Controlling lamellar orientation of Ti-47.5Al-5Nb-2.5V-1Cr alloy by conventional casting

This paper explores the control of lamellar orientation in alpha-solidified TiAl alloy by anti-gravity investment casting. The macrostructures and microstructures in iso-section plate and variable-section blade have been investigated in detail. The results show that the macrostructures of both plate and blade body consist of a number of columnar crystals growing inwards from the surface, while their microstructures are composed of a number of lamellar colonies with preferred orientation and a few uncontrolled colonies. In the plates, the lamellae between adjacent colonies are almost parallel to each other. In the section along the radial direction of blade body, on the other hands, the angle of lamellae between adjacent colonies is controlled within 15 degrees. The misorientation between adjacent colonies originates from the tilted growth of the alpha dendrites caused by the variable-section character of the blade. In addition, the formation of uncontrolled lamellar colonies is investigated in plate and blade.