Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence...Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.展开更多
In order to clarify the dispersion of SiC particles in straight-blade mechanical stirring of A1-SiCp liquid, the dispersion of SiC particles in A356-3.5% SiCp （volume fraction） liquid in a cylindrical crucible was s...In order to clarify the dispersion of SiC particles in straight-blade mechanical stirring of A1-SiCp liquid, the dispersion of SiC particles in A356-3.5% SiCp （volume fraction） liquid in a cylindrical crucible was studied. The relationship between rotating speed of stirrer and radial relative deviation of SiCp content in A356 liquid between the center and the periphery of crucible was established in the conditions of 35° for the gradient angle a of blade and 10 mm/s for the speed of moving up and down of stirrer. The results show that the radial relative deviation of SiCp content increases gradually with increasing the rotating speed of stirrer. When the rotating speed of stirrer is 200 r/min, the vertical dispersion of SiC particles in A356 liquid is even, but the radial relative deviation of SiCp content is 0.24. Consequently, the northomogeneous dispersion of SiC particles in A356 liquid is mainly resulted from the nonhomogeneous radial dispersion of SiC particles.展开更多
Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical...Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical expression for the drift velocity based on the two-phase mixture theory in turbulent open channels is firstly introduced.The influence of particle inertia on sediment dispersion was investigated through three different aspects including vertical dispersion,motion,and flux properties based on the drift velocity.Results show that the dispersion of suspended sediment in turbulent open-channel flows is affected by three major processes including turbulence of water sediment mixtures,particle random motion,and collisions among particles,of which the contributions of particle turbulence and collisions to the sediment dispersion are remarkable for particles of high inertia.With respect to the vertical mean velocity and sediment flux,it shows that the predictive results agree well with the measurements when the term of particle inertia is considered.As a result,particle inertia considerably affects the behavior of suspended sediment.In particular,the influence of inertia must be accounted for in circumstances of flows laden with high-inertia particles.展开更多
基金Project (51071056) supported by the National Natural Science Foundation of ChinaProjects (HEUCFR1132, HEUCF121712) supported by the Fundamental Research Funds for the Central Universities of China
文摘Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.
基金Project(50974010) supported by the National Natural Science Foundation of ChinaProject(3093023) supported by the Natural Science Foundation of Beijing,ChinaProject(2009JBM091) supported by the Fundamental Research Funds for the Central Universities of China
文摘In order to clarify the dispersion of SiC particles in straight-blade mechanical stirring of A1-SiCp liquid, the dispersion of SiC particles in A356-3.5% SiCp （volume fraction） liquid in a cylindrical crucible was studied. The relationship between rotating speed of stirrer and radial relative deviation of SiCp content in A356 liquid between the center and the periphery of crucible was established in the conditions of 35° for the gradient angle a of blade and 10 mm/s for the speed of moving up and down of stirrer. The results show that the radial relative deviation of SiCp content increases gradually with increasing the rotating speed of stirrer. When the rotating speed of stirrer is 200 r/min, the vertical dispersion of SiC particles in A356 liquid is even, but the radial relative deviation of SiCp content is 0.24. Consequently, the northomogeneous dispersion of SiC particles in A356 liquid is mainly resulted from the nonhomogeneous radial dispersion of SiC particles.
基金supported by the Natural National Science Foundation of China(Grant Nos.51379102,51039004)the National Key Technologies Research and Development Program of China during the 12th Five-Year Plan Period(Grant No.2012BAB05B01)
文摘Particle inertia effect plays a significant role in sediment dispersion which has not been fully elucidated.In this paper,the profound effect of particle inertia on the sediment dispersion was analyzed.The theoretical expression for the drift velocity based on the two-phase mixture theory in turbulent open channels is firstly introduced.The influence of particle inertia on sediment dispersion was investigated through three different aspects including vertical dispersion,motion,and flux properties based on the drift velocity.Results show that the dispersion of suspended sediment in turbulent open-channel flows is affected by three major processes including turbulence of water sediment mixtures,particle random motion,and collisions among particles,of which the contributions of particle turbulence and collisions to the sediment dispersion are remarkable for particles of high inertia.With respect to the vertical mean velocity and sediment flux,it shows that the predictive results agree well with the measurements when the term of particle inertia is considered.As a result,particle inertia considerably affects the behavior of suspended sediment.In particular,the influence of inertia must be accounted for in circumstances of flows laden with high-inertia particles.
