Influence of heating rate in α + γ dual phase field on lamellar morphology and creep property of fully lamellar Ti-48Al alloy

The fully lamellar structure of a Ti-48Al alloy was subjected to secondary annealing heat treatments with controlled heating rates in the α + γ dual phase field to produce various lamellar structures. The effects of heating rate on the microstructure and creep property were investigated. It was found that the α2 lamellar spacing, length and thickness decrease with increasing heating rate. The decrease of α2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing heating rate, since a high density of γ/α2 boundaries stabilizes the lamellar microstructure. Secondary γ precipitation in thick α2 laths may also contribute to the decrease of the minimum creep rate at the lower heating rate. On the other hand, creep rate increases at high heating rate since α2 laths become discontinuous with increasing heating rate. A reduction of creep rate by one order of magnitude was achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α2 lamellae.