Laser cladding of NiCrSiB on Monel 400 to enhance cavitation erosion and corrosion resistance

NiCrSiB modified layer was synthesized on Monel 400 by laser cladding, aiming at improving cavitation erosion and corrosion resistance. The microstructure, chemical composition, phase constituents and microhardness were investigated using scanning electron microscope (SEM), energy-dispersive spectrometer (EDS), X-ray diffractometry (XRD) and microhardness tester. The cavitation erosion and corrosion behaviors of the modified layer were also evaluated using an ultrasonic vibrator and potentiodynamic polarization measurement, respectively. Experimental results show that by varying the laser fluence, a hard NiCrSiB modified layer with little airholes, cracks or other defects could be obtained. NiCrSiB modified layer is ~1.1 mm in thickness. The microstructure of the modified layer exhibits cellular dendrite, flake-like dendrite and multiple eutectic phase. The modified layer is mainly composed of γ-Ni solid solution, chromium carbide (Cr7C3 and Cr23C6) and Ni3B. The microhardness of the modified layer is ~6.8 times that of Monel 400 substrate. Both the cavitation erosion and corrosion resistance of the modified layer are improved. In the cavitation erosion test, the cumulative erosion loss and erosion loss rate of the modified layer are one order of magnitude lower than that of the substrate. In the electrochemical corrosion test, the corrosion potentials of the substrate and the modified layer are similar. The corrosion current densities of the substrate and the modified layer are 11.12 and 1.95 μA·cm−2, respectively. By comparing their corrosion current densities, the corrosion resistance of the modified layer is about 5.7 times that of the substrate.