Simulation of solidification structures of faceted 123 peritectic crystalsin superconductive YBCO oxide

Since the micro/macro-structures affect the critical current density (J(c)) and the mechanical properties of superconductive YBCO oxides, the followin g numerical and analytical studies of solidification process of faceted 123 (YBa2Cu3O7-x) crystals fromliquid+211 (Y2BaCuO5) phases rue essential to c larify the solidification mechanism and improve the properties of YBCO. To clarify the effects of growth mode;and conditions on the microstructures of 123 crystals, two-dimensional numerical simulation of faceted peritectic g rowth of 123 crystal was performed by considering (a) growth of 123 crystal , (b) melting of 211 particles in the liquid, and (c) solute diffusion in t he liquid. The growth rate (R) of 123 crystal was approximated by: R = ag . DeltaT(k)(2), where ag was kinetic growth constant. and DeltaT(k) was kine tic undercooling of faceted interface. The kinetic melting constant (am) an d superheating (DeltaT(m)) was also used for evaluation of melting rate of 211 phase. Solute distributions in the liquid during the 123 growth were ca lculated by FDM, and the distributions of residual 211 particles and liquid pools in the faceted 123 crystals were evaluated from the experimentally o btained log-normal distributions of 211 particles in the liquid of YBCO. Th e calculated results agreed wen with the experimental ones. Transition of m acrostructures from columnar to equiaxed 123 crystals in unidirectionally s olidified YBCO was also studied experimentally and analytically. Critical t ransition conditions (:relations of growth rate (R) and temperature gradien t (G)) were calculated by equations obtained from nucleation and growth the ories, and compared with experimental results.