Preparation of bulk β-FeSi2 by synthetical control of melt cyclical superheating, solidification and cooling process

• A new method for preparing FeSi2 precursor with complete eutectic was proposed.
• Bulk FeSi2 precursor of φ18 × 17 mm in size without macroscopic defects was obtained.
• The precursor is basically transformed to β-FeSi2 after annealing at 900 °C for 150 h.

A new method of melt cyclical superheating combined with the control of solidification and cooling process as well as appropriate heat treatment was proposed to prepare bulk β-FeSi2. FeSi2 precursor of φ18 × 17 mm in size was obtained under the conditions of melt superheating temperature 1550 °C, superheating time 10 min, recycling times 3, solidification rate 30 °C/s, cooling rate 12 °C/min from solidification temperature to 700 °C and cooling naturally from 700 °C to room temperature. The precursor had homogeneous and complete α + ε eutectic structure, with the rod-like ε phase of 1–2 μm in diameter. After the precursor with complete α + ε eutectic structure were annealed at 900 °C for 150 h, both the α and ε phases totally disappeared and were transformed into β-FeSi2 except few residual Si-rich phase.