EUTECTIC SUPERALLOYS STRENGTHENED BY 6, Ni3Cb LAMELLAE AND γ'Ni3Al PRECIPITATES

摘要

By means of a screening and solidification optimization study of certain alloys located on the r-6 liquidus surface within the Ni-Cb-Cr-Al system, alloys with high temperature properties superior to those of all known superalloys were defined. One alloy, Ni - 19. 7 w/o Cb -6.0 w/o Cr - 2. 5 w/o Al, directionally solidified at 3 cm/hr met or exceeded each program goal. A second alloy, Ni - 21.75 w/o Cb - 2.55 w/o Al, although deficient in its inherent oxidation resistance, met the other program goals and combined a remarkable insensitivity of composite microstructure to solidification parameters with excellent low temperature toughness. This investigation demonstrated that useful properties for gas turbine airfoil application have been achieved by reinforcing a strong and tough gamma solid solution matrix containing precipitated gamma prime by a lamellar intermetallic compound Ni3Cb having greater strength at elevated temperature.