The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method,...The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.展开更多
Ti-Al thin sheet with dimension of 450 mm×450 mm×0.2 mm was prepared by electron beam physical vapor deposition(EB-PVD) technology. The surface and cross-section pattern of as-deposited sample were studied b...Ti-Al thin sheet with dimension of 450 mm×450 mm×0.2 mm was prepared by electron beam physical vapor deposition(EB-PVD) technology. The surface and cross-section pattern of as-deposited sample were studied by SEM and AFM,and then the composition and phase were analysed by XRD and EPMA. Finally,the effect on deposit by re-evaporation of Al was explored by calculating the ratio of re-evaporating capacity with depositing capacity of Al on the substrate. The results indicate that the evaporation process with Nb addition into the molten pool makes it earlier to reach the steady-state. The existing equiaxed crystal and columnar crystal along the cross-sectional may be caused by the transformation latent heat released during the transition course of atoms from gaseous state to solid state. The effect on deposit by re-evaporation of Al can be neglected because the re-evaporating capacity of Al is far below that of the depositing capacity.展开更多
TiAl-based alloys sheet with thickness of 0.3-0.4 mm as well as dimension of 150 mm×100 mm was fabricated successfully by using electron beam-physical vapor deposition(EB-PVD) method. The microscopic morphology a...TiAl-based alloys sheet with thickness of 0.3-0.4 mm as well as dimension of 150 mm×100 mm was fabricated successfully by using electron beam-physical vapor deposition(EB-PVD) method. The microscopic morphology and phase composition of specimens in various states were analyzed by atomic force microscope(AFM), scanning electron microscope(SEM) and X-ray diffractometer(XRD), respectively. The results indicate that the as-deposited TiAl-based alloys sheet has good surface quality and is composed of γ, α2 and τ phase. There is natural delamination inside the sheet, of which the microstructure is columnar crystal, and the component shows a gradient change along the normal direction of substrate. After the vacuum hot pressing treatment and subsequent homogenization treatment, the columnar crystal transforms into the coarse fully lamellar microstructure, the delamination phenomenon and τ phase disappear, α2 phase decreases obviously, and the composition tends to uniformization.展开更多
Large-scale Ni-based superalloy sheet was prepared by electron beam physical vapour deposition. Microstructures and micropores of as-deposited and heat treated superalloy sheets were studied by scanning electron micro...Large-scale Ni-based superalloy sheet was prepared by electron beam physical vapour deposition. Microstructures and micropores of as-deposited and heat treated superalloy sheets were studied by scanning electron microscope, atomic force microscope, and optical microscope. The results show that the as-deposited superalloy sheet is mainly composed of columnar grain, whose major axes are parallel to the normal line of the sheet. The average diameter of crystalline grains in minor axis direction is about 300nm. After heat treatment, the superalloy sheet consists of equiaxed grains, the nanopores with high interfacial energy gather and form fewer pores with larger size, and there is notable increase in toughness.展开更多
A two-dimensional kinetic Monte-Carlo(KMC) method was used to approach the thickness distribution of large scale metallic sheet deposited by electron beam physical vapor deposition(EB-PVD) on rotating substrate. The K...A two-dimensional kinetic Monte-Carlo(KMC) method was used to approach the thickness distribution of large scale metallic sheet deposited by electron beam physical vapor deposition(EB-PVD) on rotating substrate. The KMC model involves incident atom attachment, adatom diffusion and adatom detachment. The effective deposition rate and effective incident angle along substrate radial were studied as influencing factors of sheet thickness distribution. The KMC simulation results indicate that incident angle is a very important factor to affect the sheet thickness distribution as well as theory deposition mass. The experiments results show that the KMC model can predict the thickness distribution of large scale sheet deposited by EB-PVD on rotating substrate.展开更多
The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surroga...The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surrogate.Based on a previous investigation of discharge properties,product distribution and energy efficiency,the operating parameters such as CH4 concentration,applied voltage and gas flow rate can effectively affect the CH4 conversion rate,the selectivity of H2 and the properties of solid generated carbon.Nevertheless,the basic properties of RGA plasma and its role in CH4 conversion are scarcely mentioned.In the present work,a 3D RGA model,with a detailed nonequilibrium CH4/Ar plasma chemistry,is developed to validate the previous experiments on CBM conversion,aiming in particular at the distribution of H2 and other gas products.Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection,electron migration and electron diffusion,and is prominently determined by the variation of the gas flow rate and applied voltage.Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction,taking into consideration the formation and loss pathways of crucial targeted substances(such as CH4,C2H2,H2 and H radicals)and corresponding contribution rates.Additionally,the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM)and Raman spectroscopy.The results show that increasing the applied voltage and decreasing CH4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets,while the size of the graphene sheets is slightly affected by the change in gas flow rate.展开更多
