Employing low pressurized gas for shaping superplastic metal sheets into complex contours has long been adopted in the aero/auto industries and it is commonly recognized as superplastic forming （SPF）. The most undes...Employing low pressurized gas for shaping superplastic metal sheets into complex contours has long been adopted in the aero/auto industries and it is commonly recognized as superplastic forming （SPF）. The most undesired feature of SPF would be an uneven thickness distribution in the final formed part. However, there are techniques that lessen this disadvantage. Low pressurized gas was used to make a V-shaped trough containing deep uneven concavities using superplastic AA5083. The auxiliary yet influential procedure of mechanically hot bending the flat sheet into a V-shape precedes the gas-forming process. In this first quick hot-bending operation, buckling will occur if the depth of bending exceeds a certain level. The degree of buckling and associated contours will affect the thickness distribution as well as the wrinkling location in the gas-formed product. A better thickness distribution is obtainable at the cost of wrinkle formation. Wrinkling can be purposely arranged to achieve better uniform thickness distribution, but it needs to be located outside the trim line of the gas-formed semi-product. Therefore, it is critical to manipulate the hot bending procedure to yield a suitable pre-form allowing a successful sequential gas-forming process.展开更多
The hysteresis loop changes of ferroelecric SrBi_2 Ta_2 O_9 (SBT) thin films(330nm) us the temperature of forming gas (5 percent hydrogen+95 percent nitrogen) annealing weremeasured when the annealing time was 1min an...The hysteresis loop changes of ferroelecric SrBi_2 Ta_2 O_9 (SBT) thin films(330nm) us the temperature of forming gas (5 percent hydrogen+95 percent nitrogen) annealing weremeasured when the annealing time was 1min and 10min. The selected annealing temperature was at 100deg C,200 deg C 250 deg C, 300 deg C, 350 deg C,400 deg C and 450 deg C, respectively. Our resultsshowed that the ferroelectric properties were easily destroyed and the leakage current changedabruptly when the SBT thin films were in their ferroelectric phase (<270 deg C). The space chargesat the grain boundary may take an important role' in absorption polarity molecular hydrogen when theSBT thin films were in the ferroelectric phase. The oxygen recovery experiments were also performedand investigated in this work.展开更多
Complex thin-walled titanium alloy components play a key role in the aircraft,aerospace and marine industries,offering the advantages of reduced weight and increased thermal resistance.The geometrical complexity,dimen...Complex thin-walled titanium alloy components play a key role in the aircraft,aerospace and marine industries,offering the advantages of reduced weight and increased thermal resistance.The geometrical complexity,dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems,which brings new challenges to titanium alloy forming technologies.Traditional forming processes,such as superplastic forming or hot pressing,cannot meet all demands of modern applications due to their limited properties,low productivity and high cost.This has encouraged industry and research groups to develop novel high-efficiency forming processes.Hot gas pressure forming and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components,and are believed to be the cut-edge processes guaranteeing dimensional accuracy,microstructure and mechanical properties.This article intends to provide a critical review of high-efficiency titanium alloy forming processes,concentrating on latest investigations of controlling dimensional accuracy,microstructure and properties.The advantages and limitations of individual forming process are comprehensively analyzed,through which,future research trends of high-efficiency forming are identified including trends in process integration,processing window design,full cycle and multi-objective optimization.This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.展开更多
Because Elsevier takes care of JNGC＇s international institutional print subscriptions beginning from 2006,please visit the following website of Elsevier for the international Institutional orders.
Because Elsevier takes care of JNGC’s international institutional print subscriptions beginning from 2006,please visit the following website of Elsevier for the international Institutional orders.http://www.elsevier....Because Elsevier takes care of JNGC’s international institutional print subscriptions beginning from 2006,please visit the following website of Elsevier for the international Institutional orders.http://www.elsevier.com/locate/jngc展开更多
Annual subscription rate: Businesses and research institutes: US $400.00 for overseas/ RMB 400.00 for Chinese Individuals: US $240.00 for overseas/ RMB 240.00 for Chinese Please subscribe me to the Journal (starting i...Annual subscription rate: Businesses and research institutes: US $400.00 for overseas/ RMB 400.00 for Chinese Individuals: US $240.00 for overseas/ RMB 240.00 for Chinese Please subscribe me to the Journal (starting in 2002): Number of years: Total amount: US $ RMB展开更多
We investigate the effects of NO annealing and forming gas （FG） annealing on the electrical properties of a SiO2/SiC interface by low-temperature conductance measurements. With nitrogen passivation, the density of i...We investigate the effects of NO annealing and forming gas （FG） annealing on the electrical properties of a SiO2/SiC interface by low-temperature conductance measurements. With nitrogen passivation, the density of interface states （DIT） is significantly reduced in the entire energy range, and the shift of flatband voltage, AVFB, is effectively suppressed to less than 0.4 V. However, very fast states are observed after NO annealing and the response frequencies are higher than 1 MHz at room temperature. After additional FG annealing, the DIT and AVFB are further reduced. The values of the DIT decrease to less than 1011 cm-2 eV- 1 for the energy range of Ec - ET 〉/0.4 eV. It is suggested that the fast states in shallow energy levels originated from the N atoms accumulating at the interface by NO annealing. Though FG annealing has a limited effect on these shallow traps, hydrogen can terminate the residual Si and C dangling bonds corresponding to traps at deep energy levels and improve the interface quality further. It is indicated that NO annealing in conjunction with FG annealing will be a better post-oxidation process method for high performance SiC MOSFETs.展开更多
文摘Employing low pressurized gas for shaping superplastic metal sheets into complex contours has long been adopted in the aero/auto industries and it is commonly recognized as superplastic forming （SPF）. The most undesired feature of SPF would be an uneven thickness distribution in the final formed part. However, there are techniques that lessen this disadvantage. Low pressurized gas was used to make a V-shaped trough containing deep uneven concavities using superplastic AA5083. The auxiliary yet influential procedure of mechanically hot bending the flat sheet into a V-shape precedes the gas-forming process. In this first quick hot-bending operation, buckling will occur if the depth of bending exceeds a certain level. The degree of buckling and associated contours will affect the thickness distribution as well as the wrinkling location in the gas-formed product. A better thickness distribution is obtainable at the cost of wrinkle formation. Wrinkling can be purposely arranged to achieve better uniform thickness distribution, but it needs to be located outside the trim line of the gas-formed semi-product. Therefore, it is critical to manipulate the hot bending procedure to yield a suitable pre-form allowing a successful sequential gas-forming process.
