**4. Conclusions**

Stainless steel is used for manufacturing different components and considered to be a structural metal with moderate resistance to cavitation erosion. The application of PVD coatings is proposed as a promising solution, easy to implement in industrial practice, for preventing the wear of stainless steel parts. In the present work, the cavitation erosion and sliding wear mechanism of magnetron-sputtered AlTiN and TiAlN coatings deposited on SS304 stainless steel (SS) were investigated. The following conclusions have been drawn:

1. The properties of the films demonstrate that they have a satisfactory structure, i.e., they exhibit a typical columnar morphology comparable to the roughness of the SS substrate, however it varies in thickness, amounting to ≈2.7 μm for TiAlN and ≈3.8 μm for AlTiN. Also, the Rockwell and scratch test results of the films indicate their satisfactory adhesion to the SS substrate, even though a higher force of the Lc2 parameters for AlTiN than TiAlN suggests that AlTiN adheres more strongly to the substrate. The AlTiN film exhibits highly elastic behavior and high resistance to plastic deformation, i.e., its H/E and H<sup>3</sup>/E<sup>2</sup> coefficients are higher than those of TiAlN, which can be attributed to its chemical composition, i.e., a higher Al/(Ti + Al) ratio of the AlTiN film.


**Author Contributions:** Conceptualization, M.S.; Methodology, M.S.; Formal Analysis, M.S. and M.W.; Investigation, M.S., K.P. and M.K.; Writing—Original Draft Preparation, M.S.; Writing—Review & Editing, M.S.; Visualization, M.S., K.P. and M.K.; Supervision, M.S. and M.W.

**Funding:** The research was financed in the framework of the project Lublin University of Technology—Regional Excellence Initiative, funded by the Polish Ministry of Science and Higher Education (contract No. 030/RID/2018/19).

**Conflicts of Interest:** The authors declare no conflict of interest.
