Effects of Ta on microstructural stability and mechanical properties of hot corrosion resistant Ni-based single crystal superalloys during long-term thermal exposure

The effects of Ta on microstructural stability and mechanical properties of hot corrosion resistant Ni-based single crystal superalloys during long-term thermal exposure at 900 °C were investigated in the present study by comparing two experimental alloys with different content of Ta (6Ta and 6.7Ta). The results indicated that the addition of extra 0.7Ta increased the volume fraction of the γ′ precipitates and accelerated the coarsening rate of γ′ precipitates, facilitated the formation of misfit dislocation and precipitation of σ phases. The 6.7Ta alloy exhibited higher hardness and better stress rupture properties than 6Ta and the variations of stress rupture properties during the exposure for 6Ta and 6.7Ta alloy are significantly different. The effects of γ′ coarsening, formation of σ phases and misfit dislocations were taken into consideration to identify the reasons of variations of mechanical properties during the thermal exposure.