**5. Conclusions**

The present study aimed to find a new and improved possible solution for load-bearing implants. For this purpose, titanium-based carbonitrides with and without the addition of Si were investigated and compared. Both coatings obtained by the cathodic arc deposition method had an almost stoichiometric structure, being solid solution, which consisted of a mixture of TiC and TiN, with a face-centered cubic (FCC) structure. The crystallite size decreased with the addition of Si into the TiCN matrix, the crystallite size of TiCN was 16.4 nm, while for TiSiCN it was 14.6 nm. Both coated surfaces exhibited a uniform coverage, with some microparticles from the ion sputtering and ejection of the particles during the deposition process. After the addition of Si into TiCN, the Ra roughness values decreased, indicating a beneficial e ffect of Si.

All investigated surfaces had positive skewness, which is adequate for load-bearing implants, which work in corrosive environments. The hardness of the TiCN coating was 36.6 ± 2.9 GPa and it was significantly increased to 47.4 ± 1 GPa when small amounts of Si were added into the TiCN layer structure, while the elastic modulus was increased from 277 ± 8 GPa to 310 ± 2 GPa. A significant increase in resistance to plastic deformation (H<sup>3</sup>/E<sup>2</sup> ratio) from 0.63 to 1.1 was found after the addition of Si into the TiCN matrix.

The most electropositive value of corrosion potential was found for the TiSiCN coating (−14 mV), as well as the smallest value of corrosion current density (49.6 nA cm2), indicating good corrosion resistance. The TiSiCN coating exhibited the best protection after immersion in 90% DMEM + 10% FBS, the best capacitive character, indicated by the low value of Qdl**,** and the highest resistance through the pores generated by the defects of the coatings and the electrolyte ingress, indicated by Rpore and Rct.

According to the conducted research, TiSiCN coatings have shown good mechanical properties and high corrosion resistance and are a good alternative for the coating of load-bearing implants.

**Author Contributions:** Conceptualization, A.V. and C.V.; methodology, A.V.; investigation, M.D., P.S., I.G.S., and I.P.; resources, A.V.; data curation, I.P.; writing—original draft preparation, M.D., I.P., and P.S.; writing—review and editing, C.V. and A.V.; supervision, A.V. All authors have read and agreed to the published version of the manuscript.

**Funding:** The present work was supported under a gran<sup>t</sup> of the Romanian National Authority for Scientific Research, CNCS—UEFISCDI, project No. PN-III-P1-1.2-PCCDI-2017-0239/60PCCDI 2018, within PNCDI III. The EDS, SEM, XRD and nanoindentation results were acquired using the systems purchased by the infrastructure project INOVA-OPTIMA SMIS code 49164, contract No. 658/2014. A part of work is also supported by PROINSTITUTIO Project–contract No. 19PFE/17.10.2018.

**Conflicts of Interest:** The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, or in the decision to publish the results.
