A numerical model reflecting the real physical processes well has been developed to predict the coarsening manner of the second phase droplets and the microstructural evolution under the common action of nucleation, d...A numerical model reflecting the real physical processes well has been developed to predict the coarsening manner of the second phase droplets and the microstructural evolution under the common action of nucleation, diffusional growth, colliding coagulation during rapid cooling Al-ln hypermonotectic alloys. The model reflects the real physical processes well and is also applicable to other immiscible alloys.展开更多
Liquid-liquid phase separation in the undercooled Ni-20%Pb(mole fraction, the same below if not mentioned) hypermonotectic melts was investigated by the observation of the water-quenched structure and DTA analysis. Th...Liquid-liquid phase separation in the undercooled Ni-20%Pb(mole fraction, the same below if not mentioned) hypermonotectic melts was investigated by the observation of the water-quenched structure and DTA analysis. The results indicate that the number of spherical cells in the water-quenched microstructure increases with dropping temperature, and the cells gather and grow up obviously. The spherical cell origins from L1 phase separated from homogeneous melt, and is the product of monotectic reaction. Both results of the water-quenched structures and DTA analysis prove that liquid phase separation still occurs in the highly undercooled Ni-Pb hypermonotectic alloy melts, and liquid phase separation in the immiscible gap can not be fully inhibited by high undercooling and rapid solidification.展开更多
The microstructures and evolution mechanism of the undercooled Ni-20%Pb（molar fraction） alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the ...The microstructures and evolution mechanism of the undercooled Ni-20%Pb（molar fraction） alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the morphology of α-Ni phase and the distribution of Pb element in undercooled Ni-20%Pb alloys change with the increase of undercooling. The main evolution mechanisms of α-Ni are dendrite remelting and recrystallization. Pb phase in the microstructure of Ni-20%Pb hypermonotectic alloy originates from L2 phase separated from the parent melt during the cooling process through immiscible gap and L′2 phase formed at the temperature of monotectic transformation. The solubility of Pb element in α-Ni phase under high undercooling condition is up to 5.83% which is obviously higher than that under equilibrium solidification condition. The real reason that causes the solubility difference is distinct solute trapping.展开更多
Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-ln immiscible alloys and their final microstructures and morphologies were investigated. There existed a transition of columnar Al ...Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-ln immiscible alloys and their final microstructures and morphologies were investigated. There existed a transition of columnar Al grain-equiaxed grain for the thicker ribbon, but only columnar Al grain for the thinner ribbon throughout the thickness. In the columnar grain field, most of the fine In particles was distributed within the cells, but a minority of bigger In particles or short rods was perpendicularly distributed at the grain boundaries. In the equiaxed grain field, the fine In particles were located in Al grains and coarser particles were situated at the boundaries. The average particle size increased with increasing distance from the chilled surface throughout the ribbon. At the same wheel speed (same cooling rate), the average particle size increased with raising In content. At the same composition condition, the average particle size decreased with increasing wheel speed and/or decreasing ejection temperature.展开更多
A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian c...A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian collision and motion collision between the second phase droplets. The simulation results are dynamically visualized and show that the volume fraction, distribution and size of the second phase droplets satisfactorily agree with the experimental results. So the model can be used to predict the microstructural evolution of Al In immiscible alloys during the cooling process.展开更多
Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously i...Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously in solidification sample,opposite to macrosegregation in solidification sample under conventional condition. Stokes motion of the second liquid droplet (Ga) is significantly restrained un-der acoustic levitation condition. The analyses indicate that the melt vibration in the gravity direction forced by acoustic field can induce steady flow around the second liquid droplet,which influences droplet shape during its moving upward and consequently restrains Stokes motion velocity of the second liquid droplet.展开更多
文摘A numerical model reflecting the real physical processes well has been developed to predict the coarsening manner of the second phase droplets and the microstructural evolution under the common action of nucleation, diffusional growth, colliding coagulation during rapid cooling Al-ln hypermonotectic alloys. The model reflects the real physical processes well and is also applicable to other immiscible alloys.
