Directional solidification of Al-15% （mass fraction） Cu alloy was investigated by in situ and real time radiography which was performed by Shanghai synchrotron radiation facility （SSRF）. The imaging results reveal...Directional solidification of Al-15% （mass fraction） Cu alloy was investigated by in situ and real time radiography which was performed by Shanghai synchrotron radiation facility （SSRF）. The imaging results reveal that columnar to equiaxed transition （CET） is provoked by external thermal disturbance. The detaching and floating of fragments of dendrite arms are the prelude of the transition when the solute boundary layer in front of the solid-liquid interface is thin. And the dendrite triangular tip is the fracture sensitive zone. When the conditions are suitable, new dendrites can sprout and grow up. This kind of dendrite has no obvious stem and is named anaxial columnar dendrites.展开更多
To investigate the effect of three-dimension(3 D) thermal convection on columnar-to-equiaxed transition(CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3 D cellular automaton mode...To investigate the effect of three-dimension(3 D) thermal convection on columnar-to-equiaxed transition(CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3 D cellular automaton model coupled with the finite element method(CAFE). The thermal convection in the liquid phase was considered. The results show that the thermal convection in the liquid phase promotes the CET. When the convection is present, the temperature gradient at the start position of CET increases and the growth velocity of columnar dendrite decreases. The convection influences the formation of elongated equiaxed grain through changing the local temperature gradient and dendritic growth velocity.展开更多
A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduce...A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced. The ECP was applied to different stages of the solidification. The results showed that the application of the ECP in both the initial stage （the thickness of solidified shell reached 2 mm approximately） and the late stage （the thickness of solidified shell reached 14 mm approximately） of solidification can promote the columnar to equiaxed transition （CET）. The analysis showed that during solidification, a large number of nuclei around the upper surface fell off due to ECP, which subsequently showered on the melt and impinged the growth front of the columnar crystal. Therefore, the CEToccurred. In addition, this method was also employed to influence the solidification process of bearing steel, and the results showed that the structure was changed from columnar crystal to equiaxed crystal, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.展开更多
Considering the local linear superposition of the species and combining the calculation of phase diagram, the columnar and equiaxed growth behaviours are investigated systematically during solidification of multicompo...Considering the local linear superposition of the species and combining the calculation of phase diagram, the columnar and equiaxed growth behaviours are investigated systematically during solidification of multicomponent alloys. A theoretical model is developed to describe the columnar to equiaxed transition during multicomponent alloy solidification by taking account of the competition between nucleation and growth ahead of a dendrite array, which shows a good agreement with the experimental results.展开更多
Effects of strong magnetic fields on the columnar-to-equiaxed transition(CET) have been investigated experimentally.Experimental results show that the application of a strong magnetic field causes a dendrite fragmenta...Effects of strong magnetic fields on the columnar-to-equiaxed transition(CET) have been investigated experimentally.Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET.The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically.Numerical results reveal that a torque is created on cells/dendrites and equiaxed grains and the value of the thermoelectric magnetic force increases as the magnetic field intensity increase.This torque breaks cells/dendrites and drives the rotation of equiaxed grains.As a consequence,the CET will occur during directional solidification under a strong magnetic field.This may initiate a new method to induce the CET via an applied strong magnetic field during directional solidification.展开更多
In order to precisely describe the dendritic morphology and micro-segregationduring solidification process, a novel continuous model concerning the different physicalproperties in the solid phase, liquid phase and int...In order to precisely describe the dendritic morphology and micro-segregationduring solidification process, a novel continuous model concerning the different physicalproperties in the solid phase, liquid phase and interface is developed. Coupling the heat and solutediffusion with the transition rales, the dendrite evolution is simulated by cellular automatonmethod. Then, the solidification microstructure evolution of a small ingot is simulated by usingthis method. The simulated results indicate that this model can simulate the dendrite growth, showthe second dendrite arm and tertiary dendrite arm, and reveal the micro-segregation in theinter-dendritic zones. Furthermore, the columnar-to-equiaxed transition (CET) is predicted.展开更多
基金Project(51001074)supported by the National Natural Science Foundation of ChinaProject(12ZR1414500)supported by Shanghai Municipal Natural Science Fund of ChinaProject(2012CB619505)supported by the National Basic Research Program of China
文摘Directional solidification of Al-15% （mass fraction） Cu alloy was investigated by in situ and real time radiography which was performed by Shanghai synchrotron radiation facility （SSRF）. The imaging results reveal that columnar to equiaxed transition （CET） is provoked by external thermal disturbance. The detaching and floating of fragments of dendrite arms are the prelude of the transition when the solute boundary layer in front of the solid-liquid interface is thin. And the dendrite triangular tip is the fracture sensitive zone. When the conditions are suitable, new dendrites can sprout and grow up. This kind of dendrite has no obvious stem and is named anaxial columnar dendrites.
