AP-FIM investigation on γ-based titanium aluminides

The major hurdle to be overcome for commercial use of the γ-based titanium aluminides is their poor ductility under ambient temperatures. Substantial research efforts have been devoted to improve the ductility by adding alloying elements and most commercially important alloys contain certain amount of β-stabilising elements such as V, Mn, Mo, Nb, Ta, Cr etc, resulting in continuous improvement. It was not until recently however, that non-conventional β-stabilising elements from platinum group metals (PGMs), such as Ru and Pd, have also attracted attention. To understand the behaviour of alloyed intermetallics, it is very important to reveal the substitution site of the third element and the element distribution in the phases. The atom probe field ion microscope (AP-FIM) is a unique technique for observing chemical variation in the materials studied on the nanometer scale and is very suitable for these investigations. The site occupancy probability was determined for the PGM element, ruthenium, in the γ-based titanium aluminide intermetallic alloys. The AP-FIM and X-ray diffraction techniques were used for the analysis. In both techniques, the ruthenium was observed to substitute preferentially for aluminium.