Influence of solidification history on precipitation behavior of TCP phase in a completely heat-treated Ni3Al based single crystal superalloy during thermal exposure

The influence of solidification history on unstressed long-term microstructure stability of TCP in completely heat-treated Mo-rich Ni3Al based single crystal superalloys with cellular and dendritic as-cast microstructures was studied by experimental analysis and the thermodynamic calculation (by JMatPro). High temperature solution treatment can completely eliminate microsegregation of alloying elements in both as-cast cellular and dendritic samples, whereas, the influence of as-cast microstructure (solidification history) on the composition of γ phase cannot be eliminated by solution treatment: Mo, Cr and Re contents of γ phases in as-cast and heat-treated dendritic samples were both higher than those in cellular samples. Meanwhile, as compared with heat-treated cellular sample, higher area fraction of TCP phase in heat-treated dendritic sample was due to higher supersaturation degree of γ phase, rather than the difference in the microsegregation behavior of alloying elements. Even so, TCP phases in both long-term aged cellular and dendritic samples were found to be Mo-, Cr- and Re-rich P phases with close compositions.