In the present review, recent progress on the vortex identification methods are introduced with a focus on the newly proposed omega method（ Ω method）. The advantages of Ω method are summarized with many illustrati...In the present review, recent progress on the vortex identification methods are introduced with a focus on the newly proposed omega method（ Ω method）. The advantages of Ω method are summarized with many illustrating examples. Furthermore, comparing with other existing methods（e.g., Q criterion and λ2 criterion）, one of the characteristics of Ω method is its independence on the chosen threshold values for vortex identifications. The important parameters involved for the practical applications of Ω method are further discussed in detail together with the physical interpretation of the Ω and some suggestions of the future work. Other emerging topics（e.g., Lagrangian coherent structure and Rortex） are also introduced with comments.展开更多
The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg...The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg-Ag alloy, increase the nucleation ratio for Ω phase as heterogeneous nucleation centers, inhibit the growth of Ω phase during aging, and thus increase the volume fraction and decrease the spacing of Ω phase. These microstructures increase the yield strength and tensile strength. However, if both Ce and Ti are added to the alloy, they form （Ce,Ti）-contained compounds and increase the grain size during casting, but have no effects on the nucleation and the growth of Ω phase during aging. The alloy containing both Ce and Ti has a relatively lower Vicks hardness and strength compared to the alloy containing either Ce or Ti.展开更多
The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β p...The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.展开更多
As a β stabilizing element in Ti-based alloys,the effect of Mo on phase constitution,microstructure,mechanical and shape memory properties was investigated.Different compositions of Ti-xMo-3Sn alloys(where x=2,4,6,at...As a β stabilizing element in Ti-based alloys,the effect of Mo on phase constitution,microstructure,mechanical and shape memory properties was investigated.Different compositions of Ti-xMo-3Sn alloys(where x=2,4,6,at.%) were prepared by arc melting.A binary composition of Ti-6 Mo alloy was also prepared for comparison.Ti-xMo-3Sn alloys show low hardness and high ductility with 90% reduction in thickness while Ti-6 Mo alloy shows high hardness,brittle behavior,and poor ductility.Field emission scanning electron microscopy(FESEM) reveals round morphology of athermal ω(ωath) precipitates.The presence of ωath phase is also confirmed by X-ray diffraction(XRD)in both as-cast and solution-treated and quenched conditions.The optical microscopy(OM) and FESEM show that the amount of martensite forming during quenching decreases with an increase in Mo content,which is also due to β→ω transformation.The hardness trends reinforce the presence of ωath too.The shape memory effect(SME) of 9% is the highest for Ti-6 Mo-3Sn alloy.The SME is trivial due to ωath phase formation;however,the increase in SME is observed with an increase in Mo content,which is due to the reverse transformation from ωath and the stress-induced martensitic transformation.In addition,a new and very simple method was designed and used for shape memory effect measurement.展开更多
以α,"-二羟基聚二甲基硅氧烷(107硅橡胶)为基础聚合物,配以交联剂、偶联剂、催化剂等制得LED灌封用缩合型透明硅橡胶。研究了107硅橡胶的黏度,交联剂、催化剂、偶联剂等对透明硅橡胶性能的影响,考察了透明硅橡胶的耐湿热性和耐水...以α,"-二羟基聚二甲基硅氧烷(107硅橡胶)为基础聚合物,配以交联剂、偶联剂、催化剂等制得LED灌封用缩合型透明硅橡胶。研究了107硅橡胶的黏度,交联剂、催化剂、偶联剂等对透明硅橡胶性能的影响,考察了透明硅橡胶的耐湿热性和耐水紫外老化性能。结果表明:随着107硅橡胶黏度的增加,透明硅橡胶的表干时间逐渐延长,拉伸强度先增后降,拉断伸长率逐渐提高,硬度逐渐降低,剪切强度和透光率变化不大;采用聚甲基三乙氧基硅烷为交联剂时,表干时间长,力学强度高;采用二醋酸二丁基锡为催化剂时,表干时间缩短;采用N-β-(氨乙基)-γ-氨丙基甲基二甲氧基硅烷为偶联剂时,表干时间最短,剪切强度高;采用20份黏度为1 500 m Pa·s和80份黏度为12 000 m Pa·s的107硅橡胶复配作基础聚合物,25份聚甲基三乙氧基硅烷为交联剂,0. 5份N-β-(氨乙基)-γ-氨丙基甲基二甲氧基硅烷为偶联剂,0. 2份二醋酸二丁基锡为催化剂,制得的透明硅橡胶随着水紫外和湿热老化时间的延长,剪切强度均先增后降再趋于稳定,透光率先迅速下降,后缓慢下降并趋于稳定。展开更多
This paper studies the effect of Ce on the thermal stability of the Ω phase in an Al-Cu-Mg-Ag alloy by TEM and tensile testing. It has been shown that Ce substantially increases the nucleation density of the Ω phase...This paper studies the effect of Ce on the thermal stability of the Ω phase in an Al-Cu-Mg-Ag alloy by TEM and tensile testing. It has been shown that Ce substantially increases the nucleation density of the Ω phase by acting as the heterogeneous nucleation center. Most impor-tantly,Ce improves the thermal stability of the Ω phase by decreasing the diffusion velocity of Cu atoms and increasing the energy barrier of the thickening ledge nucleation,thus improving the strength of the Al-Cu-Mg-Ag alloy at both ...展开更多
