# Gamma Prime Precipitation, Dislocation Densities, and TiN in Creep-Exposed Inconel 617 Alloy

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## Abstract

Inconel 617 is a solid-solution-strengthened Ni-based superalloy with a small amount of gamma prime (γ′) present. Here, samples are examined in the as-received condition and after creep exposure at 923 K (650 °C) for 574 hours and 45,000 hours and at 973 K (700 °C) for 4000 hours. The stress levels are intermediate (estimated, respectively, as of the order of 350, 275, and 200 MPa) and at levels of interest for the future operation of power plant. The hardness of the specimens has been measured in the gage length and the head. TEM thin foils have been obtained to quantify dislocation densities (3.5 × 10^{13} for the as-received, 5.0 × 10^{14}, 5.9 × 10^{14}, and 3.5 × 10^{14} lines/m^{2} for the creep-exposed specimens, respectively). There are no previous data in the literature for dislocation densities in this alloy after creep exposure. There is some evidence from the dislocation densities that for the creep-exposed samples, the higher hardness in the gage length in comparison with the creep test specimen head is due to work hardening rather than any other effect. Carbon replicas have been used to extract gamma prime precipitates. The morphology of γ′ precipitates in the ‘as-received’ condition was spheroidal with an average diameter of 18 nm. The morphology of these particles does not change with creep exposure but the size increases to 30 nm after 574 hours at 923 K (650 °C) but with little coarsening in 45,000 hours. At 973 K (700 °C) 4000 hours, the average gamma prime size is 32 nm. In the TEM images of the replicas, the particles overlap, and therefore, a methodology has been developed to estimate the volume fraction of gamma prime in the alloy given the carbon replica film thickness. The results are 5.8 vol pct in the as-received and then 2.9, 3.2, and 3.4 vol pct, respectively, for the creep-exposed specimens. The results are compared with predictions from thermodynamic analysis given the alloy compositions. Thermodynamic prediction shows that nitrogen content is important in determining the gamma prime volume fraction. This has not previously been identified in the literature. The higher the nitrogen content, the lower the gamma prime volume fraction. This may explain inconsistencies between previous experimental estimates of gamma prime volume fraction in the literature and the results here. The observed decrease in the γ′ volume fraction with creep exposure would correspond to an increase in TiN. At present, there are insufficient experimental data to prove that this predicted relationship occurs in practice. However, it is observed that there is a higher volume fraction of TiN precipitates in the gage length of a creep sample than in the head. This suggests that secondary TiN particles are precipitating at the expense of existing γ′ due to the ingress of N from the atmosphere, possibly via creep cracks penetrating in from the surface of the gage length. This effect is not expected to be observed in real components which are much larger and operate in different atmospheres. However, this highlights the need to be conscious of this possibility when carrying out creep testing.

## Keywords

Dislocation Density Gage Length Creep Specimen Carbon Replica Thermodynamic Prediction## Notes

### Acknowledgments

The authors would like to thank ALSTOM Power Ltd. for supplying creep-exposed Inconel 617 alloys and wish to thank the U.K. Government’s Technology Strategy Board for providing financial support to carry out this work. Mr. G. Clark is thanked for help with microscopy and preparing samples for TEM analysis. Dr. R. Chantry is thanked for assistance with dislocation density analysis. Professor A. Strang and Dr. G. McColvin have provided valuable advice and guidance.

