Discrete media filled thin-walled hollow profiles are frequently used as integer structures for special purpose, e.g., in certain materials processing or architectural components. To understand the deformation of such...Discrete media filled thin-walled hollow profiles are frequently used as integer structures for special purpose, e.g., in certain materials processing or architectural components. To understand the deformation of such composite structures which is a complicate mechanics process, involving coupled elastic-plastic deformation of dense metal, compaction of particle and interaction between the filler and the wall, the forward extrusion of Al 6061 tubes filled with various particles was studied. The analysis regarding internal volume variation of round tubes during forward extrusion indicates that with the diameter reduction the volume of tubes decreases commonly. The cavity shrinkage brings about triaxial pressure on the filler, resulted in compaction and densification of it. Loose powders filling leads to higher extrusion load. Due to dissimilar migration behaviors of the particles, the load?stroke curves of the tubes filled with fine powders and coarse balls are quite different. Small Lankford value of the tube wall material leads to higher hydrostatic pressure of the filler and then more powders are compacted.展开更多
The influence of cooling rate on the microstructure of Al0.6CoCrFeNi high entropy alloy（HEA） powders was investigated. The spherical HEA powders（D50≈78.65 μm） were prepared by high pressure gas atomization. The ...The influence of cooling rate on the microstructure of Al0.6CoCrFeNi high entropy alloy（HEA） powders was investigated. The spherical HEA powders（D50≈78.65 μm） were prepared by high pressure gas atomization. The different cooling rates were achieved by adjusting the powder diameter. Based on the solidification model, the relationship between the cooling rate and the powder diameter was developed. The FCC phase gradually disappears as particle size decreases. Further analysis reveals that the phase structure gradually changes from FCC＋BCC dual-phase to a single BCC phase with the increase of the cooling rate. The microstructure evolves from planar crystal to equiaxed grain with the cooling rate increasing from 3.19×10^4 to 1.11×10^6 K/s.展开更多
In this work, under pressure 5.4 GPa and temperature 1250-1400°C, large gem-diamond single crystals with perfect shape and different content of additive boron were synthesized using temperature gradient method. H...In this work, under pressure 5.4 GPa and temperature 1250-1400°C, large gem-diamond single crystals with perfect shape and different content of additive boron were synthesized using temperature gradient method. High-purity boron powders were added as boron source into the graphite powder, and the effects of additive boron on crystal growth habit were investigated in detail. The relationship between the growth rate and the amount of additive boron was studied. The scanning electron microscopy was employed to study the morphology of boron-doped diamond crystals. Raman spectroscopy and Hall measurements were used to investigate the crystal structures and the carrier concentration, respectively. The results show that with the increase of the content of boron added into graphite powder, the crystal growth rate and the carrier concentration increase firstly, and decrease afterwards, and the zone-center phonon line at 1332 cm 1 has small shift to lower energy. The defects occur on the crystal surface when excessive boron is added in the synthesis system.展开更多
基金Project(51575066)supported by the National Natural Science Foundation of ChinaProject(2012ZX04010-081)supported by the National Key Technologies R&D Program of China
文摘Discrete media filled thin-walled hollow profiles are frequently used as integer structures for special purpose, e.g., in certain materials processing or architectural components. To understand the deformation of such composite structures which is a complicate mechanics process, involving coupled elastic-plastic deformation of dense metal, compaction of particle and interaction between the filler and the wall, the forward extrusion of Al 6061 tubes filled with various particles was studied. The analysis regarding internal volume variation of round tubes during forward extrusion indicates that with the diameter reduction the volume of tubes decreases commonly. The cavity shrinkage brings about triaxial pressure on the filler, resulted in compaction and densification of it. Loose powders filling leads to higher extrusion load. Due to dissimilar migration behaviors of the particles, the load?stroke curves of the tubes filled with fine powders and coarse balls are quite different. Small Lankford value of the tube wall material leads to higher hydrostatic pressure of the filler and then more powders are compacted.
基金Project(51471035)supported by the National Natural Science Foundation of China
文摘The influence of cooling rate on the microstructure of Al0.6CoCrFeNi high entropy alloy（HEA） powders was investigated. The spherical HEA powders（D50≈78.65 μm） were prepared by high pressure gas atomization. The different cooling rates were achieved by adjusting the powder diameter. Based on the solidification model, the relationship between the cooling rate and the powder diameter was developed. The FCC phase gradually disappears as particle size decreases. Further analysis reveals that the phase structure gradually changes from FCC＋BCC dual-phase to a single BCC phase with the increase of the cooling rate. The microstructure evolves from planar crystal to equiaxed grain with the cooling rate increasing from 3.19×10^4 to 1.11×10^6 K/s.
文摘In this work, under pressure 5.4 GPa and temperature 1250-1400°C, large gem-diamond single crystals with perfect shape and different content of additive boron were synthesized using temperature gradient method. High-purity boron powders were added as boron source into the graphite powder, and the effects of additive boron on crystal growth habit were investigated in detail. The relationship between the growth rate and the amount of additive boron was studied. The scanning electron microscopy was employed to study the morphology of boron-doped diamond crystals. Raman spectroscopy and Hall measurements were used to investigate the crystal structures and the carrier concentration, respectively. The results show that with the increase of the content of boron added into graphite powder, the crystal growth rate and the carrier concentration increase firstly, and decrease afterwards, and the zone-center phonon line at 1332 cm 1 has small shift to lower energy. The defects occur on the crystal surface when excessive boron is added in the synthesis system.
