Mechanism of TCP Phase Suppression and γ' Phase Size Regulation in Ni‐Based Alloys by Supersolidus Solution Heat Treatment

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Abstract
This study examines the impact of supersolidus solution heat treatment (SSHT) on the suppression of topologically close‐packed (TCP) phases and the regulation of γ′ phase size in two CMSX‐4 nickel‐based single‐crystal superalloys with varying Re contents (3% and 5%). The results indicate that increasing the solution termination temperature or extending the holding time effectively suppresses TCP phase formation. In the 5% Re alloy, TCP phases that form after 35 h at 1340°C are eliminated by either extending the holding time to 50 h or raising the temperature to 1350–1360°C. The average γ′ phase size is influenced by the melting zone. In the 3% Re alloy, it shows little variation. While in the 5% Re alloy, it initially decreases, then increases at 1340°C, reaching a minimum of approximately 0.36 µm after 35 h. At 1350°C, the size refines from 0.41 to 0.34 µm between 15 and 35 h, but subsequently coarsens and spheroidizes to approximately 0.52 µm after 50 h. Higher temperatures expedite the process of spheroidization. This research emphasizes that SSHT effectively suppresses TCP phases. Nonetheless, excessive temperature or prolonged duration leads to spheroidization of the γ′ phases due to excessive melting.

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