In situ observation of phase selection in undercooled Ni-Al melts

Raney-Ni type Ni-68.5 at-% Al alloys are used for catalytic applications in the chemical industry. In this work, melt undercooling experiments were performed by means of the electromagnetic levitation technique. High-energy X-ray diffraction was used to determine the solidification pathway and the origin of microstructure peculiarities in gas atomised powders. The direct observation of the phase selection in Ni-68.5 at-% Al has unambiguously revealed the primary phase formation of beta-AlNi to be independent of the level of undercooling up to a maximum of 320 K. On cooling the beta-AlNi phase undergoes a fast peritectic transformation L + AlNi -> Al(3)Ni(2) and is therefore not found in the as-solidified microstructure.