The effect of vanadium carbide（VC） on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of ...The effect of vanadium carbide（VC） on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of VC and Al5Ti1 B were also compared. The refined samples of commercial pure aluminum were examined using optical microscopy, scanning electron microscopy（SEM） and energy-dispersive spectroscopy（EDS）. The results suggest that VC is a good refiner of commercial pure aluminum. The addition of only 0.3wt% VC can decrease the grain size of aluminum to 102 μm, whereas the casting temperature and holding time have little effect on the grain size. The refining efficiency of VC is better than that of Al5Ti1 B. The VC particles in molten aluminum act as nuclei and the grain refinement of aluminum alloys by VC particles is achieved via heterogeneous nucleation.展开更多
X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+...X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+TiC, pure Ti_3AlC_2 and Ti_2AlC+Ti_3AlC_2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti_2AlC samples synthesized at 1500 ℃ by hot-pressing sintering are inhomogeneous and have a gradient structure.Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.展开更多
The effect of tin on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used for phase identificatio...The effect of tin on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used for phase identification and microstructure evaluation. The experimental results show that addition of tin can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/1Ti/1Al/0.2Sn powders at 1200-1250 ℃ under a pressure of 30 MPa. SEM images show that Ti3AlC2 samples in about 2-5 μm thick and 10-25μm long platelets can be obtained. The fracture toughness and flexural strength of Ti3AlC2 were 6.5±0.2 MPa·m^1/2 and 560±10 MPa, respectively.展开更多
Ti_(3)AlC_(2)-reinforced Ag-based composites,which are used as sliding current collectors,electrical contacts,and electrode materials,exhibit remarkable performances.However,the interfacial reactions between Ag and Ti...Ti_(3)AlC_(2)-reinforced Ag-based composites,which are used as sliding current collectors,electrical contacts,and electrode materials,exhibit remarkable performances.However,the interfacial reactions between Ag and Ti_(3)AlC_(2) significantly degrade the electrical and thermal properties of these composites.To diminish these interfacial reactions,we fabricated carbon-coated Ti_(3)AlC_(2) particles(C@Ti_(3)AlC_(2))as reinforcement and prepared Ag–10wt%C@Ti_(3)AlC_(2) composites with carbon-layer thicknesses ranging from 50–200 nm.Compared with the uncoated Ag–Ti_(3)AlC_(2) composite,Ag–C@Ti_(3)AlC_(2) was found to have a better distribution of Ti_(3)AlC_(2) particles.With increases in the carbon-layer thickness,the Vickers hardness value and relative density of Ag–C@Ti_(3)AlC_(2) gradually decreases.With a carbon-layer thickness of 150 nm,we obtained the lowest resistivity of Ag–C@Ti_(3)AlC_(2) of 29.4135.5×10^(−9)Ω·m,which is half that of Ag–Ti_(3)AlC_(2)(66.7×10^(−9)Ω·m).The thermal conductivity of Ag–C@Ti_(3)AlC_(2) reached a maximum value of 135.5 W·m^(−1)·K^(−1) with a 200-nm carbon coating(~1.8 times that of Ag–Ti_(3)AlC_(2)).These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti_(3)AlC_(2) composites.展开更多
n order to investigate the phase evolution and microstructure of aluminum containing carbon composites,- 195 graphite flake and ≤0. 074 mm aluminum powders（ Al 99%,in mass,the same hereinafter） were used as main st...n order to investigate the phase evolution and microstructure of aluminum containing carbon composites,- 195 graphite flake and ≤0. 074 mm aluminum powders（ Al 99%,in mass,the same hereinafter） were used as main starting materials. The mixture with 1 ∶ 1of graphite and aluminum was well mixed with additional 15% phenolic resin and then shaped in a hydraulic machine. The specimens were first dried at 250 ℃ for12 h,and then graphite-embedded fired at 800,1 000,1 200,1 400,and 1 600 ℃ for 3 h,respectively. XRD and SEM were used to characterize the phase compositions and section microstructure. The results show that at800 ℃ aluminum powder melts and reacts with carbon in resin forming granular Al4C3 at the edge of graphite;at 1 000 ℃,Al4C3 increases in amount and grows in volume,and AlN commences to form; at 1 200 ℃,some Al4C3 grows to tabular shape,and other Al4C3 nitridizes forming fibrous AlN; at 1 400 ℃,Al4C3 decreases because it is nitridized or oxidized forming fibrous AlN or Al2O3; at 1 600 ℃,Al4C3 disappears,AlN or Al2O3 gets big and coarse.展开更多
