Unidirectional solidification of Ni 3Al by a floating zone method

Abstract

The formation process of ductile, columnar-grained Ni 3Al with a stoichiometric composition was examined by unidirectional solidification (UDS) employing a floating zone (FZ) method, named FZ-UDS method. Quenching the solidification interface results in Ni 3Al and β-NiAl simultaneously growing from the liquid during FZ-UDS. The solidification interface morphology was lamellar at low growth rates and dendritic at high ones. The precipitated β-NiAl is considered to prevent the grain growth of Ni 3Al perpendicular to the growth direction. In addition, at low growth rates β-NiAl dissolved into the Ni 3Al matrix on cooling to room temperature, thereby leading to the columnar-grained structure of single phase Ni 3Al. At high growth rates, however, dendritic β-NiAl remained undissolved when similarly cooled.