On the stability of Ti(Mn,Al)2 C14 Laves phase in an intermetallic Ti-42Al-5Mn alloy

In order to facilitate a more widespread use of intermetallic & gamma;-TiAl based alloys in the aircraft and automotive sector, recent research focuses on the development of low-cost titanium aluminides. The strong & beta;-stabilizing effect as well as the increased ductility upon Mn addition renders this alloying element a promising candidate to fully or partially substitute other, more expensive, alloying elements such as Mo, Ta and Nb. Mn-containing & gamma;-TiAl based alloys, however, are prone to the formation of the undesired, brittle Ti(Mn,Al)2 C14 Laves phase during long-term exposure at the targeted service temperatures, which can deteriorate the ductility at ambient temperatures. In this study, the transformation kinetics as well as the chemical and thermal existence range of the C14 Laves phase in the low-cost Ti-42Al-5Mn (at.%) alloy were investigated by complementary experimental and computational approaches. In situ and ex situ high-energy X-ray diffraction in combination with microstructural investigations were used to study the occurrence and transformation kinetics of possible Laves phase formation in the course of annealing treatments. The chemical stability range of the C14 Laves phase was addressed by chemical analysis in conjunction with complementary ab initio modeling. Using these combined approaches, the critical local Mn concentration of -16 at.% for Laves phase formation within lamellar & alpha;2 and -17 at.% within & beta;o in the Ti-42Al-5Mn alloy was determined. These results should be critically considered for future design of advanced low-cost & gamma;-TiAl based alloys.