基金This work sponsored by Motorola SPS Digital DNA Laboratories. It is also supported by a grant for State Key Program for Basic Research of China. We would like to thank Dr. Peir Y. Chu of Motorola SPS for his great help, useful advice and discussion.
文摘The hysteresis loop changes of ferroelecric SrBi_2 Ta_2 O_9 (SBT) thin films(330nm) us the temperature of forming gas (5 percent hydrogen+95 percent nitrogen) annealing weremeasured when the annealing time was 1min and 10min. The selected annealing temperature was at 100deg C,200 deg C 250 deg C, 300 deg C, 350 deg C,400 deg C and 450 deg C, respectively. Our resultsshowed that the ferroelectric properties were easily destroyed and the leakage current changedabruptly when the SBT thin films were in their ferroelectric phase (<270 deg C). The space chargesat the grain boundary may take an important role' in absorption polarity molecular hydrogen when theSBT thin films were in the ferroelectric phase. The oxygen recovery experiments were also performedand investigated in this work.
基金This work was financially supported by the Program of National Natural Science Foundation of China(Nos.U1937204 and 51905124)China Postdoctoral Science Foundation(2019M661278).
文摘Complex thin-walled titanium alloy components play a key role in the aircraft,aerospace and marine industries,offering the advantages of reduced weight and increased thermal resistance.The geometrical complexity,dimensional accuracy and in-service properties are essential to fulfill the high-performance standards required in new transportation systems,which brings new challenges to titanium alloy forming technologies.Traditional forming processes,such as superplastic forming or hot pressing,cannot meet all demands of modern applications due to their limited properties,low productivity and high cost.This has encouraged industry and research groups to develop novel high-efficiency forming processes.Hot gas pressure forming and hot stamping-quenching technologies have been developed for the manufacture of tubular and panel components,and are believed to be the cut-edge processes guaranteeing dimensional accuracy,microstructure and mechanical properties.This article intends to provide a critical review of high-efficiency titanium alloy forming processes,concentrating on latest investigations of controlling dimensional accuracy,microstructure and properties.The advantages and limitations of individual forming process are comprehensively analyzed,through which,future research trends of high-efficiency forming are identified including trends in process integration,processing window design,full cycle and multi-objective optimization.This review aims to provide a guide for researchers and process designers on the manufacture of thin-walled titanium alloy components whilst achieving high dimensional accuracy and satisfying performance properties with high efficiency and low cost.
文摘Because Elsevier takes care of JNGC＇s international institutional print subscriptions beginning from 2006,please visit the following website of Elsevier for the international Institutional orders.
文摘Because Elsevier takes care of JNGC’s international institutional print subscriptions beginning from 2006,please visit the following website of Elsevier for the international Institutional orders.http://www.elsevier.com/locate/jngc
文摘Annual subscription rate: Businesses and research institutes: US $400.00 for overseas/ RMB 400.00 for Chinese Individuals: US $240.00 for overseas/ RMB 240.00 for Chinese Please subscribe me to the Journal (starting in 2002): Number of years: Total amount: US $ RMB
基金supported by the National Natural Science Foundation of China(Nos.61106080,61275042)the National Science and Technology Major Project of the Ministry of Science and Technology of China(No.2013ZX02305)
文摘We investigate the effects of NO annealing and forming gas （FG） annealing on the electrical properties of a SiO2/SiC interface by low-temperature conductance measurements. With nitrogen passivation, the density of interface states （DIT） is significantly reduced in the entire energy range, and the shift of flatband voltage, AVFB, is effectively suppressed to less than 0.4 V. However, very fast states are observed after NO annealing and the response frequencies are higher than 1 MHz at room temperature. After additional FG annealing, the DIT and AVFB are further reduced. The values of the DIT decrease to less than 1011 cm-2 eV- 1 for the energy range of Ec - ET 〉/0.4 eV. It is suggested that the fast states in shallow energy levels originated from the N atoms accumulating at the interface by NO annealing. Though FG annealing has a limited effect on these shallow traps, hydrogen can terminate the residual Si and C dangling bonds corresponding to traps at deep energy levels and improve the interface quality further. It is indicated that NO annealing in conjunction with FG annealing will be a better post-oxidation process method for high performance SiC MOSFETs.
