Defect structures, in the massive γ grains of samples which had been rapidly quenched from the high-temperature α-phase field, were studied by using transmission electron microscopy. The results revealed that the defect structures comprised dislocations, stacking faults, and antiphase boundaries which were intimately associated with dislocations or stacking faults. Contrast analysis indicated that both ½<110> and ½<101> unit dislocations were present in the massive γ phase; with the latter being linked by highly-curved non-conservative antiphase boundary. A comparison of experimental and computer-simulated transmission electron microscopic images revealed that wide stacking faults, which were created by the dissociation of ½<101> unit dislocations, lay on {111} planes and were bounded by 1/6<121> Shockley partial dislocations of all possible types. In addition, antiphase boundaries were found to begin or terminate on stacking faults at partial dislocations with a Burgers vector of 1/6<121], but not those with a vector of 1/6<112]. A model for the formation of these defects was proposed which involved the occurrence of an intermediate disordered face-centered cubic phase during the α > γ transformation.

Observations and Analyses of Dislocations and Stacking Faults in the Massive γm Phase in a Quenched Ti-46.5at%Al Alloy P.Wang, M.Kumar, D.Veeraraghavan, V.K.Vasudevan: Acta Materialia, 1998, 46[1], 13-30