## 3 Results
### Corrosion Rate Measurement
#### 3.5.2 Degradation Rate from Mass Loss Measurements In Vivo and In Vitro  
To confirm the results obtained by the potentiodynamic polarization method, the corrosion rate (\(C\Delta m\)) was determined by measuring the mass loss (\(\Delta m\)). Figure 6 shows the results of measuring \(C\Delta m\) and \(\Delta m\) of the Fe-Mn-5 Si alloy samples after annealing and after ECAP versus time of incubation or implantation. The duration of incubation in the DMEM culture medium was 1 and 14 days, and the subcutaneous implantation to mice of the Balb/c lines continued for 14 days. Studies have shown that after a day of incubation in a culture medium, the corrosion rate of the alloy in each of the states is the highest. It is 0.166 \(\pm\) 0.032 mm/year for the alloy in the annealed state and 0.171 \(\pm\) 0.070 mm/year after ECAP. Taking into account the measurement error, the obtained data are consistent with the results of the corrosion rate of the potentiodynamic study. 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. These results, taking into account the measurement error, are nearly equal to the corrosion rates of samples implanted in mice for the same period, i.e., 0.013 \(\pm\) 0.005 mm/year and 0.024 \(\pm\) 0.008 mm/year for samples in the annealed and deformed states, respectively. In addition, measurements of \(C\Delta m\) in the mass loss study confirmed that the corrosion rate of deformed samples in DMEM culture medium and after implantation in a laboratory animal for 14 days is 1.6 and 1.8 times the \(C\Delta m\) of annealed samples, respectively. This is illustrated by the \(\Delta m\) histogram in the upper part of Figure 6.  
Figure 7 shows images of the corroded surface of the samples in the annealed state (Figure 7a,b) and in the ECAP-treated state (Figure 7c,d) after their incubation in the DMEM culture medium (Figure 7a,c) and after implantation in vivo (Figure 7b,d) for 14 days. Figure 6: Corrosion rate (\(C\Delta m\)) and weight loss (\(\Delta m\)) of Fe-Mn-5 Si alloy in states after annealing and ECAP vs. duration of incubation of alloy samples in DMEM and implantation in mice during 14 days. A sufficiently thick layer of corrosion products was found on the surface of the samples. Visually, the appearance of corroed surfaces after incubation in vitro differed from the surface of the samples implanted in vivo. At the same time, the composition of the layer of corrosion products of annealed and deformed samples is almost identical and corresponds to that presented in the elemental mapping of ECAP-treated samples after implantation (Figure 8) and after incubation in vitro (Figure 9). Figure 8: Elemental mapping of surface of Fe-Mn-5 Si alloy samples in the ECAP-treated state after implantation in mouse (in vivo) (image in Figure 7d). Figure 7: SEM images of surface of Fe-Mn-5 Si alloy samples in the ECAP-treated state after incubation in DMEM (in vitro) (**a,c**) and after implantation into mouse (in vivo) (**b,d**) during 14 days. Judging by the brightness of the P and O and Ca images on the elemental mapping (Figure 8) of the corroded surface of the samples implanted in vivo, deposits of calcium phosphate, layers of oxides, as well as pure Fe, Mn and Si on the surface of the alloy are observed, which corresponds with the observations [21]. Corrosion is slowed down due to the formation of a thick layer of corrosion products, which prevents the access of oxygen, and also due to the subsequent growth of cells on the surface of the alloy. The elemental mapping of the corroded surface of the sample after ECAP, incubated in vitro, shows all the Ca\({}^{2+}\), Mg\({}^{2+}\), Na\({}^{+}\), K\({}^{+}\), Cl\({}^{-}\), SO\({}_{4}\)\({}^{2-}\), PO\({}_{4}\)\({}^{3-}\) and HCO\({}_{3}\)\({}^{-}\) ions (Figure 9) that are part of the culture media [44].