Phase equilibria among α (hcp), β (bcc) and γ (Ll0) phases in Ti-Al base ternary alloys

Phase equilibria between the alpha(A3), alpha(2) (D0(19)), beta(A2 or B2) and the gamma(L1(0)) phases in the Ti-Al base ternary systems were investigated over the temperature range 1000-1300 degrees C. The tie lines and the phase boundaries were determined by electron probe microanalysis using multiphase alloys. It was established that almost all the elements except Zr tended to partition into the beta phase rather than into the alpha, alpha(2) or the gamma phase, while Zr mostly partitioned into the gamma phase. At 1000 degrees C, in the equilibrium state between the alpha(2) and the gamma phases, V, Cr, Mo, Ta and W partitioned to the at phase rather than to the gamma phase, whereas Mn, Fe, Co, Ni, Cu and Zr tended to concentrate Into the gamma phase. The partition coefficients for the alloying elements were only slightly dependent on their concentration. Based on these data, the relative stabilizing effects of alloying elements on the alpha, alpha(2), beta and gamma phases are discussed. (C) 2000 Elsevier Science Ltd. All rights reserved.