Predicting Pathways for Synthesis of Ferromagnetic τ Phase in Binary Heusler Alloy Al-55 pct Mn Through Understanding of the Kinetics of ε–τ Transformation

Abstract

This paper outlines the detailed procedure for the synthesis of pure ferromagnetic τ phase in binary Heusler Al-55 pct Mn alloy in bulk form through casting route without any addition of stabilizers. To obtain the processing domain for the formation of the τ phase from high-temperature ε phase, isothermal transformation experiments were carried out. The structure and microstructure were characterized by X-ray diffraction and electron microscopy studies. The τ phase start times were obtained through magnetic measurements. In order to tune the casting conditions for the formation of this phase, thermal modeling was carried out to predict the heat extraction rates for copper molds of different diameters (2 to 12 mm) containing hot solids during casting process. This enabled us to estimate the diameter of the mold to be used for obtaining τ phase directly during casting. It was concluded through experimental verification that 10-mm-diameter casting in copper mold is suitable to obtain complete τ phase. A saturation magnetization of 116 emu/g at 10 K was measured for such samples. The Curie point for the τ phase was found to be 668 K (395 °C). Additionally, the cast rod exhibits a compressive strength of 1170 MPa which is higher than those of both ferrites and AlNiCo magnets.