Creep behavior and microstructural changes during short-term creep in a γ-TiAl based alloy with fully lamellar microstructure

It is well established that the interface spacing in fully lamellar microstructures has a major influence on the creep behavior of gamma-TiAl based alloys. In this paper, the dependence of the creep properties on interface spacing in fully lamellar Ti-46.5at.%Al-4at.%(Cr,Nb,Ta,B) sheet material as well as the onset of microstructural instability during short-term creep at 800degreesC was studied. Creep tests were conducted over a temperature range of 700 to 800degreesC and at stresses between 100 and 275 MPa. The results indicate that the primary creep strain as well as the minimum creep rate decrease with reduced interface spacing. A model based on the work hardening theory was applied to explain the role of the interface spacing on both the primary creep strain and secondary creep rate. The observed microstructural changes during creep are correlated with an alpha(2)-Ti3Al content exceeding the thermodynamical equilibrium caused by the formation process of the fully lamellar microstructure.