application parts and working conditions is also described, including parts of hydraulic engineering equipment, aerospace equipment, petroleum mining equipment, etc. Finally, it summarizes the key issues that restrict the comprehensive industrial application of the technology, as well as the research directions that need to be carried out in terms of process and equipment.
2019 Vol. 24 (4): 308-314 [
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495
)
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2130
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315
Effects of laser power on microstructure and properties of Ni-based alloy cladding layers
CHEN Xiaoming, JIANG Zhipeng, ZHANG Lei, LIU Wei, ZHAO Jian, FU Li
The effects of laser power on the microstructure and wear-resistant and corrosion-resistant properties of Ni-based alloy cladding coatings were studied in this paper, in order to get the optimal laser power parameters and obtain Ni-based alloy coatings with good metallurgical bonding and excellent wear resistance and corrosion resistance. The results showed that Ni-based alloy coating prepared by laser cladding is metallurgically bonded to the substrate without obvious cracks and holes, and the main composition of the Ni-based alloy coating is γ-(Ni,Fe) solid solution, and a small amount of Cr
3
C
7
phase appeared in relatively lower power. With increasing laser powers, the element contents of Ni and Cr in the cladding layers decreased, the element content of Fe in the cladding layers increased, and the thickness of cladding layers increased from 545 μm to 1 100 μm, microstructure was coarsened obviously and the transition from dendrites to cellular dendrites tendency. Meanwhile, with increasing laser powers, the microhardness decreased from 508 HV to 375 HV, and the wear resistance of the specimens decreased, but the anti-corrosion resistance was enhanced, the corrosion current density decreased from 4.347×10
-7
A/cm
2
to 8.257×10
-8
A/cm
2
.
2019 Vol. 24 (4): 315-320 [
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437
)
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806
)
321
Effect of brush hardness on electrical contact and tribological behavior of Au9Ni against Au35Ag5Cu disc
QU Qiang, ZHOU Xiong, LUO Bo, ZHANG Lei
The Au9Ni alloy wires with hardness of 230.51, 251.93 and 270.30 HV were used as the research objects. The current-carrying wear mechanism of the Au9Ni alloy wire was studied, and the relationship between hardness and its current-carrying friction and wear behavior has also been explored in atmospheric. The results show that the brush hardness has an important influence on their tribological properties of the atmospheric current. As the brush hardness increased from 230.51 HV to 270.30 HV, the average friction coefficient and contact voltage drop of the material increased from 0.82, 46.42 mV to 1.02, 98.72 mV, respectively, and during the friction period, bouncing is weakend by increased hardness the electrical noise (
R
RMS
) decrease from 6.15 mΩ to 3.37 mΩ that means the curve of friction and contact stability were improved. With the increase of hardness, the roughness of worn surface (
Ra
) decrease from 1.10 μm to 0.57 μm the wear mechanism of brush with hardness of 230.51 HV is mainly adhesive wear. As the brush hardness increases, the wear mechanism gradually evolves into a composite wear mechanism with adhesive wear and abrasive wear.
2019 Vol. 24 (4): 321-328 [
Abstract
] (
395
)
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695
)
329
Microstructure and properties of Cu-3Ag-0.5Zr alloy powder prepared by argon gas atomization
WEN Jingyu, LIU Zuming, MA Mengmei, LÜ Xueqian
Cu-3Ag-0.5Zr alloy powder was fabricated by argon gas atomization, and its particle size distribution, oxygen content, apparent density, flowability, morphology, phase and microstructure were investigated. The results show that argon gas atomized Cu-3Ag-0.5Zr alloy powders are almost spherical and normal distribution. 90% of particle size of the powders is less than 200 μm. The median diameter
D
v
(50)
is about 49.9 μm. Oxygen content (mass fraction) of Cu alloy powders with size less than 50 μm, between 50-106 μm and more than 106 μm are 0.067%, 0.039% and 0.013%, the apparent density are 4.39, 4.95 and 5.02 g/cm
3
, and the flowability are 16.59, 15.96 and 15.62 s/50 g, respectively. The microstructure of the powders is fine and homogeneous, and the average grain size is 3.82 μm. The microstructure of large particle size powders is dendritic crystal structure and the microstructure of small particle size powders is equiaxed crystal structure. There is no obvious Ag or Zr second-phase precipitation in powder matrix, and the structure of powder is a homogeneous supersaturated solid solution.
