Effect of Ru on stress rupture properties of nickel-based single crystal superalloy at high temperature

Two experimental single crystal superalloys, Ru-free alloy and Ru-containing alloy with [001] orientation, other alloying element contents being basically kept same, were cast in the directionally solidified furnace. The effect of Ru on the stress rupture properties of the single crystal superalloy was investigated at (980°C, 250 MPa), (1100°C, 140 MPa) and (1120°C, 140 MPa). The results show that Ru can enhance high temperature stress rupture properties of single crystal superalloy. The improvement effect of Ru addition on stress rupture properties decreases with increasing test temperature. The γ′ coarsening and rafting directionally are observed in Ru-free alloy and Ru-containing alloy after stress rupture test. Needle shaped TCP phases precipitated in both of alloys after stress rupture test at (1100°C, 140 MPa) and (1120°C, 140 MPa) and no TCP phase was observed in both of alloys after stress rupture test (980°C, 250 MPa). The precipitate volume fraction of TCP phases is significantly decreased by the addition of Ru. At last, the relationship between the microstructure change with Ru addition and improvement of stress rupture properties was discussed.