基金financially supported by the Ph.D.Programs Foundation of Liaoning province(201501067)the State Key Laboratory program of Light Alloy Casting Technology for High-end Equipment(LACT-002)
文摘To investigate the effect of three-dimension(3 D) thermal convection on columnar-to-equiaxed transition(CET), the CET transition during the solidification of an Al-Cu alloy was simulated by 3 D cellular automaton model coupled with the finite element method(CAFE). The thermal convection in the liquid phase was considered. The results show that the thermal convection in the liquid phase promotes the CET. When the convection is present, the temperature gradient at the start position of CET increases and the growth velocity of columnar dendrite decreases. The convection influences the formation of elongated equiaxed grain through changing the local temperature gradient and dendritic growth velocity.
基金Item Sponsored by National Natural Science Foundation of China(50674064,50734008)
文摘A new approach to applying the electric current pulse （ECP） with parallel electrodes to the promotion of the transition from columnar crystal to equiaxed crystal and the improvement of macrosegregation was introduced. The ECP was applied to different stages of the solidification. The results showed that the application of the ECP in both the initial stage （the thickness of solidified shell reached 2 mm approximately） and the late stage （the thickness of solidified shell reached 14 mm approximately） of solidification can promote the columnar to equiaxed transition （CET）. The analysis showed that during solidification, a large number of nuclei around the upper surface fell off due to ECP, which subsequently showered on the melt and impinged the growth front of the columnar crystal. Therefore, the CEToccurred. In addition, this method was also employed to influence the solidification process of bearing steel, and the results showed that the structure was changed from columnar crystal to equiaxed crystal, indicating that ECP can enhance the homogeneity of structure and composition of bearing steel.
基金This work was supported by the National High Technology Research and Development Program of China(Grant Nos.2001AA337020 and 2002AA336050)the National Natural Science Foundation of China(Grant No.50201012)National Science Fund for Distinguished Young Scholars of China(Grant No.59825108).
文摘Considering the local linear superposition of the species and combining the calculation of phase diagram, the columnar and equiaxed growth behaviours are investigated systematically during solidification of multicomponent alloys. A theoretical model is developed to describe the columnar to equiaxed transition during multicomponent alloy solidification by taking account of the competition between nucleation and growth ahead of a dendrite array, which shows a good agreement with the experimental results.
基金Natural Science Foundation of China(Nos.51790481,51790483,52130110,51901182)Natural Science Foundation of Shaanxi Province,China(No.2020JQ-157)Research Fund of the State Key Laboratory of Solidification Processing,China(No.2022-TS-01)。
基金Item Sponsored by National natural Science Foundation of China(No.51171106 and 2011CB610404)the Program for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning
文摘Effects of strong magnetic fields on the columnar-to-equiaxed transition(CET) have been investigated experimentally.Experimental results show that the application of a strong magnetic field causes a dendrite fragmentation and then the CET.The thermoelectric magnetic force acting on cells/dendrites and equiaxed grains in the mushy zone has been studied numerically.Numerical results reveal that a torque is created on cells/dendrites and equiaxed grains and the value of the thermoelectric magnetic force increases as the magnetic field intensity increase.This torque breaks cells/dendrites and drives the rotation of equiaxed grains.As a consequence,the CET will occur during directional solidification under a strong magnetic field.This may initiate a new method to induce the CET via an applied strong magnetic field during directional solidification.
文摘In order to precisely describe the dendritic morphology and micro-segregationduring solidification process, a novel continuous model concerning the different physicalproperties in the solid phase, liquid phase and interface is developed. Coupling the heat and solutediffusion with the transition rales, the dendrite evolution is simulated by cellular automatonmethod. Then, the solidification microstructure evolution of a small ingot is simulated by usingthis method. The simulated results indicate that this model can simulate the dendrite growth, showthe second dendrite arm and tertiary dendrite arm, and reveal the micro-segregation in theinter-dendritic zones. Furthermore, the columnar-to-equiaxed transition (CET) is predicted.
