Alloy Design and Processing Challenges for Advanced Power Systems: An Alloy Producer’s Perspective

Abstract:

The alloys required for fossil fuel power systems are transitioning from stainless steels that operate below 600oC to nickel-based alloys that can operate up to 760oC in advanced ultra-super critical steam turbines. This transition brings with it major metallurgical as well as economic challenges related to alloy design, melt processing, and fabrication of these large size components. The alloys, in general, must maintain creep resistance over 100,000 hours of service life while at the same time maintaining resistance to severe steam oxidation and general oxidation. A need exists for nickel-based alloys that are not only highly alloyed, but are also impervious to phase instabilities during initial processing and service. The potential exists for severe segregation when casting large ingots. This possibility must be dealt with during thermo-mechanical processing to obtain the wrought structures that can be inspected to design defect levels. This paper will detail these challenges as they have been addressed in smaller aerospace turbines and discuss strategies to overcome these problems. New computational modeling tools will play a critical role in engineering solutions for alloy design, solidification, forging, and heat treatment. Since any solution also needs to be economically viable, the paper also discusses processing cost issues in terms of the process yields and operational strategies. The use of powder metallurgy will also be reviewed as a cost effective alternative to alloys that have traditionally been cast-wrought processed.

• Periodical: Advances in Science and Technology (Volume 72)
• Pages: 22-30
• DOI: https://doi.org/10.4028/www.scientific.net/AST.72.22
• Online since: October 2010
• Authors: Gernant E. Maurer, Ashish D. Patel
• Keywords: Creep, Creep Resistant Alloy, ESR, Freckles, Phase Stability, Powder Metallurgy (PM), Sigma Phase, Superalloy, Ultra Supercritical , VAR

References

[1] P.J. Maziasz, I.G. Wright, J.P. Shingledecker, T. B Gibbons, R.R. Romanosky, Defining the Materials Issues and Research Needs for Ultra-Supercritical Steam Turbines, Fourth International Conference on Advances in Materials Technology for Fossil Power Plants; Hilton Head Island, SC; 25-28 Oct. 2004. pp.602-622. (2005).

[2] J.P. Shingledecker and I.G. Wright, Evaluation of the Materials Technology Required for a 760°C Power Steam Boiler, Materials for Advanced Power Engineering 2006. Proceedings, 8th Liege Conference, Liege, Belgium, 18-20 Sept. 2006, pp.107-119.

[3] R. Blum and R.W. Vanstone, Materials Development for Boilers and Steam Turbines Operating at 700°C, Proceedings of the Fourth International Conference of Advances in Materials Technology for Fossil Power Plants, Hilton Head Island, South Carolina, (2004).

[4] P. W. Keefe, S. O. Mancuso and G. E. Maurer, Effects of Heat Treatment and Chemistry on the Long-Term Phase Stability of a High Strength Nickel-Based Superalloy, Superalloys 1992. Proceedings of 7th International Symposium on Superalloys, Seven Springs, Pennsylvania, (1992).

DOI: 10.7449/1992/superalloys_1992_487_496

[5] F. Tancret, H. K. D. H. Bhadeshia, and D. J. C. MacKay, Design of a Creep Resistant Nickel Base Superalloy for Power Plant Applications Part 1 – Mechanical Properties Modelling, Materials Science and Technology, Vol 19, Mar. 2003, pp.283-290.

DOI: 10.1179/026708303225009788

[6] R.F. Decker, Strengthening Mechanisms in Nickel-Base Superalloys, Proceedings: Steel Strengthening Mechanism Symposium, Zurich, Switzerland, May 5 - 6, (1969).

[7] U.S. Geological Survey, 2009, Nickel statistics, in Kelly, T.D., and Matos, G.R., comps., Historical statistics for mineral and material commodities in the United States: U.S. Geological Survey Data Series 140, available online at http: /minerals. usgs. gov/ds/2005/140/nickel. pdf, Apr. 12, 10.

[8] U.S. Geological Survey, 2009, Cobalt statistics, in Kelly, T.D., and Matos, G.R., comps., Historical statistics for mineral and material commodities in the United States: U.S. Geological Survey Data Series 140, available online at http: /minerals. usgs. gov/ds/2005/140/cobalt. pdf, Apr. 12, 10.

[9] P. W. Schilke, J. J. Pepe, and R. C. Schwant, Alloy 706 Metallurgy and Turbine Wheel Application, Proceedings of the International Symposium on Superalloys 718, 625, 706 and Various Derivatives, Pittsburgh, Pennsylvania, (1994) pp.1-12.

DOI: 10.7449/1994/superalloys_1994_1_12

[10] A. D. Patel, M. Gierulal, D. J. Tallman, Bounds on Model Parameteres for Computational Analysis of the ESR Process, International Symposium on Liquid Metal Proceessing and Casting, Santa Fe, New Mexico, Sept. 20-23 2009, pp.201-212.

[11] P. Auburtin, T. Wang, S. L. Cockcroft, and A. Mitchell, Freckle Formation and Freckle Criterion in Superalloy Castings, Metallurgical and Materials Transactions B, Vol 31B, Aug. 2000, pp.801-811.

DOI: 10.1007/s11663-000-0117-9

[12] J.A. Van Den Avyle, J. A. Brooks, and A. C. Powell, Reducing Defects in Remelting Processes for High-Performance Alloys, JOM, 50 (3) (1998), pp.22-25, 49.

DOI: 10.1007/s11837-998-0374-7

[13] J. A. Dantzig and M. Rappaz, Solidification, EPFL, Switzerland (2009).

[14] K. Kajikawa, T. Sato, and H. Yamada, Freckle tendencies of Ni-Based Superalloys, International Symposium on Liquid Metal Proceessing and Casting, Santa Fe, New Mexico, Sept. 20-23 2009, pp.327-335.

[15] L. A. Jackman, G. E. Maurer, and S. Widge, White Spots in Superalloys, Proceedings of the International Symposium on Superalloys 718, 625, 706 and Various Derivatives, Pittsburgh, Pennsylvania, (1994) pp.153-166.

DOI: 10.7449/1994/superalloys_1994_153_166

[16] R. C. Sun, Determination of the Forging-Heating Schedule for a Large HASTELLOY, Alloy X Ingot, Metallurgical Transctions, vol 1 July 1970, pp.1881-1887.

DOI: 10.1007/bf02642787

[17] G. E. Maurer and A. D. Patel, Melt Processing of Superalloys: Past, Present and Future Needs, International Symposium on Liquid Metal Proceessing and Casting, Santa Fe, New Mexico, Sept. 18-21 2005, pp.185-194.

[18] D. J. Novotnak, G. E. Maurer, L. W. Lherbier, J. F. Radavich, Ed by Roger C. Reed et all. Effect of Thermal History on the Properties and Microstructure of a Large HIPed PM Superalloy Billet, Proceedings of the Eleventh International Symposium on Superalloys, Champion, Pennsylvania, (2008).

DOI: 10.7449/2008/superalloys_2008_339_343