INCONEL(R) ALLOY-783 - AN OXIDATION-RESISTANT, LOW EXPANSION SUPERALLOY FOR GAS-TURBINE APPLICATIONS

INCONEL(R) alloy 783 is art oxidation-resistant low coefficient of the rmal expansion (low CTE) superalloy developed for gas turbine applicat ions. Turbine efficiency can be increased through the use of low-CTE s hrouds 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 t hermal expansion rate over a wider temperature range. The necessary la ck of Cr minimizes resistance to both general oxidation and stress-acc elerated grain boundary oxygen enhanced cracking (SAGBO). Increased am ounts of Al in alloys strengthened by y' alone also promotes SAGBO. Al loy 783 is the culmination in the development of an alloy system with very high aluminum content that, in addition to forming y', causes bet a aluminide phase precipitation in the austenitic matrix. It was disco vered that this type of structure can be processed to resist both SAGB O and general oxidation, while providing low thermal expansion and use ful mechanical properties up to 700 degrees C. The high Al content als o reduces density to 5 percent below that of superalloys such as INCON EL alloy 718. Key aspects of the alloy development are presented, incl uding the assessment of SAGBO resistance by evaluating elevated temper ature crack growth in air The alloy, now commercially available, has b een successfully fabricated and welded into gas turbine engine compone nts.