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Soldering of Zr-based bulk metallic glass and copper by Au-12Ge eutectic alloy

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Rare Metals 2019年第1期38卷 52-58页

作者： Jun Wang Jing Cui hong-chao kou Heng Guan Jin-Shan Li State Key Laboratory of Solidification Processing Northwestern Polytechnical University

Zr-based bulk metallic glass and copper with different surface roughness were soldered using low temperature eutectic Au-12 Ge(wt%) solder on a thermomechanical simulator. The cross-sectional microstructures of the brazed joints were analyzed by scanning electron microscopy(SEM) and transmission electron microscope(TEM) in detail, and the compositional distribution along the interface was analyzed by energy-dispersive spectrometer(EDS). Results show that the surface roughness of base metals plays an important role in the quality of the brazed joint because the surface roughness can enlarge the effective contact area, which can improve the brazing surface quality between two materials. A moderate roughness of treated Zr-based metallic glass of 18 μm is shown to be the best for the soldering, while the surface roughness has a weak effect on the soldering behavior of Au-12 Ge solder on copper. After soldering, long-range diffusion of atoms occurs between the base metal and solder, and five distinct regions are formed at the joint region.

关键词： Bulk metallic glass Soldering Au-Ge eutectic alloy Interface

Solidification microstructure characteristics of Ti–44Al–4Nb–2Cr–0.1B alloy under various cooling rates during mushy zone

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Rare Metals 2016年第1期35卷 35-41页

作者： Peng Han hong-chao kou Jie-Ren Yang Guang Yang Jin-Shan Li The State Key Laboratory of Solidification Processing Northwestern Polytechnical University

Beta-solidifying TiAl alloy has great potential in the field of aero-industry as a cast *** the present work,the influence of cooling rate during mushy zone on solidification behavior of Ti-44Al-4Nb-2Cr-0.1B alloy was investigated.A vacuum induction heating device combining with temperature control system was *** Ti-44Al-4Nb-2Cr-0.1B alloy solidified from superheated was melted to β phase with the cooling rates of 10,50,100,200,400 and 700 K·min^（-1）,*** show that with the increase in cooling rate from 10 to 700 K·min^（-1）,the colony size of α_2/γ lamella decreases from 1513 to48 urn and the solidification segregation significantly *** the content of residual B2 phase within α_2/γlamellar colony decreases with the increase in cooling *** addition,the alloy in local interdendritic regions would solidify in a hypo-peritectic way,which can be attributed to the solute redistribution and enrichment of Al element in solidification.

关键词： β-solidifying TiAl alloy Cooling rate Mushyzone Solidification microstructure

Hot corrosion behavior and mechanical properties degradation of a Ni–Cr–W-based superalloy

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Rare Metals 2017年第1期36卷 23-31页

作者： Ruj-Feng Dong Tie-Bang Zhang Rui Hu hong-chao kou Jin-Shan Li State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi'an 710072 China

The effect of molten salts on the mechanical properties of a Ni–20Cr–18W(wt%)-based superalloy was investigated in this work. The hot corrosion characteristics and the microstructural evolution during the hot corrosion process were analyzed. The corrosion scale forms on the surface of the substrate, and its thickness increases gradually during the process. The element of S invades the substrate. The corrosion products mainly include Ni O,Ni_3S_2 and Cr_2O_3. The hot corrosion in molten salt makes the specimens rough and flawed. The serration grain boundaries are observed in the hot corroded *** tensile strength and elongation of the original alloy are^1023 MPa and ~15 %, respectively. After corroded for5 h, the tensile strength and elongation of the specimen decrease to ~771 MPa and ~7 % and diminish to^814 MPa and ~9 % for the specimen corroded for 10 *** hot corrosion process deteriorates the mechanical properties of the alloys. And the tensile strength and elongation of the specimen corroded for 20 h sharply decrease to ~539 MPa and ~3 %, respectively. The nonmonotonic variation of the mechanical properties of the specimen occurs for the specimens corroded for 10 h,which is related to the competition between the depredation of the molten salts and the strengthening process by carbides and the serrated grain boundaries.