## References

- 1.J.C. Hosier, and D.J. Tillack: Met. Eng. Q., 1972, vol. 12 (3), pp. 51–55.Google Scholar
- 2.R.W. Vanstone: in
*Proc. 5th International Charles Parsons Turbine Conference: Parsons 2000: Advanced Materials for 21st Century Turbine and Power Plants*, vol. 736, A. Strang, W.M. Banks, R.D. Conroy, G.M. McColvin, J.C. Neal, and S. Simpson, eds., IOM Communications, Ltd., London, 2000, pp. 91–97.Google Scholar - 3.F. Masuyama: ISIJ Int., 2001, vol. 41(6), pp. 612–625.CrossRefGoogle Scholar
- 4.R. Viswanathan, J. F. Henry, J. Tanzosh, G. Stanko, J. Shingledecker, B. Vitalis and R. Purgert: J. Mater. Eng. Perform., 2005, vol. 14(3), pp. 281-292.CrossRefGoogle Scholar
- 5.S. Chomette, J.-M. Gentzbittel and B. Viguier, J. Nucl. Mater., 2010, vol. 399, pp. 266-274.CrossRefGoogle Scholar
- 6.D. Kaoumi and K. Hrutkay, J. Nucl. Mater., 2014, vol. 454, pp. 265-273.CrossRefGoogle Scholar
- 7.A.K. Roy, M.H. Hasan and J. Pal, Mater. Sci. Eng. A, 2009, vol. A520, pp. 184-188.CrossRefGoogle Scholar
- 8.W.L. Mankins, J.C. Hosier, and T.H. Bassford: Metall. Mater. Trans. B 1974, vol. 5, pp. 2579-2590.CrossRefGoogle Scholar
- 9.Y. Hosoi, and S. Abe: Metall. Trans. A 1975, vol. 6A, pp. 1171-1178.CrossRefGoogle Scholar
- 10.S. Kihara, J.B. Newkirk, A. Ohtomo, Y. Saiga: Metall. Trans. A, 1980, vol. 11A, pp. 1019-1031.CrossRefGoogle Scholar
- 11.R. Krishna, S.V. Hainsworth, H.V. Atkinson and A. Strang: Mater. Sci. Technol., 2010, vol. 26(7), pp. 797-802.CrossRefGoogle Scholar
- 12.S. Chandra, R. Cotgrove, S.R. Holdsworth, M. Schwienheer, and M.W. Spindler: in
*Proc. ECCC Creep Conf. on Creep and Fracture in High Temperature Components-Design and Life Assessment Issues*, I.A. Shibli, S.R. Holdsworth, and G. Merckling, eds., DEStech Publications, London, 2005, pp. 178–88.Google Scholar - 13.H.-J. Penkalla, J. Wosik, E.V. Fischer, and F. Schubert: in
*Proc. 5th International Symposium on Superalloys 718, 625, 706, and Derivatives*, E.A. Loria, ed., 17–20 June 2001, Pittburgh, Pennsylvania, pp. 279–90.Google Scholar - 14.E. Gariboldi, M. Cabibbo, S. Spigarelli and D. Ripamonti: Int. J. Pressure Vessels Pip., 2008, vol. 85, pp. 63-71.CrossRefGoogle Scholar
- 15.Q. Wu, H. Song, R.W. Swindeman, J.P. Shingledecker, and V.K. Vasudevan: Metall. Mater. Trans. A, 2008, vol. 39A, pp. 2569-2585.CrossRefGoogle Scholar
- 16.O.F. Kimball, G.Y. Lai, and G.H. Reynolds: Metall. Mater. Trans. A, 1976, vol. 7A, pp. 1951-1952.CrossRefGoogle Scholar
- 17.T. Takahashi, J. Fujiwara, T. Matsushima, M. Kiyokawa, I. Morimoto, and T. Watanabe: Trans. ISIJ, 1978, vol. 18, pp. 221–224.Google Scholar
- 18.H. Kirchhöfer, F. Schubert, and H. Nickel: Nucl. Technol., 1984, vol. 66(1), 139-148.Google Scholar
- 19.K.R. Vishwakarma, N.L. Richards and M.C. Chaturvedi: Mater. Sci. Eng. A, 2008, vol. 480(1-2), pp. 517-528.CrossRefGoogle Scholar
