INVESTIGATION OF THE GAMMA-TI(CR,AL)2 PHASE AT 800-DEGREES-C AND 1000-DEGREES-C

A section of the Ti-Al-Cr ternary system, centered around the γ-TiCr2 phase was examined using five quenched bulk alloy samples and three diffusion couples. Due to the sluggishness of diffusion both at 800 °C and 1000 °C in the TiCr2 phase fields, the heat treatments produced a state of near-equilibrium in the samples rather than complete equilibrium, as desired. However, as previous studies have made use of similar, or shorter, processing schedules (6-11,14), the results of the present study should be considered as valid as the earlier works. As a confimation of the phase compositions obtained from the near-equilibrium bulk alloys, the results of a diffusion couple analysis, yielded similar compositions. It is clear, based on the above results that the γ-TiCr2, with a C14 crystal structure, does indeed extend into the Ti-Al-Cr ternary system as indicated by Suprunenko et al. (14) The γ-TiCr2 phase advances into the ternary as the b solid solution pulls away from the Ti-Cr binary system with decreasing temperature. Solubility into the ternary system is made possible by Al atoms substituting onto Cr sites, as is observed for the Al-Cr-Nb ternary system (17,18). Although the solubility of the γ-TiCr2 phase extends from about 3-19at% Al at 1000íC and from 6-24at% Al at 800íC, the exact limits of solubility are yet to be determined. © 1995.