Cavitation erosion of monolayer PVD coatings-An influence of deposition technique on the degradation process

TiN, Cr-N, W, WC and WC/a-C: H coatings produced using Physical Vapour Deposition (PVD) method were investigated. TiN and Cr-N coatings were deposited using the cathodic arc evaporation (CAE-PVD) and reactive magnetron sputtering (RMS-PVD) techniques. W, WC and WC/a-C: H coatings were produced by the reactive magnetron sputtering (RMS-PVD) technique. Coatings were exposed to cavitation using a tunnel with a system of barricades. The influence of the deposition technique on the structure of the coating as well as on the degradation process has been discussed. It has been shown which degradation processes are independent of deposition techniques and which are dependent on them. The deposition technique had a higher impact on the droplet density (over 20-fold) than the deposited compound (nearly 2-fold). The highest density of droplets had TiN coatings deposited by the CAE-PVD technique, while the lowest had W-based coatings deposited by the RMS-PVD technique. The first symptoms of cavitation erosion of PVD coatings included the removal of some droplets from the coating surface and the coating undulation. The size of droplets did not affect their removal. Droplets can be divided into 1) droplets easy removable from the coating, 2) droplets requiring specific impact energy for their removal, and 3) droplets not removable from the coating, regardless of the degree of cavitation erosion development. Regardless of the deposition technique (CAE and RMS) and coating type (TiN or Cr-N), cavitation caused the phase transformation Fe-gamma -> Fe-alpha ' in the austenitic steel substrate. The intensity of this transformation depends on the deposition technique. High intensity of the phase transformation was obtained in the RMS coatings which are characterised by a low density of droplets. On the surface of the RMS coatings a larger size of puncture was formed than on the CAE coatings. It is shown that the droplets play an important role in the degradation as they are stress concentrators and also absorb some of the impact energy and affect the amount of energy used for fracture and transferred to the substrate.

Automated summary

Different PVD deposition techniques have varying impacts on coating structure and degradation processes, with deposition technique having a higher influence on droplet density than the deposited compound. TiN coatings deposited by CAE-PVD technique have the highest droplet density, while W-based coatings deposited by RMS-PVD technique have the lowest. Cavitation erosion causes phase transformation in the steel substrate and the intensity of this transformation depends on the deposition technique and the density of droplets on the coating surface.