How Si affects the microstructural evolution and phase transformations of intermetallic ?-TiAl based alloys

Small additions of Si and C have been proven to efficiently improve the creep properties intermetallic ?-TiAl based alloys. In order exploit full potential these alloying elements, detailed studies their influence on phase transformations resulting microstructural evolution during processing heat treatments are a necessity. This work presents fundamental investigation effect in composition range up 0.65 at.% ?-solidifying TiAl alloy with nominal Ti-43.5Al-4Nb-1Mo-0.1B (in at.%). After casting subsequent treatment at 1200 °C, increases amount ? expense ?2-Ti3Al phase. Due solid solution strengthening precipitation ?-Ti5Si3 silicides highly Si-alloyed materials, an increase hardness is observed. As act as effective obstacles for grain boundaries, precipitates also control growth kinetics ? able maintain fine-grained microstructure 1300°C holding times 20 h. By utilizing in-situ high-energy X-ray diffraction experiments differential scanning calorimetry, found exhibit similar effects Al system, effectively increasing solid-solid transition temperatures, while simultaneously decreasing solidus temperature materials.