New Ag/Ti_2 SnC(Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti_2 SnC was confirmed with a contact angle of 14°. Arc erosion propertie...New Ag/Ti_2 SnC(Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti_2 SnC was confirmed with a contact angle of 14°. Arc erosion properties of Ag/10 wt%Ti_2 SnC(Ag/10 TSC) and Ag/20 wt%Ti_2 SnC(Ag/20 TSC) contacts were investigated under 400 V/100 A/AC-3 and compared with Ag/CdO contact.The Ag/10 TSC contact exhibited comparable arc erosion property to Ag/CdO contact. The fine arc erosion resistance was attributed to the good wettability between Ti_2 SnC and Ag,the good heat-conducting property of Ag/10 TSC, and the slight decomposition of Ti_2 SnC that absorbed part of electric arc energy. The excessive Ti_2 SnC significantly decreased the thermal conducting property of the Ag/20 TSC composite, resulting in the severe heat accumulation that decomposed Ti_2 SnC and deteriorated arc erosion property. The oxidation behavior of Ti_2 SnC under high electric arc temperature was also studied and then an arc erosion mechanism was proposed to get a comprehensive understanding on the arc erosion property of Ag/TSC composites.展开更多
Ti3SiC2-reintbrced Ag-maJxix composites are expected to serve as eleclrical contacts. In this study, the wettability of Ag on a Ti3SiC2 subslxate was measured by the sessile drop melkod. The Ag-Ti3SiC2 composites were...Ti3SiC2-reintbrced Ag-maJxix composites are expected to serve as eleclrical contacts. In this study, the wettability of Ag on a Ti3SiC2 subslxate was measured by the sessile drop melkod. The Ag-Ti3SiC2 composites were prepared from Ag mad Ti3SiC2 powder mix- tures by pressureless sintering. The effects of compacting pressure （100-800 MPa）, sintering temperature （850-950~C）, mad soaking time （0.5-2 h） on the microslxucture mad properties of the Ag-Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 paxticulates were uniformly distxibuted in flae Ag matrix, wiflaout reactions at the interthces between flae two phases. The prepared Ag-10wt%Ti3SiC2 had a relative density of 95% mad an electrical resistivity of 2.76 x 10 3 m~）＇cm when compacted at 800 MPa mad sintered at 950~C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; INs behavior was attxibuted to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.展开更多
Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX ...Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX phase coatings can be fabricated through firstly depositing a coating containing the three elements M,A,and X close to stoichiometry of the MAX phases using physical vapor deposition,followed by heat treatment in vacuum.In this work,Ti-Al-C coating was prepared on austenitic stainless steels by reactive DC magnetron sputtering with a compound Ti （50）Al （50） target,and CH4 used as the reactive gas.It was found that the as-deposited coating is mainly composed of Ti 3AlC antiperovskite phase with supersaturated solid solution of Al.Additionally,the ratio of Ti/Al remained the same as that of the target composition.Nevertheless,a thicker thermally grown Ti 2AlC MAX phase coating was obtained after being annealed at 800℃ in vacuum for 1 h.Meanwhile,the ratio of Ti/Al became close to stoichiometry of Ti 2AlC MAX phases.It can be understood that owing to the higher activity of Al,it diffused quickly into the substrate during annealing,and then more stable Ti 2AlC MAX phases transformed from the Ti 3AlC antiperovskite phase.展开更多
Guided by the theoretical prediction,a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V,Sn,and C mixtures at 1000°C.The chemical composition and crystal structure of this new...Guided by the theoretical prediction,a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V,Sn,and C mixtures at 1000°C.The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations,X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDS),and high resolution scanning transmission electron microscopy(HR-STEM).The stacking sequence of V2C and Sn layers results in a crystal structure of space group P63/mmc.The a-and c-lattice parameters,which were determined by the Rietveld analysis of powder XRD pattern,are 0.2981(0)nm and 1.3470(6)nm,respectively.The atomic positions are V at 4f(1/3,2/3,0.0776(5)),Sn at 2d(2/3,1/3,1/4),and C at 2a(0,0,0).A new set of XRD data of V2SnC was also obtained.Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy,satisfied Born-Huang criteria of mechanical stability,and positive phonon branches over the Brillouin zone.It also has low shear deformation resistance c44(second-order elastic constant,cij)and shear modulus(G),positive Cauchy pressure,and low Pugh’s ratio(G/B=0.500<0.571),which is regarded as a quasi-ductile MAX phase.The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.展开更多
