Control of solid-liquid interface morphology and radial composition distribution: TbDyFe single crystal growth

Optical zone melting method was adopted for the crystal growth of TbDyFe giant magnetostrictive alloys. Effects of zone-melting length and growth velocity on the quenched solid-liquid interface bending direction, curvature and corresponding radial composition distribution were investigated both experimentally and theoretically. By increasing the zone-melting length, the solid-liquid interface morphology was evolved from convex to flat and then to concave. In the case of convex solid-liquid interface, the curvature of the interface was decreased by increasing the growth velocity. When the initial interface was flat, changing growth velocity had no effect on the interface morphology under our experimental conditions. Accordingly, quite different radial composition distributions were monitored. A 110 axial oriented twinned-single crystal of TbDyFe alloy without radial composition segregation was obtained through controlling the solid-liquid interface morphology. Solid-liquid interface curvature functions were proposed with the parameters of zone-melting length, growth velocity, temperature gradient and other thermal physical parameters. Furthermore, functions of corresponding radial composition distribution were also given. The theoretical analysis shows that, the curvature of solid-liquid interface and the rate of radial composition segregation are determined by zone melting length, growth velocity and temperature gradient. Theoretical analysis results matched well with the experiments.