Patent ID: 8210240

Claim:
A directional solidification process for producing a casting, the process comprising: providing a mold with a cavity and a continuous solid facecoat on a surface within the cavity and formed from a facecoat slurry applied to the surface, the facecoat consisting of: at least 60 weight percent of a first phase consisting essentially of yttria; at most 35 weight percent of an aqueous suspension containing a particulate inorganic binder; a thixotropic organic binder; and a dispersant having the general formula H x [N(CH 2 ) y OH] z , where x has a value of 0, 1 or 2, y has a value of 1 to 8, and z=3−x, the dispersant being present in the slurry in an amount sufficient to stabilize the slurry at a pH of up to about 10; and optionally constituents excluding particulate refractory materials and inorganic binders; introducing a molten quantity of a metal alloy into the cavity of the mold so that the molten metal alloy contacts the facecoat; immersing the mold in a liquid coolant to cool and solidify the molten quantity of the metal alloy and form a casting of the metal alloy, during which an oxide layer forms on a surface of the casting, the facecoat becoming sufficiently adherent to the oxide layer such that at least a portion of the facecoat detaches from the surface of the mold and remains tightly adhered to the surface of the casting in the event the casting contracts during cooling; removing the mold from the liquid coolant; and then removing from the mold the casting with the oxide layer and at least the remnant portion of the facecoat thereon.