The microstructures and crystal growth directions of permanent mould casting（PMC） and directionally solidified（DS） Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouri...The microstructures and crystal growth directions of permanent mould casting（PMC） and directionally solidified（DS） Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α（Al） crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α（Al） crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches （110） orientation with increasing Cu content. But the resulting crystals with growth direction of （110） do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.展开更多
The double directional solidification（DS） technique was developed to control the lamellar microstructures in primary β TiAl-Nb alloys.Polysynthetically twinned（PST） crystals with lamellar boundaries parallel to o...The double directional solidification（DS） technique was developed to control the lamellar microstructures in primary β TiAl-Nb alloys.Polysynthetically twinned（PST） crystals with lamellar boundaries parallel to or inclined 45o to the growth direction were achieved due to the complete peritectic transformation during directional solidification of the alloys with the dendritic solid/liquid interface.The PST crystals with aligned lamellar boundaries only parallel to the growth direction were produced when lamellar grains with lamellar boundaries in the same orientation were seeded by themselves under appropriate growth conditions.Low boron addition is harmful to align the lamellar orientation because of the growth of non-peritectic α phase.Due to the larger yttria particles and boride ribbons in the directionally solidified TiAl-Nb alloys,the tensile plastic elongations of the alloys are only close to 2%.展开更多
The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances （Di=30-60 nm） and wire diameters （Dw=22-46 nm） were investigated in detail. It was found...The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances （Di=30-60 nm） and wire diameters （Dw=22-46 nm） were investigated in detail. It was found that the array＇s best annealing temperature and crys- talline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious influence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variation of the array＇s magnetic properties after magnetic field annealing.展开更多
A stretch-release strategy is proposed to analyze the problem of surface energy-induced stress fields in nanocrystals,which is resolved into a stretch sub-problem and a release sub-problem using the superposition prin...A stretch-release strategy is proposed to analyze the problem of surface energy-induced stress fields in nanocrystals,which is resolved into a stretch sub-problem and a release sub-problem using the superposition principle.The surface effect of silicon nanowires with hexagonal cross-sections is analyzed by the proposed method.The severe stress concentration near the triple junctions of the wire surfaces and the large shear stress on the plane{111}is quantified,which provides a solid mechanical explanation for the kink phenomena in growth transition from direction〈111〉to〈112〉observed in experiments.Different from the conventional view of negligible surface effect for bulk material,we found that there exists a size-independent part of the surface effect on the stress in the order of tens or hundreds of mega Pascal,which corresponds to the stretch-induced biaxial stress in the surface layer and the shape influence of the geometry of nanocrystals.This size-independent part could well explain the size-independent kinking phenomenon during the growth of silicon nanowires.展开更多
We analyze thickness-stretch vibrations of a plate of hexagonal crystal carrying an array of micro-rods with their bottoms fixed to the top surface of the plate.The rods undergo longitudinal vibrations when the crysta...We analyze thickness-stretch vibrations of a plate of hexagonal crystal carrying an array of micro-rods with their bottoms fixed to the top surface of the plate.The rods undergo longitudinal vibrations when the crystal plate is in thickness-stretch motion.The plate is modeled by the theory of anisotropic elasticity.The rods are modeled by the one-dimensional structural theory for extensional vibration of rods.A frequency equation is obtained and solved using perturbation method.The effect of the rod array on the resonant frequencies of the crystal plate is examined.The results are potentially useful for using thickness-stretch modes of crystal plates to measure the mechanical properties of microrod arrays.展开更多
基金Project(51061010)supported by the National Natural Science Foundation of ChinaProject(NCET-10-0023)supported by the Program for New Century Excellent Talents in University of ChinaProject(J201103)supported by the Program for Hongliu Outstanding Talents of Lanzhou University of Technology,China
文摘The microstructures and crystal growth directions of permanent mould casting（PMC） and directionally solidified（DS） Al-Cu alloys with different contents of Cu were investigated. Simultaneously, the effects of pouring temperature on the microstructure and crystal growth direction of permanent mould casting pure Al were also discussed. The results indicate that the α（Al） crystals in the pure Al do not always keep common columnar grains, but change from the columnar grains to columnar dendrites with developed arms as the pouring temperature rises. The growth direction also varies with the change of pouring temperature. Cu element has similar effects on the microstructures of the PMC and DS casting Al-Cu alloys and the α（Al） crystals gradually change from columnar crystals in turn to columnar dendrites and developed equiaxed dendrites as the Cu content increases. The crystal growth direction in the PMC alloys gradually approaches （110） orientation with increasing Cu content. But the resulting crystals with growth direction of （110） do not belong to feathery grains. There are also no feathery grains to form in all of the DS Al-Cu alloys.
