Cavitation erosion behavior of nanocomposite Ti–Si–C–N and Ti/Ti–Si–C–N coatings deposited on 2Cr13 stainless steel using a Plasma Enhanced Magnetron Sputtering process

In the work presented in this paper, the liquid droplet erosion resistance of two nanocomposite Ti–Si–C–N single layer coatings (SMR1 and SMR3) and one multilayer structured nanocomposite Ti/Ti–Si–C–N coating (SMR2) on 2Cr13 stainless steel has been investigated by means of cavitation erosion. Three sets of 2Cr13 samples were deposited using a Plasma Enhanced Magnetron Sputtering (PEMS) process using different parameters to 35 µm, 68 µm and 59 µm thick. The cavitation erosion resistance of the coatings was evaluated with a vibratory cavitation apparatus in distilled water and in a 3 wt.% NaCl solution; the latter was used to simulate an aggressive environment. The surface and cross-sectional morphologies of the samples were studied using scanning electron microscopy (SEM) before and after the cavitation erosion tests. The results from the investigation indicate that the three coatings exhibited excellent cavitation erosion resistance in both media compared with the uncoated substrate. The cavitation erosion resistance of the thicker single layer coating SMR3 and the multilayer coating SMR2 was especially pronounced, while SMR1 was not so satisfactory because microcracks extended to the substrate due to its small thickness. The SMR2 coating effectively prevented the propagation of the microcracks in a manner of layer-by-layered spallation, owing to its multilayer structure. Even though the coatings improved the erosion resistance of the substrate, the SEM study revealed that there were many micro-droplets and V-shaped defects in the coatings, which formed the nucleation sites for the coating spallation. Therefore, if the size and the number density of the micro-droplets can be reduced and the coatings can be made more homogeneous, without V-shaped defects, the cavitation erosion resistance of coated 2Cr13 steel should be further improved.