Surface recrystallization of a single crystal nickel-base superalloy

Abstract

The recrystallization behavior of a single crystal nickel-base superalloy was investigated by shot peening and subsequent annealing. Two kinds of recrystallization microstructures, which are intensively dependent on the annealing temperature, are shown in the nickel-base superalloy after shot peening and subsequent annealing. Surface recrystallized grains are obtained when the superalloy is annealed at solution treatment temperature. The nucleation of recrystallization originates from the dendritic core, where rapid dissolution of γ′ particles occurs. Cellular recrystallization is observed after annealing at lower temperatures. Cellular structures induced by high diffusivity of the moving boundary and more γ′ particles dissolution led by residual stress are developed from the surface region. Recrystallized kinetics of the shot-peened alloy annealed at 1050°C accords with the Johnson-Mehl-Avrami-Kolmogorov equation. The low Avrami exponent is caused by the inhomogeneous distribution of stored energy, the decreasing of stored energy during recovery, and the strong resistance of boundary migration by γ′ particles.

Keywords

nick-base superalloy / single crystals / recrystallization / shot peening / annealing

References

[1] Wang D.L., Jin T., Yang S.Q., et al. Surface recrystallization and its effect on rupture life of SRR99 single crystal superalloy. Mater. Sci. Forum, 2007, 546–549, 1229.

[2] Jo C.Y., Cho H.Y., Kim H.M. Effect of recrystallisation on microstructural evolution and mechanical properties of single crystal nickel base superalloy CMSX-2: Part 1. Microstructural evolution during recrystallization of single crystal. Mater. Sci. Technol., 2003, 19(12): 1665.

[3] Paul U., Sahm P.R., Goldschmidt D. Inhomogeneities in single-crystal components. Mater. Sci. Eng. A., 1993, 173(1–2): 49.

[4] Ohta Y., Nakagawa Y.G., Tsuji J. Recrystallization behavior of nickel-base single crystal superalloys. J. Jpn. Inst. Metals, 1990, 54(1): 84.

[5] Bürgel R., Portella P.D., Preuhs J. Recrystallization in single crystals of nickel base superalloys. Superalloys 2000, 2000 Warrendale, TMS, 229.

[6] Okazaki M., Hiura T., Suzuki T. Effect of local cellular transformation on fatigue small crack growth in CMSX-4 and CMSX-2 at high temperature. Superalloys 2000, 2000 Warrendale, TMS, 505.

[7] Fuchs G.E. Solution heat treatment response of a third generation single crystal Ni-base superalloy. Mater. Sci. Eng. A, 2001, 300(1–2): 52.

[8] Porter A., Ralph B. The recrystallization of nickel-base superalloys. J. Mater. Sci., 1981, 16(3): 707.

[9] Mahajan S., Pande C.S., M. A., et al. Imam, Formation of annealing twins in f.c.c. crystals. Acta Mater., 1997, 45(6): 2633.

[10] Hupalo M.F., Padilha A.F., Sandim H.R.Z. Cold swaging, recovery and recrystallization of oligocrystalline incoloy MA956: Part II. Annealed state. ISIJ Int., 2004, 44(11): 1902.

[11] Humphreys F.J., Hatherly M. Recrystallization and Related Annealing Phenomena, 2004 2nd ed. New York, Elsevier, 232.