The activation of slip at room temperature in lamellae of α2-phase in a 48at%Al alloy was studied by means of transmission electron microscopy. It appeared that slip activity occurred mainly at, or near to, the intersection of certain cross-lamellar deformation twins (in γ-TiAl) with the α2-phase lamellae. In polycrystalline samples which had been heat-treated so as to give a duplex microstructure with a significant lamellar component, only dislocations with Burgers vectors of the form, 1/3<11▪0>, were activated. Essentially no dislocations with a Burgers vector of 1/3<11▪6> (c-component dislocations) were observed after deformation in tension at room temperature. It was found that, for these samples, slip in the α2-phase could occur either via a slip transmission process or via the stress-induced activation of sources in the interfaces between α2 and γ. The resultant defects were super-dislocations, with Burgers vectors of 1/3<11▪0>, gliding on prismatic {1¯1▪0} and/or pyramidal {2¯2▪1} planes. In samples of polysynthetically twinned crystals, deformed in compression parallel to [111]γ||[00▪1]α, activity of c-component dislocations was observed. It was shown that the experimental results were consistent with the stress-induced activation of sources in interfaces, rather than with the transmission of slip from γ-TiAl.

Activation of Slip in Lamellae of α2-Ti3Al in TiAl Alloys J.M.K.Wiezorek, X.D.Zhang, W.A.T.Clark, H.L.Fraser: Philosophical Magazine A, 1998, 78[1], 217-38