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Due to their low coefficients of thermal expansion, lNCOLOY@ alloys 903, 907 and 909 have contributed to improved efficiency in many aircraft engines designed since the mid '70's. The application of these Cr-free superalloys was, however, limited by inadequate oxygen environment resistance. The alloys were susceptible to both general oxidation and SAGBO (Stress Accelerated Grain Boundary Oxygen) embrittlement. Until just recently development efforts had focused on improving SAGBO resistance, but had ignored general oxidation resistance.* Compositions shown are in weight % unless stated otherwise.

Age-hardenable iron-nickel-cobalt alloys that combine high strength with controlled thermal-expansion characteristics have attractive properties for various applications at temperatures to 650°C (1200oF). However, the alloys have had very poor notchrupture strength unless stressed in the direction of retained warm work. Stress-rupture properties in air were further deteriorated by