## 2 Materials and Methods
### Coating Characterization Methods  
Surface morphology and coating thickness were characterized in Scanning Electron Microscopy (SEM) FEI Inspect F50. The chemical compositions were determined using an energy-dispersive X-ray spectrometer (EDS) Ametek, Octane Super-A. The coating adhesion on the carbide substrates was evaluated following the Daimler-Benz test method with a conical Rockwell C intender (120\({}^{\circ}\) diamond cone, 200 \(\upmu\)m radius) and a load of 1471 N [21]. The damages caused by the indentation on the layer adjacent to edges of the impressions were evaluated in scanning electron microscopy. The assessment of the coating adhesion was based on six-mode scales. HF1 to HF4 indicate sufficient adhesion, whereas HF5 and HF6 refer to poor adhesion to the substrate. Microhardness was measured using a Vickers microhardness indenter with 40 gf (MMT-XrA, MATSUZAWA CO., Yokosuka, Japan) according to ASTM E384. The tribological behavior of the coated carbide specimens was evaluated through the dry sliding wear test and dry sand-rubber wheel abrasion testing (DSRW). Five coated carbide samples were tested using both wear tests.  
The dry sliding wear test was carried out using a pin-on-disk instrument (Tribometer TRB3, Anton-Paar, Graz, Austria) according to ASTM standard G99. A ball made of Al\({}_{2}\)O\({}_{3}\) and having a diameter of 6 mm was used as a counter body. The tests were conducted using a constant normal load of 10 N and a sliding distance of 10\({}^{6}\) mm. The selected sliding speeds were 50 mm/s, 100 mm/s and 250 mm/s. Tests were conducted at 24 \({}^{\circ}\)C and 65% of relative humidity. A Surtronic S-100 Series surface profiler was used to measure the depth and width of the wear tracks at ten different locations in order to calculate wear rates. The morphology and composition of the worn surfaces, i.e., coated samples and alumina balls were characterized in Scanning Electron Microscopy equipped with an Energy-Dispersive X-ray Spectrometer. Three-body abrasion tests were performed according to ASTM standard G65 (procedure C), which is defined specifically for the use on thin coatings. The abrasive body was silica sand AFS 50/70. The sand flow rate, the applied force, and the wheel revolution were 330 g/min, 130 N, and 100, respectively. The latter parameters resulted in a lineal abrasion of 71,800 mm. The wear rate of each tested specimen was calculated as shown in Equation (1) [22].  
\[\text{Volume loss},\ \text{mm}^{3}=\frac{\text{mass loss}(\text{g})}{\text{density }(\text{g}/\text{cm}^{3})}\times 1000 \tag{1}\]  
\begin{table}
\begin{tabular}{c c c c} \hline
**Coating** & **Target** & **Temperature Deposition** & **Bilayer Period** \\ \hline CrN/AlTiN & Cr and TiSi80/20 & 250 \({}^{\circ}\)C & 1:1 \\ \hline CrN/CrCN & Cr & 250 \({}^{\circ}\)C & 1:1 \\ \hline CrN/CrCN/DLC & Cr & 250 \({}^{\circ}\)C & 1:1 \\ \hline CrCN/TiSiCN & Cr and AlTi67/33 & 250 \({}^{\circ}\)C & 1:1 \\ \hline \end{tabular} The purity of all targets was 99.999 wt.%. The diameter of all targets was 150 mm. The DLC layer is a-C: H, dopped with Cr element.  
\end{table}
Table 1: Target material, temperature deposition and bilayer periods of the coatings deposited at Aurora Co.  
The adjusted volume loss (AVL) value was calculated according to the Equation (2) as the rubber wheel decreased in diameter [22].  
\[\text{AVL}=\text{measured volume loss}\ \times\frac{228.6\ \text{mm}\ (9\ \text{in.})}{\text{wheel diameter after use}} \tag{2}\]