The formation mechanism of stoichiometry Ti_5Si_3 by mechanical alloying (MA)from elemental powders has been investigated. The results of XRD and SEM analyses of the powdershow that Ti_5Si_3 can be synthesized by MA i...The formation mechanism of stoichiometry Ti_5Si_3 by mechanical alloying (MA)from elemental powders has been investigated. The results of XRD and SEM analyses of the powdershow that Ti_5Si_3 can be synthesized by MA in a planetary mill with two different formationmechanisms. Ti_5Si_3 was formed gradually with the mechanical collusion reaction (MCR) mechanismunder a lower impact energy, and the Ti_5Si_3 was formed abruptly with the self-propagatinghigh-temperature synthesis (SHS) formation mechanism under a higher impact energy.展开更多
The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium ma...The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium matrix composites were prepared by discharge plasma sintering(SPS)and argon protective sintering(APS).The results show that the two processes have a negligible effect on the composition and hardness of the samples,but the hardness of the two samples is significantly improved by adding SiCp.The apparent porosity of SPS process is obviously smaller than that of APS process,whereas,the apparent porosity increases slightly with the addition of SiCp.The oxide layer thickness and mass gain of the samples obtained by SPS process are smaller than those obtained by APS process.The oxide thickness and mass gain of both processes are further reduced by adding SiCp.The SPS composites showed the best high temperature oxidation resistance.Therefore,TMCs with Si Cp by SPS can effectively improve the high-temperature oxidation behavior of the materials.展开更多
For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,he...For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.展开更多
By doping gas transport agents (GTA), the combustion process and structural formation of SHS can be significantly varied. In this paper, Ti5Sis was synthesized by SHS method using AICI3·6H2O as GTA. The effect of...By doping gas transport agents (GTA), the combustion process and structural formation of SHS can be significantly varied. In this paper, Ti5Sis was synthesized by SHS method using AICI3·6H2O as GTA. The effect of GTA was studied by measuring combustion process parameters. XRD and SEM were used to determine the phases and microstructures of products. The structural formation of 7V6Si3 with different GTA contents was studied by CFQ method. Three mechanisms were deduced.展开更多
First principles study is reported for the band structures, site and angular momentum decomposed density of states. and the electronic charge density distributions in high-temperature structural materials D88-Ti5Si3 w...First principles study is reported for the band structures, site and angular momentum decomposed density of states. and the electronic charge density distributions in high-temperature structural materials D88-Ti5Si3 with the addition of low-rate metalloid: carbon, boron, nitrogen and oxygen. It shows that how the addition of metalloid atoms can stabilize Nowotny phase of Ti,Si3 from the viewpoint of the electron structure.展开更多
By performing P doping on the Si sites in the topological semimetal Mo_(5)Si_(3),we discover strong-coupling superconductivity in Mo_(5)Si_(3-x)P_(x)(0.5≤x≤2.0).Mo_(5)Si_(3)crystallizes in the W_(5)Si_(3)-type struc...By performing P doping on the Si sites in the topological semimetal Mo_(5)Si_(3),we discover strong-coupling superconductivity in Mo_(5)Si_(3-x)P_(x)(0.5≤x≤2.0).Mo_(5)Si_(3)crystallizes in the W_(5)Si_(3)-type structure with space group of I4/mcm(No.140),and is not a superconductor itself.Upon P doping,the lattice parameter a decreases while c increases monotonously.Bulk superconductivity is revealed in Mo_(5)Si_(3-x)P_(x)(0.5≤x≤2.0)from resistivity,magnetization,and heat capacity measurements.T_(c)in Mo_(5)Si_(1.5)P_(1.5)reaches as high as 10.8 K,setting a new record among the W_(5)Si_(3)-type superconductors.The upper and lower critical fields for Mo_(5)Si_(1.5)P_(1.5)are 14.56 T and 105 mT,respectively.Moreover,Mo_(5)Si_(1.5)P_(1.5)is found to be a fully gapped superconductor with strong electron-phonon coupling.First-principles calculations suggest that the enhancement of electron-phonon coupling is possibly due to the shift of the Fermi level,which is induced by electron doping.The calculations also reveal the nontrivial band topology in Mo_(5)Si_(3).The T_(c)and upper critical field in Mo_(5)Si_(3-x)P_(x) are fairly high among pseudobinary compounds.Both of them are higher than those in NbTi,making future applications promising.Our results suggest that the W_(5)Si_(3)-type compounds are ideal platforms to search for new superconductors.By examinations of their band topologies,more candidates for topological superconductors can be expected in this structural family.展开更多
