Microstructural analysis of creep exposed IN617 alloy

Nickel base alloys such as IN617 are one of the preferred choices for steam turbine components used by fossil fuelled power generation plants. IN617 is a solid-solution-strengthened nickel-based superalloy containing ~23% Cr, 12% Co, and 9% Mo with low content of precipitation-strengthening elements Al, Ti and Nb. In the ‘as-received’ (solution-annealed condition), the microstructure consists of primary carbides (M23C6) and occasional TiN particles dispersed in a single-phase austenitic matrix. Owing to high temperature exposure and the creep deformation processes that occur in-service, evolution of the microstructure occurs. This results in secondary precipitation and precipitate coarsening, both on grain boundaries and intragranularly in areas of high dislocation density. The influence of creep deformation on the solution-treated IN617 alloy at an operating condition of 650˚C/574 Hrs, with emphasis on the morphology and distribution of carbide/nitride precipitation is discussed. The applied stress was at an intermediate level.