Cavitation erosion mechanisms in stainless steels and in composite metal-ceramic HVOF coatings

Cavitation erosion is a leading cause of hydraulic machinery erosion: imploding cavitation bubbles cause impacts, pitting, and mass loss leading to the component׳s failure. Damage can be mitigated by the use of protective coatings tailored to resist pitting and crack nucleation, to greatly increase the part׳s lifetime. Coatings deposited with the High Velocity Oxy-Fuel (HVOF) process demonstrate low porosity, high hardness and high adhesion. In this work, the cavitation erosion behavior of martensitic and ferritic stainless steels and HVOF coatings prepared from pure Fe3Al powder and Fe3Al reinforced with nitride and boride phases was investigated using the G32 vibratory setup. The results are compared with coatings sprayed from commercial powders: WC-CoCr and Cr3C2-NiCr. HVOF coatings exhibit slightly lower erosion rates than martensitic stainless steels. The mechanical properties were evaluated using depth sensing indentation: higher hardness was associated with better cavitation erosion resistance for steels, but not for the coatings. The composite coatings' wear mechanisms followed a matrix erosion pattern accompanied by ceramic grain removal.