Creep behavior of γ-TiAl sheet material with differently spaced fully lamellar microstructures

Recent investigations have shown that the interface spacing in fully lamellar microstructures has a major influence on the creep behavior of γ-TiAl based alloys [Scr. Mater. 37 (1998) 1025; Scr. Mater. 35 (1996) 1391; Mater. Sci. Eng. A239–240 (1997) 419; Intermetallics 7 (1999) 171]. In order to study the dependence of interface spacing on creep, fully lamellar microstructures exhibiting different interface spacings but comparable colony size were adjusted in Ti–46.5 at.% Al–4 at.% (Cr, Nb, Ta, B) sheet material by appropriate heat treatments. Creep tests were conducted in a temperature range of 700–800 °C and stresses between 100 and 260 MPa. The results indicate that the primary creep strain as well as the minimum creep rate decreases with decreasing interface spacing. In addition, apparent activation energies and stress exponents were determined as a function of the interface spacing in order to describe the creep controlling mechanisms. A model assumption, which considers the limitation of the free dislocation path by stored dislocations as well as by geometrical obstacles was applied to explain the role of the interface spacing on primary creep strain and secondary creep rate.