Method for treating superalloy castings

Abstract

A method for treating investment cast superalloy castings wherein the portions of the castings which solidify directly against the mold walls comprise a substantially continuous or encapsulating skin of a metallic and/or nonmetallic composition. In such castings, defects in the form of material voids, including defects present immediately beneath the skin, are eliminated by the application of heat and pressure. The castings are heated to temperatures sufficient to achieve metal movement in the form of yield or creep, and a pressure of at least about 10,000 psi is applied by means of a surrounding gaseous atmosphere. The heat and pressure application deforms the material in the area of the voids and consolidates this material to substantially remove the voids and to thereby improve the performance characteristics of the castings. The encapsulating skin also serves as a protective coating during the hot isostatic pressing whereby contamination of the casting by elements such as oxygen or nitrogen in the furnace atmosphere is avoided, or drastically reduced. By eliminating surface defects and avoiding surface contamination, the investment castings are cast to substantially exact final dimensions since finishing operations are minimized.