In-situ Observation of Solidification Process of GH4169 Superalloy at Different Cooling Rates

The solidification process of the GH4169 superalloy was in-situ observed at the cooling rate of 5, 50, 200 K·min-1 by means of confocal laser scanning microscopy combined with an infrared image furnace. The variation of solid phase content at the free surface and temperature as well as time was calculated by image process software. Using optical microscopy to observe the solid microstructure of the superalloy cooled at different rates, the secondary dendrite arm spacing of the alloy cooled at different rates was calculated. The results show that with the decrease of temperature during the GH4169 superalloy solidification process, the dendrite grew continuously and the new nucleation formed. The dendrite structure refined obviously with increasing the cooling rate. The transformation process of solid to liquid was in order of initial stable increasing stage, stable and rapid growth stage and residual liquid transformation stage. The increase of cooling rate led to the decrease of secondary dendrite arm spacing after solidification, and the precipitates got more uniform and fine.