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Advanced lightweight TiAl based intermetallic systems, capable of surviving elevated temperatures, have been a topic of interest, considering their ever-increasing demands in aerospace industries. The optimization of solidification and processing methods stands as a pivotal factor in microstructural engineering for TiAl systems, aiming to attain desired mechanical properties. The present study focuses on two distinct alloy systems , a commercial grade 2nd generation, i.e., Ti–48Al–2Cr–2Nb (at. %), and a newly developed 3rd generation, i.e., Ti–45Al–2Cr-7.5Nb-0.2B (at. %) alloys. Interestingly, the variation in the solidification path, triggered by higher Nb content along with a minor amount of B, accounts for the substantial microstructural refinement for the 3rd generation TiAl alloy. Nevertheless, prominent segregation of Nb and Cr to the β 0 phase is observed in both the as-cast microstructure, which restricts the applicability of the alloys. Remarkably, a novel bilamellar-biglobular (BLBG) microstructure consisting of γ and α 2 phases in both lamellar and globular morphologies is achieved through heat treatment for both categories of alloy. Elevated temperature tensile testing depicts an exceptional strength-ductility combination for 3rd generation BLBG microstructure. Excellent twin-twin activity and twin-induced plasticity effect are observed to govern the deformation mechanism . Overall, the path of solidification, phase distribution, and its effect on the deformation mechanism are thoroughly analyzed, which is of particular interest from a design and application point of view. • Refinement in (α 2 + γ) colony size is noted for 3rd as compared to 2nd generation TiAl alloy. • Enrichment of β 0 phase with Nb and Cr is noted for both as-cast TiAl alloys. • β 0 .→ (α 2 ) g transformation forms bilamellar-biglobular (BLBG) microstructure upon heat treatment of TiAl alloys. • Twin induced plasticity (TWIP) effect is noted to dictate the deformation for this microstructure. • Excellent combination of elevated temperature strength and ductility is attained for heat treated TiAl-7.5Nb alloy.
Nath et al. (Mon,) studied this question.