关键词： Ni-based superalloys Hot corrosion behavior Microstructural evolution Grain boundary Mechanical properties

Evolution of microstructure and hardness in a dual-phase Al0.5CoCrFeNi high-entropy alloy with different grain sizes

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Rare Metals 2020年第2期39卷 156-161页

作者： Hao-Xue Yang Jin-Shan Li Tong Guo William-Yi Wang hong-chao kou Jun Wang State Key Laboratory of Solidification Processing Northwestern Polytechnical UniversityXi’an710072China

Cold-rolling with subsequent annealing was carried out to produce recrystallized structures with different grain sizes in an Al0.5CoCrFeNi high-entropy alloy to systematically investigate the grain growth behavior and varying *** results show that recrystallized microstructures can be achieved through an annealing process at 1200℃for 75 min to 16 h,and the average grain size in this study ranges from 5.33 to 30.03 μ*** hardness shown to be affected through grain coarsening was then measured as a function of the grain size,and it is found to follow the classical Hall-Petch strengthening.

关键词： High-entropy alloy Grain growth Recrystallization Grain boundary Hall-Petch effect

Limitation of the Johnson-Mehl-Avrami equation for the kinetic analysis of crystallization in a Ti-based amorphous alloy

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International Journal of Minerals,Metallurgy and Materials 2010年第3期17卷 307-311页

作者： Jun Wang hong-chao kou Hui Chang Xiao-feng Gu Jin-s han Li hong Zhong Lian Zhou State Key Laboratory of Solidification Processing Northwestern Polytechnical University Xi＇an 710072 China School of Information Technology Jiangnan University Wuxi 214122 China

The primary crystallization of the Ti40Zr25NisCu9Bc18 amorphous alloy was studied by isochronal differential scanning calorimetry （DSC）. The activation energy was determined by the Kissinger-Akahim-Sunose method. Trying to analyze the crystallization kinetics of the Ti40Zr25NigCu9Be18 amorphous alloy by two different methods, it was found that the crystallization kinetics did not obey the Johnson-Mehl-Avrami equation. A modified method in consideration of the impingement effect was proposed to perform kinetic analysis of the isochronal crystallization of this alloy. The kinetic parameters were then obtained by the linear fitting method based on the modified kinetic equation. The results show that the isochronal crystallization kinetics of the amorphous Ti40Zr25Ni8CugBe18 alloy is heating rate dependent, and the discrepancy between the Johnson-Mehl-Avrami method and the modified method increases with the increase of heating rate.

关键词： amorphous alloys crystallization kinetics Johnson-Mehl-Avrami equation impingement

Microstructure Evolution and Phase Transformation of Ti–6.5Al–2Zr–Mo–V Alloy During Thermohydrogen Treatment

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Acta Metallurgica Sinica(English Letters) 2015年第4期28卷 505-513页

作者： hong-chao kou Han-Lei Zhang Yu-Dong Chu Dong Huang Hai Nan Jin-Shan Li State Key Laboratory of Solidification Processing Northwestern Polytechnical University Beijing Institute of Aeronautical Materials

Thermohydrogen treatment （THT） is an effective way to refine microstructure and improve the mechanical properties of the titanium alloys. In the current work, as-cast Ti-6.5Al-2Zr-Mo-V alloy was hydrogenated with different hydrogen contents and processed solution aging. Accordingly, the microstructure evolution and phase transformation were analyzed. Results show that during solution aging, eutectoid decomposition occurs and the product is a mixture of coarse primaryα, fine eutectoid product and undecomposed βH. The size of primary α is closely dependent on the hydrogen content, and large primary α can be obtained at medium hydrogen content. Further, the influence of hydrogen content on the growth of primary α phase was revealed. The primary α is much fine, and the eutectoid product is relatively homo- geneous with 0.984 wt% H. After THT, the ultimate strength is beyond 1,100 MPa that has increased by 23.15% compared with that in as-cast state.

