## Materials and Methods
### Nanoinindentation Tests  
Instrumented indentation was applied in order to determine the mechanical behavior of the under-study coatings. Nanoindentation tests implicate the contact of an indenter to a material's surface and its penetration to a predetermined depth or load. The indentation force is measured along with the penetration depth. Figure 1 illustrates a typical loading and unloading procedure, presenting the parameters that are needed to characterize the contact geometry. This figure shows a standard elastoplastic material with the loading OA and unloading AB' segments. The area W1 (OAB') represents the plastic work that is done in the elastoplastic case. The area W2 (ABB') corresponds to the elastic work that is recovered during the unloading segment. The unloading curve is a straight line (AB) and h\({}_{r}\) = h\({}_{max}\) (W2 = 0) in the case of purely plastic material. In this case, penetration depth is the displacement into the sample starting from its surface [45; 53; 54; 55].  
Figure 1: Schematic of nanoindentation load-depth curve of an elastoplastic material, where h\({}_{max}\) is the maximum depth, h\({}_{e}\) is the elastic depth rebound, h\({}_{r}\) is the residual impression depth, h\({}_{a}\) is the displacement of the surface at the perimeter, and h\({}_{f}\) is the contact indentation depth.  
The nanoindentation tests were performed on a Shimadzu DUH211S device with a resolution of 0.2 \(\mu\)N. The indenter was a Berkovich diamond tip (the tip shape is a three-sided pyramid, with a triangular projected geometry and an included angle of 65.3\({}^{\circ}\); tip radius 0.1 \(\mu\)m). Several points were selected while using an optical microscope implemented to the indenter and these were distributed on the surface of the coating. At least twenty measurements were performed per coating sample.  
Preceding a nanoindentation test, the indentation tip is driven toward the specimen surface. After contact is achieved, the indenter penetrated the surface, to a depth around 1.3 \(\mu\)m, with a constant loading rate of 70 mN/s, until a maximum force of 200 mN. As soon as maximum force was reached, the indenter was removed with the same loading rate to a value of zero.  
The modulus and the hardness of the coatings were determined based on the work of [PERSON] and [PERSON] [56]. The indentation hardness can be determined as a function of the maximum penetration depth by [45; 53; 54; 55]:  
\[H=\frac{P_{max}}{A} \tag{1}\]  
where \(P_{\max}\) is the maximum applied load that was measured at the maximum depth of penetration (\(h_{\max}\)) and \(A\) is the projected contact area between the indenter and the specimen. For a perfect Berkovich indenter, \(A\) can be expressed as a function of the contact indentation depth \(h_{\mathrm{f}}\) as:  
\[A=3\sqrt{3}h_{f}^{2}tan^{2}65.3=23.96h_{f}^{2} \tag{2}\]  
The contact indentation, \(h_{\mathrm{f}}\), can be determined from the following expression:  
\[h_{f}=h_{max}-\varepsilon\frac{P_{max}}{S} \tag{3}\]  
where \(\varepsilon\) is a geometric constant \(\varepsilon=0.75\) for a pyramidal indenter and \(S\) is the contact stiffness that can be determined as the slope of the unloading curve at the maximum loading point, i.e.  
\[S=\left(\frac{dP}{dh}\right)_{h=h_{max}} \tag{4}\]  
The reduced elastic modulus \(E_{\mathrm{r}}\) is given by:  
\[E_{r}=\frac{S}{2\beta}\sqrt{\frac{\pi}{A}} \tag{5}\]  
where \(\beta\) is a constant that depends on the geometry of the indenter. For the Berkovich indenter, \(\beta=1.034\). The specimen elastic modulus (\(E_{\mathrm{s}}\)) can then be calculated as:  
\[\frac{1}{E_{r}}=\frac{1-\
u_{s}^{2}}{E_{s}}+\frac{1-\
u_{i}^{2}}{E_{i}} \tag{6}\]  
where \(E_{i,s}\), and \(\
u_{i,s}\) are the elastic modulus and the Poisson's ratio, respectively, for the indenter and the specimen. For a diamond indenter, \(E_{i}\) is 1140 GPa and \(\
u_{i}\) is 0.07. The specimen's hardness \(H\) and elastic modulus \(E_{s}\) were obtained from the set of equations given above.