2019 Vol. 24 (4): 329-333 [
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484
)
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(608 KB) (
558
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334
Effect of forging on magnetic properties of powder metallurgy pure iron soft magnetic materials
XIN Lijun, JIANG Limin, ZHANG Guang’an, WANG Hongjian, ZHOU Qi
The soft magnetic material of pure iron was prepared by powder metallurgy method, and then hot forging was carried out. The density and magnetic properties of the forgings at different forging temperatures and pressures were tested, the microstructure was detected and the optimal forging process of pure iron soft magnetic material of powder metallurgy was obtained. The results show that the density and magnetic properties of the forgings can be improved effectively by increasing the forging pressure and forging temperature. With the increase of forging pressure, the saturation magnetization
M
s increases and the coercivity
H
c decreases and then increases. With the increase of forging temperature, both
M
s and
H
c increase. The density and relative density of pure iron soft magnetic material are 7.821 g/cm and 99.38% respectively,
M
s=2.024 T and
H
c=997.3 A/m, at forging temperature and pressure of 1 200 ℃ and 1 166 MPa. After annealing at 1 450 ℃, the
H
c of forgings decreases to 437.0 A/m.
2019 Vol. 24 (4): 334-339 [
Abstract
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363
)
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763
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340
Preparation of powder metallurgy Fe-13Cr-0.5Mo-3Nb breathable steel and application in mold
CHEN Gang, ZHU Lihua, WU Xusheng, SHEN Shucheng
In this work, a high carbon and niobium-containing stainless steel Fe-13Cr-0.5Mo-3Nb was proposed. A porous breathable steel was fabricated by powder metallurgy. The effects of powder size, green density, sintering temperature on the structures and properties of the steel were studied. And the applying property of injection molded was researched. The results show that the breathable steel has high strength, good breathability and excellent corrosion resistance prepared by the powder size of 96-120 μm, the average green density is 5.6 g/cm
3
, and the sintering temperature is 1 280 ℃. The yield strength and corrosion resistance of the breathable steel are 295 MPa and 0.016 mm/y, respective. Moreover, the surface quality of the injection molded product can be improved. Compared with imported similar materials, the mechanical properties of die strength index can be improved obviously on the basis of ensuring good air breathability and corrosion resistance.
2019 Vol. 24 (4): 340-349 [
Abstract
] (
506
)
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(823 KB) (
641
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349
Microstructures and mechanical properties of ZrH
2
/6060 aluminum alloy fabricated by selective laser melting
TU Cheng, LIU Yunzhong, HU Liang, ZHOU Zhiguang
The 6060+1%ZrH
2
composite powder was prepared by short-time low energy ball milling with 1% (mass fraction ,the same as below) submicron ZrH
2
powder added into 6060 aluminum alloy atomized powder. Then 6060 aluminium alloy containing zirconium was prepared by Selective laser melting (SLM) forming process. The microstructures and mechanical properties of 6060 aluminium alloy were analyzed and tested with different SLM process conditions. The effects of ZrH
2
addition on the microstructures and mechanical properties of 6060 aluminium alloy were studied. The results show that the density of 6060 aluminium alloy increases from 93.8% to 97.8% after adding 1% submicron ZrH
2
, and the cracking of formed sample is restrained. The surface spheroidization phenomenon is weakened, the surface quality is remarkably improved, the surface is smooth, and there are no large pores and other defects. The grain size of the formed sample is significantly refined from 56 μm to 3 μm. Compared with 6060 aluminum alloy without sub-micron addition of ZrH
2
, the tensile strength, yield strength, elongation and micro-hardness of AA6060+Zr specimens increase by 26.0%, 73.0%, 126.8% and 21.8% respectively.
2019 Vol. 24 (4): 349-357 [
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481
)
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921
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358
Effect of diamond structure on the adhesion of the nanoscale diamond film coated to WC-Co cemented carbide
DENG Biao, ZHOU Kechao, XIAO He, WEI Qiuping, MA Li, YI Mingkun, LUO Yijie, LI Liang
Diamond structure has an important effect on the adhesion of diamond film coated cemented carbides. In this paper, the WC-Co substrate was pretreated by two-step method, and the hot-filament chemical vapor deposition (HFCVD) actor was used to fabricate nano-scale diamond films under the condition of 2%, 3% and 4%CH
4
concentration in CH
4
/H
2
/Ar atmosphere, respectively. The surface morphology, section morphology and the sp
3
/sp
2
phase of the films were analyzed by SEM and Raman, respectively. The adhesion properties of the films were evaluated by scratch test. The results show that increasing the concentration of methane can effectively refine the grain of the diamond, which is beneficial to obtain nanocrystalline diamond. As the the grain size of diamond decreases from hundreds of nanometers to tens of nanometers, the sp
2
phase in the film and the nucleation density increases. The critical loads of diamond films deposited on each sample are 15.2, 6.9 and 9.1 N, respectively. Combined with the microstructure of the films, it can be concluded that the diamond film with high purity and high nucleation density contributes to the improvement of the adhesion of the nano-scale diamond film.
