## 3 Results and Discussion  
### Effect of Test Parameters on TiCrN Thin Film  
It can be observed from Figure 1a that the substrate current is linearly proportional to the chromium cathode current at constant coating time and Ti cathode current. Over the entire range of Cr current (80 to 175 A) in the TiCrN coatings, the phase constituent was found to gradually shift from cubic TiN to cubic CrN, as shown in the XRD patterns in Figure 1b. The XRD spectrum was matched with the standard JCPDS files as per the ICDD database and the identified peaks corresponding to cubic TiN (No. 38-1420), cubic CrN (No. 6-2494), and TiCrN (No. 38-1420) are shown in Figure 1b. With the increase in the current value, the lattice constant of TiN is found to change from 4.23 to 4.24 A\({}^{\circ}\). The observed change in lattice constant with the change in current is due to the substitution of \"Ti\" atoms by Cr atoms in the TiN matrix resulting in the formation of a solid solution TiN(Cr). Similarly, at higher values of current (current \(>\) 185 A), the coatings contain a cubic CrN(Ti) phase with partial substitution of Cr atoms with Ti atoms (lattice constant of 4.15 instead of 4.14 for CrN). This observed change in phase constitution from TiN-TiCrN-CrN is expected to change residual stress.  
The SEM image shows the microstructure, and the EDS spectra shows the presence of Ti and Cr elements (Figure 2).  
Expected coating thickness is calculated by using the empirical relation [15] (Equation (1)),  
\[t_{Expected}=0.0025\times I_{\mathrm{s}}\ \times T_{Depo} \tag{1}\]  
where Is is the substrate current in ampere. TDepo is the deposition time in minute. tExpected and tActual are the target thickness and actual measured thickness of the coating, respectively.  
Figure 1: (**a**) Variation in substrate current at different Cr cathode currents. (**b**) X-ray diffraction (XRD) spectra of the deposited TiCrN coatings with chromium current variations.  
The film thicknesses of all the deposited coatings were obtained using a Calo tester CT 250 (PLATIT advanced coating systems product) which is shown in Figure 3a,b. The samples were cleaned with an alcohol solution and placed in the sample container appropriately. The Calo tester consists of a holder for the surface to be tested and a steel sphere of a known diameter (30 mm) that is rotated against the surface by a rotating shaft connected to a motor whilst diamond paste (1 \(\mu\) suspension) is applied to the contact area. The sphere is rotated for a short period (90 s) of time but due to the abrasive nature of the diamond paste, this is sufficient to wear a crater through thin coatings. An optical microscope (Zeiss Axio Cam MRc5) is used to take two measurements after the Calo test across the crater and the coating thickness is calculated using a simple geometrical equation.  
\[d=\left(A^{2}-B^{2}\right)/4D\]  
where d is the coating thickness and D is the diameter of the sphere (d << D). The values of A, B, and D can be obtained from the Calo tester as shown in Figure 3c,d.  
Table 3 displays the thicknesses of all coatings deposited. The coating thickness was computed using the calotte grinding measuring instrument depicted in Figure 3e. For each coating evaluation, five observations were taken, and the average value was used to determine the coating thickness of each sample. Figure 3f demonstrates that there are minor deviations between the expected and the actual thickness.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Sample** & **I\({}_{\mathbf{S}}\) (A)** & **T\({}_{\mathbf{Depo.}}\) (min)** & **t\({}_{\mathbf{Expected}}\) (\(\mu\)m)** & **t\({}_{\mathbf{Actual}}\) (\(\mu\)m)** \\ \hline T1 & 6.5 & 180 & 2.925 & 2.85 \\ T2 & 6.8 & 180 & 3.06 & 3.10 \\ T3 & 7.7 & 180 & 3.46 & 3.20 \\ T4 & 8.6 & 180 & 3.87 & 3.25 \\ T5 & 9.6 & 120 & 2.88 & 2.60 \\ T6 & 7.0 & 180 & 3.15 & 3.00 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Dependence of coating thickness on substrate current.  
Figure 2: EDS spectra showing titanium and chromium peaks along with SEM image of sample T2.