Orientation Selection and Microstructural Evolution in Directionally Solidified Tb_0.3Dy_0.7Fe_1.95

Abstract

Tb_0.3Dy_0.7Fe_1.95 alloy was directionally solidified by using a modified Bridgman technique at a wide range of growth rates of 5 to 100 cm/h. The directionally grown samples exhibited plane front solidification morphology up to a growth rate of 90 cm/h. Typical island banding feature was observed closer to the chilled end, which eventually gave rise to irregular peritectic coupled growth (PCG). The PCG gained prominence with an increase in the growth rate. The texture study revealed formation of strong 〈311〉 texture in a lower growth rate regime, 〈110〉 and “rotated 〈110〉” in an intermediate growth regime, and 〈112〉 in a higher growth rate regime. In-depth analysis of the atomic configuration of a solid–liquid interface revealed that the growth texture is influenced by the kinetics of atomic attachment to the solid–liquid interface, which is intimately related to a planar packing fraction and an atomic stacking sequence of the interfacial plane. The mechanism proposed in this article is novel and will be useful in addressing the orientation selection mechanism of topologically closed packed intermetallic systems. The samples grown at a higher growth rate exhibit larger magnetostriction (λ) and dλ/dH owing to the absence of pro-peritectic (Tb,Dy)Fe₃ and formation of 〈112〉 texture, which lies closer to the easy magnetization direction (EMD).