Metallography Evaluation of Cast and Wrought Ni-Base Superalloys

Abstract:

. The Ni-base superalloys have an interesting history and evolution since they start to be used in aero jet engines. Microstructures of superalloys have dramatically changed through the years as modern technology of its casting or forging becomes more sophisticated. The first superalloys have polyedric microstructure consist of gamma solid solution, some fraction of gamma prime and of course grain boundaries. As demands on higher performance of aero jet engine increases, the changes in superalloys microstructure become more significant. Further step in microstructure evolution was directionally solidified alloys with columnar gamma prime particles. The latest microstructures are mostly monocrystalline, oriented in [001] direction of FCC gamma matrix. What does not changed through the years is elementary FCC structure of matrix and fundamental group of alloying elements. All microstructure changes bring necessity of proper preparation and evaluation of microstructure. Except already mentioned structures have gamma double prime and various carbides form appear. These structural parameters have mainly positive influence on important mechanical properties of superalloys. However, some detrimental phases as Laves, σ-phase appears as well and have negative influence on heat resistance of superalloys. Paper deals with such microstructural evaluation of both groups of alloys – cast and wrought as well. Microstructure evaluation helps to describe mechanism at various loading and failure of progressive superalloys. Such example where microstructure evaluation is employed is fractography of failure surfaces after fatigue tests, which are as example of metallography evaluation described in this paper as secondary objective. Fatigue test done in this article were at high frequency with push-pull loading, so called high frequency fatigue loading (HFFL) and at low frequency three point flexure, so called low frequency fatigue loading (LFFL).

• Periodical: Materials Science Forum (Volume 891)
• Pages: 414-419
• DOI: https://doi.org/10.4028/www.scientific.net/MSF.891.414
• Online since: March 2017
• Authors: Juraj Belan*, Alan Vaško, Lenka Kuchariková, Eva Tillová
• Keywords: Gamma Double Prime, Gamma Prime, Gamma Solid Solution, Light Microscopy, Ni-Base Casting, Scanning Electron Microscopy (SEM), Wrought Alloys

References

[1] J.F. Radavich, Electron Metallography of Alloy 718, in: E.A. Loria (Ed. ), Superalloys 7X3, 625, 706 and Various Derivatives, The Minerals, Metals &Materials Society, 1997, pp.17-26.

DOI: 10.7449/1997/superalloys_1997_17_26

[2] G. Vander Voort, E.P. Manilova, Metallographic Techniques for Superalloys, Microscopy and Microanalysis S02 (2004) 690-691.

DOI: 10.1017/s1431927604883442

[3] Information on http: /www. georgevandervoort. com/metallography/general/nickel-alloys/ 20001279-metallography-of-superalloys. html.

[4] J. F. Radavich, Metallography of Alloy 718, Journal of Metals 40 (1988) 42.

[5] P. Skočovský, T. Podrábsky, Colour metallography of ferrous alloys, EDIS, Žilina, (2001).

[6] J. Belan, Study of advanced materials for aircraft jet engines using quantitative metallography, in: R.K. Agarwal (Ed. ), Recent Advances in Aircraft Technology, IN-TECH -Open Access publisher of Scientific Books and Journals, Croatia, 2012, pp.49-74.

DOI: 10.5772/37254

[7] M.J. Donachie, S.J. Donachie, Superalloys – A Technical Guide, 2nd edition, ASM International, USA (2002).

[8] A. Pineau, S.D. Antolovich, High temperature fatigue of nickel-base superalloys – A review with special emphasis on deformation modes and oxidation, Engineering Failure Analysis 16 (2009) 2668-2697.

DOI: 10.1016/j.engfailanal.2009.01.010

[9] A.D. Cetel, D.N. Duhl, Microstructure – property relationships in advanced nickel base superalloy airfoil castings, in: 2nd International SAMPE Metals Conference, USA 1988, p.37 – 48.

[10] J. Belan, L. Hurtalová, A. Vaško, E. Tillová, Metallography evaluation of IN 718 after applied heat treatment, Manufacturing technology: journal for science, research and production 14 (2014) 262-267.

DOI: 10.21062/ujep/x.2014/a/1213-2489/mt/14/3/262