Laser surface remelting of Fe-based alloy coatings deposited by HVOF

Fe-based alloy coatings were deposited onto Fe360A (ISO 630) substrates by the High Velocity Oxy-Fuel (HVOF) technique. A Nd:YAG laser was used to remelt surfaces of the coatings. The experimental parameters were determined using an orthogonal experimental design approach. The microstructure and microhardness were studied using a metallographic microscope and a microhardness tester. The phase compositions were investigated by X-Ray Diffractomer (XRD). The effect of laser surface remelting on the corrosion resistance of Fe-based alloy coatings was evaluated by electrochemistry methods using a 10 wt.% NaOH solution. It was found that there were four types of typical shapes of laser surface remelting pools. Large holes inside the coatings could be avoided when the remelted thickness was equal to or greater than the thickness of as-sprayed coatings. The microstructure of the laser surface remelted coatings was homogeneous, and its microhardness was promoted from an average of 600 HV0.1 to 900 HV0.1 because of emergence of the high hardness compounds such as SiO2 and Fe3Si after laser surface treatment. The remelted thickness was found to have a linear relationship with the laser power density, while the microhardness of laser surface remelted coatings exhibited a parabolic relationship. Analysis of the polarization curves showed that the free corrosion current density of laser surface remelted coatings could be lowered down from 25.63 μA/cm2 to 12.99 μA/cm2. Results of the electrochemical impedance spectroscopy (EIS) also indicated that laser surface remelting could improve the corrosion resistance of Fe-based alloy coatings.