Rejuvenation of hot section components of gas turbine has been conventionally carried out to assess and extend the service lifetime. In this research, an attempt was made to study the effects of rejuvenation heat treatment cycle on the restored microstructure and γ′ precipitates progression in an IN738LC vane after about 12 years of service. The received microstructure of exposed vane exhibited relatively continuous γ′ located at grain boundaries, γ-γ′ eutectic, and coarse spherical irregular-shaped γ′ precipitates. The rejuvenation heat treatments were carried out using full-solution treatment (1200 °C/2 h), followed by cooling at different quench media which are water quenching (WQ), air cooling (AC), and furnace cooling (FC). The aging heat treatments were then carried out in three modes: conventional (CHT), stabilization (SHT), and multi-stage (MHT) heat treatments. Scanning electron microscopy (SEM) indicated that the initial solution treatment stage was vital for maximum eliminating of mentioned harmful microstructural features formed through thermal exposure. It was perceived that air cooling (AC) reduced γ′ precipitate size and volume fraction compared to WQ and FC routes. It was also indicated that while CHT yields a bimodal γ′ distribution (coarse and fine γ′), SHT offers uniformly distributed medium-sized γ′ phase. Also, the novel MHT cycle created a dual-mode γ′ amount with a higher coarse γ′ precipitates. Moreover, a theoretical model for microstructure changes of rejuvenated alloy was suggested. Lastly, an adjusted rejuvenation heat treatment cycle was suggested which can enhance high-temperature durability of the stationary vanes.

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