## 5 Conclusions  
The study considers the ultrafine grained austenitic Fe-Mn-5 Si alloys as a promising material for implantable devices. Structural and phase evolution during ECAP makes it possible to obtain a set of optimal functional properties necessary for the manufacture of a biocompatible degradable implantable device:  
1. Long-term annealing resulted in the formation of an initial coarse-grained structure with a large number of annealing twins, which allowed the samples to withstand ECAP at 400 \({}^{\circ}\)C for up to four passes. 2. The highest possible strain degrees and deformation temperatures were used to achieve an ultrafine-grained structure in a fully austenitic state, which will make it possible to use MRI as an implantable device control. 3. ECAP at a temperature of 400 \({}^{\circ}\)C leads to the formation in the Fe-Mn-5 Si alloy of an ultrafine-grained austenitic predominantly twin structure with a twin thickness of 11 \(\pm\) 1 nm. 4. The structure obtained after ECAP determined a high level of strength characteristics (\(\sigma_{\text{UTS}}\) = 1419 \(\pm\) 14 MPa, \(\sigma_{\text{YS}}\) = 1352 \(\pm\) 6 MPa) with sufficiently high plasticity (\(\varepsilon\) = 4%) for such a state. 5. The increase in strength after ECAP is accompanied by a decrease in [PERSON]'s modulus by more than 2.6 times compared with the measured values in the annealed state. This result is important for the development of alloys for bioresorbable implants. This confirms the biomechanical compatibility of the implant and bone. 6. The potentiodynamic polarization method revealed only a slight increase in the corrosion rate of the ECAP-treated alloy (0.25 \(\pm\) 0.02 mm/year) compared to the alloy in the annealed state (0.21 \(\pm\) 0.02 mm/year) with a significant shift in the corrosion potential of the Fe-Mn-5 Si alloy in comparison with the corrosion potential of commercially pure iron. 7. The corrosion rate of the alloy in both states obtained by the mass loss measurements during incubation for a day confirmed the results of the potentiodynamic study. 8. Increasing the duration of the alloy incubation in the culture medium up to 14 days significantly reduces the corrosion rate to 0.018 \(\pm\) 0.002 mm/year for the annealed state and to 0.028 \(\pm\) 0.003 mm/year for the alloy after ECAP. 9. The mass loss study confirmed that the corrosion rate of deformed samples after in vitro incubation and in vivo implantation for 2 weeks is 1.6 and 1.8 times the \(C\Delta m\) of annealed samples, respectively. 10. In vivo implantation revealed a less localized corrosion damage of the alloy sample after ECAP. Such damage is more preferable for practical use, since it will not lead to premature failure of thin implantable devices. 11. It was established that samples of the Fe-Mn-5 Si alloy did not have a cytopathogenic effect on blood cells. According to the results of the study of hemolysis and cytotoxicity, the alloy was found to be biocompatible. 12. It was found that the degradation of samples of the Fe-Mn-5 Si alloy after ECAP and annealing does not have a systemic toxic effect on the functioning of the main organs of the animal body. It confirms the alloy's biocompatibility in vivo. Thus, ECAP can contribute to a significant increase in performance and reduce the weight of implanted devices, which is important for the creation of implants to replace skeletal defects, due to a significant increase in the specific strength of the Fe-Mn-5 Si alloy. The high specific strength of the alloy obtained by ECAP makes it possible to vary the dimensions of the implant over a wide range. This, in turn, provides additional opportunities to control the implant degradation time. Also, the small size of the implanted device will reduce the toxic effect of a foreign body on the human body. Conceptualization, N.A. and O.R. ; methodology, N.P., M.K. and S.D. ; software, G.R., A.B. and I.S. ; validation, O.R., E.K. and N.M.; formal analysis, N.A. and O.R. ; investigation, O.R., A.B., N.M., E.L., N.P., D.S., G.B., G.R., I.S. and O.C.