An ω phase with a primitive hexagonal crystal structure has been found to be a ωmmon metastable phase in body-centered cubic （bcc） metals and alloys. In general, ω phase precipitates out as a high density of nano...An ω phase with a primitive hexagonal crystal structure has been found to be a ωmmon metastable phase in body-centered cubic （bcc） metals and alloys. In general, ω phase precipitates out as a high density of nanoscale particles and can obviously strengthen the alloys; however, ωarsening of the ω particles significantly reduces the alloy ductility. The ω phase has ωherent interfacial structure with its bcc matrix phase, and its lattice parameters are aω ---- x/2 x abcc and ωbcc= v/3/2 abcc abet. The ωmmon { 112} （111）-type twinning in bcc metals and alloys can be treated as the product of the ω ~ bcc phase transition, also known as the ω-lattice mechanism. The ω phase＇s behavior in metastable 13-type Ti alloys will be briefly reviewed first since the ω phase was first found in the alloy system, and then the existence of the ω phase in carbon steels will be discussed. Carbon plays a crucial role in promoting the ω formation in steel, and the ω phase can form a solid solution with various carbon ωntents. Hence, the martensitic substructure can be treated as an ct-Fe matrix embedded with a high density of nanoscale ω-Fe particles enriched with carbon. The reωgnition of the ω phase in steel is expected to advance the understanding of the relationship between the microstructure and mechanical properties in bcc steels, as well as the behavior of martensitic transformations, twinning formation, and martensitic substructure.展开更多
An atomic transition model of a face-centered cubic （fcc） crystal to a primitive hexagonal co and body-centered cubic （bcc） structures has been crystallographically built. The fcc structure can transform into the ...An atomic transition model of a face-centered cubic （fcc） crystal to a primitive hexagonal co and body-centered cubic （bcc） structures has been crystallographically built. The fcc structure can transform into the co structure through a local shuffling or displacement of atoms about 0.4014 А in iron for aecc iron = 3.59 ,А The bcc structure can form either after the co formation or concurrently by the similar mechanism, or the co structure can be treated as an intermediate stage during the transition of fcc - bcc. Such a transition （fcc- ω ＋ co ＋ bcc transition） can be confirmed by Widmanstitten pattern formed in an iron meteorite, pearlitic structure and martensite composed of bcc-ferrite and ultra-fine co particles in iron--carbon steels. The present fcc-bcc orientation relationship matches with Pitsch＇s one.展开更多
In this note,property （ω）and property 1 （ω）are variants of Weyl’s theorem. By means of topological uniform descent, the sufficient and necessary conditions of a bounded linear operator defined on a Hilbert spac...In this note,property （ω）and property 1 （ω）are variants of Weyl’s theorem. By means of topological uniform descent, the sufficient and necessary conditions of a bounded linear operator defined on a Hilbert space that satisfies property 1 （ω） and property （ω）is studied. Moreover, property 1 （ω）and property （ω）of 2 2operator matrices are discussed as well.展开更多
Further exploration of the fteld theory as first proposed by Yu (1989) is here presented to cover the equation of motion of a test particle which induces gravitational radiation. The same theory is shown to contain an...Further exploration of the fteld theory as first proposed by Yu (1989) is here presented to cover the equation of motion of a test particle which induces gravitational radiation. The same theory is shown to contain an exact gravitational radiation equation derived as a logical consequence of field equations without extra postulates. In this general dynamic context the theory is renamed 'The field Theory'.展开更多
基金Project supported by the National Natural Science Foundation of China(Grant Nos.51506051,51606221)
文摘In the present review, recent progress on the vortex identification methods are introduced with a focus on the newly proposed omega method（ Ω method）. The advantages of Ω method are summarized with many illustrating examples. Furthermore, comparing with other existing methods（e.g., Q criterion and λ2 criterion）, one of the characteristics of Ω method is its independence on the chosen threshold values for vortex identifications. The important parameters involved for the practical applications of Ω method are further discussed in detail together with the physical interpretation of the Ω and some suggestions of the future work. Other emerging topics（e.g., Lagrangian coherent structure and Rortex） are also introduced with comments.