基金Project (2011CB605500) supported by the National Basic Research Program of ChinaProject (FRF-MP-10-005B) supported by the Fundamental Research Funds for the Central Universities,China
文摘The double directional solidification（DS） technique was developed to control the lamellar microstructures in primary β TiAl-Nb alloys.Polysynthetically twinned（PST） crystals with lamellar boundaries parallel to or inclined 45o to the growth direction were achieved due to the complete peritectic transformation during directional solidification of the alloys with the dendritic solid/liquid interface.The PST crystals with aligned lamellar boundaries only parallel to the growth direction were produced when lamellar grains with lamellar boundaries in the same orientation were seeded by themselves under appropriate growth conditions.Low boron addition is harmful to align the lamellar orientation because of the growth of non-peritectic α phase.Due to the larger yttria particles and boride ribbons in the directionally solidified TiAl-Nb alloys,the tensile plastic elongations of the alloys are only close to 2%.
基金ACKNOWLEDGMENTS This work was supported by the National Nature Science Foundation of China （No.50171033）, the National Key Project of Fundamental Research of China （No.2005CB623605）, and the Scientific Research Foundation for the Doctor of Hefei University of Technology （No.035032）.
文摘The effects of magnetic field annealing on the properties of Fe48Co52 alloy nanowire arrays with various interwire distances （Di=30-60 nm） and wire diameters （Dw=22-46 nm） were investigated in detail. It was found that the array＇s best annealing temperature and crys- talline structure did not show any apparent dependence on the treatment of applying a 3 kOe magnetic field along the wire during the annealing process. For arrays with small Dw or with large Di, the treatment of magnetic field annealing also had no obvious influence on their magnetic performances. However, such a magnetic field annealing constrained the shift of the easy magnetization direction and improved the coercivity and the squareness obviously for arrays with large Dw or with small Di. The difference in the intensity of the effective anisotropic field within the arrays was believed to be responsible for this different variation of the array＇s magnetic properties after magnetic field annealing.
基金the National Natural Science Foundation of China(Grant No.11872237)the Natural Science Foundation of Shanghai(Grant No.18ZR1414600)the Challenging Project from China Academy of Engineering Physics.
文摘A stretch-release strategy is proposed to analyze the problem of surface energy-induced stress fields in nanocrystals,which is resolved into a stretch sub-problem and a release sub-problem using the superposition principle.The surface effect of silicon nanowires with hexagonal cross-sections is analyzed by the proposed method.The severe stress concentration near the triple junctions of the wire surfaces and the large shear stress on the plane{111}is quantified,which provides a solid mechanical explanation for the kink phenomena in growth transition from direction〈111〉to〈112〉observed in experiments.Different from the conventional view of negligible surface effect for bulk material,we found that there exists a size-independent part of the surface effect on the stress in the order of tens or hundreds of mega Pascal,which corresponds to the stretch-induced biaxial stress in the surface layer and the shape influence of the geometry of nanocrystals.This size-independent part could well explain the size-independent kinking phenomenon during the growth of silicon nanowires.
基金supported by the National Natural Science Foundation of China (Grant No. 10932004)the Industrial Technology Research Program of the City of Ningbo (Grant No. 2007B10052)the WONG K C Magna Fund of Ningbo University
文摘We analyze thickness-stretch vibrations of a plate of hexagonal crystal carrying an array of micro-rods with their bottoms fixed to the top surface of the plate.The rods undergo longitudinal vibrations when the crystal plate is in thickness-stretch motion.The plate is modeled by the theory of anisotropic elasticity.The rods are modeled by the one-dimensional structural theory for extensional vibration of rods.A frequency equation is obtained and solved using perturbation method.The effect of the rod array on the resonant frequencies of the crystal plate is examined.The results are potentially useful for using thickness-stretch modes of crystal plates to measure the mechanical properties of microrod arrays.
