Corrosion properties of laser cladded CrCoNi medium entropy alloy coating

CrCoNi medium entropy alloy is an intriguing new material showing excellent mechanical properties but little is known about its corrosion properties. In this study, CrCoNi coating is fabricated by laser cladding, and its corrosion resistance and passive film properties in 3.5 wt% NaCl solution and 0.5 M H2SO4 solution have been investigated and compared with SS304. Optical microscope (OM) and Scanning electron microscope (SEM) shows that CrCoNi coating is near-fully dense without evident defects. In 3.5 wt% NaCl solution, CrCoNi coating is more easily corroded than SS304 while its passive film stability is better. The passive film formed on CrCoNi coating is a n-type semiconductor which consists of a single Cr oxide layer and the X-ray photoelectron spectroscopy (XPS) results reveal the presence of Cl- ion. In 0.5 M H2SO4 solution, CrCoNi coating exhibits better corrosion resistance than SS304. Electrochemical impedance spectroscopy (EIS) measurements reveal a slight pitting behavior during immersion and XPS results reveal that the Cr oxide and its hydroxides are the primary constituents of the passive film. Energy dispersive spectrometer (EDS) mapping shows Cr plays an important role in preventing pitting corrosion in both test solutions.