In the present work, in-situ Ti_(5)Si_(3) reinforced special brasses were prepared by melt reaction method. The synthesized Ti_(5)Si_(3) phase shows various morphologies in brasses with different Ti_(5)Si_(3) content,...In the present work, in-situ Ti_(5)Si_(3) reinforced special brasses were prepared by melt reaction method. The synthesized Ti_(5)Si_(3) phase shows various morphologies in brasses with different Ti_(5)Si_(3) content, and the3 D morphological evolution of primary Ti_(5)Si_(3)and its growth mechanism were investigated. The Ti_(5)Si_(3) crystal, which bears D8_(8) hexagonal crystal structure, grows along <0001> direction and is revealed by{1010} faces during growth. With the increase of Ti_(5)Si_(3) content in the brasses, the morphology of primary Ti_(5)Si_(3)significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition,the influence of Ti_(5)Si_(3) volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti_(5)Si_(3), and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti_(5)Si_(3) containing hollows appears in the brass. That is mainly due to the fact that the Ti_(5)Si_(3) is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.展开更多
A series of Gd_5Si_(2)BO_(13):Eu^(3+)and non-rare earth Bi^(3+)ions doped Gd_5Si_(2)BO_(13):Eu^(3+)phosphors was successfully synthesized via high-temperature solid-state method,and the as-obtained phosphors were stud...A series of Gd_5Si_(2)BO_(13):Eu^(3+)and non-rare earth Bi^(3+)ions doped Gd_5Si_(2)BO_(13):Eu^(3+)phosphors was successfully synthesized via high-temperature solid-state method,and the as-obtained phosphors were studied on their phase structures,luminescence characteristics,thermal stability and luminescence lifetime.Transient fluorescence spectroscopy data show that the addition of Bi^(3+)can obviously enhance the emission intensity of Eu^(3+)in the near-ultraviolet band owing to energy transfer from Bi^(3+)to Eu^(3+).Besides,the addition of Bi^(3+)can improve the thermal stability of a single-doped phosphor Gd_5Si_(2)BO_(13):0.35Eu^(3+)from 70.33%to 87.45%at 150℃and the quantum yield from 58.80%to 78.61%at room temperature.Finally,Gd_5Si_(2)BO_(13):Eu^(3+),Bi^(3+)was used to encapsulate white light-emitting diodes(WLEDs)with green((Ba,Sr)_(2)SiO_(4):Eu^(2+))and blue(BaMgAI_(10)O_(17):Eu^(2+))commercial phosphors.The color rendering index of WLEDs was calculated to be larger than 90,and the color temperature was estimated to be 4300-4500 K,which demonstrate that Gd_5Si_(2)BO_(13):Eu^(3+),Bi^(3+)can be regarded as a red phosphor with great potential application.This paper can provide a new insight into design of high-efficiency phosphors by introducing non-rare earth Bi^(3+)ions via energy transfer from Bi^(3+)to Eu^(3+).展开更多
The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying method.Consequently,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an aver...The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying method.Consequently,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an average grain size of 54 nm.After low temperature sintering at 1600°C,the Mo-Y_(2)O_(3)alloys maintaining a high density(99.6%)have the finest grain size(620 nm)comparing with available literature about oxide dispersion strengthened molybdenum alloy(ODS-Mo).The oxide particles remain their small size(mainly<50 nm)within Mo grains and at Mo grain boundaries.Furthermore,the Y_(5)MO_(2)O_(12)particles were firstly observed within Mo matrix,and its formation can absorb nearby oxygen impurities,which involves the purification of Mo matrix.The mechanical properties show that Mo-Y_(2)O_(3)alloy possess a high hardness of 487±28 HV_(0.2),a high yield strength of 902 MPa,a high compressive strength of1110 MPa,respectively.Our work suggests that freeze-drying and subsequent low temperature sintering can shed light on the preparation of ultrafine ODS-Mo alloys with high performance.展开更多
基金the supports of the National Natural Science Foundation of China (No. 51901153)Natural Science Foundation of Shanxi Province,China (No. 201901D211096)。
基金the National Natural Science Foundation of China(No.52004342)Innovation-driven Project of Central South University,China(No.150240015)Natural Science Fund for Outstanding Young Scholar of Hunan Province,China(No.2021JJ20065).
文摘The formation mechanism of stoichiometry Ti_5Si_3 by mechanical alloying (MA)from elemental powders has been investigated. The results of XRD and SEM analyses of the powdershow that Ti_5Si_3 can be synthesized by MA in a planetary mill with two different formationmechanisms. Ti_5Si_3 was formed gradually with the mechanical collusion reaction (MCR) mechanismunder a lower impact energy, and the Ti_5Si_3 was formed abruptly with the self-propagatinghigh-temperature synthesis (SHS) formation mechanism under a higher impact energy.
