In order to study the successive deposition and solidification processes of uniform alloy droplets during the drop-on-demand three dimensional（3D） printing method,based on the volume of fluid（VOF） method,a 3D nume...In order to study the successive deposition and solidification processes of uniform alloy droplets during the drop-on-demand three dimensional（3D） printing method,based on the volume of fluid（VOF） method,a 3D numerical model was employed.In this model,the 7075 alloy with larger temperature range for phase change was used.The simulation results show that the successive deposition and solidification processes of uniform 7075 alloy droplets can be well characterized by this model.Simulated droplets shapes agree well with SEM images under the same condition.The effects of deposition and solidification of droplets result in vertical and L-shaped ridges on the surface of droplets,and tips of dendrites appear near the overlap of droplets due to rapid solidification.展开更多
The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adi...The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adiabatic calorimetric method as a function of the flight distance. A droplet solidification simulation model has been used to compare with the experimental data. The results show that the enthalpy released by the droplets in the calorimeter is 11.88 J/g and 22.29 J/g less than the simulated values up to a certain flight distance at 0.485 m and 0.460 m for 150 μm and 185 μm droplets respectively, but agrees with the expected values at larger distance. The nucleation of the droplets takes place at the distance where the experimental and simulated enthalpy values agree. The droplets quenched before nucleation solidify into metastable supersaturated solid solution and have large undercooling. The formation of the metastable structure in the droplets has been verified metallographically and by calculations based on a thermodynamic model.展开更多
The metastable liquid phase separation occurs in the ternary Cu50Fe37.5Co12.5 peritectic alloy droplets during free fall. The separated alloy melt rapidly solidifies and evolves core-shell microstructure composed of L...The metastable liquid phase separation occurs in the ternary Cu50Fe37.5Co12.5 peritectic alloy droplets during free fall. The separated alloy melt rapidly solidifies and evolves core-shell microstructure composed of L1(Cu) and L2(Fe,Co) phases. Based on the determination of the phase transition temperature, the core-shell microstructure evolution, the interfacial energy, the temperature gradient and the Marangoni migration are analyzed. The interfacial energy of the separated liquid phase increases with the decrease of the temperature. The temperature gradient changes from large to small along the radius direction from inside to outside in the alloy droplet. The Marangoni force (FM) acting on the micro-droplet of L2(Fe,Co) phase increases with the increase of the size of the L2(Fe,Co) phase, and decreases with the increase of undercooling. Driven by FM, the micro-droplet of L2(Fe,Co) phase migrates from outside to inside in the alloy droplet, collides and coagulates each other during migration, and then forms different types of core-shell microstructures.展开更多
基金Projects (51005186,51221001) supported by the National Natural Science Foundation of ChinaProject (85-TZ-2013) supported by the Research Fund of the State Key Laboratory of Solidification Processing(NWPU),ChinaProject (20126102110022) supported by the Doctoral Fund of Ministry of Education of China
文摘In order to study the successive deposition and solidification processes of uniform alloy droplets during the drop-on-demand three dimensional（3D） printing method,based on the volume of fluid（VOF） method,a 3D numerical model was employed.In this model,the 7075 alloy with larger temperature range for phase change was used.The simulation results show that the successive deposition and solidification processes of uniform 7075 alloy droplets can be well characterized by this model.Simulated droplets shapes agree well with SEM images under the same condition.The effects of deposition and solidification of droplets result in vertical and L-shaped ridges on the surface of droplets,and tips of dendrites appear near the overlap of droplets due to rapid solidification.
文摘The undercooling and solidification of 150 μm and 185 μm droplets of Sn 5%Pb alloy prepared by the uniform droplet spray (UDS) process have been investigated. The enthalpy of the droplet has been measured by non adiabatic calorimetric method as a function of the flight distance. A droplet solidification simulation model has been used to compare with the experimental data. The results show that the enthalpy released by the droplets in the calorimeter is 11.88 J/g and 22.29 J/g less than the simulated values up to a certain flight distance at 0.485 m and 0.460 m for 150 μm and 185 μm droplets respectively, but agrees with the expected values at larger distance. The nucleation of the droplets takes place at the distance where the experimental and simulated enthalpy values agree. The droplets quenched before nucleation solidify into metastable supersaturated solid solution and have large undercooling. The formation of the metastable structure in the droplets has been verified metallographically and by calculations based on a thermodynamic model.
基金Supported by the National Natural Science Foundation of China (Grant Nos.50121101,50395105)NPU Youth Scientific and Technological Innovation Foundation (Grant No.W016223)
文摘The metastable liquid phase separation occurs in the ternary Cu50Fe37.5Co12.5 peritectic alloy droplets during free fall. The separated alloy melt rapidly solidifies and evolves core-shell microstructure composed of L1(Cu) and L2(Fe,Co) phases. Based on the determination of the phase transition temperature, the core-shell microstructure evolution, the interfacial energy, the temperature gradient and the Marangoni migration are analyzed. The interfacial energy of the separated liquid phase increases with the decrease of the temperature. The temperature gradient changes from large to small along the radius direction from inside to outside in the alloy droplet. The Marangoni force (FM) acting on the micro-droplet of L2(Fe,Co) phase increases with the increase of the size of the L2(Fe,Co) phase, and decreases with the increase of undercooling. Driven by FM, the micro-droplet of L2(Fe,Co) phase migrates from outside to inside in the alloy droplet, collides and coagulates each other during migration, and then forms different types of core-shell microstructures.
