Rejuvenation heat treatment of service-degraded FSX-414 cobalt-based Superalloy: Microstructural restoration and enhanced creep resistance

Creep behavior of service-degraded FSX-414 cobalt-based superalloy after long-term exposure at 850 °C was investigated. The degraded microstructure is characterized by continuous M 23 C 6 carbide networks along grain boundaries, coarsened precipitates, and partial dissolution of eutectic carbides, leading to reduced mechanical performance. A rejuvenation heat treatment (1180 °C/4 h + 980 °C/10 h) was applied to restore the degraded structure. Microstructural analysis revealed the transformation of continuous grain boundary carbides into fine, discrete M 23 C 6 precipitates with a more uniform distribution. Creep tests at 850 °C under 110 MPa demonstrated a significant improvement after treatment. The creep life increased from 27.84 h to 97.34 h (≈250% increase), while the steady-state creep rate decreased markedly. In addition, the total strain was significantly reduced from 12.86% to 0.85%, indicating a substantial improvement in deformation resistance. The enhanced performance is attributed to refined carbide morphology and improved microstructural homogeneity, suppressing grain boundary sliding and dislocation motion. These findings demonstrate that rejuvenation treatment is an effective strategy for extending the service life of high-temperature components.