PSI - Issue 23

Ivo Šulák et al. / Procedia Structural Integrity 23 (2019) 161–166 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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4. Conclusions

The following conclusions can be drawn from the experimental study of fatigue crack initiation and early crack propagation in superalloy MAR-M247 cyclically strained with total strain range of 1%. (I) Plastic strain localization into PSBs manifests itself by the formation of pronounced surface relief. PSMs start as thin extrusions at the very early stage of cycling (2% of N f ) which are later (5% of N f ) accompanied by parallel intrusions. The density of PSMs and PSBs differs from grain to grain. At the intersection of two PSMs from two different slip systems, typical quadrilateral cracks can be formed. (II) The fatigue cracks nucleated at the tip of sharp intrusions and subsequently propagated as stage I cracks parallel to one of the active slip planes. (III) Two regimes of different extrusion growth rate were identified during cyclic straining. Early fast extrusion growth is followed by a longer domain with approximately ten times lower extrusion growth rate. Acknowledgements The support of this work by the project CZ.01.1.02/0.0/0.0/15_019/0002421 is acknowledged. The authors would like to express their thanks to NenoVision s.r.o. for providing the possibility to use their unique microscopic technique CPEM. Buque, C., 2001. Persistent slip bands in cyclically deformed nickel polycrystals1. Int. J. Fatigue 23, 459 – 466. E ssmann, U., Gösele, U., Mughrabi, H., 1981. A model of extrusions and intrusions in fatigued metals I. Point -defect production and the growth of extrusions. Philos. Mag. A 44, 405 – 426. Man, J., Obrtlík, K., Polák, J., 2009. Extrusions and Intrusions in Fat igued Metals. Part 1. State of the Art and History\dag. Philos. Mag. 89, 1295 – 1336. Mughrabi, H., Bayerlein, M., Wang, R., 1991. Direct measurement of the rate of extrusion growth in fatigued copper mono- and polycrystals, in: Proceedings of the 9th International Conference on Strength of Metals and Alloys - ICSMA 9. London: Freund Publishing, pp. 879 – 896. Mughrabi, H., Wang, R., Differt, K., Essmann, U., 1983. Fatigue Crack Initiation by Cyclic Slip Irreversibilities in High-Cycle Fatigue. Presented at the Fatigue Mechanisms, USA, pp. 5 – 45. Obrtlík, K., Juliš, M., Man, J., Podrábský, T., Polák, J., 2010. Extrusion and intrusion evolution in cyclically strained cas t superalloy Inconel 738LC using confocal laser scanning microscope and AFM. J. Phys. Conf. Ser. 240, 012054. Polák, J., 1998. Models of fatigue crack initiation. Kovové Materiály 36, 171– 182. Polák, J., 1987. On the role of point defects in fatigue crack initiation. Mater. Sci. Eng. 92, 71– 80. Polák, J., Man, J., 2016. Experimental evidence and phy sical models of fatigue crack initiation. Int. J. Fatigue, Variable Amplitude Loading 91, Part 2, 294 – 303. Polák, J., Mazánová, V., Heczko, M., Kuběna, I., Man, J., 2017. Profiles of persistent slip markings and internal structure o f underlying persistent slip bands: Profiles of PSMs and structure of PSBs. Fatigue Fract. Eng. Mater. Struct. 40, 1101 – 1116. https://doi.org/10.1111/ffe.12567 Polák, J., Petráš, R., Chai, G., Škorík, V., 2016. Surface profile evolution and fatigue crack initiation in Sanicro 25 steel at room temperature. Mater. Sci. Eng. A 658, 221 – 228. Šulák, I., Obrtlík, K., 2017a. Fatigue Crack Initiation in Nickel -Based Superalloy MAR-M247 at High Temperature. Key Eng. Mater. 754, 27 – 30. Šulák, I., Obrtlík, K., 2017b. Effect of tensile dwell on high-temperature low-cycle fatigue and fracture behaviour of cast superalloy MAR-M247. Eng. Fract. Mech., XVIII International Colloquium Mechanical Fatigue of Metals 185, 92 – 100. Šulák, I., Obrtlík, K., Čelko, L., 2016. High -temperature low-cycle fatigue behaviour of HIP treated and untreated superalloy MAR-M247. Kov. Mater. 54, 471 – 481. References