Comparison of the Resistance to Cavitation Erosion and Slurry Erosion of Four Kinds of Surface Modification on 13-4 Ca6NM Hydro-Machinery Steel

The cavitation and slurry jet erosion resistance of surface-coated and thermochemically treated CA6NM 13-4 steel were evaluated in this work. The cavitation erosion experiments followed the ASTM G32 standard, while the slurry jet erosion tests were performed using a homemade tribometer. CA6NM steel was used as substrate and as reference material for all wear experiments. The surface treatments included plasma nitriding and salt bath nitro-carburization, while the coatings evaluated were thermal-sprayed WC-10Co4Cr and a commercial grade elastomeric coating. The microstructures were studied by scanning electron microscopy (SEM) and x-ray diffraction (XRD), and the mechanical properties were estimated by nanoindentation. From the results analysis, it was found that the plasma nitriding permitted high improvement against slurry jet erosion, similarly to the WC-10Co4Cr coating. Moreover, the thermochemical treatments of plasma nitriding and salt bath nitrocarburizing showed better increments of cavitation resistance when compared to the coatings evaluated. Based on these findings, comments on the challenges involved in the manufacture route for hydropower runners with enhanced performance against wear are included.