The time evolution of the cross-shock electrostatic potential jump during one specific high Mach number quasi-parallel shock reformation cycle is examined via a 1D hybrid simulation.It is shown that when the average v...The time evolution of the cross-shock electrostatic potential jump during one specific high Mach number quasi-parallel shock reformation cycle is examined via a 1D hybrid simulation.It is shown that when the average value of the electrostatic potential jump is low,its instant value can be large so that the shock is in a favorable profile to directly reflect the incident ions.Our simulation also suggests that,for the ones that finally become injected ions(which can be further accelerated by diffusive shock acceleration mechanism),the first step of their reflections should be mainly attributed to the electrostatic potential jump,instead of the magnetic force,as stated in some previous studies.展开更多
Numerical investigations on the flow field in Ti-Al melt during rectangular cold crucible directional solidification were carried out. Combined with the experimental results, 3-D finite element models for calculating ...Numerical investigations on the flow field in Ti-Al melt during rectangular cold crucible directional solidification were carried out. Combined with the experimental results, 3-D finite element models for calculating flow field inside melting pool were established, the characteristics of the flow under different power parameters were further studied. Numerical calculation results show that there is a complex circular flow in the melt, a rapid horizontal flow exists on the solid/liquid interface and those flows confluence in the center of the melting pool. The flow velocity v increases with the increase of current intensity, but the flow patterns remain unchanged. When the current is 1000 A, the vmax reaches 4 mm/s and the flow on the interface achieves 3 mm/s. Flow patterns are quite different when the frequency changes from 10 kHz to 100 kHz, the mechanism of the frequency influence on the flow pattern is analyzed, and there is an optimum frequency for cold crucible directional solidification.展开更多
A 0.7 mm-thick wavy γ-TiAl sheet with fully lamellar microstructure was fabricated by hot pressing Ti/Al alternate foils with heat treatment of 640 °C, 15 h＋850 °C, 35 h＋1350 °C, 2 h. The intermetall...A 0.7 mm-thick wavy γ-TiAl sheet with fully lamellar microstructure was fabricated by hot pressing Ti/Al alternate foils with heat treatment of 640 °C, 15 h＋850 °C, 35 h＋1350 °C, 2 h. The intermetallic compounds formed during heat treatments were identified by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. TiAl3 was the only observed phase at the Ti/Al interface when Al foils were not consumed. After being annealed at 850 °C for 35 h, the microstructure was composed of α-Ti, α2-Ti3Al, γ-TiAl and TiAl2. A fully lamellar microstructure formed after annealing at 1350 °C. Most of the angles between the lamellar interface and the sheet plane are below 30°. Using thinner starting foils is favorable to produce sheets with fine microstructure.展开更多
Effects of hydrogenation on ambient deformation behaviors of Ti-45Al alloy were studied.The stress-strain curves demonstrate that the plastic deformation of the hydrogenated alloys becomes more remarkable than that of...Effects of hydrogenation on ambient deformation behaviors of Ti-45Al alloy were studied.The stress-strain curves demonstrate that the plastic deformation of the hydrogenated alloys becomes more remarkable than that of the unhydrogenated alloy. Meanwhile,the compression strength and maximum strain are reduced.Both the hydride and hydrogen atoms in the interstices affect the compression deformation behaviors.The reason of the hydrogen-induced embrittlement is that the hydride is easy to become the nucleus of the cracks.And the variation of plastic deformation process is attributed to hydrogen-promoted emission,multiplication and motion of dislocation.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 40931053,41174114 and 41121003the Ocean Public Welfare Scientific Research Project,State Oceanic Administration People’s Republic of China(No 201005017)the Fundamental Research Funds for the Central Universities(WK2080000010).
文摘The time evolution of the cross-shock electrostatic potential jump during one specific high Mach number quasi-parallel shock reformation cycle is examined via a 1D hybrid simulation.It is shown that when the average value of the electrostatic potential jump is low,its instant value can be large so that the shock is in a favorable profile to directly reflect the incident ions.Our simulation also suggests that,for the ones that finally become injected ions(which can be further accelerated by diffusive shock acceleration mechanism),the first step of their reflections should be mainly attributed to the electrostatic potential jump,instead of the magnetic force,as stated in some previous studies.
基金Project (2011CB605504) supported by the National Basic Research Program of China
文摘Numerical investigations on the flow field in Ti-Al melt during rectangular cold crucible directional solidification were carried out. Combined with the experimental results, 3-D finite element models for calculating flow field inside melting pool were established, the characteristics of the flow under different power parameters were further studied. Numerical calculation results show that there is a complex circular flow in the melt, a rapid horizontal flow exists on the solid/liquid interface and those flows confluence in the center of the melting pool. The flow velocity v increases with the increase of current intensity, but the flow patterns remain unchanged. When the current is 1000 A, the vmax reaches 4 mm/s and the flow on the interface achieves 3 mm/s. Flow patterns are quite different when the frequency changes from 10 kHz to 100 kHz, the mechanism of the frequency influence on the flow pattern is analyzed, and there is an optimum frequency for cold crucible directional solidification.
基金Project (50771041) supported by the National Natural Science Foundation of ChinaProject (05-0350) supported by the New Century Excellent Talents in University, China
文摘A 0.7 mm-thick wavy γ-TiAl sheet with fully lamellar microstructure was fabricated by hot pressing Ti/Al alternate foils with heat treatment of 640 °C, 15 h＋850 °C, 35 h＋1350 °C, 2 h. The intermetallic compounds formed during heat treatments were identified by scanning electron microscopy （SEM） and X-ray diffraction （XRD）. TiAl3 was the only observed phase at the Ti/Al interface when Al foils were not consumed. After being annealed at 850 °C for 35 h, the microstructure was composed of α-Ti, α2-Ti3Al, γ-TiAl and TiAl2. A fully lamellar microstructure formed after annealing at 1350 °C. Most of the angles between the lamellar interface and the sheet plane are below 30°. Using thinner starting foils is favorable to produce sheets with fine microstructure.
基金Project(50771041)supported by the National Natural Science Foundation of China。
文摘Effects of hydrogenation on ambient deformation behaviors of Ti-45Al alloy were studied.The stress-strain curves demonstrate that the plastic deformation of the hydrogenated alloys becomes more remarkable than that of the unhydrogenated alloy. Meanwhile,the compression strength and maximum strain are reduced.Both the hydride and hydrogen atoms in the interstices affect the compression deformation behaviors.The reason of the hydrogen-induced embrittlement is that the hydride is easy to become the nucleus of the cracks.And the variation of plastic deformation process is attributed to hydrogen-promoted emission,multiplication and motion of dislocation.
