Grain refinement in cast Ti-46Al-8Nb and Ti-46Al-8Ta alloys via massive transformation

Some of the advantages and disadvantages of massive transformation, which has emerged as a grain refinement technique for cast Ti-46Al-8Nb and Ti-46Al-8Ta alloys, are discussed. The most significant advantages of the treatment technique, include its simplicity and exclusion of boron as a refining agent. It is expected that the second advantage can be beneficial for ductility, considering that coarse borides reduce the tensile ductility in cast TiAl alloys. The main problem faced in developing the massive transformation, as a useful processing technique for TiAl alloys, relates to the fact that high and narrow cooling rates windows are required for the massive transformation. It is found that high cooling rates can lead to crack formation, while being difficult to achieve in thick sections. Another problem associated with the technique is, the need to gather information about the temperature range at which these alloys transform into a convoluted structure.