Phase stability and decomposition processes in TiAl based intermetallics

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 1995-02, Vol.192, p.922-929
• Main Authors: Nakai, Kiyomichi, Ono, Toshiaki, Ohtsubo, Hiroyuki, Ohmori, Yasuya
• Format: Article
• Language: English
• Subjects: Aluminium; Decomposition; Intermetallics; Phase stability; Titanium
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/0921-5093(94)03322-6

The high-temperature phase equilibria and the phase decomposition of α and β phases were studied by crystallographic analysis of the solidification microstructures of Ti-48at.%Al and Ti-48at.%Al-2at.%X (X = Mn, Cr, Mo) alloys. The effects on the phase stability of Zr and O atoms penetrating from the specimen surface were also examined for Ti-48at.%Al and Ti-50at.%Al alloys. The third elements Cr and Mo shift the β phase region to higher Al concentrations, and the β phase is ordered to the β 2 phase. The Zr and O atoms stabilize β and α phases respectively. In the Zr-stabilized β phase, α 2 laths form with accompanying surface relief, and stacking faults which relax the elastic strain owing to lattice deformation are introduced after formation of α 2 order domains. Thus shear is thought to operate after the phase transition from β to α 2 by short-range diffusion. A similar analysis was conducted for the TiAl binary system, and the transformation was interpreted from the CCT diagram constructed qualitatively.