Microstructural Evolution of an Experimental Third Generation Single Crystal Superalloy after Long-term Thermal Exposure at 1100 °C

The effects of thermal exposure at 1100 °C for 100∼800 h on microstructure of an experimental third generation single crystal superalloy were investigated. The γα particles in dendrite core gradually become coarsen and very irregular by γα precipitates dissolving resulting from elements diffusion with increasing exposure time. The γα precipitates in interdendritic region vary from cuboidal morphology, fusing together, and rafting with the increase of exposure time. The various γα particles behaviors between dendritic core and interdendritic region are attributed to the segregation of refractory elements. After 300 h a small amount of needle-shaped TCP phases are found in dendrite core and the mount of TCP phases increases with increasing exposure time. There is no TCP phase in interdendritic region until 800 h. TEM and EDX measurements show that TCP phases observed in these samples are identified as σ phase enriched Re and W elements.