## 3 Results and Discussion
These factors are proposed as possible contributors, though further investigation would be required to confirm their impact. The number of mechanical cycles until the fracture of the coated wires is summarized in Table 2. The average value, Nf_ald_mean, is 293,875 mechanical cycles. The standard deviation, SD_ald, is again large (SD_ald is 476,896 mechanical cycles). There is an obvious increase in Nf_ald (Nf_ald/Nf = 39). While the mean value and standard deviation (SD) were calculated for the data in Table 2, it is important to note that these calculations should be interpreted with caution, as the values are derived from measurements under different loading conditions, which may influence the results. \begin{table}
\begin{tabular}{c c c} \hline
**NiTi Sample ID** & **Nf** & **Nf\_mean** & **SD** \\ \hline No\_ALD\_wire\_1 & 2772 & \\ \hline No\_ALD\_wire\_2 & 12,860 & \\ \hline No\_ALD\_wire\_3 & 1262 & \\ \hline No\_ALD\_wire\_4 & 10,925 & \\ \hline No\_ALD\_wire\_5 & 15,360 & \\ \hline No\_ALD\_wire\_6 & 2032 & \\ \hline \end{tabular}
\end{table} 
Table 1: List of fatigue-tested NiTi wire samples without ALD coating. Nf is the number of mechanical cycles (0 to 700 MPa, with the minimum stress between 0 and 50 MPa) at room temperature until fracture occurred. SD stands for standard deviation. Figure 4: Energy-dispersive X-ray spectrum from the (**a**) as-purchased and the (**b**) coated-NiTi-wire sample. Accelerating voltage and counting time were 5 kV and 100 s, respectively. An analysis of the load applied during the ALD process (1.7, 2.2, 2.8 kg) reveals a correlation between Nf_ald and the load level. However, the correlation cannot be evaluated as statistically significant due to the low number of tests. It is noteworthy that annealed NiTi wire exhibiting a superelastic effect typically endures only a few thousand loading cycles when subjected to stresses in the range of 0-700 MPa at room temperature. However, the strain of the superelastic wire at the stress level around 700 MPa is several times greater than that of the as-cold drawn NiTi wire. Figure 5a-f present the stress-strain diagrams with cyclically applied stress in the range of 0-700 MPa, up to the fracture of individual non-coated wire samples. Similarly, Figure 6 illustrates the stress-strain diagrams up to fracture at room temperature for individual ALD-coated samples (a)-(e), as well as the electrical resistance versus the number of loading cycles (f) for the NiTi wire sample ALD_wire_3. The cyclic behavior is stable, with minimal accumulated plastic deformation, and the stress-strain curves are nearly linear. A narrow hysteresis is observed in each individual stress-strain curve (not shown in the figure). Figure 6e illustrates an accidental overshoot of the applied tensile stress. Nevertheless, this overshoot did not lead to wire failure. The electrical resistance varies with the number of mechanical cycles applied. After an initial decrease during the first 500 cycles, the electrical resistance increases with the number of cycles. The two sharp drops in electrical resistance in panel (f) (black curve) are artifacts caused by some sudden changes in electrical connection between the sample and the clamping system. The brown curve represents the electrical resistance data after compensation for these two artificial drops. In the compensated curve, the initial electrical resistance value is lower than the value immediately preceding wire fracture. Generally, electrical resistance is proportional to the elongation of the tested wires and can indicate microstructural changes after many tensile loading cycles [38]. Figure 7 shows the HAADF images that were obtained to identify the individual layers adjacent to the surface. The top layer is a tungsten-based layer applied by the STEM (Scanning Transmission Electron Microscopy (FEI Quanta, FEI Tecnai: Thermo Fisher Scientific, WA, USA)) operator to manipulate the lamella. Below the tungsten-based layer, there is a naturally formed titanium dioxide layer.