INVESTMENT-CASTING OF NIAL SINGLE-CRYSTAL ALLOYS

Significant progress has been made in the understanding of solidificat ion conditions, microstructure evolution, and defect formation during investment casting of NiAl single crystals. The high liquidus temperat ures of NiAl alloys result in a larger dendrite arm spacing than is fo und in superalloy Rene N5. Because of their higher thermal conductivit ies, NiAl alloys have higher cooling rates and lower temperature gradi ents during solidification than Rene N5. These differences give NiAl a lloys a lower tendency to form freckles and a higher tendency to form equiaxed grains. However, with the aid of process modeling, single cry stals of various shapes of NiAl alloys have been produced.