Morphological evolution of γ′ phase in K465 superalloy during prolonged aging

The specimens of K465 superalloy were aged, respectively at 850, 950 and 1050 °C in order to investigate morphological changes of γ′ phase. The γ′ precipitates had the cubic shape and regular alignment with the positive and larger misfit before 800 h at 850 °C, 600 h at 950 °C, and 100 h at 1050 °C. When the tested alloy was aged from 600 to 1000 h at 950 °C and 100–300 h at 1050 °C, γ′ precipitates were coalesced and gradually lost the cubic morphology, and the magnitude of lattice misfit between γ and γ′ phases was gradually decreased with the increase of aging time. The γ′ precipitates were elongated into plate with the negative misfit of smaller absolute value, and the misfit magnitude was decreased with the increase of aging time after 1000 h at 950 °C and 300 h at 1050 °C. The loss of the cubic shape of γ′ precipitates was caused by the reduction of misfit magnitude and the movement of dislocation into γ′ precipitates. The formation of elongated γ′ precipitates was related to the negative misfit of smaller absolute value and the dislocation networks and wall formed at the γ′/γ interfaces.