Microstructural stability and creep behavior of a lamellar γ-TiAl based alloy with extremely fine lamellar spacing

Lamellar Ti-46Al-1.5Cr-2Mo-0.25Si-0.3B (in at.%) specimens with two different extremely fine lamellar spacings were produced and investigated. The average lamellar spacing was determined to be 200 and 35 nm, respectively. Creep tests at 700 degreesC have shown a distinct primary creep regime for both material conditions. After annealing for 24 h at 1000 degreesC the primary creep strain for both materials is significantly decreased. The steady-state creep for the specimens with the wider lamellar spacing appears to be similar to the creep behavior prior to annealing while the creep rate of the material with the previously smaller lamellar spacing is significantly higher. Optical microscopy and TEM-studies show that the microstructure of the specimens with the wider lamellar spacing is nearly unchanged, whereas the previously finer material was completely recrystallized to an equiaxed gamma microstructure with a low creep resistance. The dissolution of the fine lamellar microstructure was also observed during creep tests at 800 degreesC as manifested in an acceleration of the creep rate. (C) 2002 Elsevier Science Ltd. All rights reserved.