PSI - Issue 47

Yurii Sharkeev et al. / Procedia Structural Integrity 47 (2023) 849–854 Yurii Sharkeev et al. / Structural Integrity Procedia 00 (2023) 000 – 000

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In the ultrafine- grained alloy (σ = 295 MPa, N = 1. 6∙ 10 9 cycles) a misoriented fragmented substructure is formed (Fig. 3 c, d). The average size of structural elements of β -phase after gigacycle testing was 0.2±0.1 µm. The microstructure is characterized by a high density of dislocations, which form a misoriented fragmented substructure (Fig. 3 c, marked by arrows). After failure, a fragmentation of the microstructure and a slight refinement of the structural elements of the main phase can be observed. In the microstructure, in addition to matrix subgrains of  - phase, grains of  -phase at the boundaries and at the junctions of the grains are present, as well as precipitations of  -phase particles inside  -phase grains (Fig. 3 d). For a UFG alloy, the grain size is too small for the formation of intragranular dislocation structures, where grain boundaries can play a significant role in dislocation annihilation during gigacycle tests (Mughrabi et al. 2010). 4. Conclusion The implementation of severe plastic deformation consisting of multi-step pressing and multi-pass rolling in grooved rolls allowed us to obtain an ultrafine-grained state in the Ti-45 wt.% Nb alloy, which provided a significant increase in mechanical properties while maintaining the elastic modulus and a moderate decrease in ultimate plasticity. Moreover, the Ti – 45 wt.% Nb alloy in the ultrafine-grained state demonstrated higher fatigue properties under gigacycle loading. The ultrafine-grained structure in the Ti – 45 wt.% Nb alloy is stable under gigacycle loading and provides a service life of up to 10 9 and more cycles with higher fatigue strength. In contrast to the samples of alloys with a coarse-grained structure, in which dislocation networks and cells are formed after a gigacycle test, in samples in an ultrafine grained state, the nature of the microstructure practically does not change during testing, but a high density of dislocations was formed. Its presence is due to the fact that the formed ultrafine grain has the maximum size for the formation of intragranular dislocation structures, while the grain boundaries play a significant role in the annihilation of dislocations during gigacycle tests. Funding The work was performed according to the Government Research Assignment for the Institute of Strength Physics and Materials Science of the Siberian Branch of the Russian Academy of Sciences (ISPMS SB RAS), project No. The authors are grateful to the research group of Prof. Oleg Naimark (Perm’, Russia) and our colleagues from the ISPMS SB RAS (Tomsk, Russia) for participation in the implementation of scientific research and discussion of the results. Exp erimental research was conducted using the equipment of the Common Use Center “Nanotech” at the Institute of Strength, Physics, and Materials Science, SB RAS (ISPMS SB RAS, Tomsk, Russia). References Ozaki, T., Matsumoto, H., Watanabe, S., Hanada, S. Beta Ti alloys with low Young’s modulus. Materials Transaction 45, 2776 – 2779. Geetha, M., Singh, A.K., Asokamani, R., Gogia, A.K. Ti-based biomaterials, the ultimate choice for orthopedic implants − A review. Progress. In Materials Science 54, 397 – 425. Walker, J., Shadanbaz, S., Woodfield, T.B., Staiger, M.P., Dias, G.J. Magnesium biomaterials for orthopedic application: A review from a biological perspective. Journal of Biomedical Materials Research Part B Applied Biomaterials 102, 1316 – 1331. Reck, A., Pilz, S., Thormann, U., Alt, V., Gebert, A., Călin, M., Heiß, C., Zimmermann, M. Effects of thermomechanical histor y and environment on the fatigue behavior of (β) -Ti-Nb implant alloys. Matec Web of Conferences 165, 06001. Bonisch, M., Calin, M., Humbeeck, J., Skrotzki, W., Eckert, J. Factors influencing the elastic moduli, reversible strains and hysteresis loops in martensitic Ti – Nb alloys. Materials. Science. Engineering C 48, 511 – 520. Sharkeev, Yu., Eroshenko, A., Legostaeva, E., Kovalevskaya, Z., Belyavskaya, O., Khimich, M., Epple, M., Prymak, O., Sokolova, V., Zhu, Q., Sun, Z., Zhang, H. Development of Ultrafine – Grained and Nanostructured Bioinert Alloys Based on Titanium, Zirconium and Niobium and Their Microstructure, Mechanical and Biological Properties. Metals 12(7), 1136. Niinomi, M., Liu, Y., Nakai, M., Liu, H., Li, H. Biomedi cal titanium alloys with Young’s moduli close to that cortical bone. Regenerative Biomaterials 3, 173 – 185. FWRW-2021-0004. Acknowledgements