Microstructural control through seeding and directional solidification of TiAl alloys containing Mo and C

Abstract Seeding of the high temperature α phase was used to control the final lamellar orientation of directionally solidified TiAl alloys. Alloys of TiAl containing small amounts (less than 1.5 at.%) of Mo and C were investigated as possible seed materials. Suitable seed compositions were determined by quickly heating specimens to a temperature just below the melting temperature, holding, and then cooling to room temperature. A small composition window in the Ti–Al–Mo and Ti–Al–Mo–C systems suitable for the seeding approach was identified in which the original lamellar orientation was restored after heat treatment. Directional solidification experiments between 5 and 40 mm/h were performed to produce ingots with an aligned lamellar microstructure. The directionally solidified ingots were found to exhibit a high yield stress with a reasonably large tensile elongation at room temperature.