The Antarctic Ice Sheet(AIS)has been losing ice mass and contributing to the rise in the global sea-level(GSL)for the last 4 decades,as quantified by using satellite observations.We developed a framework for implement...The Antarctic Ice Sheet(AIS)has been losing ice mass and contributing to the rise in the global sea-level(GSL)for the last 4 decades,as quantified by using satellite observations.We developed a framework for implementing the state-of-the-art input-output(IO)method that has the advantage of explicit estimation of the mass balance of individual glaciers,basins and the continent.We estimated the mass balance of the AIS from 2013 to 2018 using improved observations and updated datasets recently made available,including annual ice flow velocity maps from the Inter-mission Time Series of Land Ice Velocity and Elevation(ITS_LIVE)dataset,the Bed Machine and the Princess Elizabeth Land(PEL)Earth System Science Data(ESSD)datasets,and the surface mass balance from the RACMO 2.3 system.For example,using the improved ice thickness data,the proposed method for ice discharge estimation enables a 10%reduction of uncertainty in ice discharge.During the period of 2013–2018,an ice discharge acceleration of 6.9±6.5 Gt yr^(–2)in West Antarctica(WA)was detected,which contributed significantly to the estimated mass loss of~1069 Gt(–178.2±108.9 Gt yr^(–1))in the AIS.On the other hand,Queen Maud Land,East Antarctica(EA),showed clearly a mass gain rate of 56.0±10.0 Gt yr^(–1)due to the regional increase in surface mass balance.Our results extended the estimation period by 3 years in comparison to the published study using the same annual velocity maps from the ITS_LIVE dataset.Furthermore,our results,along with those from other studies using the IO method,reassures the acceleration of recent mass loss in WA and Wilkes Land in EA,which are caused by glacier thinning and ice shelf basal melting.Compared with the long-term mass balance record since 1979,our results suggest that the mass loss in AIS accelerated in the last decade.The developed framework can be modified for mass balance estimation of the AIS or for other ice sheets by using velocity maps from other satellite data or from different periods.展开更多
基金Projects(90205034, 90405016) supported by the National Natural Science Foundation of China
文摘The TiAl-based alloys sheet with 150 mm×100 mm×0.4 mm and the TiAl/Nb laminated composites with 150 mm×100 mm×0.2 mm were fabricated by using electron beam-physical vapor deposition(EB-PVD) method, respectively. The microstructure and properties of the sheet were investigated by AFM, SEM and EDS. The results show that the TiAl based alloys sheet has a good surface quality, and its microstructure is columnar crystal. The component of the alloys indicates a regular and periodical gradient change which leads to the spontaneous delamination along the normal direction of substrate. In the TiAl/Nb laminated composites alternating overlaid by TiAl of 24 layers and Nb of 23 layers, the interface of each layer evenly distributed throughout the cross-section is transparent, and the interlayer spacing is about 8μm. The component of TiAl layers also changes regularly along the normal direction of substrate, but no delamination phenomenon is found. The TiAl/Nb laminated composites have better ductility than the TiAl-based alloys sheet.
基金Project(NCET2004) supported by the Program for New Century Excellent Talents in University, China
文摘Ti-Al thin sheet with dimension of 450 mm×450 mm×0.2 mm was prepared by electron beam physical vapor deposition(EB-PVD) technology. The surface and cross-section pattern of as-deposited sample were studied by SEM and AFM,and then the composition and phase were analysed by XRD and EPMA. Finally,the effect on deposit by re-evaporation of Al was explored by calculating the ratio of re-evaporating capacity with depositing capacity of Al on the substrate. The results indicate that the evaporation process with Nb addition into the molten pool makes it earlier to reach the steady-state. The existing equiaxed crystal and columnar crystal along the cross-sectional may be caused by the transformation latent heat released during the transition course of atoms from gaseous state to solid state. The effect on deposit by re-evaporation of Al can be neglected because the re-evaporating capacity of Al is far below that of the depositing capacity.
基金Project(90405016) supported by the National Natural Science Foundation of China
文摘TiAl-based alloys sheet with thickness of 0.3-0.4 mm as well as dimension of 150 mm×100 mm was fabricated successfully by using electron beam-physical vapor deposition(EB-PVD) method. The microscopic morphology and phase composition of specimens in various states were analyzed by atomic force microscope(AFM), scanning electron microscope(SEM) and X-ray diffractometer(XRD), respectively. The results indicate that the as-deposited TiAl-based alloys sheet has good surface quality and is composed of γ, α2 and τ phase. There is natural delamination inside the sheet, of which the microstructure is columnar crystal, and the component shows a gradient change along the normal direction of substrate. After the vacuum hot pressing treatment and subsequent homogenization treatment, the columnar crystal transforms into the coarse fully lamellar microstructure, the delamination phenomenon and τ phase disappear, α2 phase decreases obviously, and the composition tends to uniformization.