The effect of Mg and Si additon to Al matrix on infiltration kinetics and rates of Al alloys pressureless infiltration into porous SiCp preform was investigated by observing the change of infiltration distance with ti...The effect of Mg and Si additon to Al matrix on infiltration kinetics and rates of Al alloys pressureless infiltration into porous SiCp preform was investigated by observing the change of infiltration distance with time as the Al alloys infiltrate into SiCp preforms at different temperatures.The results show that infiltration of SiCp preforms by Al melt is a thermal activation process and there is an incubation period before the infiltration becomes stable.With the increase of Mg content in the Al alloys from 0wt% to 8wt%,the infiltration will become much easier,the incubation period becomes shorter and the infiltration rate is faster,but these effects are not obvious when the Mg content is higher than 8wt%.As for Si addition to the Al alloys,it has no obvious effect on the incubation period,but the infiltration rate increases markedly with the increase of Si content from 0wt% to 12wt% and the rate has no obvious change when the content is bigger than 12wt%.The effect of Mg and Si on the incubation period is related to the infiltration mechanism of Al pressureless infiltration into SiCp preforms and their impact on the infiltration rate is a combined result from viscosity and surface tension of Al melt and SiC-Al wetting ability.展开更多
基金financially supported by the Department of Science and Technology of Sichuan Province (Nos. 2015KJT0081-2015G, 2015GZ0052, and 13CGZH0200)
文摘The effect of vanadium carbide（VC） on the grain size of commercial pure aluminum was experimentally investigated by varying the content of VC, the holding time, and casting temperature. The refining efficiencies of VC and Al5Ti1 B were also compared. The refined samples of commercial pure aluminum were examined using optical microscopy, scanning electron microscopy（SEM） and energy-dispersive spectroscopy（EDS）. The results suggest that VC is a good refiner of commercial pure aluminum. The addition of only 0.3wt% VC can decrease the grain size of aluminum to 102 μm, whereas the casting temperature and holding time have little effect on the grain size. The refining efficiency of VC is better than that of Al5Ti1 B. The VC particles in molten aluminum act as nuclei and the grain refinement of aluminum alloys by VC particles is achieved via heterogeneous nucleation.
文摘X-ray diffraction (XRD) analysis on different polished surfaces normal to the hot pressing direction reveals that the phase compositions of the polished surfaces from the outside to the inside are pure TiC, Ti_3AlC_2+TiC, pure Ti_3AlC_2 and Ti_2AlC+Ti_3AlC_2, no matter elemental powder or TiC is used as raw materials. It is found that ternary-layered carbide Ti_2AlC samples synthesized at 1500 ℃ by hot-pressing sintering are inhomogeneous and have a gradient structure.Electron probe X-ray micro-analysis (EPMA) indicates that the Al content along the hot pressing axis is parabolic, it is the highest in the center and the lowest at the both ends, while the Ti content is constant along the axis. The experimental result reveals that the evaporation of Al in samples in an open system during hot pressing sintering results in a gradient structure.
基金Funded by the National Natural Science Foundation of China (No.20771088, No.50572080) Doctoral Foundation of Wuhan University of Technology (No.471-38650142)
文摘The effect of tin on synthesis of Ti3AlC2 by spark plasma sintering （SPS） from TiC/Ti/Al powders was investigated. X-ray diffraction （XRD） and scanning electron microscopy （SEM） were used for phase identification and microstructure evaluation. The experimental results show that addition of tin can considerably accelerate the synthesis reaction of Ti3AlC2 and fully dense, essentially single-phase polycrystalline Ti3AlC2 could be successfully obtained by sintering 2TiC/1Ti/1Al/0.2Sn powders at 1200-1250 ℃ under a pressure of 30 MPa. SEM images show that Ti3AlC2 samples in about 2-5 μm thick and 10-25μm long platelets can be obtained. The fracture toughness and flexural strength of Ti3AlC2 were 6.5±0.2 MPa·m^1/2 and 560±10 MPa, respectively.
