The effects of yeast culture and direct-fed microbes on the growth performance of weaner lambs was examined.Thirty-two Hu lambs with inihtial weight of 22.20(±0.75) kg were randomly assigned to one of four treatm...The effects of yeast culture and direct-fed microbes on the growth performance of weaner lambs was examined.Thirty-two Hu lambs with inihtial weight of 22.20(±0.75) kg were randomly assigned to one of four treatments:basal diet without additive(control),added with yeast culture at 15 g/head/d(YEC),YEC plus Bacillus licheniformis preparation at 2.3 g/head/d(YBL) or plus Clostridium butyricum preparation at 2.3 g/head/d(YCB).The feeding trial lasted 75 d with 15 d for adaptation.Feed intake was not influenced(P>0.05) by treatment.Average daily gain of growing lambs was 102,114,90,and 89 g/d in control,YEC,YBL,and YCB,respectively,with no significant difference(P>0.05) among treatments,but the carcass weight of YEC lambs was significantly higher(P<0.05) than that of other treatments.Total volatile fatty acids and acetate to propionate ratio in the rumen were unaffected,although the butyric acid concentration was higher(P<0.05) in the rumen fluid of YCB lambs compared with YEC lambs and slightly higher(P>0.05) than in controls and YBL lambs.Solid-associated fungi population relative to total rumen bacteria 16S ribosomal DNA was significantly lower(P<0.05) in YBL lambs(3.55) compared with those on YCB(23.12).There was little difference in blood glucose and plasma urea-N concentrations among the treatments.Blood concentrations of creatinine and globulin were significantly higher(P<0.05) in YBL lambs,compared with the control and YEC-fed animals,and no difference with YCB lambs.Total protein and triglycerides in blood were significantly(P<0.05) higher in YBL lambs,compared with controls.These serum biochemical parameters suggest that treatment increased amounts of absorbable protein but not efficiency of protein utilization and in YBL and YCB lambs.The results indicated that yeast culture improve growth performance,while little advantage could be expected from combining yeast culture with either the B.licheniformis preparation or C.butyricum preparation.More research using lower doses of B.licheniformis preparation or C.butyricum preparation in combination with yeast culture is warranted.展开更多
The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg cont...The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.展开更多
Taking Al-2%mole-Cu binary alloy as an example, the influence of grain orientation on competitive growth of dendrites under different competitive modes was investigated by using the three-dimensional(3-D) phasefield m...Taking Al-2%mole-Cu binary alloy as an example, the influence of grain orientation on competitive growth of dendrites under different competitive modes was investigated by using the three-dimensional(3-D) phasefield method. The result of phase-field simulation was verified by applying cold spray and directional remelting. In the simulation process, two competitive modes were designed: in Scheme 1, the monolayer columnar grains in multilayer columnar crystals had different orientations; while in Scheme 2, they had the same orientation. The simulation result showed that in Scheme 1, the growth of the dendrites, whose orientation had a certain included angle with the direction of temperature gradient, was restrained by the growth of other dendrites whose direction was parallel to the direction of temperature gradient. Moreover, the larger the included angle between the grain orientation and temperature gradient, the earlier the cessation of dendrite growth. The secondary dendrites of dendrites whose grain orientation was parallel to the temperature gradient flourished with increasing included angles between the grain orientation and temperature gradient. In Scheme 2, the greater the included angle between grain orientation and temperature gradient, the easier the dendrites whose orientation showed a certain included angle with temperature gradient inserted between those grew parallel to the temperature gradient, and the better the growth condition thereafter. Some growing dendrites after intercalation were deflected to the temperature gradient, and the greater the included angle, the lower the deflection. The morphologies of the competitive growth dendrites obtained through simulation can also be found in metallographs of practical solidification experiments. This implies that the two modes of competitive growth of dendrites characterized in the simulation do exist and frequently appear in practical solidification processes.展开更多
A self-made directional solidification setup was used to prepare high purity aluminum ingots of 100mm in diameter. The morphology of the growth interface was detected by SEM and AFM, and the grain lattice orientation ...A self-made directional solidification setup was used to prepare high purity aluminum ingots of 100mm in diameter. The morphology of the growth interface was detected by SEM and AFM, and the grain lattice orientation was detected by XRD. The results indicate that the grains suffer competitive growth under any conditions in experiments. The lattice orientation of the preferred grains is determined by the flow field above the solid-liquid interface. The horizontal lattice position does not change during the growth process. However, the lattice orientation in the growth direction varies with the growth velocity and approaches to [100] gradually during the growth process.展开更多
Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[11...Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[11-20] seed(a-sapphire) were used to prepare sapphire by edge-defined film-fed growth(EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×103 and 3.9×103 cm-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid(SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.展开更多
The microstructures of （Ti-45%Al）（（molar） （fraction）） alloy directionally solidified at different growth rates in alumina tube by electromagnetic heating zone melting were studied. The measured temperature gra...The microstructures of （Ti-45%Al）（（molar） （fraction）） alloy directionally solidified at different growth rates in alumina tube by electromagnetic heating zone melting were studied. The measured temperature gradient of the system is about 104K/m. The microstructures show that the primary solidified phase is β phase at different growth rates. The growth at low rates from 1.94×10-6m/s to 4.16×10-6m/s results in a transient solid/liquid interface structure from planar to shallow cellular. This transient rate is larger than the theoretical value of (vc=6.94×10-7m/s.) Compared with vt=vc/k=1.01×10-6m/s, the cellular-dendritic transient rate of experiment is observed in the range of 1.67×10-52.50×10-5m/s. The primary arm spacing decreases with increasing growth rate.展开更多
A self-made directional solidification device was used to fabricate d 80 mm high purity aluminum ingots. SEM and AFM were used to detect the shape of grain boundaries. The orientation of the grain was studied by X-ray...A self-made directional solidification device was used to fabricate d 80 mm high purity aluminum ingots. SEM and AFM were used to detect the shape of grain boundaries. The orientation of the grain was studied by X-ray diffractometry. The results show that the nucleation points locate at the intersections of three adjacent grains. The lattice orientation of grains does not alter in the horizontal direction, but gradually approaches the optimum growth direction in the vertical direction during the growth process. All the grains suffer the competition and only the one whose orientation is closest to the preferred direction can occupy the final growth space.展开更多
Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influen...Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.展开更多
To date, complex components of available reagents have been used for directional induction of neural stem cells into dopaminergic neurons, resulting in a poor ability to repeat experiments. This study sought to invest...To date, complex components of available reagents have been used for directional induction of neural stem cells into dopaminergic neurons, resulting in a poor ability to repeat experiments. This study sought to investigate whether a homogenate of the substantia nigra of adult rats and/or basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons. Tyrosine hydroxylase-positive cells were observed exclusively after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor for 48 hours in vitro. However, in the groups treated with homogenate supernatant or basic fibroblast growth factor alone, tyrosine hydroxylase expression was not observed. Moreover, the content of dopamine in the culture medium of subventricular zone neurons was significantly increased at 48 hours after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor. Experimental findings indicate that the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons in the substantia nigra with the ability to secrete dopamine.展开更多
The main purpose of this research was to analyze the impact<span style="font-family:;" "=""> </span><span style="font-family:Verdana;">the Chinese foreign direct in...The main purpose of this research was to analyze the impact<span style="font-family:;" "=""> </span><span style="font-family:Verdana;">the Chinese foreign direct investment (FDI), remittances, and foreign aid have had to human capital growth (HCG) and brain drain. The study data </span><span style="font-family:Verdana;">were</span><span style="font-family:Verdana;"> collected from five African countries (Nigeria, Kenya, Ghana, South Africa, and Morocco) from 2009 to 2018. Secondary sources were used in data collection, then autoregressive distributed lag (ARDL) modeling was used in the analysis. Before modelling was done, co-integration tests and panel unit were applied. The results revealed that Chinese FDI, remittances, and foreign aid had a significant and positive impact on HCG in the long</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">but not the short-run. Besides, remittances, Chinese FDI, and foreign aid demonstrated significant negative impacts on brain drain in the long term, not in the short term. This study makes important practical and theoretical contributions about the roles of Chinese FDI, remittances, and foreign aid in the reduction of brain drain and the growth of human capital.</span>展开更多
