The Microstructural Evolution of Inconel Alloy 740 During Solution Treatment, Aging, and Exposure at 760 °C

Abstract

In this study, the microstructural evolution of Inconel alloy 740 during solution treatment and aging was characterized using optical and scanning electron microscopy. During double solution heat treatment, carbon is liberated from the dissolution of MC carbides during the first solution treatment at 1150°C, and fine MC carbides are precipitated on gamma grain boundaries during the second solution treatment at 1120°C. Due to the concurrent decrease in carbon solubility and the increase in the contribution of grain boundary diffusion at lower temperatures, the MC carbides on the gamma grain boundaries provide a localized carbon reservoir that aids in M 23 C 6 carbide precipitation on gamma grain boundaries during exposure at 760°C. The c¢ phase, which is the key strengthening phase in alloy 740, is incorporated into the alloy microstructure during aging at 850°C. The main source of microstructural instability observed during exposure at 760°C was the coarsening of the c¢ phase.

Variations in overall- and phase-hardness of a new Ni-based superalloy during isothermal aging

“…The Inconel 740, a relatively new member of Ni-based superalloy family, was developed for the applications to steam boiler tubing in 'Advanced Ultra-SuperCritical (A-USC)' fossil power plants [1][2][3][4]. Since the target steam condition of the new boiler system is above 375 bar and 700 • C, this alloy was designed to have excellent performances (such as good microstructure stability, high resistance to coal-ash-corrosion/oxidation, and high creep-rupture strength) at high temperature up to 770 • C [1][2][3][4].…”

“…Since the target steam condition of the new boiler system is above 375 bar and 700 • C, this alloy was designed to have excellent performances (such as good microstructure stability, high resistance to coal-ash-corrosion/oxidation, and high creep-rupture strength) at high temperature up to 770 • C [1][2][3][4].…”

Effects of long term thermal exposure on microstructure and mechanical property evolution of a new wrought Ni–Fe based superalloy

“…1 shows the equilibrium phase diagram based on the chemical composition of the alloy. It seems that the main phases are similar to that of the precipitation-strengthened Ni-base superalloys [16]. The main strengthening phase is γ , which precipitates at 935°C.…”

High-temperature microstructural evolution and quantification for alloys IN740 and IN740H: comparative study

“…It is usually found in regions where the Cr rich M 23 C 6 also develop. The benefit of such phase at low volume fractions is still controversial although it is generally accepted that its absence is preferable [10][11][12]. At 750 o C the presence of η phase becomes a factor to strongly take into account.…”