Advances in optimisation of mechanical properties in cast TiAl alloys

The room temperature tensile properties of a number of cast TiAl-based alloys, which have been grain-refined either by additions of boron or by a new quenching and ageing treatment, have been assessed. It has been found that in the alloys which have been grain-refined by boron addition, the size of the titanium boride particles, which is strongly influenced by the size of the cast samples, is an important factor in limiting the tensile ductility. The tensile properties of samples which have been quenched and aged can be significantly improved and it has been shown that this grain refinement technique, which is based on the massive transformation, can be applied to a wide range of alloys. Quenching to above the ductile-to-brittle temperature, but below the temperature at which the massive transformation occurs, reduces the tendency for cracking during this type of heat treatment. The potential for producing cast components using these two approaches to grain-refinement is discussed.