TiAl-based alloys are potentially used as high-temperature structural materials with a high specific strength in the range of^900°C.However,the mechanical properties of TiAl-based alloys are extremely anisotropic...TiAl-based alloys are potentially used as high-temperature structural materials with a high specific strength in the range of^900°C.However,the mechanical properties of TiAl-based alloys are extremely anisotropic with respect to the lamellar orientation of the microstructures.A balance combination of room-temperature ductility and strength can be achieved when the lamellar orientation are aligned parallel to the tensile stress direction.Lamellar orientation control of TiAl-based alloys by directional solidification technique has been widely studied in recent years.Two different directional solidification processes can be used to modify the lamellar orientation.One is a seeding technique and the other is adjusting the solidification path.This paper reviews the principles of the two methods and their progress.The influence of alloy composition and solidification parameters on lamellar orientation control is also discussed.展开更多
Using a Bridgman vertical vacuum furnace,Ti-45Al-8Nb-(W,B,Y) (at.%) bars,which were prepared from a plasma arc melting (PAM) ingot,were directionally solidified at growth rates of 10,15,and 20 μm/s.Polysynthetic twin...Using a Bridgman vertical vacuum furnace,Ti-45Al-8Nb-(W,B,Y) (at.%) bars,which were prepared from a plasma arc melting (PAM) ingot,were directionally solidified at growth rates of 10,15,and 20 μm/s.Polysynthetic twinned (PST) crystal with an aligned lamellar microstructure was obtained at the growth rate of 15 μm/s because of high Nb addition.The principle of PST crystal growth and the effect of Nb element were discussed.The results of investigations on microstructure and micromechanical properties of the directionally solidified (DS) bars of Ti-45Al-8Nb-(W,B,Y) alloy are briefly summarized.展开更多
In order to avoid contamination from the crucible and to modify the structures,a new solidification method based on cold crucible technology was used to prepare silicon ingots.A silicon ingot with square cross section...In order to avoid contamination from the crucible and to modify the structures,a new solidification method based on cold crucible technology was used to prepare silicon ingots.A silicon ingot with square cross section was directionally solidified with a cold crucible.The mechanism of the cold crucible directional solidification of silicon ingot was revealed.Due to the induction heat that was released in the surface layer and the incomplete contact between the crucible and the melt,the lateral heat loss was reduced and the silicon ingot was directionally solidified.The structures,dislocation defects and the grain growth orientation of the ingot were determined.The results show that neither intergranular nor intragranular precipitates are found in the ingot,except for the top part that was the last to solidify.The average dislocation density is about 1 to 2×106 cm-2.The grains are preferentially <220> orientated.展开更多
A new seed making method with cold crucible by power off technique was proposed. The cold crucible quenched seed with columnar structure has a similar cross-section shape as that of the cold crucible,and can be direct...A new seed making method with cold crucible by power off technique was proposed. The cold crucible quenched seed with columnar structure has a similar cross-section shape as that of the cold crucible,and can be directly used for the directional solidification processes. The proposed method can significantly simplify the seeded directional solidification process and avoid the contamination from the seed machining.展开更多
基金supported by the earmarked fund from China Agriculture Research System,Ministry of Agriculture,China(CARS-372)
文摘The effects of yeast culture and direct-fed microbes on the growth performance of weaner lambs was examined.Thirty-two Hu lambs with inihtial weight of 22.20(±0.75) kg were randomly assigned to one of four treatments:basal diet without additive(control),added with yeast culture at 15 g/head/d(YEC),YEC plus Bacillus licheniformis preparation at 2.3 g/head/d(YBL) or plus Clostridium butyricum preparation at 2.3 g/head/d(YCB).The feeding trial lasted 75 d with 15 d for adaptation.Feed intake was not influenced(P>0.05) by treatment.Average daily gain of growing lambs was 102,114,90,and 89 g/d in control,YEC,YBL,and YCB,respectively,with no significant difference(P>0.05) among treatments,but the carcass weight of YEC lambs was significantly higher(P<0.05) than that of other treatments.Total volatile fatty acids and acetate to propionate ratio in the rumen were unaffected,although the butyric acid concentration was higher(P<0.05) in the rumen fluid of YCB lambs compared with YEC lambs and slightly higher(P>0.05) than in controls and YBL lambs.Solid-associated fungi population relative to total rumen bacteria 16S ribosomal DNA was significantly lower(P<0.05) in YBL lambs(3.55) compared with those on YCB(23.12).There was little difference in blood glucose and plasma urea-N concentrations among the treatments.Blood concentrations of creatinine and globulin were significantly higher(P<0.05) in YBL lambs,compared with the control and YEC-fed animals,and no difference with YCB lambs.Total protein and triglycerides in blood were significantly(P<0.05) higher in YBL lambs,compared with controls.These serum biochemical parameters suggest that treatment increased amounts of absorbable protein but not efficiency of protein utilization and in YBL and YCB lambs.The results indicated that yeast culture improve growth performance,while little advantage could be expected from combining yeast culture with either the B.licheniformis preparation or C.butyricum preparation.More research using lower doses of B.licheniformis preparation or C.butyricum preparation in combination with yeast culture is warranted.
