Growth of nickel-base superalloy bicrystals by the seeding technique with a modified Bridgman method

Abstract

Abstract A process for consistently growing large bicrystals (16 × 63 × 100 mm) of a NiCrFe ternary alloy in ceramic-shell molds by a modified Bridgman method was established. A pair of single-crystal seeds, oriented along the [0 0 1] direction, was used to grow each bicrystal with a prescribed tilt-boundary orientation. Initial processing parameters were established by using a commercial single-crystal casting (PWA-1480) superalloy. It was found that, to be successful, adequate superheating of the molten tip of the seed crystals is required prior to alloy casting in addition to the usual considerations of melt superheat, thermal gradient, and withdrawal rate. The development of this process and the specific process parameters are reviewed. General guidelines derived from this study are presented and discussed.