基金Funded by the Key Projects of Equipment Pre-research Foundation of the Ministry of Equipment Development of the Central Military Commission of China(No.6140922010201)the Key R&D Plan of Zhenjiang in 2018(No.GY2018021)。
文摘The effects of SiC particles(SiCp)on high temperature oxidation behavior of titanium matrix composites(TMCs)under different powder metallurgy processes were investigated.In situ Ti C+Ti_(5)Si_(3)reinforced titanium matrix composites were prepared by discharge plasma sintering(SPS)and argon protective sintering(APS).The results show that the two processes have a negligible effect on the composition and hardness of the samples,but the hardness of the two samples is significantly improved by adding SiCp.The apparent porosity of SPS process is obviously smaller than that of APS process,whereas,the apparent porosity increases slightly with the addition of SiCp.The oxide layer thickness and mass gain of the samples obtained by SPS process are smaller than those obtained by APS process.The oxide thickness and mass gain of both processes are further reduced by adding SiCp.The SPS composites showed the best high temperature oxidation resistance.Therefore,TMCs with Si Cp by SPS can effectively improve the high-temperature oxidation behavior of the materials.
基金National Natural Science Foundation of China(Grant No.51571004).
文摘For hypereutectic Nb-Si based alloys,primary Nb_(5)Si_(3)phases typically grow in a faceted mode during equilibrium or near-equilibrium solidification,which damages the ductility and toughness.To address this issue,here we artificially manipulate the growth morphology of Nb_(5)Si_(3)using electron beam surface melting(EBSM)and subsequent annealing treatments.Results show that such a non-equilibrium solidification pathway enables the transition from faceted growth to non-faceted dendritic growth of Nb_(5)Si_(3),along with evident microstructure refinement,generation of metastableβ-Nb_(5)Si_(3)phases and elimination of chemical segregation.The transformation fromβ-Nb_(5)Si_(3)toα-Nb_(5)Si_(3)and Nb solid solution(Nbss)particles is triggered by the annealing treatment at 1450°C for 5 h.Also,we find the annealing-mediated formation of inherited Nb_(5)Si_(3)dendrites that maintain the dendritic morphology of the original as-solidifiedβ-Nb_(5)Si_(3)dendrites.This work thus provides a feasible routine to obtain thermally stable and refinedα-Nb_(5)Si_(3)dendrites in hypereutectic Nb-Si based alloys.
基金Supported by the National Natural Science Fund (No. 59872024) and the National Excellent Young Scientist Fund of China(No. 59925207).
文摘By doping gas transport agents (GTA), the combustion process and structural formation of SHS can be significantly varied. In this paper, Ti5Sis was synthesized by SHS method using AICI3·6H2O as GTA. The effect of GTA was studied by measuring combustion process parameters. XRD and SEM were used to determine the phases and microstructures of products. The structural formation of 7V6Si3 with different GTA contents was studied by CFQ method. Three mechanisms were deduced.
文摘First principles study is reported for the band structures, site and angular momentum decomposed density of states. and the electronic charge density distributions in high-temperature structural materials D88-Ti5Si3 with the addition of low-rate metalloid: carbon, boron, nitrogen and oxygen. It shows that how the addition of metalloid atoms can stabilize Nowotny phase of Ti,Si3 from the viewpoint of the electron structure.
基金supported by the National Key Research and Development Program of China(2018YFA0704200,2021YFA1401800,2018YFA0305602,and 2017YFA0302904)the National Natural Science Foundation of China(12074414,12074002,and 11774402)the Strategic Priority Research Program of Chinese Academy of Sciences(XDB25000000)。
文摘By performing P doping on the Si sites in the topological semimetal Mo_(5)Si_(3),we discover strong-coupling superconductivity in Mo_(5)Si_(3-x)P_(x)(0.5≤x≤2.0).Mo_(5)Si_(3)crystallizes in the W_(5)Si_(3)-type structure with space group of I4/mcm(No.140),and is not a superconductor itself.Upon P doping,the lattice parameter a decreases while c increases monotonously.Bulk superconductivity is revealed in Mo_(5)Si_(3-x)P_(x)(0.5≤x≤2.0)from resistivity,magnetization,and heat capacity measurements.T_(c)in Mo_(5)Si_(1.5)P_(1.5)reaches as high as 10.8 K,setting a new record among the W_(5)Si_(3)-type superconductors.The upper and lower critical fields for Mo_(5)Si_(1.5)P_(1.5)are 14.56 T and 105 mT,respectively.Moreover,Mo_(5)Si_(1.5)P_(1.5)is found to be a fully gapped superconductor with strong electron-phonon coupling.First-principles calculations suggest that the enhancement of electron-phonon coupling is possibly due to the shift of the Fermi level,which is induced by electron doping.The calculations also reveal the nontrivial band topology in Mo_(5)Si_(3).The T_(c)and upper critical field in Mo_(5)Si_(3-x)P_(x) are fairly high among pseudobinary compounds.Both of them are higher than those in NbTi,making future applications promising.Our results suggest that the W_(5)Si_(3)-type compounds are ideal platforms to search for new superconductors.By examinations of their band topologies,more candidates for topological superconductors can be expected in this structural family.
