Phase distribution in rapidly solidified TiAl alloys

Abstract

There is at present a great deal of interest in the intermetallic compound γ-TiAl, particularly with regard to its use as an aircraft engine or aerospace structural material. This compound possesses an attractive combination of properties, including high melting temperature, low density, high modulus, and good oxidation and creep resistance, but is somewhat deficient in room temperature ductility due to its crystal structure, which is the Ll0 face-centered tetragonal structure consisting of alternating (002) planes of Ti and Al. The Ti-Al equilibrium phase diagram in the vicinity of γ-TiAl shows that γ-TiAl forms via a peritectic reaction and thus, in order to minimize segregation and to insure maximum homogeneity, it is desirable to produce γ-TiAl alloys by rapid solidification. It is then useful, in order to establish a baseline for advanced alloy design, to have an understanding of the microstructures resulting from rapid solidification. In this paper, we report the results of microstructural studies of binary Ti-Al alloys varying in stoichiometry from 46 to 70 at. % Al which were rapidly solidified into the form of ribbon using melt spinning.