Effect of alloying additions on β′ precipitation in NiAl–Ti base alloys Original Research Article

The precipitation of β′–Ni2AlTi is investigated in NiAl–3Ti–X (X=Cu, Hf) alloys to determine the effects of alloying additions. Hf enhanced the precipitation of β′ and both Ti and Hf were found to partition to the β′ phase. Atom Location by Channeling Enhanced Microanalysis (ALCHEMI) results indicate that Hf has a strong preference to reside on Al sites. Cu was found to enhance β′ precipitation, but only when added to replace Ni in the composition. In this case, the β′ phase was enriched in Ti but not Cu. By relating the stability of the phases with nearest neighbor pair interactions, it is shown that Hf increases the stability of β′ phase, while Cu decreases the stability of the matrix β phase relative to β′.