基金This study was financially supported by the State Key Fundamental Research Project on Al, China (No. 2005CB623704).
文摘The effects of Ce and Ti additions on the microstructures and mechanical properties of an Al-Cu-Mg-Ag alloy have been studied, It has been shown that either Ce or Ti can decrease the as-cast grain size of the Al-Cu-Mg-Ag alloy, increase the nucleation ratio for Ω phase as heterogeneous nucleation centers, inhibit the growth of Ω phase during aging, and thus increase the volume fraction and decrease the spacing of Ω phase. These microstructures increase the yield strength and tensile strength. However, if both Ce and Ti are added to the alloy, they form （Ce,Ti）-contained compounds and increase the grain size during casting, but have no effects on the nucleation and the growth of Ω phase during aging. The alloy containing both Ce and Ti has a relatively lower Vicks hardness and strength compared to the alloy containing either Ce or Ti.
基金supported from the National Natural Science Foundation of China(No.51401221,51622401 and 51628402)support from the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB06050100)
文摘The microstructure evolution and phase composition of an α+β titanium alloy, Ti-3Al-5Mo-4.5V(wt.%),have been investigated. Electron probe micro analysis(EPMA) quantitative results manifest that the stability of β phase decreases with increasing quenching temperature, which is influenced by the significant variation of β-stabilizing elements concentration. Detailed microstructure analysis shows that the β→ωphase transformation does occur when quenching at 750℃ and 800 ℃. The ω-reflections change from incommensurate ω-spots(750 ℃) to ideal ω-spots(800 ℃) as the β stability of the alloy decreases. Further the decrease of β phase stability encourages the formation of athermal α " martensite, which has the following orientation relationships: [111]β//[110]α",[100]p//[100]α " and [-110]p//[00-1]α" with respect to the β matrix.
基金the Higher Education Commission (HЕС) Pakistan for provision of research funding (Project No. 20-3844/R&D/HEC/14) under National Research Program for Universities (NRPU)
文摘As a β stabilizing element in Ti-based alloys,the effect of Mo on phase constitution,microstructure,mechanical and shape memory properties was investigated.Different compositions of Ti-xMo-3Sn alloys(where x=2,4,6,at.%) were prepared by arc melting.A binary composition of Ti-6 Mo alloy was also prepared for comparison.Ti-xMo-3Sn alloys show low hardness and high ductility with 90% reduction in thickness while Ti-6 Mo alloy shows high hardness,brittle behavior,and poor ductility.Field emission scanning electron microscopy(FESEM) reveals round morphology of athermal ω(ωath) precipitates.The presence of ωath phase is also confirmed by X-ray diffraction(XRD)in both as-cast and solution-treated and quenched conditions.The optical microscopy(OM) and FESEM show that the amount of martensite forming during quenching decreases with an increase in Mo content,which is also due to β→ω transformation.The hardness trends reinforce the presence of ωath too.The shape memory effect(SME) of 9% is the highest for Ti-6 Mo-3Sn alloy.The SME is trivial due to ωath phase formation;however,the increase in SME is observed with an increase in Mo content,which is due to the reverse transformation from ωath and the stress-induced martensitic transformation.In addition,a new and very simple method was designed and used for shape memory effect measurement.
