## 2 Materials and Methods
### Nitrogen Ion Implantation  
The circular saw blades described above were implanted using the semi-industrial gaseous ion implanter, with a non-mass-separated ion beam, exploited in National Centre for Nuclear Research Swierk (Otwock, Poland), described in detail elsewhere [22]. Before the processing, the saw blades were washed in high purity acetone. Next, three saw blades described above were put together in a package and placed in the implanter chamber (Figure 2). Nitrogen of 5N purity was used as the source of the implanted ions. The total implanted dose of nitrogen ions was 5 \(\times\) 10\({}^{17}\) cm\({}^{-2}\) (2 \(\times\) 2.5 \(\times\) 10\({}^{17}\) cm\({}^{-2}\)) and ions were implanted at 50 kV acceleration voltage. The current of the continuous ion beam was about 300 \(\mu\)A, which gives the ion current densities from about 15 \(\mu\)A/cm\({}^{2}\) for the assumed value of the implantation area of 20 cm\({}^{2}\) (ion beam diameter is about 50 mm, without a significant decrease in current density). The maximum estimated temperature value of the implanted tools did not exceed 200 \({}^{\circ}\)C. The time of the ion implantation was 11 h 40 min. (700 min) per stage. Such values of the main parameters of the implantation correlate with previous investigations, e.g., [1,4]. The ion implantation was provided in two stages. The details of these are presented in Figure 3. In the first stage, the ion beam axis was moved about 50 mm with respect to the axis of the saw blades. In the second stage, the ion beam axis was moved to near the tangent of the saw blades. In both cases, the saw blades rotated with the rotation speed of 0.3 s\({}^{-1}\), i.e., 18 rpm. Figure 1: Circular saw blade used for investigations (**left**) and its GSML teeth geometry (**right**). Figure 2: Main view of the ion implanter (**left**) and view of the circular saw blade’s package inside the implanter vacuum chamber (**right**). The ion implantation processes were supported by Monte Carlo simulations of the main parameters of the depth profiles of the implanted elements (such as peak volume dopant concentration \(N_{max}\), projected range \(R_{p}\), range straggling \(\Delta R_{p}\), kurtosis and skewness) [23], using freeware-type code SRIM-2013.00--The Stopping and Range of Ions in Matter [24]. The simulation was performed for 100,000 implanted ions of nitrogen to three kinds of the implanted surface, i.e., W-C-Co material (substitute of WC-Co), and for the comparison, to two main components of WC-Co carbide, i.e., W-C (substitute of WC) material and Co. W-C-Co and W-C materials were used because the modelling codes treat the sample as a set of atoms that do not form chemical compounds. The tool manufacturer does not provide the exact original composition of the cemented carbide used. Therefore, the material parameters of the popular in industry KCR08 carbide have been applied to the modelling. The composition of the W-C-Co material was: 90.86% of tungsten, 5.94% of carbon and 3.2% of cobalt in weight percentages, i.e., 47.4% of tungsten, 47.4% of carbon and 5.2% of cobalt in atomic percentages. Its density adopted for the simulation was 15.2 g/cm\({}^{3}\). WC density of 15.63 g/cm\({}^{3}\) and Co density of 8.9 g/cm\({}^{3}\) were adopted in the other cases. The implanted nitrogen was delivered as two kinds of ions, i.e., N\({}_{2}\)\({}^{+}\) + N\({}^{+}\), in the ratio \(\sim\)1:1, so there were two elementary charges per three atoms. For example, in the case of the N\({}_{2}\) molecule implanted with the acceleration voltage of 50 kV (see Table 1), each atom carries the energy of 25 keV, according to the law of energy conservation. It means that, for example, for a total fluence of 2.5 \(\times\) 10\({}^{17}\) cm\({}^{-2}\), the fluence of 0.83 \(\times\) 10\({}^{17}\) cm\({}^{-2}\) is implanted with the energy of 50 keV and the fluence of 1.67 \(\times\) 10\({}^{17}\) cm\({}^{-2}\) is implanted with the energy of 25 keV.