基金financially supported by the National Natural Science Foundation of China(Grant No.51061010)the Program for New Century Excellent Talents in University of China(Grant No.NCET-10-0023)the Program for Hongliu Outstanding Talents of Lanzhou University of Technology
文摘The microstructures and crystal growth directions of permanent mould casting and directionally solidified Al-Mg alloys with different Mg contents have been investigated. The results indicate that the effect of Mg content on microstructure is basically same for the alloys prepared by these two methods. The primary grains change from cellular crystals to developed columnar dendrites, and then to equiaxed dendrites as the Mg content is increased. Simultaneously, both the cellular or columnar grain region and the primary trunk spacing decrease. All of these changes are mainly attributed to the constitutional supercooling resulting from Mg element. Comparatively, the cellular or columnar crystals of the directionally solidified alloys are straighter and more parallel than those of the permanent mould casting alloys. These have straight or wavy grain boundaries, one of the most important microstructure characteristics of feathery grains. However, the transverse microstructure and growth direction reveal that they do not belong to feathery grains. The Mg seemingly can affect the crystal growth direction, but does not result in the formation of feathery grains under the conditions employed in the study.
基金funded by the National Natural Science Foundation of China(Grant Nos.:11504149,11364024,51661020)
文摘Taking Al-2%mole-Cu binary alloy as an example, the influence of grain orientation on competitive growth of dendrites under different competitive modes was investigated by using the three-dimensional(3-D) phasefield method. The result of phase-field simulation was verified by applying cold spray and directional remelting. In the simulation process, two competitive modes were designed: in Scheme 1, the monolayer columnar grains in multilayer columnar crystals had different orientations; while in Scheme 2, they had the same orientation. The simulation result showed that in Scheme 1, the growth of the dendrites, whose orientation had a certain included angle with the direction of temperature gradient, was restrained by the growth of other dendrites whose direction was parallel to the direction of temperature gradient. Moreover, the larger the included angle between the grain orientation and temperature gradient, the earlier the cessation of dendrite growth. The secondary dendrites of dendrites whose grain orientation was parallel to the temperature gradient flourished with increasing included angles between the grain orientation and temperature gradient. In Scheme 2, the greater the included angle between grain orientation and temperature gradient, the easier the dendrites whose orientation showed a certain included angle with temperature gradient inserted between those grew parallel to the temperature gradient, and the better the growth condition thereafter. Some growing dendrites after intercalation were deflected to the temperature gradient, and the greater the included angle, the lower the deflection. The morphologies of the competitive growth dendrites obtained through simulation can also be found in metallographs of practical solidification experiments. This implies that the two modes of competitive growth of dendrites characterized in the simulation do exist and frequently appear in practical solidification processes.
基金Project(2002AA336072) supported by the High-tech Research and Development Program of ChinaProject(03XD14009) supported by the Program of Shanghai Subject Chief Scientist
文摘A self-made directional solidification setup was used to prepare high purity aluminum ingots of 100mm in diameter. The morphology of the growth interface was detected by SEM and AFM, and the grain lattice orientation was detected by XRD. The results indicate that the grains suffer competitive growth under any conditions in experiments. The lattice orientation of the preferred grains is determined by the flow field above the solid-liquid interface. The horizontal lattice position does not change during the growth process. However, the lattice orientation in the growth direction varies with the growth velocity and approaches to [100] gradually during the growth process.
