Increase in γ/α 2 Lamellar Boundary Density and its Effect on Creep Resistance of TiAl Alloy

Several lamellar microstructures of a Ti-48 % Al alloy were made by changing heating rate in the α+ dual phase field, and their creep properties were investigated at 1150 K. Average spacing and average length of α 2 lamellae 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 the heating rate, since a high density of γ/α 2 boundaries stabilizes lamellar microstructure during creep. On the other hand creep rate increases at high heating rate, since α 2 lamellar length becomes shorter with increasing heating rate. A reduction of creep rate by one order of magnitude is achieved at the optimum heating rate providing the best combination of narrow spacing and sufficiently long length of α 2 lamellae.