Columnar to equiaxial crystal transition(CET)is an important technological feature in many casting processes.This work investigated the CET during the solidification of Mg-Gd-Zn alloys by combining synchrotron radiati...Columnar to equiaxial crystal transition(CET)is an important technological feature in many casting processes.This work investigated the CET during the solidification of Mg-Gd-Zn alloys by combining synchrotron radiation in-situ imaging and phase-field method.Results show that the grain size,dendrite tip radius,and secondary dendrite arm spacing(SDAS)all exponentially decrease with an increase in cooling rate(Vc).The variation in the radius of the dendritic tip is similar to the prediction of the Hunt model,while the variation in the SDAS is close to the Bouchard-Kirkaldy model.It is worth noting that the CET is promoted by a decrease in the temperature gradient(G)and an increase in the cooling rate(Vc).In both equiaxed and columnar crystal regions,the dendrite tip growth rate and solid phase volume fraction increase with increasing G and Vc.In addition,the CET process has been predicted by simulation.The results are consistent with the predictions of the GTK model,which is important for the in-depth study of the dendrite morphology in different crystallization regions.In the final stage,the effects of different critical subcooling degrees and nucleation densities on the CET were explored.The results show that increasing the critical nucleation supercooling degree can inhibit the generation of equiaxial crystals,while increasing the nucleation density helps to promote the CET.展开更多
A quantitative multi-phase-field model for non-isothermal and polycrystalline solidification was developed and applied to dilute multicomponent alloys with hexagonal close-packed structures.The effects of Lewis coeffi...A quantitative multi-phase-field model for non-isothermal and polycrystalline solidification was developed and applied to dilute multicomponent alloys with hexagonal close-packed structures.The effects of Lewis coefficient and undercooling on dendrite growth were investigated systematically.Results show that large Lewis coefficients facilitate the release of the latent heat,which can accelerate the dendrite growth while suppress the dendrite tip radius.The greater the initial undercooling,the stronger the driving force for dendrite growth,the faster the growth rate of dendrites,the higher the solid fraction,and the more serious the solute microsegregation.The simulated dendrite growth dynamics are consistent with predictions from the phenomenological theory but significantly deviate from the classical JMAK theory which neglects the soft collision effect and mutual blocking among dendrites.Finally,taking the Mg-6Gd-2Zn(wt.%)alloy as an example,the simulated dendrite morphology shows good agreement with experimental results.展开更多
The Al3Ti compound has potential application in the high temperature structure materials due to its low density,high strength and stiffness.The mechanical behaviors of the material under different loading rates were s...The Al3Ti compound has potential application in the high temperature structure materials due to its low density,high strength and stiffness.The mechanical behaviors of the material under different loading rates were studied using compression tests.The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate.Therefore,a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately.However,it is still short of professional research on the material model for Al3Ti.In this study,the mate rial model was developed on the basis of JH-2 constitutive equations using the experimental data.The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model.Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately.This work provides more support for the theoretical and numerical research on the intermetallic.展开更多
基金financially supported by the Postdoctoral Research Project of Henan Province(No.202101003)the Key Research Programs of Higher Education Institutions in Henan Province(Nos.24A450003,23A460016)+2 种基金the Henan Provincial Key Laboratory of Intelligent Manufacturing of Machinery and Equipment Open Subjects(No.IM202308)the Zhengzhou University of Light Industry Doctoral Research Initiation Fund(No.2019BSJJ005)the Henan Provincial Science and Technology Tackling Project(No.23A460016).
文摘Columnar to equiaxial crystal transition(CET)is an important technological feature in many casting processes.This work investigated the CET during the solidification of Mg-Gd-Zn alloys by combining synchrotron radiation in-situ imaging and phase-field method.Results show that the grain size,dendrite tip radius,and secondary dendrite arm spacing(SDAS)all exponentially decrease with an increase in cooling rate(Vc).The variation in the radius of the dendritic tip is similar to the prediction of the Hunt model,while the variation in the SDAS is close to the Bouchard-Kirkaldy model.It is worth noting that the CET is promoted by a decrease in the temperature gradient(G)and an increase in the cooling rate(Vc).In both equiaxed and columnar crystal regions,the dendrite tip growth rate and solid phase volume fraction increase with increasing G and Vc.In addition,the CET process has been predicted by simulation.The results are consistent with the predictions of the GTK model,which is important for the in-depth study of the dendrite morphology in different crystallization regions.In the final stage,the effects of different critical subcooling degrees and nucleation densities on the CET were explored.The results show that increasing the critical nucleation supercooling degree can inhibit the generation of equiaxial crystals,while increasing the nucleation density helps to promote the CET.
基金the National Natural Science Foundation-Youth Science Foundation Project(No.51901208)the Henan University Key Scientific Research Project(No.20B430020)+1 种基金the Key Scientific and Technological Projects in Henan Province(Nos.202102210016,202102210272)the Major Innovation Project of Zhengzhou City(No.23101000010).
文摘A quantitative multi-phase-field model for non-isothermal and polycrystalline solidification was developed and applied to dilute multicomponent alloys with hexagonal close-packed structures.The effects of Lewis coefficient and undercooling on dendrite growth were investigated systematically.Results show that large Lewis coefficients facilitate the release of the latent heat,which can accelerate the dendrite growth while suppress the dendrite tip radius.The greater the initial undercooling,the stronger the driving force for dendrite growth,the faster the growth rate of dendrites,the higher the solid fraction,and the more serious the solute microsegregation.The simulated dendrite growth dynamics are consistent with predictions from the phenomenological theory but significantly deviate from the classical JMAK theory which neglects the soft collision effect and mutual blocking among dendrites.Finally,taking the Mg-6Gd-2Zn(wt.%)alloy as an example,the simulated dendrite morphology shows good agreement with experimental results.
基金The authors gratefully acknowledge the financial support from National Natural Science Foundation of China(No.11602230)the Program for Innovative Research Team in Science and Technology in the University of Henan Province(No.18IRTSTHN015)Key Scientific Projects of University in Henan Province(20B430021).
文摘The Al3Ti compound has potential application in the high temperature structure materials due to its low density,high strength and stiffness.The mechanical behaviors of the material under different loading rates were studied using compression tests.The results indicate that Al3Ti is a typical brittle material and its compressive strength is dependent on the strain rate.Therefore,a series of rate-dependent constitutive equations are needed to describe its mechanical behaviors accurately.However,it is still short of professional research on the material model for Al3Ti.In this study,the mate rial model was developed on the basis of JH-2 constitutive equations using the experimental data.The model was then applied in simulating the impact process of Ti/Al3Ti metal-intermetallic laminate composites so as to validate the established model.Good agreement between simulation and experiment results shows the constitutive model predict the material responses under high rate and large deformation accurately.This work provides more support for the theoretical and numerical research on the intermetallic.
