Investigation on High Thermal Stability and Creep Resistant Modified Inconel 718 with Combined Precipitation of γ" and γ'

Abstract

One of the recent advances in INCONEL 718 development is intended to find a modified Alloy 718 with high thermal structure stability and creep resistance to be used beyond the ceiling temperature of 650°C. Twelve heats of modified Alloy 718 with chemical composition variation were designed to study the effect of Al, Ti, Nb and MO on yN and y’ precipitation morphology and on microstructure stability and high temperature mechanical properties above 650°C. Detail TEM and high resolution electron microscopy (HREM) study has shown that associated precipitation and compact morphology of yU and y’ in modified 718 Alloys characterize with higher thermal stability than separate precipitation of yN and y’ in conventional INCONEL 718. Creep rupture life depends not only on Nb f Al -jTi content but also on coefficient k = 2/(Al +Ti/Nb)‘+ (Al/Ti)* l Nb. Long time aging stability study at 650, 700 and 750°C for 5000 hrs has shown that the modified Alloy 718 with associated precipitation and compact morphology of y” and y’ expresses excellent thermal structural stability. * This research project in supported by China National Natural Science Foundation under the contract NO: 58971944 Superalloys 718,625,706 and Various Derivatives Edited by E.A. Loria The Minerals, Metals&Materials Society, 1994