Phase equilibria among α-Fe(Al, Cr, Ti), liquid and TiC and the formation of TiC in Fe3Al-based alloys

In the context of the development of high-strength Fe3Al-based alloys, phase equilibria among α-Fe(Al, Cr, Ti), liquid and TiC phases in the Fe–Al–Cr–Ti–C quinary system and the formation of TiC were determined. A pseudo-eutectic trough (L ⇔ α + L + TiC) exists at 1470 °C at around Fe–26Al–5Cr–2Ti–1.7C on the vertical section between Fe–26Al–5Cr (α) and Ti–46C (TiC) in at.%. Large faceted TiC precipitates form from the melt after the formation of primary α phase even in hypoeutectic alloys. The TiC formation is thought to be due to the composition change of the liquid towards the hypereutectic compositions by solidification of the primary α. In order to remove the faceted TiC, which are unfavourable for strengthening the material, two different processing routes have been successfully tested: (i) solidification with an increased rate to reduce the composition variation of the liquid during solidification, and (ii) unidirectional solidification to separate the light TiC precipitates from the melt.