Investigation on the Microstructure, Texture and Magnetostriction of Directionally Solidified Alloys

Effect of V addition on the microstructure and magnetostriction of directionally solidified Tb0.3Dy0.7Fe1.95 has been investigated. The microstructure of V added alloys (Tb0.3Dy0.7 with , 0.025, 0.05, and 0.075) indicate that Fe-50？at.% V is formed as primary phase, which subsequently undergoes spinodal decomposition. The spinodially decomposed Fe-rich phase reacts with the liquid and forms the matrix phase, (Tb,Dy)Fe2. The V-rich spinodally decomposed product, on the other hand, exists as remnant phase without undergoing any metallurgical transformation. Texture studies indicate that the grains of (Tb,Dy)Fe2 show /rotated and orientations for all compositions investigated in the directionally solidified condition. An improvement in magnetostriction has been noticed for small addition of V and with further addition the magnetostrictive property decreases. The formation of additional phases containing vanadium is attributed to be the reason when V is added in higher concentration levels. 1. Introduction The recent research and development work on Tb-Dy-Fe-based magnetostrictive material is aimed mostly at improving the magnetostrictive property through (i) grain orientation by directional solidification and (ii) through microstructural modification by selective alloying additions, followed by appropriate heat treatment [1–7]. Directional solidification under high temperature gradient serves to produce a microstructure that consists of mainly the Laves phase, (Tb,Dy)Fe2, and the minor phase (Tb,Dy)-rich with no significant evidence for the coexistence of other phases [4]. While attempting to grow longer rods (80–100？mm) during directional solidification, maintenance of high temperature gradient as to propitiate such microstructural features will be difficult since the solidification front moves away from the chilled plate, encountering a drop in the temperature gradient. The reduced temperature gradient promotes formation of (Tb,Dy)Fe3 as the primary phase and its conversion into (Tb,Dy)Fe2 does not lead to completion due to the sluggishness of the peritectic reaction, (Tb,Dy)Fe3 + L → (Tb,Dy)Fe2. The unreacted (Tb,Dy)Fe3, therefore, affects the magnetostrictive property of the material [8]. Selective alloying additions are known to cause enhancement in the chosen property by way of suppressing the formation of this deleterious phase. The addition of magnetic elements such as Co, Ni, Mn is known to have less significant effect on the functional property of the material although it profoundly triggers changes in the physical properties such as spin