Mo_(2)Ga_(2)C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties.To understand this unique MAX phase structure and promote possible future applications,the structure,chemical bonding,...Mo_(2)Ga_(2)C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties.To understand this unique MAX phase structure and promote possible future applications,the structure,chemical bonding,and mechanical and thermodynamic properties of Mo_(2)Ga_(2)C were investigated by first-principles.Using the“bond stiffness”model,the strongest covalent bonding(1162 GPa)was formed between Mo and C atoms in Mo_(2)Ga_(2)C,while the weakest Ga–Ga(389 GPa)bonding was formed between two Ga-atomic layers,different from other typical MAX phases.The ratio of the bond stiffness of the weakest bond to the strongest bond(0.33)was lower than 1/2,indicating the high damage tolerance and fracture toughness of Mo_(2)Ga_(2)C,which was confirmed by indentation without any cracks.The high-temperature heat capacity and thermal expansion of Mo_(2)Ga_(2)C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K.Because of the metal-like electronic structure,the electronic excitation contribution became more significant with increasing temperature above 300 K.展开更多
基金financially supported by the National Natural Science Foundation of China (Grant Nos. 51731004, 51671054, and 51501038)the Fundamental Research Funds for the Central Universities in China (Grant Nos. 2242018K40108 and 2242018K40109) were highly appreciated
文摘New Ag/Ti_2 SnC(Ag/TSC) composites with uniform microstructure were prepared by powder metallurgy. The superior wettability between Ag and Ti_2 SnC was confirmed with a contact angle of 14°. Arc erosion properties of Ag/10 wt%Ti_2 SnC(Ag/10 TSC) and Ag/20 wt%Ti_2 SnC(Ag/20 TSC) contacts were investigated under 400 V/100 A/AC-3 and compared with Ag/CdO contact.The Ag/10 TSC contact exhibited comparable arc erosion property to Ag/CdO contact. The fine arc erosion resistance was attributed to the good wettability between Ti_2 SnC and Ag,the good heat-conducting property of Ag/10 TSC, and the slight decomposition of Ti_2 SnC that absorbed part of electric arc energy. The excessive Ti_2 SnC significantly decreased the thermal conducting property of the Ag/20 TSC composite, resulting in the severe heat accumulation that decomposed Ti_2 SnC and deteriorated arc erosion property. The oxidation behavior of Ti_2 SnC under high electric arc temperature was also studied and then an arc erosion mechanism was proposed to get a comprehensive understanding on the arc erosion property of Ag/TSC composites.
基金financially supported by the National Natural Science Foundation of China(Nos.51731004,51671054,and 51501038)“the Fundamental Research Funds for the Central Universities”in China
文摘Ti3SiC2-reintbrced Ag-maJxix composites are expected to serve as eleclrical contacts. In this study, the wettability of Ag on a Ti3SiC2 subslxate was measured by the sessile drop melkod. The Ag-Ti3SiC2 composites were prepared from Ag mad Ti3SiC2 powder mix- tures by pressureless sintering. The effects of compacting pressure （100-800 MPa）, sintering temperature （850-950~C）, mad soaking time （0.5-2 h） on the microslxucture mad properties of the Ag-Ti3SiC2 composites were investigated. The experimental results indicated that Ti3SiC2 paxticulates were uniformly distxibuted in flae Ag matrix, wiflaout reactions at the interthces between flae two phases. The prepared Ag-10wt%Ti3SiC2 had a relative density of 95% mad an electrical resistivity of 2.76 x 10 3 m~）＇cm when compacted at 800 MPa mad sintered at 950~C for 1 h. The incorporation of Ti3SiC2 into Ag was found to improve its hardness without substantially compromising its electrical conductivity; INs behavior was attxibuted to the combination of ceramic and metallic properties of the Ti3SiC2 reinforcement, suggesting its potential application in electrical contacts.
