# Deposition of 3 YSZ-TiC PVD Coatings with High-Power Impulse Magnetron Sputtering (HiPTMS)
## 4 Discussion  
A parameter study based on the HiPIMS parameters of the working gas flow, frequency, on-time cathode, on-time bias and offset bias was conducted, and the influence of the mentioned parameters on the measured current at the substrate table was determined. As expected, by using the conductive target material, the disappearing anode effects were not observed during all of our measurements. The authors did not expect a maximum table current with a low gas load, as shown in Figure 1. However, one can interpret the low gas load as the formation of a third working gas, presumably consisting of carbon monoxide, which is produced by the decomposition of the target itself. With this autogenously formed working gas, the maximum table currents at an expected unstable gas mix of argon and krypton are possible. Zirconia \begin{table}
\begin{tabular}{c c c} \hline \hline
**Element** & **Target** & **Coating** \\ \hline Carbon (C) & 24.7 \(\pm\) 2.1 & 29.2 \(\pm\) 1.1 \\ Oxygen (O) & 47.0 \(\pm\) 4.1 & 34.5 \(\pm\) 1.5 \\ Titanium (Ti) & 11.7 \(\pm\) 0.6 & 15.1 \(\pm\) 0.5 \\ Yttrium (Y) & 0.7 \(\pm\) 0.1 & 1.3 \(\pm\) 0.3 \\ Zirconium (Zr) & 15.9 \(\pm\) 2.0 & 19.9 \(\pm\) 1.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Atomic composition (as a percentage) of the 3 YSZ-TiC target material and coating. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Gas Mix** & **t\({}_{\text{p,on (\upmu s)}}\)** & **t\({}_{\text{s,on (\upmu s)}}\)** & **ts, Offset (\(\upmu\)s)** & **Max. Table** \\
150 Ar0 Kr & 20 & 50 & 20 & 152.1 \\
100 Ar50 Kr & 30 & 40 & 30 & 114.1 \\
50 Ar200 Kr & 30 & 60 & 30 & 79.6 \\
0 Ar550 Kr & 20 & 40 & 20 & 56.7 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Highest values of the maximum table currents. All measurements were executed with a 500 Hz HiPIMS frequency. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Property** & **Unit** & **Values** \\ \hline Hardness & GPa & 24.5 \(\pm\) 2.5 \\ Young’s modulus & GPa & 415 \(\pm\) 44 \\ Thickness & \(\upmu\)m & 0.9 \(\pm\) 0.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mechanical properties of a 3 YSZ-titanium carbide (TiC) coating on WC-Co specimens. (ZrO\({}_{2}\)) and titanium carbide (TiC) are known for their reactive behavior with each other in high-energy environments [15], so it is possible that the oxygen from ZrO\({}_{2}\) reduces the TiC and takes part in the sputtering process as a third working gas. In our study, we also tried to restart the plasma with a low gas load, and it did not ignite, another indication of the formation of a carbon monoxide gas from the target material. The EDX measurements strengthen this theory, because the coating lost a significant amount of oxygen. The EDX values of carbon are often not that reliable. Another theory behind the high currents is based on HiPIMS technology. The two peaks in the gas flow mix measurements are probably a case of a dominating self-sputtering mechanism, based on the [PERSON] model of self-sputtering shown elsewhere [16]. With a high gas load mix, the gas sputtering of argon and krypton dominates the process. Due to the low ionization energy of metals (here zirconium and titanium) compared with argon, the concentration of the doubly charged metal ions of the sputtered species is expected to be high [17]. High doubly charged metal ions are necessary for the self-sputtering process. Like [PERSON] and [PERSON], we needed an ignition phase of the plasma [18; 19]. In our case, we started our discharge with a higher gas mix. By reducing our gas mix (e.g., 150 sccm Ar, 0 sccm Kr), we sponsored the shift from gas sputtering to self-sputtering. The dominating metal ion species created more and more secondary electrons and led to high discharge currents. The currents measured at the table were also an indication of the self-sputtering runaway described by [PERSON] and [PERSON] [16; 17].