13th International Conference on Fracture June 16–21, 2013, Beijing, China -8- 5. Conclusions A study of the growth of hold time cracks in IN718 and Allvac718Plus at high temperatures has led to the following conclusions. • Growth of cracks in IN718 during dwell time show a mix between different growth modes with a marked shift in crack growth mode towards intergranularity with branching compared to fatigue crack growth under the same conditions. • The growth mode during dwell time cracking is shifting towards more intergranular with increased branched cracking with increasing temperature for IN718 but local plasticity is still present. • The dwell time cracking mode for Allvac718Plus is pure intergranular at high temperature with less pronounced local plasticity. • Intergranular nanosized voids observed close to the crack tip region could be the responsible for intergranular cracking in both alloys. • The origin of the nanosized voids is either pure mechanical or a result of oxidation of grain boundary precipitates Acknowledgements The authors wish to great fully acknowledge Turbo Power consortium, Siemens Industrial Turbines, Volvo Aero Corporation. Agora Materiae and Strategic Faculty Grant AFM at Linköping University are also acknowledged. 2.4. References 1. Melih Cemal Kushan, S.C.U., Yagiz Uzunonat, and Fehmi Diltemiz, Recent Advances in Aircraft Technology, in ALLVAC 718 Plus™ Superalloy for Aircraft Engine Applications, R. Agarwal, Editor. 2012, InTech. 2. Lei Zheng, G.S., Ye Meng, Reda Chellali & Ralf Schlesiger, Mechanism of Intermediate Temperature Embrittlement of Ni and Ni-based Superalloys. Critical Reviews in Solid State and Materials Sciences, 2012. 37:3(181-214). 3. Gustafsson, D., Moverare, Johan, Johansson, Sten, Simonsson, Kjell, Hornqvist, M. Mansson, T, Sjöström, Sören, Influence of high temperature hold times on the fatigue crack propagation in Inconel 718. International Journal of Fatigue, 2011. 33(11): p. 1461-1469. 4. Gustafsson, D., Moverare, Johan, Simonsson, Kjell, Johansson, Sten, Hörnqvist, Magnus, Månsson, Tomas, Sjöström, Sören, Fatigue Crack Growth behaviour of Inconel 718 - the Concept of a Damaged Zone Caused by High Temperature Hold Times. Procedia Engineering, 2011. 10: p. 2821-2826. 5. David Gustafsson, Johan Moverare, Kjell Simonsson, Sten Johansson, Magnus, Hörnqvist, Tomas Månsson, and Sören Sjöström, Fatigue crack growth behaviour of Inconel 718 – the concept of a damaged zone caused by high temperature hold times, in ICM11, P. Engineering, Editor. 2011, Accepted: Como Lake Italy. p. 2821-2826.
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