基金Funded by the Special Fund of Jiangsu Province for the Transformation of Scientific and Technological Achievements(No.BA2012049)the Priority Academic Program Development of Jiangsu Higher Education Institutions
文摘Sapphire, belonging to hexagonal crystal system, is typically anisotropic which makes it direction-sensitive. To research the effects of growth directions on properties of sapphire, c-[0001] seed(c-sapphire) and a-[11-20] seed(a-sapphire) were used to prepare sapphire by edge-defined film-fed growth(EFG) method. The samples were analyzed through lattice integrity, dislocation and corrosion performance by double-crystal XRD, OM, AFM, SEM and EDX. It was shown that the lattice integrities of two growth-direction crystals were both well due to the small FWHM values. While the average densities of dislocation in c-sapphire and a-sapphire were 9.2×103 and 3.9×103 cm-2 respectively, the energy of dislocation in c-sapphire was lower than that in a-sapphire. During Strong Phosphoric Acid(SPA) etching, the surface of c-sapphire basically kept smooth but in a-sapphire there were many point-like corrosion pits where aluminum and oxygen atoms lost by 2:1. Our work means that it will be promising for growing c-[0001] seed sapphire by EFG if aided by parameter optimization.
基金Projects(50271020 50395102) supported by the National Natural Science Foundation of China
文摘The microstructures of （Ti-45%Al）（（molar） （fraction）） alloy directionally solidified at different growth rates in alumina tube by electromagnetic heating zone melting were studied. The measured temperature gradient of the system is about 104K/m. The microstructures show that the primary solidified phase is β phase at different growth rates. The growth at low rates from 1.94×10-6m/s to 4.16×10-6m/s results in a transient solid/liquid interface structure from planar to shallow cellular. This transient rate is larger than the theoretical value of (vc=6.94×10-7m/s.) Compared with vt=vc/k=1.01×10-6m/s, the cellular-dendritic transient rate of experiment is observed in the range of 1.67×10-52.50×10-5m/s. The primary arm spacing decreases with increasing growth rate.
基金Project(2002AA6070) supported by the Hi-tech Research and Development Program of China
文摘A self-made directional solidification device was used to fabricate d 80 mm high purity aluminum ingots. SEM and AFM were used to detect the shape of grain boundaries. The orientation of the grain was studied by X-ray diffractometry. The results show that the nucleation points locate at the intersections of three adjacent grains. The lattice orientation of grains does not alter in the horizontal direction, but gradually approaches the optimum growth direction in the vertical direction during the growth process. All the grains suffer the competition and only the one whose orientation is closest to the preferred direction can occupy the final growth space.
基金supported by the National Natural Science Foundation of China(Nos.50395103 and 50271057)the Shaanxi Provincial Natural Science Foundation of China(No.200304E104).
文摘Two new classes of growth morphologies, called doublons and seaweed, were simulated using a phase-field method. The evolution of doublon and seaweed morphologies was obtained in directional solidification. The influence of orientation and velocity on the growth morphology was investigated. It was indicated that doublons preferred growing with its crystallographic axis aligned with the heat flow direction. Seaweed, on the other hand, could be obtained by tilting the crystalline axis to 45°. Stable doublons could only exist in a range of velocity regime. Beyond this regime the patterns formed would be unstable. The simulation results agreed with the reported experimental results qualitatively.
基金sponsored by the General Program of Yunnan Provincial Application Basic Research, No. 2008ZC109M
文摘To date, complex components of available reagents have been used for directional induction of neural stem cells into dopaminergic neurons, resulting in a poor ability to repeat experiments. This study sought to investigate whether a homogenate of the substantia nigra of adult rats and/or basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons. Tyrosine hydroxylase-positive cells were observed exclusively after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor for 48 hours in vitro. However, in the groups treated with homogenate supernatant or basic fibroblast growth factor alone, tyrosine hydroxylase expression was not observed. Moreover, the content of dopamine in the culture medium of subventricular zone neurons was significantly increased at 48 hours after induction with the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor. Experimental findings indicate that the homogenate supernatant of the substantia nigra from adult rats and basic fibroblast growth factor could directionally induce neural stem cells derived from the subventricular zone of embryonic rats to differentiate into dopaminergic neurons in the substantia nigra with the ability to secrete dopamine.