基金financial support of the National Natural Science Foundation of China(Nos.51731004 and 51671054)the Natural Science Foundation of Jiangsu Province(No.BK20181285)the Fundamental Research Funds for the Central Universities,China(No.2242019K 40056).
文摘Ti_(3)AlC_(2)-reinforced Ag-based composites,which are used as sliding current collectors,electrical contacts,and electrode materials,exhibit remarkable performances.However,the interfacial reactions between Ag and Ti_(3)AlC_(2) significantly degrade the electrical and thermal properties of these composites.To diminish these interfacial reactions,we fabricated carbon-coated Ti_(3)AlC_(2) particles(C@Ti_(3)AlC_(2))as reinforcement and prepared Ag–10wt%C@Ti_(3)AlC_(2) composites with carbon-layer thicknesses ranging from 50–200 nm.Compared with the uncoated Ag–Ti_(3)AlC_(2) composite,Ag–C@Ti_(3)AlC_(2) was found to have a better distribution of Ti_(3)AlC_(2) particles.With increases in the carbon-layer thickness,the Vickers hardness value and relative density of Ag–C@Ti_(3)AlC_(2) gradually decreases.With a carbon-layer thickness of 150 nm,we obtained the lowest resistivity of Ag–C@Ti_(3)AlC_(2) of 29.4135.5×10^(−9)Ω·m,which is half that of Ag–Ti_(3)AlC_(2)(66.7×10^(−9)Ω·m).The thermal conductivity of Ag–C@Ti_(3)AlC_(2) reached a maximum value of 135.5 W·m^(−1)·K^(−1) with a 200-nm carbon coating(~1.8 times that of Ag–Ti_(3)AlC_(2)).These results indicate that the carbon-coating method is a feasible strategy for improving the performance of Ag–C@Ti_(3)AlC_(2) composites.
文摘n order to investigate the phase evolution and microstructure of aluminum containing carbon composites,- 195 graphite flake and ≤0. 074 mm aluminum powders（ Al 99%,in mass,the same hereinafter） were used as main starting materials. The mixture with 1 ∶ 1of graphite and aluminum was well mixed with additional 15% phenolic resin and then shaped in a hydraulic machine. The specimens were first dried at 250 ℃ for12 h,and then graphite-embedded fired at 800,1 000,1 200,1 400,and 1 600 ℃ for 3 h,respectively. XRD and SEM were used to characterize the phase compositions and section microstructure. The results show that at800 ℃ aluminum powder melts and reacts with carbon in resin forming granular Al4C3 at the edge of graphite;at 1 000 ℃,Al4C3 increases in amount and grows in volume,and AlN commences to form; at 1 200 ℃,some Al4C3 grows to tabular shape,and other Al4C3 nitridizes forming fibrous AlN; at 1 400 ℃,Al4C3 decreases because it is nitridized or oxidized forming fibrous AlN or Al2O3; at 1 600 ℃,Al4C3 disappears,AlN or Al2O3 gets big and coarse.
基金supported by the National Natural Science Foundation of China (No.51004010)the Research Fund for the Doctoral Program of Higher Education of China (No.20090006120022)
文摘The effect of Mg and Si additon to Al matrix on infiltration kinetics and rates of Al alloys pressureless infiltration into porous SiCp preform was investigated by observing the change of infiltration distance with time as the Al alloys infiltrate into SiCp preforms at different temperatures.The results show that infiltration of SiCp preforms by Al melt is a thermal activation process and there is an incubation period before the infiltration becomes stable.With the increase of Mg content in the Al alloys from 0wt% to 8wt%,the infiltration will become much easier,the incubation period becomes shorter and the infiltration rate is faster,but these effects are not obvious when the Mg content is higher than 8wt%.As for Si addition to the Al alloys,it has no obvious effect on the incubation period,but the infiltration rate increases markedly with the increase of Si content from 0wt% to 12wt% and the rate has no obvious change when the content is bigger than 12wt%.The effect of Mg and Si on the incubation period is related to the infiltration mechanism of Al pressureless infiltration into SiCp preforms and their impact on the infiltration rate is a combined result from viscosity and surface tension of Al melt and SiC-Al wetting ability.