2019 Vol. 24 (4): 358-364 [
Abstract
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415
)
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737
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365
Effects of nano-TiB
2
particles on microstructure and mechanical properties of AA2024 deposited by selective laser melting
HU Liang, LIU Yunzhong, TU Cheng, ZHOU Zhiguang
With a broad freezing range and a high content of alloy elements, 2024 prepared by selective laser melting still has some defects like hot tearing and columnar grains. In this work, TiB
2
/2024 composite powders with different nanoscale TiB
2
contents were prepared by low-energy ball milling and used for selective laser melting process. The effects of TiB
2
content on the phase, microstructure and mechanical properties of 2024 aluminium alloy were studied by means of X-ray diffraction, metallographic microscope, EBSD and SEM. The results show that the addition of 1% nano-TiB
2
makes the coarse columnar grains transform into equiaxed grains, and improve density of SLM samples the grain size decreases from 19.9 μm to 4.25 μm and the relative density increases from 97.3% to 98.2%. Tensile strength, elongation and micro-hardness increase by 23%, 208% and 5.1%, respectively. Furthermore, tensile strength and elongation reach 401.2 MPa and 10.4% respectively at T6 state. When the mass fraction of TiB
2
increases to 3%, the refining effect is weakened to 3.97 μm, and the agglomeration of nano-TiB
2
grew to micron-scale. The density and comprehensive mechanical properties of the samples decreases sharply.
2019 Vol. 24 (4): 365-373 [
Abstract
] (
554
)
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1062
)
374
Effect of atomization pressure on particle size and morphology of Inconel 625 alloy powder for selective laser melting
LI Xiang, ZENG Keli, HE Pengjiang, LUO Hao, ZONG Wei, SONG Xinqiang, ZHU Jie
Inconel 625 alloy powders for selective laser melting were prepared by vacuum induction furnace melting-high purity argon atomization with atomization pressure of 3.5-5.0 MPa. The particle size distribution and morphology of the powders were characterized by scanning electron microscopy. At the same time, the yield of 45-105 μm granular powder with different atomization pressure was calculated. The results show that the particle size distribution of Inconel 625 alloy powder prepared by vacuum atomization is lognormal distribution, and the curve of particle size distribution has obvious double peaks, which conforms to the secondary breaking mechanism of gas atomization powder. With increasing atomized gas pressure, the particle size becomes finer and the powder yield in the target section increases, but when the atomizing pressure exceeds 4.5 MPa, the particle size changes insignificantly. Furthermore, with the atomization pressure increasing, the more satellite will be produced, and the sphericity of the powder will decrease. And the optimum value of atomization pressure is 4.5 MPa. The average diameter
d
m
of the powder is 72.2 μm, and the yield of 45-105 μm granular powder is 78.1%. The sphericity of the powder is good, which fully meets the requirements of selective laser melting equipment for powder.
2019 Vol. 24 (4): 374-378 [
Abstract
] (
532
)
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486
)
379
Effect of reaction temperature and reaction atmosphere on the synthesis of ZrSiO
4
SONG Keqi, FAN Jinglian, CHENG Huichao, LIU Tao, HAN Yong
ZrSiO
4
was synthesized from nanosized ZrO
2
powders and nanosized amorphous SiO
2
powders by solid-state reaction. The initial reaction temperature and the temperature at the highest yield in air, the effect of the reaction atmosphere vacuum and air on the synthesis of ZrSiO
4
and corresponding microstructure were studied. The results show that the initial reaction temperature of ZrSiO
4
can be as low as 1 225 ℃ when the reaction time is 4 h in air atmosphere. When holding time is extended to 8 h, the initial reaction temperature of ZrSiO
4
synthesis can be further reduced to 1 200 ℃. When synthesized in air, oxygen promotes the transformation of amorphous SiO
2
to cristobalite, which makes the formations of ZrSiO
4
increase rapidly above 1 300 ℃. When synthesized in vacuum, because amorphous SiO
2
is wrapped on the surface of ZrO
2
particle at high temperature, it is helpful to obtain fine ZrSiO
4
grains by blocking the growth of ZrO
2
particles.
2019 Vol. 24 (4): 379-384 [
Abstract
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518
)
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744
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385
Microstructure and properties of powder metallurgical Cu-Cr-Zr alloy by heat-treatment and deformation
ZHAO Fan, LIU Zuming, LÜ Xueqian, LI Quan, PENG Kai
Two-stage heat treatment/deformation processing with solution/cold-rolling and aging/cold-rolling of Cu-Cr-Zr alloy prepared by SPS was carried out, the microstructure, mechanical properties and electrical conductivity of the alloy were investigated. The results show that the SPSed Cu-Cr-Zr alloy matrix structure with uniform composition and fine grains, as well as the multi-scale of nano and sub-micron and multi-structure second phase with uniform distribution on the matrix were obtained by solution treated at 980 ℃ for 50 min, cold-rolled at 30% deformation, aged at 450 C for 2 h and cold-rolled at 70% deformation. The interactions of precipitation strengthening of the multi-scale second phase and strain hardening improved the strength and conductivity of the Cu-Cr-Zr alloy, and its tensile strength and electrical conductivity were 625 MPa and 79%IACS respectively, which were 143% and 20% higher than that of SPSed alloy.
2019 Vol. 24 (4): 385-390 [
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632
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(900 KB) (
995
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