MICROSTRUCTURAL CONTROL THROUGH SEEDING AND DIRECTIONAL SOLIDIFICATION OF TiAl ALLOYS CONTAINING Mo AND C

Abstract

Seeding of the high temperature ? 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. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.