Planification of amorphous carbon coatings via periodically transitional sp2/sp3 bonds to enhance cavitation erosion resistance

In the marine sector, hydraulic machinery suffers severe damage from cavitation erosion. Although amorphous carbon (a-C) coatings are an effective measure to enhance the cavitation erosion resistance (CER), their widespread application is hindered by their metastable nature characterized by internal stress. In this study, a planification strategy was employed via different sp2/sp3 distributions (including uniform ones with different sp2/sp3 levels and periodically transitional ones with different periods), aiming to construct a pure a-C coating that enhances CER on 316L stainless steel by modulating the bias during magnetron sputtering. The effects of the sp2/sp3 distributions on the microstructure, chemical bonding, adhesion strength, fracture toughness, corrosion resistance and CER was investigated and compared with the coatings featuring uniform sp2/sp3 distributions. The results show that the periodic-mode coatings exhibit much higher CER due to their lower internal stress, excellent adhesion strength, enhanced fracture toughness and high corrosion resistance. After the cavitation erosion test for 4 h, the periodic-mode coatings only show striped structures without any coating delamination, along with less graphitization tendency during cavitation erosion. Hence, the design approach of periodic sp2/sp3 carbon bonds provides a promising new direction for marine equipment with improved CER and potential applications in various other environments. [Display omitted] •A planification strategy is successfully employed to optimize a-C coatings by modulating the distribution of carbon bonds.•The periodic transition of sp2 and sp3 bonds in a-C coatings effectively mitigates the internal stress.•The periodic-mode a-C coatings exhibit superior adhesion strength and fracture toughness compared to the constant-mode coatings.•The periodic-mode coatings show improved cavitation erosion resistance with the striped morphology appearing four times later than the constant-mode coatings.•The enhanced cavitation resistance of periodic-mode coatings is due to low internal stress, high toughness, and reduced graphitization.