Growth Kinetics Of Columnar Crystal Interface In Undercooled Multicomponent Melt

Columnar crystal is an important microstructure pattern,and its growth technology,especially the growth technology of a single crystal,plays an important role in improving the performance of semiconductor,optical and other related products.In this thesis,modelling of columnar crystal growth in multicomponent melt which is affected by flow and anisotropic surface tension are established respectively.The approximate analytical solution of columnar crystal growth is obtained by using multiscale method,and the morphological stability of columnar crystal interface is analyzed.In addition,the effect of external magnetic field on the stability of mushy layer with density gradients driven flow is discussed.The main work is as follows:(1)The growth of columnar crystals in multicomponent melt subjected to flow is studied,and the approximate analytical expression for growth morphology of columnar crystals is given by using the multiscale method,which reveals the influence of flow on the morphology of the columnar crystal interface.The results show that far-field flow has remarkable influence on the growth of columnar crystal,which makes the columnar crystal no longer remains round and deflect towards the upstream direction.The incoming straining flow accelerates growth velocity of the interface,while the outgoing straining flow decreases growth velocity of the interface,namely,the straining flow makes the interface of columnar crystal deformed.Furthermore,the dispersion relations of the growth rate of amplitude of the perturbed interface are derived.The results show that the flow has instability effect on the growth of cylindrical crystal.(2)The effect of anisotropic surface tension on the growth of columnar crystals in multicomponent melt is studied,and the approximate analytical solution of the growth morphology of columnar crystals is given by using the multiscale method,which reveals the influence of anisotropic surface tension on the morphology of the columnar crystal interface.It is found that the concave and convex formation of columnar crystal interface is more significant with the increase of anisotropic surface tension,and the interface morphology of columnar crystal in dilute alloy melt is less affected by anisotropic surface tension than that in pure melt.Furthermore,the dispersion relations of the growth rate of amplitude of the perturbed interface are obtained.Compared with pure melt,the perturbation growth rate of columnar crystal in multicomponent melt is smaller,and the perturbation growth rate in preferred direction of crystal growth is larger.(3)The linear stability method is used to analyze the effect of external magnetic field on the stability of mushy layer,including direct mode and oscillation mode.The results show that in the oscillation mode,external magnetic field brings a stabilizing effect on the mushy layer,but in the direct mode,the effect of external magnetic field on stability of the mushy layer is uncertain.