Abstract: INCONEL725 is a highly corrosion resistant nickel based alloy capable of being age-hardened to high strength levels.The microstructure observations and the phase iden-tification after a standard heat treatment were investiguted.The results show that the precipitation phases include the strengthening phases γ′，γ″and δ phase,pri-mary carbide phase TiC,as well as M6C corbide and a little extent MC(mainly TiC) precipitates which nucleate mainly at grain boundaries.An isothermal aging study was carried out on this alloy for up to 10000 hours at 599℃.This additional aging did not affect the tensile strength.However,microstructures show that the thermal exposure has a little additional effect.With increasing the exposure time,the size of γ″ phase slightly increases,almost no change for γ′ phase,while M6C carbides pre-cipitated at grain boundaries have an increased and complex tendency on a few grain boundaries.The experimental results illustuate the excellent structure stability of the age-hardenable IN725 at 599℃.

Key words: superalloy, INCONEL725, microstructure,