Structure stability of Ni-Cr-Co base superalloy aged at 704 ℃ and 760 ℃

Thermodynamic calculation, SEM, TEM, XRD, phase extraction and chemical analysis were employed to study the structure stability of a new Ni-Cr-Co base superalloy aged at 704 ℃ and 760 ℃ for long time. The results show that the precipitates of alloy standard heat-treated and heat-treated at 704 ℃ and 760 ℃ for time up to 2 000 h are γ′, MC, M 23C 6 and M 6C, and η phases are also formed at grain boundaries and in the matrix of sample heat-treated at 760 ℃ as well. With increase in aging time, the mass fractions of γ′(+η), MC, M 23C 6 and M 6C in all samples have no large changes and their chemical compositions are stable at the same temperature, but the γ′ precipitates grow obviously. The γ′-to-η transformation in sample heat-treated at 760 ℃ takes place with prolonged aging time. The η precipitates form a Widmansttten pattern in samples heat-treated at 760 ℃. The new alloy maintains a better structure stability during prolonged aging at 704 ℃, but a worse structure stability during prolonged aging at 760 ℃.