A composition window in the TiAl–Mo–Si system suitable for lamellar structure control through seeding and directional solidification

The thermal stability of the lamellar microstructure of cast Ti–46Al–1.5Mo–(0–3)Si (at.%) alloys was investigated to find suitable seed compositions for growing ingots of these alloys with the aligned lamellar microstructure through seeding and directional solidification. In order for the seeding to be made successfully, the original orientation of the lamellar microstructure must be restored upon heating to and cooling from the melting temperature. In this study, the lamellar stability was determined by examining whether or not the lamellar structure in the as-cast alloys is preserved after quickly heating to just below melting temperature, holding, and then cooling to room temperature. This requirement was found to be fulfilled for the Si contents larger than 1.0 at.%. Ti–46Al–1.5Mo–1Si and Ti–46Al–1.5Mo–1.5Si (at.%) alloys are typical examples of alloys which can be used as seed materials. Directional solidification experiments of Ti–46Al–1.5Mo–1Si alloy were performed using Ti–46Al–1.5Mo–1.5Si alloy as a seed material and ingots with the aligned lamellar microstructure were obtained.