Structure and corrosion resistance properties of Ni-Fe-B-Si-Nb amorphous composite coatings fabricated by laser processing

Ni-based amorphous composite coatings with a composition of Ni40.8Fe27.2B18Si10Nb4 have been prepared on a mild steel substrate by high power diode laser cladding plus laser remelting processes. The microstructure of the coating was studied by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). Polarization tests and electrochemical impedance spectroscopy (EIS) measurements were employed to study corrosion behavior of the coatings in 3.5% NaCl solution. The corrosion resistance properties of bulk metallic glasses (BMGs) ribbon with same nominal composition and 316L stainless steel were also measured for comparison. It was found that the laser remelted coatings exhibit dense amorphous structure matrix embedded by some crystal phases. Due to the existence of grain boundaries, the Ni-based amorphous composite coating exhibits worse corrosion resistance than BMGs ribbon. While the laser remelted coating shows better corrosion resistance properties than 316L stainless steel and laser cladded coating. A capacitive loop and a straight line are shown in the Nyquist plot, indicating that a Warburg element can be drawn in the equivalent electrical circuit representative of the laser remelted coating. (C) 2013 Elsevier B.V. All rights reserved.