SOLID-PHASE EQUILIBRIA IN THE TI-RICH PART OF THE TI-AL SYSTEM

The solid-state-phase equilibria in the Ti-rich portion of the Ti-Al s ystem (0-50%Al) have been investigated at temperatures between 800-deg rees-C and 1415-degrees-C by electron probe microanalysis (EPMA) and b y transmission electron microscopy (TEM) on diffusion couples as well as on annealed alloys. The TEM observations on the diffusion couples a s well as on annealed alloys. The TEM observations on the diffusion co uples show that the phase field alpha2 (ordered hexagonal DO19) extend s up to the beta (bcc A2) phase field, leading to two peritectoid tran sformations, beta + alpha --> alpha2 at T = 1210 +/- 10-degrees-C and beta + alpha2 --> alpha at T = 1160 +/- 10-degrees-C (alpha: hexagonal A3). The diffusion-couple experiments yield the tie lines of the obse rved phase equilibria. The present results confirm the existence of a eutectoid transition alpha --> alpha2 + gamma (gamma: ordered fcc L10) at about T = 1120 +/- 10-degrees-C. An updated phase diagram based on these data is presented.