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

Abstract

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 α 2 lamellar spacing, length and thickness decrease with increasing heating rate. The decrease of α 2 lamellar spacing is most effective at lower heating rate, and minimum creep rate decreases with increasing heating rate, since a high density of γ/α 2 boundaries stabilizes the lamellar microstructure. Secondary γ precipitation in thick α 2 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 α 2 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 α 2 lamellae.