Screening for O phase in advanced γ–TiAl alloys

This is a screening study using high-energy X-ray diffraction measurements to determine whether an orthorhombic phase forms in γ-based TiAl alloys of different compositions. The 13 alloy compositions investigated were chosen to be either close to commercial alloys or to identify the effects of different single alloying elements on the formation of orthorhombic phase. The orthorhombic O phase with Cmcm structure was found in several of those γ-TiAl alloys after an aging heat treatment at 550 °C for 20 h. The presence of different β-stabilising elements such as niobium, tantalum, molybdenum or vanadium did promote the formation of orthorhombic phase, while micro alloying elements such as carbon or boron were neutral in this respect. Furthermore, a limit for aluminium was also found, below which the orthorhombic O phase is formed in the alloys investigated. This limit lies between 46 at.% and 47 at.%.