Insights into the effects of Re and Ta on TCP phase evolution in nickel-based SX superalloys: Experimental and simulation analysis

This study explores the effects of Re and Ta interactions on TCP (topologically close-packed) phase precipitation in experimental alloys under long-term thermal exposure. TCP phase is thoroughly examined and analyzed in terms of its location, morphology evolution, structural identification, and phase transition, employing thermodynamic calculations and first-principles analysis. The main findings indicate that the standard heat treatment used in the experiment does not fully eliminate microstructure segregation. Particularly, W and Re exhibit significant segregation in the dendrite region, resulting in preferential TCP phase formation in this region. Re induces destabilization of the gamma-matrix and greatly enhances TCP phase precipitation, whereas Ta enhances the supersaturation of the gamma-matrix. The interaction between Ta and Re further enhances the precipitation of the TCP phase. Thermodynamic calculations and first-principles analysis indicate that Re significantly improves the driving force of TCP phase precipitation from the gamma-matrix, whereas the effect of Ta is found to be slight. Under thermal exposure at 900 degrees C, the sigma-phase is firstly observed in the 8Ta2Re alloy, exhibiting a long needle-like shape, followed by subsequent evolutions resulting in the transition to the P-phase. The phase transition from the sigma-phase to the P-phase is governed by the diffusion of elements, with Ni playing a crucial role in continuous diffusion.

Automated summary

This study investigates the effects of Re and Ta interactions on the precipitation of the TCP phase in experimental alloys under long-term thermal exposure. The study finds that microstructure segregation is not fully eliminated even with standard heat treatment, and the interaction between Re and Ta enhances the formation of the TCP phase. Thermodynamic calculations and first-principles analysis reveal that Re significantly improves the driving force of TCP phase precipitation. The study also observes a phase transition from the sigma-phase to the P-phase, with Ni playing a crucial role in the diffusion process.