Synergistic effect of ruthenium and rhenium on microstructure stability of advanced single crystal superalloys

Abstract

In order to study the influence mechanisms of microstructure stability of high generation single crystal superalloys, the D1 and D2 alloys which contain 6%(mass fraction) Ru and 4.5%Ru respectively were prepared after complete heat treatment and long-term aging at 980 ℃ for 1000 h. The microstructure and alloying element distribution at different scales were examined and the results were analyzed combining with thermodynamic calculation. The results show that there are still high content of refractory elements segregating in the dendrite region after complete heat treatment, inducing to TCP precipitation in the dendrite after long-term aging. Ru and Re are the main forming elements of TCP in both D1 and D2 alloys, and more TCP phase precipitates in D1 alloy which contains more Ru than in D2 alloy. Because both Ru and Re can increase the d-orbital energy level of single crystal superalloy, higher Ru and Re content leads to more TCP phase precipitation. However, since Ru can reduce the segregation degree of Re in γ phase, the increase of Ru content can reduce the adverse effect of Re on the microstructure stability of single crystal superalloy. In this study, Ru plays a more significant role in promoting TCP phase precipitation, leading to more TCP phase precipitating in D1 alloy than in D2 alloy after long-term aging at 980 ℃ for 1000 h.

Keywords

• single crystal superalloy
• ruthenium
• rhenium
• tcp phase
• synergistic effect