INCONEL® alloy 783 is an oxidation-resistant low coefficient of thermal expansion (low CTE) superalloy developed for gas turbine applications. Turbine efficiency can be increased through the use of low-CTE shrouds and case components that maintain tight blade tip clearances at different turbine operating temperatures. To achieve low CTE, alloys based on Ni–Fe–Co compositions require Cr content be maintained at low levels. Added Cr lowers the Curie temperature and thereby increases thermal expansion rate over a wider temperature range. The necessary lack of Cr minimizes resistance to both general oxidation and stress-accelerated grain boundary oxygen enhanced cracking (SAGBO). Increased amounts of Al in alloys strengthened by γ′ alone also promotes SAGBO. Alloy 783 is the culmination in the development of an alloy system with very high aluminum content that, in addition to forming γ′, causes β aluminide phase precipitation in the austenitic matrix. It was discovered that this type of structure can be processed to resist both SAGBO and general oxidation, while providing low thermal expansion and useful mechanical properties up to 700°C. The high Al content also reduces density to 5 percent below that of superalloys such as INCONEL alloy 718. Key aspects of the alloy development are presented, including the assessment of SAGBO resistance by evaluating elevated temperature crack growth in air. The alloy, now commercially available, has been successfully fabricated and welded into gas turbine engine components.

Smith, D. F., and Smith, J. S., “A History of Controlled, Low Thermal Expansion Superalloys,” Physical Metallurgy of Controlled Expansion Invar-Type Alloys, TMS, Warrendale, PA, 1990, p. 253.
Sadananda, S., “Creep Crack Growth in Alloy 718,” Metallurgical Transactions, Vol. 8A, Mar. 1977.
Liu, C. T., and Sikka, V., “Nickel Aluminides for Structural Uses,” Journal of Metals, May 1986, pp. 19–21.
Heck, K. A., “The Effects of Silicon and Processing on the Structure and Properties of INCOLOY Alloy 909,” Physical Metallurgy of Controlled Expansion Invar-Type Alloys, TMS, Warrendale, PA, 1990, p. 273.
Heck, K. A., Smith, D. F., Holderby, M. A., and Smith, J. S., “Three Phase Controlled Expansion Superalloys With Oxidation Resistance,” Superalloys 1992, TMS, Warrendale, PA, 1992, p. 217.
This content is only available via PDF.
You do not currently have access to this content.