Microstructure and chemical homogeneity of high NB gamma based TiAl alloys in different conditions of processing

Titanium aluminides based on the general composition (in at.%) Ti-45Al-(5 - 10 Nb) exhibit several desired properties for high temperature applications involving the use as structural materials in aerospace and automotive engines. These alloys combine high mechanical strength and good corrosion resistance at elevated temperatures with appreciable ductility at ambient temperature. Thus, these materials are thought to extend the service range of conventional titanium aluminides towards higher stresses and temperatures. However, in view of the anticipated higher strength level, quality issues associated with ingot production and subsequent processing are of major concern. These involve micro- and macrosegregation in cast products, as well as the structural and chemical inhomogeneities, which retain in hot worked material. The present paper reports an analytical study which has been performed in order to assess the structural and chemical homogeneity after different stages of processing involving casting, homogenization, primary hot working, and secondary hot working, In this context, specimen with a nominal composition of Ti-45Al-10Nb (at.%) prepared by different routes of ingot processing have been examined by scanning electron microscopy and energy dispersive x-ray analysis. The present studies show that a smart choice of hot working and annealing steps allows it both to tailor a fully lamellar or fine grained structure and improve the structural and chemical homogeneity.