The influence of conjugate natural convective heat transfer on the temperature field in a monocrystalline sapphire tape in the Stepanov method

Natural convective heat transfer in the system “monocrystalline tape – environment – walls of the growth vessel”, geometrically similar to the simplified scheme of the upper part of the heat node in the Stepanov method, is studied numerically by the finite element method in the conjugate formulation. The calculations were performed with a Prandtl number equal to 0.68 (argon), in the range of Grashof numbers 1000 ≤ Gr ≤ 25000 and with a discrete set of tape lengths in the range from 1 to 5.

Application of the liquid bridges theory to find the melt menisci shape when growing cylindrical crystals

A vertical liquid bridge of small volume between a conical shaper and a convex crystallization front was investigated. Two variants of the front crystallization shape selection are considered: a conical and a spherical fronts. A variational statement of the original problem is given. As the boundary conditions we used the condition of engagement at the edge of the shaper and a given growth angle at the crystallization front. The Bond number was assumed to be small, and to find a solution of the problem the asymptotic approach was applied. The calculations are carried out for small diameter cylindrical sapphire crystals, grown from the melt by the Stepanov method. The results of the menisci shapes calculations are presented. The comparison of the results of calculations for conical and spherical crystallization fronts is carried out.

Образование дендритной структуры в кристаллах NiFeGaCo при выращивании способом Степанова

The process of growing crystals of the Ni-Fe-Ga-Co alloy by the Stepanov method has been developed. It was found that the structural perfection is disturbed by the formation of dendrites, which are distributed inhomogeneously both along the length and in the cross sections of the crystals. The blocking effect on the dendrites of crystals of the martensite phase, which appears when the samples are cooled to the temperature of the transition of the crystal to the martensite state, is found. The elemental composition of dendritic formations was studied and it was shown that the iron content in the dendrite is approximately 30% higher, and the gallium content is 40% lower than in the matrix. Based on the modeling of heat transfer processes in the real growth zone, taking into account the experiments performed, recommendations were obtained for suppressing the formation of dendrites