Al-Ti合金の凝固組織形態と溶質の分布

抄録

The morphological transition from planar to cellular interface in Al-Ti alloys occurs at a constant value of C₀•R/G and the cell-dendrite transition occurs at a constant value of C₀•R^1/2/G, where C₀ is the initial solute concentration, R growth rate and G temperature gradient. As the planar interface breaks down to form depressions, a rod-like cored substructure is formed in each cell when the interfacial morphology changes successively from depressions to irregular cells, elongated cells and hexagonal cells. The rod-like substructure is transformed into the dendrite as the cellular interface changes into dendritic. The length of rods and dendrites becomes shorter with an increase in C₀•R/G. The cored region is enriched with Ti, and its content is about 2.5-4.0 times of the initial solute concentration. The matrix of cellular and dendritu interface is extremely depleted in the solute, and its concentration is about 1/3-1/5 of C₀.
The diffusion coefficient for the solute Ti in the liquid Al at the liquidus temperature is calculated to be 0.87×10^-5cm²/sec.