Microstructure and Corrosion Behaviour of Ni-P Laser Surface Alloys

Abstract

Two different coat thickness electroless Ni-P deposits on mild steel were laser treated at different laser scanning rates. To generate a coated surface of various square centimeters, five laser tracks were realized overlapping 50% of each other. The Ni-P coated samples treated in this way were microstructurally characterized and its corrosion behaviour on 0.1M Na₂SO₄ solution was determined. As a consequence of the laser interaction, a dendritic solidification microstructure was obtained for all the Ni-P coatings–initially amorphous–tested independently of its coat thickness or the laser treatment condition. The low corrosion resistance of laser treated Ni-P coatings of 45 μm coat thickness makes them not suitable for technological applications. However, laser treatment of Ni-P coated samples with the maximum coat thickness tested (180 μm) enhances its corrosion resistance in the medium studied.