基金Project(50171055) supported by the National Natural Science Foundation of China Project(2004E108) supported by Shaanxi Natural Science Foundation, China+1 种基金 Project(03JK132) supported by Shaanxi Education Bureau Foundation, China Project(200208) supported by the Doctorate Creation Foundation of Northwestern Polytechnical University
文摘Liquid-liquid phase separation in the undercooled Ni-20%Pb(mole fraction, the same below if not mentioned) hypermonotectic melts was investigated by the observation of the water-quenched structure and DTA analysis. The results indicate that the number of spherical cells in the water-quenched microstructure increases with dropping temperature, and the cells gather and grow up obviously. The spherical cell origins from L1 phase separated from homogeneous melt, and is the product of monotectic reaction. Both results of the water-quenched structures and DTA analysis prove that liquid phase separation still occurs in the highly undercooled Ni-Pb hypermonotectic alloy melts, and liquid phase separation in the immiscible gap can not be fully inhibited by high undercooling and rapid solidification.
文摘The microstructures and evolution mechanism of the undercooled Ni-20%Pb（molar fraction） alloy were investigated systematically by high undercooling solidification technique. The experiment results indicate that the morphology of α-Ni phase and the distribution of Pb element in undercooled Ni-20%Pb alloys change with the increase of undercooling. The main evolution mechanisms of α-Ni are dendrite remelting and recrystallization. Pb phase in the microstructure of Ni-20%Pb hypermonotectic alloy originates from L2 phase separated from the parent melt during the cooling process through immiscible gap and L′2 phase formed at the temperature of monotectic transformation. The solubility of Pb element in α-Ni phase under high undercooling condition is up to 5.83% which is obviously higher than that under equilibrium solidification condition. The real reason that causes the solubility difference is distinct solute trapping.
基金The authors gratefully appreciate the American Ernerson R]ec-kric Co.for Lhe financial support.
文摘Melt spinning rapid solidification technique was employed to fabricate homogeneous Al-ln immiscible alloys and their final microstructures and morphologies were investigated. There existed a transition of columnar Al grain-equiaxed grain for the thicker ribbon, but only columnar Al grain for the thinner ribbon throughout the thickness. In the columnar grain field, most of the fine In particles was distributed within the cells, but a minority of bigger In particles or short rods was perpendicularly distributed at the grain boundaries. In the equiaxed grain field, the fine In particles were located in Al grains and coarser particles were situated at the boundaries. The average particle size increased with increasing distance from the chilled surface throughout the ribbon. At the same wheel speed (same cooling rate), the average particle size increased with raising In content. At the same composition condition, the average particle size decreased with increasing wheel speed and/or decreasing ejection temperature.
文摘A numerical model has been developed to describe the microstructural evolution of Al In immiscible alloys through the miscibility gap. The model considers the common action of nucleation, diffusible growth, Brownian collision and motion collision between the second phase droplets. The simulation results are dynamically visualized and show that the volume fraction, distribution and size of the second phase droplets satisfactorily agree with the experimental results. So the model can be used to predict the microstructural evolution of Al In immiscible alloys during the cooling process.
基金Supported by the National Natural Science Foundation of China (Grant Nos. 50121101, 50271058, 50395105 and 50301012)
文摘Containerless treatment of Bi-58.5at%Ga hypermonotectic alloy is successfully performed with acous-tic levitation technique. Under acoustic levitation condition,the second phase (Ga) distributes almost homogeneously in solidification sample,opposite to macrosegregation in solidification sample under conventional condition. Stokes motion of the second liquid droplet (Ga) is significantly restrained un-der acoustic levitation condition. The analyses indicate that the melt vibration in the gravity direction forced by acoustic field can induce steady flow around the second liquid droplet,which influences droplet shape during its moving upward and consequently restrains Stokes motion velocity of the second liquid droplet.
