Effect of alloying additions on beta ' precipitation in NiAl-Ti base alloys

The precipitation of beta ' -Ni2AlTi is investigated in NiAl-3Ti-X (X=Cu, H f) alloys to determine the effects of alloying additions. Hf enhanced the p recipitation of beta ' and both Ti and Hf were found to partition to the be ta ' phase. Atom Location by Channeling Enhanced Microanalysis (ALCHEMI) re sults indicate that Hf has a strong preference to reside on Al sites. Cu wa s found to enhance beta ' precipitation, but only when added to replace Ni in the composition. In this case, the beta ' phase was enriched in Ti but n ot Cu. By relating the stability of the phases with nearest neighbor pair i nteractions, it is shown that Hf increases the stability of beta ' phase, w hile Cu decreases the stability of the matrix beta phase relative to beta ' . (C) 2001 Acta Materialia Inc. Published by Elsevier Science Ltd. All righ ts reserved.