基金supported by the National Natural Science Foundation of China (Grant No.51522106 and Grant No.51401229)the National Science and Technology Major Project of China (Grant No.2015ZX06004-001)the Ningbo Municipal Natural Science Foundation (Grant No.2014A610013)
文摘Due to the excellent corrosion resistance and high irradiation damage resistance,Ti 2AlC MAX phase is considered as a candidate for applications as corrosion resistant and irradiation resistant protective coating.MAX phase coatings can be fabricated through firstly depositing a coating containing the three elements M,A,and X close to stoichiometry of the MAX phases using physical vapor deposition,followed by heat treatment in vacuum.In this work,Ti-Al-C coating was prepared on austenitic stainless steels by reactive DC magnetron sputtering with a compound Ti （50）Al （50） target,and CH4 used as the reactive gas.It was found that the as-deposited coating is mainly composed of Ti 3AlC antiperovskite phase with supersaturated solid solution of Al.Additionally,the ratio of Ti/Al remained the same as that of the target composition.Nevertheless,a thicker thermally grown Ti 2AlC MAX phase coating was obtained after being annealed at 800℃ in vacuum for 1 h.Meanwhile,the ratio of Ti/Al became close to stoichiometry of Ti 2AlC MAX phases.It can be understood that owing to the higher activity of Al,it diffused quickly into the substrate during annealing,and then more stable Ti 2AlC MAX phases transformed from the Ti 3AlC antiperovskite phase.
基金This study is supported by Thousand Talents Program of Sichuan Province,the Open Project of State Key Laboratory Cultivation Base for Nonmetal Composites and Functional Materials(17kffk01)Outstanding Young Scientific and Technical Talents in Sichuan Province(2019JDJQ0009)and the National Natural Science Foundation of China(No.51741208).
文摘Guided by the theoretical prediction,a new MAX phase V2SnC was synthesized experimentally for the first time by reaction of V,Sn,and C mixtures at 1000°C.The chemical composition and crystal structure of this new compound were identified by the cross-check combination of first-principles calculations,X-ray diffraction(XRD),energy dispersive X-ray spectroscopy(EDS),and high resolution scanning transmission electron microscopy(HR-STEM).The stacking sequence of V2C and Sn layers results in a crystal structure of space group P63/mmc.The a-and c-lattice parameters,which were determined by the Rietveld analysis of powder XRD pattern,are 0.2981(0)nm and 1.3470(6)nm,respectively.The atomic positions are V at 4f(1/3,2/3,0.0776(5)),Sn at 2d(2/3,1/3,1/4),and C at 2a(0,0,0).A new set of XRD data of V2SnC was also obtained.Theoretical calculations suggest that this new compound is stable with negative formation energy and formation enthalpy,satisfied Born-Huang criteria of mechanical stability,and positive phonon branches over the Brillouin zone.It also has low shear deformation resistance c44(second-order elastic constant,cij)and shear modulus(G),positive Cauchy pressure,and low Pugh’s ratio(G/B=0.500<0.571),which is regarded as a quasi-ductile MAX phase.The mechanism underpinning the quasi-ductility is associated with the presence of a metallic bond.
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.51972080 and 51772077)the Shenzhen Science and Technology Program(Grant No.KQTD2016112814303055)the science foundation of National Key Laboratory of Science and Technology on Advanced Composites in Special Environments.
文摘Mo_(2)Ga_(2)C is a new MAX phase with a stacking Ga-bilayer as well as possible unusual properties.To understand this unique MAX phase structure and promote possible future applications,the structure,chemical bonding,and mechanical and thermodynamic properties of Mo_(2)Ga_(2)C were investigated by first-principles.Using the“bond stiffness”model,the strongest covalent bonding(1162 GPa)was formed between Mo and C atoms in Mo_(2)Ga_(2)C,while the weakest Ga–Ga(389 GPa)bonding was formed between two Ga-atomic layers,different from other typical MAX phases.The ratio of the bond stiffness of the weakest bond to the strongest bond(0.33)was lower than 1/2,indicating the high damage tolerance and fracture toughness of Mo_(2)Ga_(2)C,which was confirmed by indentation without any cracks.The high-temperature heat capacity and thermal expansion of Mo_(2)Ga_(2)C were calculated in the framework of quasi-harmonic approximation from 0 to 1300 K.Because of the metal-like electronic structure,the electronic excitation contribution became more significant with increasing temperature above 300 K.
