In situ small-angle X-ray scattering study of the perovskite-type carbide precipitation behavior in a carbon-containing intermetallic TiAl alloy using synchrotron radiation

Intermetallic γ-TiAl based alloys of the latest generation, e.g. TNM alloys with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B (in at.%), exhibit the potential to be used in modern high-performance combustion engines due to their low density, high strength and creep resistance as well as their good oxidation properties at elevated temperatures. Alloying with C can further improve the high-temperature performance by both solid solution hardening and/or carbide formation. In this study, starting from a supersaturated TNM-1C alloy the precipitation behavior and thermal stability of perovskite-type carbides Ti3AlC during isothermal annealing and ensuing re-heating to 1200 °C are quantified by means of an in situ small-angle X-ray scattering experiment using synchrotron radiation. Complementarily, the formed hierarchical structures on the nano-scale, i.e. p-type carbide precipitates within ultra-fine γ-lamellae of the α2/γ-colonies, were investigated by means of monochromatic high-energy X-ray diffraction in combination with scanning and transmission electron microscopy. Additionally, an explanation of an obtained diffraction phenomenon is given, i.e. streak formation that is caused by the very small lamellar spacing of the γ-phase within the α2/γ-colonies. It was also found that the geometrically well-defined nanostructure allows a correlation between the γ-lath thickness and a characteristic dimension of p-type carbides.