Microstructure and creep strength of fully-lamellar TiAl alloys containing beta-phase

Abstract

Effect of microstructure on creep strength in TiAl–Fe–V–B alloys, with a fully transformed lamellar structure, has been investigated using the Larson–Miller parameter. Since these alloys are characterized by addition of iron and vanadium to improve castability, the fine grains of the β phase surrounding γ grains is present in as-cast materials. This work focused on the optimization of metallurgical features to improve creep strength through understanding of the β phase. A fully lamellar TiAl alloy with the β phase surrounding lamellar colonies showed poor creep strength. Iron works as a strong β stabilizer and causes a peak in the amount of the β phase at approximately 1523 K. In order to improve creep strength, an effectual heat treatment process was investigated to eliminate the β phase. On the basis of these experimental results, further alloy development is also discussed.