In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heatin...In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.展开更多
A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian c...A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian collision and motion collision between the second phase droplets. The simulation results are dynamically visualized and show that the volume fraction, distribution and size of the second phase droplets satisfactorily agree with the experimental results. So the model can be used to predict the microstructural evolution of Al In immiscible alloys during the cooling process.展开更多
The liquid phase behavior of the fine-grained 5083 AI alloy obtained through thermomechanical process was investigated during the tensile tests in a temperature range of 380-570℃ and strain rate range of 4.17× 1...The liquid phase behavior of the fine-grained 5083 AI alloy obtained through thermomechanical process was investigated during the tensile tests in a temperature range of 380-570℃ and strain rate range of 4.17× 10^-4- 1.0× 10^-2 s^-1. The maximum elongation 530% of the fine-grained 5083 AI alloy was obtained at 550℃ and 4.17× 10^-4 s^-1. Fracture analysis by scanning electron microscopy （SEM） indicated that the formation of filament （formed by liquid phase） was greatly affected by the tensile temperature and strain rate. The results also showed that the optimum morphology of formed filament was obtained at 550℃ and a strain rate of 4.17× 10^-4 s^-1. The effect of liquid phase on superplastic deformation of the alloy was further discussed.展开更多
Wetting phenomenon occurring between liquid metals and solid materials is important in manytechnological processes involving a liquid phase. The fundamentals of wetting with the emphasis on metal-ce-ramic systems are ...Wetting phenomenon occurring between liquid metals and solid materials is important in manytechnological processes involving a liquid phase. The fundamentals of wetting with the emphasis on metal-ce-ramic systems are briefly described and various technologically important processes are analysed in relationwith liquid metal-solid wetting.展开更多
The liquid-solid phase change process of a simple one-dimensional slab is studied in this paper.By taking entransy dissipation minimization as optimization objective,the optimal external reservoir temperature profiles...The liquid-solid phase change process of a simple one-dimensional slab is studied in this paper.By taking entransy dissipation minimization as optimization objective,the optimal external reservoir temperature profiles are derived by using optimal control theory under the condition of a fixed freezing or melting time.The entransy dissipation corresponding to the optimal heat exchange strategies of minimum entransy dissipation is 8/9 of that corresponding to constant reservoir temperature operations,which is independent of all system parameters.The obtained results for entransy dissipation minimization are also compared with those obtained for the optimal heat exchange strategies of minimum entropy generation and constant reservoir temperature operations by numerical examples.The obtained results can provide some theoretical guidelines for the choice of optimal cooling or heating strategy in practical liquid-solid phase change processes.展开更多
TiO2 nanowire arrays were successfully fabricated by liquid-phase deposition method using porous alumina templates. The obtained TiO2 nanowires were characterized using Raman spectroscopy, X-ray diffraction （XRD）, s...TiO2 nanowire arrays were successfully fabricated by liquid-phase deposition method using porous alumina templates. The obtained TiO2 nanowires were characterized using Raman spectroscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, field emission scanning electron microscopy （FE- SEM）, transmission electron microscopy （TEM）, and selected area electron diffraction （SAED） analysis. Results of electron microscopic observations indicated that the nanowires were smooth and uniform with a diameter of about 50-80 nm and several micrometers in length. SAED, Raman, and XRD mea- surements showed that TiO2 nanowires were single-crystalline with a pure rutile structure after heating at 800 ~C for 10 h. In this situation, the nanowire constituents grew preferentially along the 〈001〉 direction. Furthermore, the formation process and mechanistic study of the Ti02 nanowire arrays were proposed and discussed in detail. The nanowires are clearly produced by the deposition of TiO2 particles on the inner wall of the template nanochannels.展开更多
The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Her...The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Here, a facile bottom-up solution-synthesis with spark plasma sintering(SPS) process has been developed to build n-type Bi2Te3-xSex bulk nanocomposites, which substantially improves the power factor and decreases the lattice thermal conductivity by tuning the interface scattering of phonons and electrons. The stoichiometric composition in ternary Bi2Te3-xSex nanocomposites is also tuned to optimize the carrier concentration and lattice thermal conductivity. The optimized bulk nanocomposite Bi2Te2.7Se0.3 exhibits a ZT of 1.1 at^371 K, which is comparable to the corresponding commercially available ingots. Our results demonstrate the great potential of the solution-processed n-type Bi2Te3-xSex nanocomposites for cost-effective thermoelectric applications.展开更多
Anatase nanoparticles were successfully prepared via a facile microwave assisted liquid phase deposition （MW-LPD） process with hexafluorotitanate ammonium （NH4）2TiF6 as precursor. Compared with the conventional LP...Anatase nanoparticles were successfully prepared via a facile microwave assisted liquid phase deposition （MW-LPD） process with hexafluorotitanate ammonium （NH4）2TiF6 as precursor. Compared with the conventional LPD processes, the MW-LPD technique could provide high yield quickly and crystallinity in a diluted precursor solution at a low temperature. The products were characterized by XRD and TEM. Their photocatalytic activities were also investigated by the photodegradation of methylene blue （MB） as a model molecule.展开更多
基金supported by the Natural Science Foundation of Henan Province(Grant No.152107000047)
文摘In this study, a two-step heating process is introduced for transient liquid phase （ TLP） diffusion bonding fo r sound joints with T91 heat resistant steels. At first, a short-time higher temperature heating step is addressed to melt the interlayer, followed by the second step to complete isothermal solidification at a low temperature. The most critical feature of our new method is producing a non-planar interface at the T9／ heat resistant steels joint. We propose a transitional liquid phase bonding of T91 heat resistant steels by this approach. Since joint microstructures have been studied, we tested the tensile strength to assess joint mechanical property. The result indicates that the solidified bond may contain a primary solid-solution, similar composition to the parent metal and free from precipitates. Joint tensile strength of the joint is not lower than parent materials. Joint bend＇s strengths are enhanced due to the higher metal-to-metal junction producing a non-planar bond lines. Nevertheless, the traditional transient liquid phase diffusion bonding produces planar ones. Bonding parameters of new process are 1 260 °C for 0. 5 min and 1 230 °C fo r 4 min.
