Investigation of Survived Solidification Features After Hot Isostatic Pressing in Third Generation γ-TiAl Alloys: Ti–45Al–(5, 10)Nb–0.2B–0.2C

The effect of niobium (Nb) content in titanium aluminide (TiAl) with the composition Ti–45Al–(5, 10)Nb–0.2B–0.2C manifests in terms of change in the sequence of phase evolution during solidification. In the present investigation, the consequent evolution of microstructure, phases, and crystallographic texture has been examined for the survived solidification features after hot isostatic pressing (HIP). It has been observed that 10 at. pct of Nb in γ-TiAl alloy ensures excellent grain refinement and random texture through the ingot. Because of phase transformation during cooling, the orientation relationship is maintained between the evolved phases. A subdued thermal gradient, related to the basic grain refinement mechanism by constitutional undercooling and by the change of the solidification path, persists during solidification for the two Nb containing alloys and maintains \(\beta\) $\beta$ grain growth kinetics at different locations in the ingot. The two different types of γ–γ lamellae have been identified which is related to the two different types of the transformation mechanism. The microhardness also has been investigated from the periphery to the central region of the casted and HIPed circular pancake. A novel mechanism has been proposed for the different types of γ–γ lamellae formation and the mechanism of the crystallographic orientation evolution during the solidification of these alloys.