文摘Large-scale Ni-based superalloy sheet was prepared by electron beam physical vapour deposition. Microstructures and micropores of as-deposited and heat treated superalloy sheets were studied by scanning electron microscope, atomic force microscope, and optical microscope. The results show that the as-deposited superalloy sheet is mainly composed of columnar grain, whose major axes are parallel to the normal line of the sheet. The average diameter of crystalline grains in minor axis direction is about 300nm. After heat treatment, the superalloy sheet consists of equiaxed grains, the nanopores with high interfacial energy gather and form fewer pores with larger size, and there is notable increase in toughness.
文摘A two-dimensional kinetic Monte-Carlo(KMC) method was used to approach the thickness distribution of large scale metallic sheet deposited by electron beam physical vapor deposition(EB-PVD) on rotating substrate. The KMC model involves incident atom attachment, adatom diffusion and adatom detachment. The effective deposition rate and effective incident angle along substrate radial were studied as influencing factors of sheet thickness distribution. The KMC simulation results indicate that incident angle is a very important factor to affect the sheet thickness distribution as well as theory deposition mass. The experiments results show that the KMC model can predict the thickness distribution of large scale sheet deposited by EB-PVD on rotating substrate.
基金supported by the Foundation for Innovative Research Groups of National Natural Science Foundation of China (No. 51621005)China Postdoctoral Science Foundation (No. 2018M630672)
文摘The use of atmospheric rotating gliding arc(RGA)plasma is proposed as a facile,scalable and catalyst-free approach to synthesizing hydrogen(H2)and graphene sheets from coalbed methane(CBM).CH4 is used as a CBM surrogate.Based on a previous investigation of discharge properties,product distribution and energy efficiency,the operating parameters such as CH4 concentration,applied voltage and gas flow rate can effectively affect the CH4 conversion rate,the selectivity of H2 and the properties of solid generated carbon.Nevertheless,the basic properties of RGA plasma and its role in CH4 conversion are scarcely mentioned.In the present work,a 3D RGA model,with a detailed nonequilibrium CH4/Ar plasma chemistry,is developed to validate the previous experiments on CBM conversion,aiming in particular at the distribution of H2 and other gas products.Our results demonstrate that the dynamics of RGA is derived from the joint effects of electron convection,electron migration and electron diffusion,and is prominently determined by the variation of the gas flow rate and applied voltage.Subsequently,a combined experimental and chemical kinetical simulation is performed to analyze the selectivity of gas products in an RGA reaction,taking into consideration the formation and loss pathways of crucial targeted substances(such as CH4,C2H2,H2 and H radicals)and corresponding contribution rates.Additionally,the effects of operating conditions on the properties of solid products are investigated by scanning electron microscopy(SEM)and Raman spectroscopy.The results show that increasing the applied voltage and decreasing CH4 concentration will change the solid carbon from its initial spherical structure into folded multilayer graphene sheets,while the size of the graphene sheets is slightly affected by the change in gas flow rate.
基金supported by the National Key Research&Development Program of China(Grant No.2017YFA0603102)the National Natural Science Foundation of China(Grant Nos.41730102,41771471,41941006&4201101408)+1 种基金the Shanghai Science and Technology Development Funds(Grant No.21ZR1469700)supported by the Central University Research Fund。
文摘The Antarctic Ice Sheet(AIS)has been losing ice mass and contributing to the rise in the global sea-level(GSL)for the last 4 decades,as quantified by using satellite observations.We developed a framework for implementing the state-of-the-art input-output(IO)method that has the advantage of explicit estimation of the mass balance of individual glaciers,basins and the continent.We estimated the mass balance of the AIS from 2013 to 2018 using improved observations and updated datasets recently made available,including annual ice flow velocity maps from the Inter-mission Time Series of Land Ice Velocity and Elevation(ITS_LIVE)dataset,the Bed Machine and the Princess Elizabeth Land(PEL)Earth System Science Data(ESSD)datasets,and the surface mass balance from the RACMO 2.3 system.For example,using the improved ice thickness data,the proposed method for ice discharge estimation enables a 10%reduction of uncertainty in ice discharge.During the period of 2013–2018,an ice discharge acceleration of 6.9±6.5 Gt yr^(–2)in West Antarctica(WA)was detected,which contributed significantly to the estimated mass loss of~1069 Gt(–178.2±108.9 Gt yr^(–1))in the AIS.On the other hand,Queen Maud Land,East Antarctica(EA),showed clearly a mass gain rate of 56.0±10.0 Gt yr^(–1)due to the regional increase in surface mass balance.Our results extended the estimation period by 3 years in comparison to the published study using the same annual velocity maps from the ITS_LIVE dataset.Furthermore,our results,along with those from other studies using the IO method,reassures the acceleration of recent mass loss in WA and Wilkes Land in EA,which are caused by glacier thinning and ice shelf basal melting.Compared with the long-term mass balance record since 1979,our results suggest that the mass loss in AIS accelerated in the last decade.The developed framework can be modified for mass balance estimation of the AIS or for other ice sheets by using velocity maps from other satellite data or from different periods.
