Method for treating superalloy castings

In a method for the production of a superalloy part which is characterized by specific nominal dimensions and which must be produced with close tolerances, the improvement comprising the steps of preparing an investment casting mold defining a cavity dimensioned to minimize the need for machining to final dimensions, including nucleating agents in the molten metal engaging surfaces of the mold to promote rapid nucleation and freezing of said metal, pouring molten metal of said superalloy composition into said mold, and solidifying the molten metal in said mold, the solidified casting portions adjacent said molten metal engaging surfaces comprising a sound, substantially continuous skin, and wherein defects in the form of material voids are located immediately beneath the skin, locating the casting in a chamber subsequent to complete solidification thereof and without any surface finishing operations whereby said skin remains intact, introducing a surrounding gaseous atmosphere into the chamber, applying pressure to the casting through the atmosphere between about 10,000 psi and 50,000 psi, heating the casting to an elevated temperature, said skin being of sufficient thickness to substantially prevent the penetration of said gas into said voids, said casting being at said temperature for a period of time during application of said pressure sufficient to permit metal movement in the casting when the casting is subjected to said pressure, the combination of heat, pressure and time serving to achieve said metal movement and to substantially eliminate said voids by deforming and consolidating the material in the area of said voids, and thereafter subjecting said casting to a finishing operation which removes only the nonmetallic components on the part surfaces including mold material, any superfluous gate and runner portions, and only that additional amount of metallic material necessary to assure complete removal of said nonmetallic components.