Microstructural changes and mechanical properties of Incoloy 800 after 15 years service

Microstructure and mechanical properties of Incoloy 800 superalloy before (as-received) and after 15 years service exposure were evaluated. The metallurgical variations such as formation and growth of the secondary precipitates, phase transformation of titanium carbide to Cr23C6 + Ni16Ti6Si7 and decomposition of primary carbides were characterized during the long-term service of Alloy 800. It was shown that some of chromium and iron elements were moved from solid solution to the carbides during the service exposure. It was found that due to the formation of precipitates during service, the strength and hardness of Alloy 800 were improved, while the ductility and toughness were reduced.