Influence of thermal exposure on microstructure and stress rupture property of a Re-containing Ni-based single crystal superalloy

In this study, the microstructural evolution and microstructure-property relationship of a Re-containing single crystal superalloy after long-term thermal exposure for up to 20,000 h at 900 °C have been investigated. The results showed that the microstructure of the experimental alloy significantly degraded after thermal exposure, including the coarsening of γʹ precipitates, the decrease of γʹ volume fraction and the morphology evolution of γʹ precipitates from cubic to spherical. The magnitude of γ/γʹ misfits decreased obviously and then remained stable. The rupture life of the alloy at 900 °C/330 MPa dropped dramatically after thermal exposure for 2000 h, which was mainly caused by the obvious reduction of γʹ volume fraction, the decreased magnitude of γ/γʹ misfits and the coarsening of γʹ precipitates. The rupture life of the alloy decreased slowly from 2000 h to 20,000 h, although γʹ size continued to increase from 680 nm to 1648 nm. The primary reason for this period was the unchanged γʹ volume fraction and the lower magnitude of γ/γʹ misfits.