文摘以α,"-二羟基聚二甲基硅氧烷(107硅橡胶)为基础聚合物,配以交联剂、偶联剂、催化剂等制得LED灌封用缩合型透明硅橡胶。研究了107硅橡胶的黏度,交联剂、催化剂、偶联剂等对透明硅橡胶性能的影响,考察了透明硅橡胶的耐湿热性和耐水紫外老化性能。结果表明:随着107硅橡胶黏度的增加,透明硅橡胶的表干时间逐渐延长,拉伸强度先增后降,拉断伸长率逐渐提高,硬度逐渐降低,剪切强度和透光率变化不大;采用聚甲基三乙氧基硅烷为交联剂时,表干时间长,力学强度高;采用二醋酸二丁基锡为催化剂时,表干时间缩短;采用N-β-(氨乙基)-γ-氨丙基甲基二甲氧基硅烷为偶联剂时,表干时间最短,剪切强度高;采用20份黏度为1 500 m Pa·s和80份黏度为12 000 m Pa·s的107硅橡胶复配作基础聚合物,25份聚甲基三乙氧基硅烷为交联剂,0. 5份N-β-(氨乙基)-γ-氨丙基甲基二甲氧基硅烷为偶联剂,0. 2份二醋酸二丁基锡为催化剂,制得的透明硅橡胶随着水紫外和湿热老化时间的延长,剪切强度均先增后降再趋于稳定,透光率先迅速下降,后缓慢下降并趋于稳定。
基金the Natural Science Foundation of Hunan Province (No. 07JJ3117)the Chinese Postdoctoral Science Foundation (No. 20070410303)the High Technology Research and Development Program of Hunan Province, China (No. 06FJ2007).
文摘This paper studies the effect of Ce on the thermal stability of the Ω phase in an Al-Cu-Mg-Ag alloy by TEM and tensile testing. It has been shown that Ce substantially increases the nucleation density of the Ω phase by acting as the heterogeneous nucleation center. Most impor-tantly,Ce improves the thermal stability of the Ω phase by decreasing the diffusion velocity of Cu atoms and increasing the energy barrier of the thickening ledge nucleation,thus improving the strength of the Al-Cu-Mg-Ag alloy at both ...
文摘An ω phase with a primitive hexagonal crystal structure has been found to be a ωmmon metastable phase in body-centered cubic （bcc） metals and alloys. In general, ω phase precipitates out as a high density of nanoscale particles and can obviously strengthen the alloys; however, ωarsening of the ω particles significantly reduces the alloy ductility. The ω phase has ωherent interfacial structure with its bcc matrix phase, and its lattice parameters are aω ---- x/2 x abcc and ωbcc= v/3/2 abcc abet. The ωmmon { 112} （111）-type twinning in bcc metals and alloys can be treated as the product of the ω ~ bcc phase transition, also known as the ω-lattice mechanism. The ω phase＇s behavior in metastable 13-type Ti alloys will be briefly reviewed first since the ω phase was first found in the alloy system, and then the existence of the ω phase in carbon steels will be discussed. Carbon plays a crucial role in promoting the ω formation in steel, and the ω phase can form a solid solution with various carbon ωntents. Hence, the martensitic substructure can be treated as an ct-Fe matrix embedded with a high density of nanoscale ω-Fe particles enriched with carbon. The reωgnition of the ω phase in steel is expected to advance the understanding of the relationship between the microstructure and mechanical properties in bcc steels, as well as the behavior of martensitic transformations, twinning formation, and martensitic substructure.
文摘An atomic transition model of a face-centered cubic （fcc） crystal to a primitive hexagonal co and body-centered cubic （bcc） structures has been crystallographically built. The fcc structure can transform into the co structure through a local shuffling or displacement of atoms about 0.4014 А in iron for aecc iron = 3.59 ,А The bcc structure can form either after the co formation or concurrently by the similar mechanism, or the co structure can be treated as an intermediate stage during the transition of fcc - bcc. Such a transition （fcc- ω ＋ co ＋ bcc transition） can be confirmed by Widmanstitten pattern formed in an iron meteorite, pearlitic structure and martensite composed of bcc-ferrite and ultra-fine co particles in iron--carbon steels. The present fcc-bcc orientation relationship matches with Pitsch＇s one.
基金Supported by the Fundamental Research Funds for the Central Universities(GK200901015)Project for Outstanding Young and Middle-aged Researchers initiated by Tianshui Normal University(TSY201205)
文摘In this note,property （ω）and property 1 （ω）are variants of Weyl’s theorem. By means of topological uniform descent, the sufficient and necessary conditions of a bounded linear operator defined on a Hilbert space that satisfies property 1 （ω） and property （ω）is studied. Moreover, property 1 （ω）and property （ω）of 2 2operator matrices are discussed as well.
文摘Further exploration of the fteld theory as first proposed by Yu (1989) is here presented to cover the equation of motion of a test particle which induces gravitational radiation. The same theory is shown to contain an exact gravitational radiation equation derived as a logical consequence of field equations without extra postulates. In this general dynamic context the theory is renamed 'The field Theory'.
