Microstructure of titanium aluminide prepared by centrifugal investment casting for automotive turbocharger

From a technical perspective, many of the unique properties of titanium aluminides that make them attractive for high-temperature structural applications also make the processing of these alloys into useful products challenging. Cast titanium aluminide (TiAl) is on the verge of commercialization, particularly in the vehicle industry, owing to its low production cost. In this study, the centrifugal castability of a TiAl (Ti-47% Al, mole fraction) turbocharger was investigated by simulation. Actual casting was carried out in vacuum using an induction melting furnace coupled to an Al2O3 crucible. Experimental verification indicated that the numerical simulation results were in agreement with the experimental results. The crystal structure, microstructure, and chemical composition of the TiAl prepared by centrifugal casting were studied by X-ray diffractometry, optical microscopy, field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS). The FE-SEM and EDS examinations of the TiAl casting showed that the thickness of the oxide layer (alpha-case) was typically less than 30 mu m.