EBSD characterisation of massive γ nucleation and growth in a TiAl-based alloy

The influence of interrupted cooling on the massive transformation in Ti46Al8Nb

“…4(e) from the alpha and from regions (1) and (2) in the massive gamma, show firstly that the (0001) in the alpha is parallel with a (111) in region (1) and secondly that region (2) is twin-related to region (1) and is twinned about this (111); this type of behaviour has been reported earlier (e.g. [15]) Thus within the whole of this massively transformed region the orientation relationship between the original (111) and the matrix (0001) is maintained. More complex orientation relationships can be generated during growth of the massive phase as illustrated below.…”

A numerical model for the description of the lamellar and massive phase transformations in TiAl alloys

“…Based on the reported observations [12,22], massive g grains are assumed to nucleate heterogeneously at a/a grain boundaries. The volumetric nucleation rate is calculated with the following expression coming from classical nucleation theory: Fig.…”

“…Although bulk nucleation has been reported [9,19], it is generally accepted that nucleation of massive g occurs predominantly at grain boundaries. Gamma nuclei generally exhibit a Blackburn orientation relationship with one of the adjacent a grains while they grow at the expense of the other grain by the movement of highly mobile incoherent interfaces [20][21][22]. It has been suggested also that lamellae nucleated on grain boundaries serve as a precursor of massive g which would develop from the incoherent interface of the lamella in the adjacent grain where it has no orientation relationship [20].…”

“…It has been suggested also that lamellae nucleated on grain boundaries serve as a precursor of massive g which would develop from the incoherent interface of the lamella in the adjacent grain where it has no orientation relationship [20]. Massive grains nucleated on grain boundaries grow with a hemispherical morphology owing to the immobile coherent interface with one of the adjacent a grains [21,22]. Massive growth occurs at a high velocity which is controlled by the mobility of interface and involves frequent twinning events [22].…”

“…Massive grains nucleated on grain boundaries grow with a hemispherical morphology owing to the immobile coherent interface with one of the adjacent a grains [21,22]. Massive growth occurs at a high velocity which is controlled by the mobility of interface and involves frequent twinning events [22]. As growth proceeds, the grain boundaries are progressively covered by massive grains and the nucleation rate diminishes.…”