Effects of Cobalt on solidification characteristics and as-cast microstructure of an advanced nickel-based single crystal superalloys

Abstract

Containing Re and Ru, an advanced Ni-based single crystal superalloys with different cobalt (Co) content (5.9 wt.%, 9.0 wt.% and 12.0 wt.%, respectively) were investigated to study the effects of Co on solidification characteristics and as-cast microstructure. In the aspect of solidification characteristics, the solidus, especially the precipitation temperature of γ′ phase of the alloys decreases gradually with the increase of Co. Furthermore, the dendritic segregation of refractory elements, such as Re, W and Cr, is restrained. With regard to as-cast microstructure, the results show that primary dendrite spacing shorten significantly since Co increased from 5.9 to 9.0 wt.%, and the content of γ/γ′ eutectic is lowest in the alloy with 9.0 wt.% Co. The addition of Co decreases the size of γ′ and homogenizes the size of γ′ between the dendrite core and the interdendritic region. A customized heat treatment schedule is implemented for the three alloys based on the research.