基金supported financially by the National Key Research and Development Program of China(Nos.2018YFE0306103 and 2017YFB0306105)the National Natural Science Foundation of China(Nos.51771040,51690163 and51525401)The Science and Technology Innovation Project of Ningbo(No.2018B10030)。
文摘In the present work, in-situ Ti_(5)Si_(3) reinforced special brasses were prepared by melt reaction method. The synthesized Ti_(5)Si_(3) phase shows various morphologies in brasses with different Ti_(5)Si_(3) content, and the3 D morphological evolution of primary Ti_(5)Si_(3)and its growth mechanism were investigated. The Ti_(5)Si_(3) crystal, which bears D8_(8) hexagonal crystal structure, grows along <0001> direction and is revealed by{1010} faces during growth. With the increase of Ti_(5)Si_(3) content in the brasses, the morphology of primary Ti_(5)Si_(3)significantly changes from fibers to hexagonal prisms to short-rods with hollow. In addition,the influence of Ti_(5)Si_(3) volume fraction and morphology on the wear behavior of special brass was also revealed. It was substantiated that the wear resistance increases with the increasing volume fraction of Ti_(5)Si_(3), and the corresponding wear mechanism changes from delamination to slight adhesive wear and abrasive wear. However, the friction coefficient shows an abnormal increase when most of the Ti_(5)Si_(3) containing hollows appears in the brass. That is mainly due to the fact that the Ti_(5)Si_(3) is easier to break and fall off resulted by the hollow as a crack source, which makes it unable to resist the plastic deformation of the contact surface during the sliding.
文摘A series of Gd_5Si_(2)BO_(13):Eu^(3+)and non-rare earth Bi^(3+)ions doped Gd_5Si_(2)BO_(13):Eu^(3+)phosphors was successfully synthesized via high-temperature solid-state method,and the as-obtained phosphors were studied on their phase structures,luminescence characteristics,thermal stability and luminescence lifetime.Transient fluorescence spectroscopy data show that the addition of Bi^(3+)can obviously enhance the emission intensity of Eu^(3+)in the near-ultraviolet band owing to energy transfer from Bi^(3+)to Eu^(3+).Besides,the addition of Bi^(3+)can improve the thermal stability of a single-doped phosphor Gd_5Si_(2)BO_(13):0.35Eu^(3+)from 70.33%to 87.45%at 150℃and the quantum yield from 58.80%to 78.61%at room temperature.Finally,Gd_5Si_(2)BO_(13):Eu^(3+),Bi^(3+)was used to encapsulate white light-emitting diodes(WLEDs)with green((Ba,Sr)_(2)SiO_(4):Eu^(2+))and blue(BaMgAI_(10)O_(17):Eu^(2+))commercial phosphors.The color rendering index of WLEDs was calculated to be larger than 90,and the color temperature was estimated to be 4300-4500 K,which demonstrate that Gd_5Si_(2)BO_(13):Eu^(3+),Bi^(3+)can be regarded as a red phosphor with great potential application.This paper can provide a new insight into design of high-efficiency phosphors by introducing non-rare earth Bi^(3+)ions via energy transfer from Bi^(3+)to Eu^(3+).
基金the National Natural Science Foundation of China(No.51822404)the Natural Science Foundation of Tianjin(No.18JCYBJC17900)+1 种基金supported by the Science and Technology Program of Tianjin(Nos.19YFZCGX00790 and 18YFZCGX00070)Researchers Supporting Project number(No.RSP-2021/6),King Saud University,Riyadh,Saudi Arabia。
文摘The ultrafine Mo-Y_(2)O_(3)composite powders were successfully synthesized by innovative freeze-drying method.Consequently,the freeze-dried Mo-Y_(2)O_(3)composite powders with high sintering activities possess an average grain size of 54 nm.After low temperature sintering at 1600°C,the Mo-Y_(2)O_(3)alloys maintaining a high density(99.6%)have the finest grain size(620 nm)comparing with available literature about oxide dispersion strengthened molybdenum alloy(ODS-Mo).The oxide particles remain their small size(mainly<50 nm)within Mo grains and at Mo grain boundaries.Furthermore,the Y_(5)MO_(2)O_(12)particles were firstly observed within Mo matrix,and its formation can absorb nearby oxygen impurities,which involves the purification of Mo matrix.The mechanical properties show that Mo-Y_(2)O_(3)alloy possess a high hardness of 487±28 HV_(0.2),a high yield strength of 902 MPa,a high compressive strength of1110 MPa,respectively.Our work suggests that freeze-drying and subsequent low temperature sintering can shed light on the preparation of ultrafine ODS-Mo alloys with high performance.
