Can local hot spots induce α₂/γ lamellae during incomplete massive transformation of γ-TiAl alloys?

Oil quenching is applied to a Ti-45Al-7.5b alloy (in at%) in order to investigate the occurrence of local ‘‘hot spots’’ during rapid cooling from the single a-phase region. After quenching the microstructure consists of large a2-Ti3Al grains and a small volume fraction of massively transformed gm-TiAl particles. The majority of the gm-particles show a featureless a2/gm interface, whereas in the immediate vicinity of some gm-particles lamellar a2/g-structures exist, exhibiting a Blackburn orientation relationship. The extension into the a2-parent grain is in the range of 1–10 µm. In this study it is investigated, if the diffusion-controlled formation of the g-laths is triggered by the release of latent heat during the a/gm transformation, which leads to a local increase in temperature by a hot spot effect. A theoretical model is presented, which describes the temperature conditions around the hot spot. The model predicts that the life time of the hot spot is much too short to generate g-laths observed with a length of 1–10 µm