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

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 beta phase surrounding gamma grains is present in as-cast materials. This work focused on the optimization of metallurgical features to improve creep strength through understanding of the beta phase. A fully lamellar TiAl alloy with the beta phase surrounding lamellar colonies showed poor creep strength. Iron works as a strong beta stabilizer and causes a peak in the amount of the beta phase at approximately 1523 K. In order to improve creep strength, an effectual heat treatment process was investigated to eliminate the beta phase. On the basis of these experimental results, further alloy development is also discussed. (C) 2002 Elsevier Science B.V. All rights reserved.