Solidification of an article extension from a melt using an integral mandrel and ceramic mold

摘要

A method for providing an integral extension on an article, involves: (i) selecting an article comprising an extension end having a cross-sectional shape, an extension bonding surface and an outer surface defined by the cross-sectional shape, the extension end having a microstructure comprising a superalloy composition and a directionally oriented crystal structure; (ii) attaching a mandrel to the extension bonding surface, the mandrel having a cross-sectional shape that is compatible with the cross-sectional shape of the extension end and an outer surface that communicates with the outer surface of the extension end; (iii) forming a ceramic mould over the outer surface of the mandrel and the outer surface of the extension end, the mould having a mould cavity with a shape that is defined by the mandrel and that is adapted to define the shape of an integral extension, the mould having at least one gating means that communicates with the mould cavity; (iv) dipping the extension end of the article into a bath of a molten material having an alloy composition that is compatible with the superalloy so that the molten material enters the mould through the gating means and contacts the mandrel; (v) holding the mandrel in contact with the molten material for a time sufficient to allow the mandrel to be melted back to the bonding surface, the melted mandrel intermixing with and becoming part of the molten material, the holding time also being sufficient to allow the extension bonding surface to be heated by and interact with the molten material as a microstructure growth seed; and (vi) withdrawing the extension end from the molten material under controlled thermal conditions and at a rate which causes the molten material to solidify on the growth seed at an interface between them as an integral extension that conforms to the shape of the mould cavity and has a microstructure that is compatible with the microstructure of the extension end. The controlled thermal conditions comprise maintaining a temperature gradient within the article such that the temperature is highest at the interface and decreases within the article as a function of increasing distance from the interface. Also claimed is a method as described above where in step (iii) a preformed ceramic mould is attached to the bonding surface instead of being formed on it.