Study On Solidification Behaviours Of Zn-Ag Peritectic Alloys Under A High Magnetic Field

For the past few years,Zn-based alloys have been widely concerned as biodegradable implant materials owing to their ideal corrosion rates and excellent biocompatibility.The physical and chemical properties of the alloys are closely related to the structure.Therefore,it is of great importance to control its structure in the solidification stage.As an extreme physical field,the high magnetic fields can input tremendous energy into materials without any contact.As a result,the solidification behaviours of alloys can be significantly affected.Therefore,it is expected to control structure of Zn-base alloys if the high magnetic fields are applied in its solidification stage.Based on this,hypoperitectic Zn-Ag alloy was solidified under different high magnetic fields(HMFs)in this work.The changes in distribution,morphology,size and alignment of primary ?-AgZn3 phases were investigated under the HMFs.The magnetic-field-induced changes in crystallographic orientation of primary?-AgZn3 and peritectic ?-Zn phases were studied.Distribution of Ag in peritectic ?-Zn solid solution,three-dimensional(3D)shape of the primary ?-AgZn3 dendrites and specific orientation relationship between the primary ?-AgZn3 and peritectic ?-Zn phases were explored.And the mechanism of effect of the high magnetic fields on the structure changes was analyzed.The results show that without the HMFs the primary ?-AgZn3 dendrites align randomly and distribute inhomogeneously in the whole specimen,the primary ?-AgZn3 dendrites vary in morphology and size from the top to the bottom of the specimen.With increasing the HMFs,the macrostructures become homogenous gradually,and the primary ?-AgZn3 dendrites tend to align regularly.Two orthogonal principal axes of crosslike shape dendrites in the longitudinal sections are parallel and perpendicular to the HMF direction,respectively.Under a 12 T HMF,strong<0001>AgZn3 fiber and {0001}Zn basal textures are well developed:the c-axes of primary ?-AgZn3 and peritectic ?-Zn crystals are parallel and perpendicular to the HMF direction,respectively.Irrespective of the HMFs,the Ag content in the peritectic?-Zn solid solution gradually decreases outward from the central primary ?-AgZn3 dendrites.Meanwhile,the primary ?-AgZn3 dendrites grow preferentially along<0001>and<1010>directions and display various 3D shapes with strong anisotropy.Additionally,a specific crystallographic orientation relationship:[1213]AgZn3//[1210]Zn;(0111)AgZn3//(1011)Zn;(1010)AgZn3//(0002)Zn exists between the primary ?-AgZn3 and peritectic ?-Zn phases.The macrostructural homogeneity results from the HMF-induced magnetic viscosity resistance force.The well-developed<0001>AgZn3 fiber and {0001}Zn basal textures are mainly attributed to the magnetocrystalline anisotropy of the ?-AgZn3 crystals and the specific OR between the primary ?-AgZn3 and peritectic ?-Zn phases,respectively.Besides,the peritectic?-Zn crystals cohere well with the primary ?-AgZn3 crystals in preferential orientations under the HMFs should be considered as an important reason of textures development well.This work enriches the theoretical foundation of peritectic alloy solidification under the high magnetic fields,and to some extent,provides a new perspective on the exploitation and fabrication of biodegradable Zn-based alloys.