关键词： Titanium alloy Hydrogen Heat treatment Phase transformation Eutectoid decomposition Mechanical property

Solidification characteristics of high Nb-containing γ-TiAl-based alloys with different aluminum contents

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Rare Metals 2015年第6期34卷 381-386页

作者： Yi Liu Rui Hu hong-chao kou Jun Wang Tie-Bang Zhang Jin-Shan Li Ji Zhang The State Key Laboratory of Solidification Processing School of Materials Science and Engineering Northwestern Polytechnical University Institute of High Temperature Materials China Iron and Steel Research Institute Group

The effect of A1 content on the microstructure and solidification characteristics of Ti-A1-Nb-V-Cr alloys in as-cast and isothermally treated states was investigated using X-ray diffraction （XRD）, scanning electron microscopy （SEM） equipped with energy dispersive spectroscope （EDS）, and transmission electron microscopy （TEM）. The typical solidification characteristics are due to the joint influence of both the crystal temperature range and the solidification path. The wide crystallization temperature range contributes to obtaining coarse dendrites in the as-cast Ti47A17Nb2.5V1.0Cr （at%） alloy solidifying through the peritectic reaction. The β-solidifying Ti46A17Nb2.5V1.0Cr （at%） alloy with the narrow crystallization temperature range is attributed to the formation of a homogeneous finegrained microstructure. However, the crystallization temperature range of Ti48A17Nb2.5V1.0Cr （at%） alloy is equivalent to that of Ti46A17Nb2.5V1.0Cr alloy, but it is solidified by peritectic reaction, leading to the formation of finer dendrites.

关键词： Titanium aluminide Crystal temperaturerange Peritectic reaction Dendrite morphology Al-equivalent

Physical properties of WSTi3515S burn-resistant titanium alloy

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Rare Metals 2016年第5期35卷 361-366页

作者： Yun-Jin Lai Ping-Xiang Zhang Xue-Min Zhang Xiang-hong Liu Yong Feng hong-chao kou Fan-Jiao Ma Wei-Dong Zeng State Key Laboratory of Solidification Processing Northwestern Polytechnical University Western Superconducting Technologies Co. Ltd. School of Materials Science and Engineering Chang’an University

Development of burn-resistant titanium alloys is the most direct way of mitigating the ignition and propagation of titanium fires in jet engines. WSTi3515S alloy（Ti–35V–15Cr–0.3Si–0.1C） is a new high alloying beta type burn-resistant titanium alloy, belonging to Ti–V–Cr type alloys which have been made significant progress in engineering technology in the past 5 years. The physical properties of WSTi3515S burn-resistant titanium alloy such as the elastic properties and thermal properties were measured and analyzed in different conditions. The results show that both the Young＇s modulus and shear modulus of WSTi3515S alloy decrease slightly with the temperature increasing at the tested temperature range. The Poisson＇s ratio of WSTi3515S alloy is around 0.36. However, the thermal properties such as the specific heat, thermal diffusivity, thermal conductivity and thermal expansion increase with the temperature increasing, which results from the strengthening of lattice heat vibration at elevated temperature. And the room temperature density of WSTi3515S alloy is 5.295 gácm^（-3）.

关键词： Physical properties WSTi3515S alloy Extrusion Burn-resistant

Dry-sliding tribological properties of AlCoCrFeNiTi_(0.5)high-entropy alloy

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Rare Metals 2022年第12期41卷 4266-4272页

作者： Yuan Yu Jun Wang Jin-Shan Li hong-chao kou Si-Zhe Niu Sheng-Yu Zhu Jun Yang Wei-Min Liu State Key Laboratory of Solidification Processing School of Materials Science and EngineeringNorthwestern Polytechnical UniversityXi'an 710072China State Key Laboratory of Solid Lubrication Lanzhou Institute of Chemical PhysicsChinese Academy of SciencesLanzhou 730000China

High-entropy alloys(HEAs),with a new alloying concept,could possess many unique mechanical and functional *** current work investigated whether one such alloy offers potential for bearing surfaces under dry *** dry,reciprocating sliding wear characteristics of AlCoCrFeNiTi0.5alloy were investigated under various applied loads and sliding *** electron microscopy(TEM) and scanning electron microscopy(SEM) were utilized to characterize internal structure and wear surfaces of the alloy,*** is found that the AlCoCrFeNiTi0.5alloy preserves better wear resistance than Fe77Ni23solid solution alloy,Ti-46Al-2Cr-2Nb intermetallic alloy,or a wear-resistant steel AISI52100,especially under higher *** wear rate increases slowly with the applied loads increasing and keeps steady under different sliding *** wear mechanisms are abrasive wear,adhesive wear and oxidative *** nano-sized Fe-Cr solid solution and Al-NiTi rich intermetallic phase precipitated in the dendritic regions and the formation of oxidation play important roles in the good wear resistances of this high-entropy alloy.

关键词： High-entropy alloy Sliding wear Hardness Surface analysis