Experimental studies here demonstrated that the surface grooving technique, combined with atomic force microscopic observations, was an excellent method for measuring interfacial energies in Ti-Al alloys. Atomistic calculations linked the 3 lowest-energy interfaces to TiAl/TiAl interfaces that corresponded (in increasing order of energy) to the twin, 120° rotated twin and pseudo-twin. The measured ratios of the energies of these interfaces were found to be in very good agreement with the bond-counting model when the results of first-principles calculations of the energies of antiphase boundaries and self-interstitial stacking faults were incorporated into the model. The TiAl/Ti3Al interfaces generally had higher energies than did TiAl/TiAl interfaces, and they split into 2 groups which corresponded to interfaces with and without an antiphase boundary. The energies of the latter group were higher. The existence of these 2 types of TiAl/Ti3Al interface was suggested to explain the 2 observed sub-groups of high-energy interfaces. Due to their high energies, these interfaces were expected to be the lowest energy paths for crack propagation in polysynthetically twinned crystals.

L.Lu, R.Siegl, A.Girshick, D.P.Pope, V.Vitek: Scripta Materialia, 1996, 34[6], 971-6