High-temperature transformation pathways for metastable ferromagnetic binary Heusler (Al–55 at.%Mn) alloy
2017
Palanisamy, Dhanalakshmi | Srivastava, Chandan | Madras, Giridhar | Chattopadhyay, Kamanio
The present manuscript probes the decomposition behaviour of the ferromagnetic binary metastable Heusler alloy in the Al–Mn system. The ferromagnetic ordered tetragonal phase (L1₀, popularly known as τ phase), which is metastable in nature, was synthesised from the melt through a copper mould chill casting process using 10-mm diameter mould. Isothermal and non-isothermal heat treatments were carried out to understand the decomposition sequence of τ phase at high temperatures. The metastable phase undergoes, on heating, a eutectoid-like decomposition of [Formula: see text], where [Formula: see text] is the intermetallic phase Al₈Mn₅. Both the phases are present in the equilibrium diagram. The two phases at higher temperature further transform to a single phase ε having a hexagonal structure. We show through in situ X-ray diffraction studies that [Formula: see text] transforms to a disordered bcc phase ([Formula: see text]) prior to the transformation to the ε-phase. The overall sequence of phase decomposition during heating can be given as [Formula: see text]. The high-temperature [Formula: see text] phase cannot be retained through quenching experiment and its existence can only be established by in situ studies.
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