Study On Deformation And Recrystallization Texture In Fe₈₁Ga₁₉ Thin Sheets

The excellent comprehensive properties,including large saturated magnetostriction coefficient at low applied magnetic field,high mechanical strength,high permeability,high Curie temperature and low temperature dependence,make Fe-Ga alloy become a better candidate in actuation,sensing,and energy harvesting applications in last decade.Since Fe-Ga alloy exhibits the largest magnetostriction coefficient along<100>direction,and thin sheet is expected to reduce the serious eddy current loss led by high electrical conductivity.It is desirable to produce ?(<100>//RD)textured Fe-Ga polycrystalline thin sheet with excellent magnetostrictive performance.The secondary recrystallization Goss({110}<001>)texturewas achieved by the effect of inhibitor and surface energy.Compared with the magnetostriction coefficient in single crystal,there exists a much room for improvement.The key issue of current research is lack of the accurate control of microstructure and texture in rolling and annealing.Moreover,the precipitation of inhibitor and effect of surface energy require complex preparation process and special atmosphere.Therefore,it is necessary todevelop simplified and efficient methods to prepare Fe-Ga thin sheet with ideal texture and larger magnetostriction coefficient.Recrystallization texture strongly depends on deformation texture and microstructure.The factors,such as initial orientation,grain size and deformation condition,have important influences on deformation texture and microstructure.The secondary recrystallization ?grains can significantly increase the magnetostriction coefficient in Fe-Ga sheet,which is very sensitive to the factors such as material composition,distribution of grain size and grain boundary,and annealing condition.However,there is still lack of a systematic study on the key issues in Fe-Ga sheet,which includes the evolution of cold rolling microstructure and texture,formation mechanism of primary and secondary recrystallization texture.In the present study,strong Goss texture of Fe81Ga19 thin sheet was successfully produced by conventional method,including hot rolling,cold rolling and annealing.Furthermore,microstructure and texture development was analyzed by X-ray diffraction and electron backscattered diffraction(EBSD).The hot band has a significant effect on the microstructure and texture of cold rolled and recrystallized Fe81Ga19 sheet.The evident texture gradient in cold rolled and annealed thin sheet can be attributed to the deformation inhomogeneity from hot bands.The normalization annealing significantly declines the inhomogeneity of cold rolling and recrystallization texture,enhances ? texture and improves magnetostriction coefficient.The strong Goss texture can be obtained in primarily recrystallized sheets when cold rolling reduction reaches 60?70%.The variation of recrystallization texture with cold rolling reduction can be attributed to the characteristic of thermodynamics and kinetics during nucleation and grain growth of recrystallized grains with different orientations.The microstructure and texture of rolling and recrystallization exhibit an evident dependence on initial grain size prior to cold rolling.The quantity and characteristic of shear bands change with the increase of initial grain size,resulting in an inhomogeneity of recrystallization.The feature of cold rolling texture transforms from strong y fiber(<111>//ND)with peak at {111}<112>and {111}<110>to strong a texture with peak at{001}-{112}<110>with the increase of initial grain size,and the recrystallization texture transforms from dominating Goss to strong a.It is proposed that the core issue of texture optimization is to regulate the characteristic of shear band and deformation texture for promoting superior nucleation and beneficial deformed matrix.The generalized preferred nucleation mechanism that final texture is decided by the whole nucleation process rather than early recrystallization stage is proposed to interpret the formation of recrystallization texture in Fe81Ga19 sheet.Goss-dominant primary recrystallization texture through sheet thickness was achieved by controlling rolling and annealing processes in Fe81Ga19 thin sheet.Since Goss grains mainly nucleate in the shear bands of deformed y grains,the proper intensity and quantity of shear bands guarantee sufficient nucleation sites,advantageous grain size,and efficient grain growth for primary recrystallization Goss grains.A simplified and efficient preparation method for Goss-textured Fe81Ga19 sheet with excellent magnetostriction by secondary recrystallization is proposed.The normal grain growth is effectively inhibited by a quantity of low angle grain boundary in the matrix.The less quantity of low angle grain boundary and higher fraction of high energy grain boundary around Goss grain induce the abnormal grain growth.Primary recrystallization texture has a significant effect on the secondary recrystallization in Fe81Ga19 sheet.In the present study,the manufacturing process of Fe81Ga19 thin sheet is similar to the industrial method of steel sheets,which,therefore,provides a theoretical and technological foundation to optimize recrystallization texture and industrialize Fe-Ga and other BCC thin sheets.