文摘The main purpose of this research was to analyze the impact<span style="font-family:;" "=""> </span><span style="font-family:Verdana;">the Chinese foreign direct investment (FDI), remittances, and foreign aid have had to human capital growth (HCG) and brain drain. The study data </span><span style="font-family:Verdana;">were</span><span style="font-family:Verdana;"> collected from five African countries (Nigeria, Kenya, Ghana, South Africa, and Morocco) from 2009 to 2018. Secondary sources were used in data collection, then autoregressive distributed lag (ARDL) modeling was used in the analysis. Before modelling was done, co-integration tests and panel unit were applied. The results revealed that Chinese FDI, remittances, and foreign aid had a significant and positive impact on HCG in the long</span><span style="font-family:;" "=""> </span><span style="font-family:Verdana;">but not the short-run. Besides, remittances, Chinese FDI, and foreign aid demonstrated significant negative impacts on brain drain in the long term, not in the short term. This study makes important practical and theoretical contributions about the roles of Chinese FDI, remittances, and foreign aid in the reduction of brain drain and the growth of human capital.</span>
基金supported by the 973 project(2011CB610406,2011CB605504)NSFC project(51331005)Heilongjiang project(JC201209)
文摘TiAl-based alloys are potentially used as high-temperature structural materials with a high specific strength in the range of^900°C.However,the mechanical properties of TiAl-based alloys are extremely anisotropic with respect to the lamellar orientation of the microstructures.A balance combination of room-temperature ductility and strength can be achieved when the lamellar orientation are aligned parallel to the tensile stress direction.Lamellar orientation control of TiAl-based alloys by directional solidification technique has been widely studied in recent years.Two different directional solidification processes can be used to modify the lamellar orientation.One is a seeding technique and the other is adjusting the solidification path.This paper reviews the principles of the two methods and their progress.The influence of alloy composition and solidification parameters on lamellar orientation control is also discussed.
基金supported by the National Natural Science Foundation of China (No. 50771013)
文摘Using a Bridgman vertical vacuum furnace,Ti-45Al-8Nb-(W,B,Y) (at.%) bars,which were prepared from a plasma arc melting (PAM) ingot,were directionally solidified at growth rates of 10,15,and 20 μm/s.Polysynthetic twinned (PST) crystal with an aligned lamellar microstructure was obtained at the growth rate of 15 μm/s because of high Nb addition.The principle of PST crystal growth and the effect of Nb element were discussed.The results of investigations on microstructure and micromechanical properties of the directionally solidified (DS) bars of Ti-45Al-8Nb-(W,B,Y) alloy are briefly summarized.
基金financially supported by the National Natural Science Foundation of China (No.50804012)the Natural Science Foundation of Hei Longjiang Province,China (No.E201002)
文摘In order to avoid contamination from the crucible and to modify the structures,a new solidification method based on cold crucible technology was used to prepare silicon ingots.A silicon ingot with square cross section was directionally solidified with a cold crucible.The mechanism of the cold crucible directional solidification of silicon ingot was revealed.Due to the induction heat that was released in the surface layer and the incomplete contact between the crucible and the melt,the lateral heat loss was reduced and the silicon ingot was directionally solidified.The structures,dislocation defects and the grain growth orientation of the ingot were determined.The results show that neither intergranular nor intragranular precipitates are found in the ingot,except for the top part that was the last to solidify.The average dislocation density is about 1 to 2×106 cm-2.The grains are preferentially <220> orientated.
基金Project(50395102) supported by the National Natural Science Foundation of China
文摘A new seed making method with cold crucible by power off technique was proposed. The cold crucible quenched seed with columnar structure has a similar cross-section shape as that of the cold crucible,and can be directly used for the directional solidification processes. The proposed method can significantly simplify the seeded directional solidification process and avoid the contamination from the seed machining.
