PARTIAL ISOTHERMAL SECTIONS OF TI-AL-V TERNARY DIAGRAM

The phase equilibria between the titanium aluminides, Ti3Al and TiAl, and V have been investigated in the temperature range 1473-873 K. Micr ostructures were characterised using light, scanning electron, and tra nsmission electron microscopy and the nature of the phases present was established via X-ray diffractometry, electron diffraction, and energ y dispersive X-ray analysis. A series of isothermal sections have been determined and are compared with those obtained in earlier studies. O rdering of the high temperature bcc beta phase to a simple cubic B2 (b eta2) structure was observed: the ordering temperature was found to de crease with increasing V content, whereas the opposite effect was obse rved with Al. The effect of oxygen is to stabilise the alpha phase and to shift the alpha2 + beta2 + gamma field in the V rich direction. Th e lattice parameters Of alpha2 and beta phases decrease with additions of Al and V: empirical equations have been developed to predict these changes.