Investigation on long-term creep rupture properties and microstructure stability of Fe-Ni based alloy Ni-23Cr-7W at 700°C

Long-term creep rupture properties and microstructural stability of Fe-Ni based alloy Ni-23Cr-7W (HR6W, ASME Code Case 2684) were experimentally investigated. Crept specimens at 700 degrees C for durations up to 37,667 h were chosen, the microstructure evolution during creep was characterized. Besides the MC and M23C6 carbides found in the as-received sample, the formation of alpha-W phase, alpha-Cr phase and Laves phase in crept samples were confirmed with scanning/transmission electron microscopes. Statistical quantitative image analysis was used to evaluate the precipitation behavior and growth kinetics for the main strengthening precipitate, Laves phase. The alloy was proven to have good microstructural stability without observable coarsening of strengthening precipitates during long-term creep up to around 37,667 h. It was also verified that the growth kinetics of Laves phase can be well described by the Johnson-Mehl-Avrami-Kolmogorov equation. (C) 2012 Elsevier B.V. All rights reserved.