- 20.R. Krishna, S.V. Hainsworth, S.P.A. Gill, A. Strang, and H.V. Atkinson: Metall. Mater. Trans. A, 2013, vol. 44A, pp. 1419-1429.CrossRefGoogle Scholar
- 21.P.J. Ennis and W.J. Quadakkers: in
*Proc. 7th Int. Charles Parson Turbine Conf. on Power Generation in an Era of Climate Change*, A. Strang, W.M. Banks, G.M. McColvin, J.E. Oakey, and R.W. Vanstone, eds., Institute of Materials, London, 2007, pp. 509–18.Google Scholar - 22.M. Avrami: J. Chem. Phys., 1941, vol. 9(2), pp. 177–184.CrossRefGoogle Scholar
- 23.W. Johnson and R. Mehl: Trans. Am. Inst. Min. Metall. Eng. 1939, vol. 135, pp. 416-458.Google Scholar
- 24.J.R. Yang and H.K.D.H. Bhadeshia: Weld. J. Res. Suppl., 1990, vol. 69, 305s–307s.Google Scholar
- 25.R. Hambleton, W.M. Rainforth and H. Jones: Philos. Mag. A, 1997, vol. 76(5), pp. 1093-1104.CrossRefGoogle Scholar
- 26.R.K. Ham: Phil. Mag., 1961, vol. 6, pp. 1183-1184.CrossRefGoogle Scholar
- 27.P. Hirsch, P. Howie, R.B. Nicholson, D.W. Pashley and M.J. Whelan: Electron Microscopy of Thin Crystals, Krieger, New York, N.Y. 1977.Google Scholar
- 28.N. Saunders, Z. Guo, X. Li, A.P. Miodownik, and J.-P. Schillé: in
*Superalloys 2004*, K.A. Green, T.M. Pollock, and H. Harada, eds., TMS (The Minerals, Metals & Materials Society), Warrendale, PA, 2004, pp. 849–58.Google Scholar - 29.Thermo-Calc Software AB (Version 4), http://www.thermocalc.com, SE-113 47: Stockholm, Sweden, August 2006.Google Scholar
- 30.C.P. Blankenship Jr, E. Hornbogen, and E.A. Starke Jr.: Mater. Sci. Eng. A, 1993, vol. 169A, pp. 33-41.CrossRefGoogle Scholar
- 31.Inconel alloy 617 datasheet, Publication Number SMC-029, Copyright © Special Metals Corporation, 2005.Google Scholar
- 32.S.V. Prikhodko, H. Yang, A.J. Ardell, J.D. Carnes, and D.G. Isaak, Metall. Mater. Trans. A, 1999, vol. 30A, pp. 2403-08.CrossRefGoogle Scholar
- 33.W.D. Nix and H. Gao, J. Mech. Phys. Solids, 1998, vol. 46, pp. 411–25.CrossRefGoogle Scholar
- 34.U. Krupp and H.J. Christ, Metall. Mater. Trans. A, 2000, vol. 31A, pp. 47–56.CrossRefGoogle Scholar
- 35.K. Yuan, R. Peng, X.H. Li, S. Johansson, and Y. Wang:
*MATEC Web of Conferences Vol. 14 (2014), EUROSUPERALLOYS 2014—2nd European Symposium on Superalloys and their Applications, Giens, France, May 12–16, 2014*, vol. 14, 16004. doi:10.1051/matecconf/20141416004Google Scholar - 36.J. Wosik, B. Dubiel, A. Kruka, H.-J. Penkalla, F. Schubert, A. Czyrska-Filemonowicz: Mater. Charact., 2001, vol. 46, pp. 119–123.CrossRefGoogle Scholar
- 37.I.M. Lifshitz and V.V. Slyozov: J. Phys. Chem. Solids, 1961, vol. 19, pp. 35-50.CrossRefGoogle Scholar
- 38.C. Wagner: Z. Elektrochem., 1961, vol. 65, pp. 581-591.Google Scholar
- 39.R. Krishna, S.V. Hainsworth, S.P.A. Gill, A. Strang, and H.V. Atkinson: in
*Proc. 2nd Int. ECCC Conf. on ‘Creep & Fracture in High Temperature Components—Design & Life assessment’*, I.A. Shibli and S.R. Holdsworth, eds., 21–23 April 2009, Zurich, pp. 764–76.Google Scholar