文摘A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian collision and motion collision between the second phase droplets. The simulation results are dynamically visualized and show that the volume fraction, distribution and size of the second phase droplets satisfactorily agree with the experimental results. So the model can be used to predict the microstructural evolution of Al In immiscible alloys during the cooling process.
文摘The liquid phase behavior of the fine-grained 5083 AI alloy obtained through thermomechanical process was investigated during the tensile tests in a temperature range of 380-570℃ and strain rate range of 4.17× 10^-4- 1.0× 10^-2 s^-1. The maximum elongation 530% of the fine-grained 5083 AI alloy was obtained at 550℃ and 4.17× 10^-4 s^-1. Fracture analysis by scanning electron microscopy （SEM） indicated that the formation of filament （formed by liquid phase） was greatly affected by the tensile temperature and strain rate. The results also showed that the optimum morphology of formed filament was obtained at 550℃ and a strain rate of 4.17× 10^-4 s^-1. The effect of liquid phase on superplastic deformation of the alloy was further discussed.
文摘Wetting phenomenon occurring between liquid metals and solid materials is important in manytechnological processes involving a liquid phase. The fundamentals of wetting with the emphasis on metal-ce-ramic systems are briefly described and various technologically important processes are analysed in relationwith liquid metal-solid wetting.
基金supported by the Program for New Century Excellent Talents in Universities of China (Grant No 20041006)the Foundation for the Authors of National Excellent Doctoral Dissertation of China (Grant No 200136)
文摘The liquid-solid phase change process of a simple one-dimensional slab is studied in this paper.By taking entransy dissipation minimization as optimization objective,the optimal external reservoir temperature profiles are derived by using optimal control theory under the condition of a fixed freezing or melting time.The entransy dissipation corresponding to the optimal heat exchange strategies of minimum entransy dissipation is 8/9 of that corresponding to constant reservoir temperature operations,which is independent of all system parameters.The obtained results for entransy dissipation minimization are also compared with those obtained for the optimal heat exchange strategies of minimum entropy generation and constant reservoir temperature operations by numerical examples.The obtained results can provide some theoretical guidelines for the choice of optimal cooling or heating strategy in practical liquid-solid phase change processes.
基金supported by the Institute of Science and High Technology and Environmental Sciences(No.1/1859)
文摘TiO2 nanowire arrays were successfully fabricated by liquid-phase deposition method using porous alumina templates. The obtained TiO2 nanowires were characterized using Raman spectroscopy, X-ray diffraction （XRD）, scanning electron microscopy （SEM）, field emission scanning electron microscopy （FE- SEM）, transmission electron microscopy （TEM）, and selected area electron diffraction （SAED） analysis. Results of electron microscopic observations indicated that the nanowires were smooth and uniform with a diameter of about 50-80 nm and several micrometers in length. SAED, Raman, and XRD mea- surements showed that TiO2 nanowires were single-crystalline with a pure rutile structure after heating at 800 ~C for 10 h. In this situation, the nanowire constituents grew preferentially along the 〈001〉 direction. Furthermore, the formation process and mechanistic study of the Ti02 nanowire arrays were proposed and discussed in detail. The nanowires are clearly produced by the deposition of TiO2 particles on the inner wall of the template nanochannels.
基金supported by the Natural Science Foundation of SZU (2017003)Shenzhen Science and Technology Research Grant (JCYJ20150324141711684)+2 种基金Singapore National Research Foundation (NRF-RF2009-06)an Investigator-ship Award (NRFNRFI2015-03)Ministry of Education (Singapore) via an AcRF Tier2 Grant (MOE2012-T2-2-086)
文摘The much slower progress in enhancing the thermoelectric performance of n-type Bi2Te3 than that of p-type Bi2Te3 based materials in the past decade hinders the widespread use in power generation and refrigeration. Here, a facile bottom-up solution-synthesis with spark plasma sintering(SPS) process has been developed to build n-type Bi2Te3-xSex bulk nanocomposites, which substantially improves the power factor and decreases the lattice thermal conductivity by tuning the interface scattering of phonons and electrons. The stoichiometric composition in ternary Bi2Te3-xSex nanocomposites is also tuned to optimize the carrier concentration and lattice thermal conductivity. The optimized bulk nanocomposite Bi2Te2.7Se0.3 exhibits a ZT of 1.1 at^371 K, which is comparable to the corresponding commercially available ingots. Our results demonstrate the great potential of the solution-processed n-type Bi2Te3-xSex nanocomposites for cost-effective thermoelectric applications.
文摘Anatase nanoparticles were successfully prepared via a facile microwave assisted liquid phase deposition （MW-LPD） process with hexafluorotitanate ammonium （NH4）2TiF6 as precursor. Compared with the conventional LPD processes, the MW-LPD technique could provide high yield quickly and crystallinity in a diluted precursor solution at a low temperature. The products were characterized by XRD and TEM. Their photocatalytic activities were also investigated by the photodegradation of methylene blue （MB） as a model molecule.
