Influence of Discontinuous Precipitation on the Creep Behavior of a β-Solidified γ-TiAl Based Alloy

Owing to their excellent high temperature properties, intermetallic gamma-TiAl based alloys are potentially suitable materials for applications in the aviation and automotive industry. In order to adjust a fine lamellar microstructure with optimum properties, the forging process is followed by a multi-stage heat treatment. During the final annealing process, a discontinuous precipitation reaction, a so-called cellular reaction, may occur which decomposes the fine lamellae in the alpha(2)/gamma colonies. A stable microstructure is a crucial factor in the development of highly creep resistant alloys. In the scope of this work, various heat treatments were performed in order to adjust microstructures with a varying proportion of discontinuous precipitation. Furthermore, creep tests were performed at 800 degrees C and 150 MPa. Scanning electron microscopy in the back-scattered electron mode was used to characterize the microstructure's morphology. The respective phase fractions were determined by X-ray diffractometry. It could be shown that the creep resistance decreases with an increasing amount of discontinuous precipitation.