Effect of Aging Time at High Temperature on Microstructural Evolution Behavior of a Nickel-Based Single Crystal Superalloy

The microstructural evolution behavior of one kind of nickel-based single crystal superalloy aged at elevated temperature was investigated. The short-term exposures were performed at 980, 1050 and 1100 °C for 20, 50 and 100 h, and long time agings were carried on from 200 to 800 h at 1100 °C. Microstructure observation was carried out by field emission scanning electron microscope (FE-SEM). Electron Probe Micro Analyzer (EPMA) was employed to determine the composition of TCP phase. The microhardness was tested to all the aged specimens. The results show that in short-term aging, the coarsening of γ′ particles in this superalloy follows the standard r3-t kinetics of diffusion-controlled particle growth and coarsening rate constants were calculated. During long-term aging, for samples exposed for 400 h at 1100 °C, the rafted structure has developed completely and TCP precipitates has formed. The composition of TCP phase is mainly composed of Re and W. In addition, under some conditions of short time aging, TCP phases are found to precipitate from the alloy. The microhardnesses of all the aged specimens exhibit no obvious changes.