PSI - Issue 2_B

Hans-Jürgen Christ et al. / Procedia Structural Integrity 2 (2016) 557–564 Christ et al./ Structural Integrity Procedia 00 (2016) 000–000

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 Under conditions, where a mixed type of crack propagation takes place, intergranular and transgranular areas appear side by side in the fracture surface indicating that the respective crack growth mechanisms act locally and widely independent of each other.  The experimental results are in very satisfactory agreement with the idea that dynamic embrittlement occurs according to the damage zone model. This means, a damage zone ahead of the crack tip is formed during the dwell time and crack propagation through this damage zone takes place in the cyclic (fatigue) part before the next dwell time.  On the basis of the experimental findings a crack propagation model was developed, which is simple, phenomenological, but closely related to the relevant mechanisms.  Simulation calculations for crack growth rates under dynamic embrittlement conditions were carried out and yielded a very satisfying agreement with the experimental data indicating that the assumptions used are justified. References Antunes, F.V., Ferreira, J.M., Branco, C.M., Byrne, J., 2000. High temperature fatigue crack growth in Inconel 718. Mater. High Temper. 17, 439-448. Gustafsson, D., Moverare, J.J., Johansson, S., Simonsson, K., Hörnqvist, M.L., Månsson, T., Sjösström, S., 2011. Influence of high temperature hold times on the fatigue crack propagation in Inconel 718. Inter. J. Fatigue 33, 1461-1469. Gustafsson, D.; 2012. High temperature fatigue crack propagation behaviour of Inconel 718. PhD thesis, University of Linköping, Linköping, Sweden, 2012. Hörnqvist, M.L., Viskari, L., Stiller, K., Stöberg, G., 2010. Half-time fatigue crack growth of Allvac 718Plus. Proc. of 7 th Intern. Symp. on Superalloy 718 & Derivatives, Pittsburgh, PA, USA, 705-717. Kang, B.S.-J., Zhang, P.L., Ellathur. M., 1995. Stress accelerated grain boundary oxygen embrittlement on creep crack growth of nickel-base superalloys. in “Fatigue and fracture at elevated temperatures”. American Society of Mechanical Engineers, Vol. AD50, 225-254. Krupp, U., 2005. Dynamic embrittlement–Time-dependent quasi-brittle intergranular fracture at high temperatures. Int. Mater. Rev. 50, 83-97. Krupp, U., 2007. Fatigue crack propagation in metals and alloys. Wiley-VCH, Weinheim, Germany. Ma, L., Chang, K.-M., 2003. Identification of SAGBO-induced damage zone ahead of crack tip to characterize sustained loading crack growth in Alloy 783. Scripta Mater. 48, 1271-1276. Ma, L., Liu, X., Chang, K.-M., 2006. Reply to comment on identification of SAGBO-induced damage zone ahead of crack tip to characterize sustained loading crack growth in Alloy 783. Scripta Mater. 54, 309-311. Pfaendtner, J., McMahon, C. J., 2001. Oxygen-induced intergranular cracking of Ni-base alloy at elevated temperatures – An example of dynamic embrittlement. Acta Mater. 49, 3369-3377. Solomon, H.D., Coffin, L.F., 1973. Effects of frequency and environment on fatigue crack growth in A286 at 1100F. in: ASTM STP 520: Fatigue at elevated temperature , Carden, A.E. et al. (Ed.), ASTM, West Conshohocken, PA, USA, 112-124. Viskari, L., Cao, Y., Norell, M., Sjöber G., Stiller, K., 2011. Grain boundary microstructure and fatigue crack growth in Allvac 718Plus superalloy. Mater. Sc. Eng. A 528, 2570-2580. Wackermann, K, 2015. Einfluss einer zyklischen Belastung auf die Versprödungskinetik von Legierungen am Beispiel der 475°C-Versprödung von Duplexstahl und der dynamischen Versprödung einer Nickelbasislegierung , PhD thesis, Universität Siegen, Siegen, Germany, 2015. Wagenhuber, P., Trindade, V.B., Krupp, U., 2005. The role of oxygen-grain boundary diffusion during intercrystalline oxidation and intergranular fatigue crack propagation in Alloy 718. Proc. of 6 th Intern Symposium on Superalloys 718, 625, 706 and Derivatives, Loria, E.A. (Ed.), Pittsburgh, PA, USA, TMS, 591-600. Wei, R.P., Landes, J.D., 1969. Correlation between sustained-load and fatigue crack growth in high strength steels. Mater. Research and Standards 9, 25-46. Wei, R.P, Miller, C., Huang, Z., Simmons, G.W., Harlow, D.G., 2009. Oxygen enhanced crack growth in nickel-based superalloys and material damage prognosis. Eng. Fracture Mechanics 76, 715-727. Xu, Y., 1999. Crack propagation associated with stress-assisted diffusion of impurities under creep conditions , PhD thesis, University of Pennsylvania, Philadelphia, PA, USA, 1999. Zhao, L.G., Tong, J., Hardy, M.C., 2010. Predication of crack growth in a nickel-based superalloy under fatigue-oxidation conditions. Eng. Fracture Mech. 77, 925-938.

Acknowledgements

The authors thank Deutsche Forschungsgemeinschaft (German Science Foundation) for financial support of this study. MAN Turbo&Diesel SE is gratefully acknowledged for providing the alloy investigated.