Microstructural evolution and corrosion properties of Fe-based amorphous coating by laser cladding on 316L stainless steel

The aim of the present study was to investigate the feasibility of fabrication of a Fe53.4Cr20Mo16Cu0.6C10 amorphous and amorphous-crystalline crack-free layer with desirable corrosion resistance and hardness using the laser surface melting technique The phase analysis of clad layers has been characterised by X-ray diffraction (XRD). Also, the microstructure and phase analysis of the cross-section of clad layers has been studied by scanning electron microscopy, field emission scanning electron microscopy, and energy dispersive spectrometry. The effect of laser scanning speed on microstructure, corrosion behaviour, and hardness was investigated at 4, 6, and 8 mm s-1. The results showed that a high fraction of amorphous phase (90%) has been obtained at an 8 mm s−1 scan rate. The coating thickness is more than 150 μm, fully dense having low porosity. The corrosion resistance of Fe-based coatings was investigated by potentiodynamic polarisation and electrochemical impedance spectroscopic tests, and pitting corrosion evaluated in HCl solutions. The laser-treated material coatings had a lower current density than the substrate due to the formation of an amorphous phase, and the corrosion resistance values were 56, 162, and 141 Ω.cm2 for 4, 6, and 8 mm s−1 scanning rate samples respectively. It was found that high corrosion resistance is related to coating with a 6 m s−1 scan rate due to the mixture of galvanic effects and amorphous structure. The average measured micro-hardness of the coatings demonstrated that the sample formed from the highest scan rate possessed the highest micro-hardness, which was 824 HV.