Abstract: The influence of melt superheating treatment on the solid/liquid (S/L) interface morphology of directionally solidified Ni-based superalloy DZ125 is investigated to elucidate the relationship between melt characteristic and S/L interface stability. The results indicate that the interface morphology is not only related to the withdrawal velocity (R) but also to the melt superheating temperature (T_s) when the thermal gradient of solidification interface remains constant for different T_s with appropriate superheating treatment regulation. The interface morphology changes from cell to plane at R of 1.1 μm/s when T_s increases from 1500°C to 1650°C, and maintains plane with further elevated T_s of 1750°C. However, the interface morphology changes from coarse dendrite to cell and then to cellular dendrite at R of 2.25 μm/s when T_s increases from 1500°C to 1650°C and then to 1750°C. It is proved that the solidification onset temperature and the solidification interval undergo the nonlinear variation when T_s increases from 1500°C to 1680°C, and the turning point is 1650°C at which the solidification onset temperature and the solidification interval are all minimum. This indicates that the melt superheating treatment enhances the solidification interface stability and has important effect on the solidification characteristics.

Key words: Melt superheating treatment, Directional solidification interface morphology, Solidification characteristics, Multi-component alloy