Effects of Ru on the microstructure and phase stability of a single crystal superalloy

Abstract

Two experimental single crystal superalloys, the Ru-free alloy and the Ru-containing alloy with [001] orientation, were cast in a directionally solidified furnace, while other alloying element contents were kept unchanged. The effects of Ru on the microstructure and phase stability of the single crystal superalloy were investigated. γ′ directional coarsening and rafting were observed in the Ru-free alloy and Ru-containing alloy after long-term aging at 1070°C for 800 h. Needle-shaped σ topologically close packed (TCP) phases precipitated and grew along the fixed direction in both the alloys. The precipitating rate and volume fraction of TCP phases decreased significantly by adding Ru. The compositions of γ and γ′ phases measured using an energy-dispersive X-ray spectroscope (EDS) in transmission electron microscopy (TEM) analysis showed that the addition of Ru lessened the partition ratio of TCP forming elements, Re, W and Mo, and decreased the saturation degrees of these elements in γ phase, which can enable the Ru-containing alloy to be more resistant to the formation of TCP phases. It is indicated that the addition of Ru to the Ni-based single crystal superalloy with high content of the refractory alloying element can enhance phase stability.

Keywords

superalloys / nickel alloys / single crystals / ruthenium / microstructure / phase stability

References

[1] G.L. Erickson, The development and application of CMSX-10, [in] Superalloys 1996, Pennsylvania, 1996, p.35.

[2] W.S. Walston, K.S. O’Hara, E.W. Ross, T.M. Pollock, and W.H. Murphy, René N6: Third generation single crystal superalloy, [in] Superalloys 1996, Pennsylvania, 1996, p.27.

[3] Fuchs G.E. Solution heat treatment response of a third generation single crystal Ni-base superalloy. Mater. Sci. Eng. A, 2001, 300, 52

[4] Acharya M.V., Fuchs G.E. The effect of long term thermal exposures on the microstructure and properties of CMSX-10 single crystal superalloys. Mater. Sci. Eng. A, 2004, 381, 143

[5] O. Lavigne, C. Ramusat, S. Drawin, P. Caron, D. Boivin, and J.L. Pouchou, Relationships between microstructural instabilities and mechanical behavilour in new generation nickel-based single crystal superalloys, [in] Superalloys 2004, Pennsylvania, 2004, p.667.

[6] Yeh A.C., Tin S. Effect of Ru on the high temperature phase stability of Ni-base single crystal superalloys. Metall. Mater. Trans. A, 2006, 37, 2621

[7] Hobbs R.A., Zhang L., Rae C.M.F., Tin S. The effect of ruthenium on the intermediate to high temperature creep response of high refractory content single crystal nickel-base superalloys. Mater. Sci. Eng. A, 2008, 489, 65

[8] Carroll L.J., Feng Q., Mansfield J.F., Pollock T.M. Elemental partitioning in Ru-containing nickel-base single crystal superalloys. Mater. Sci. Eng. A, 2007, 457, 292

[9] Y.F. Han, W.Y. Ma, Z.Q. Dong, S.S. Li, and S.K. Gong, Effect of ruthenium on microstructure and stress rupture properties of a single crystal nickel-base superalloy, [in] Superalloys 2008, Pennsylvania, 2008, p.91.

[10] D. Argence, C. Vernault, Y. Desvallees, and D. Fournier, MC-NG: A 4th generation single crystal superalloy for future aeronautical turbine blades and vanes, [in] Superalloys 2000, Pennsylvania, 2000, p.829.

[11] S. Walston, A. Cetel, R. MacKay, K. O’Hara, D. Duhl, and R. Dreshfield, Joint development of a fourth generation single crystal superalloy, [in] Superalloys 2004, Pennsylvania, 2004, p.15.

[12] Sato A., Harada H., Yokokawa T., Murakumo T., Koizumi Y., Kobayashi T., Imai H. The effect of ruthenium on the phase stability of fourth generation Ni-base single crystal superalloys. Scripta Mater., 2006, 54, 1679

[13] Shi Z.X., Li J.R., Liu S.Z., Luo Y.S., Zhao J.Q. Effect of Hf content on the microstructures and stress rupture properties of DD6 single crystal superalloy. Rare Met. Mater. Eng., 2010, 39(8): 1334

[14] Pyczak F., Neumeier S., Göken M. Influence of lattice misfit on the internal stress and strain states before and after creep investigated in nickel-base superalloys containing rhenium and ruthenium. Mater. Sci. Eng. A, 2009, 510–511, 295.

[15] K.S. O’Hara, W.S. Walston, E.W. Ross, and R. Darolia, Nickel Base Superalloy and Article, U.S. Patent, No.5482789, 1996.

[16] S. Neumeier, F. Pyczak, and M. Göken, The influence of Ruthenium and Rhenium on the local properties of the γ- and γ′-phase in Nickel-base superalloys and their consequences for alloy behavior, [in] Superalloys 2008, Pennsylvania, 2008, p.109.

[17] C.M.F. Rae, M.S.A Karunaratne, C.J. Small, R.W. Broomfield, C.N. Jones, and R.C. Reed, Topologically close packed phases in an experimental rhenium-containing single crystal superalloy [in] Superalloys 2000, Pennsylvania, 2000, p.767.