Effects of ruthenium and nickel on the microstructure and corrosion properties of a laser alloyed AISI 316L stainless steel surface

Four AISI 316L samples were laser surface alloyed with: 100wt% Ru powder, 100wt% Ni powder, and a mixture of Ni and Ru powders, 50wt% Ni-50wt% Ru and 80wt%Ni-20wt%. The laser power, beam diameter, and scan speed were fixed at 4 kW, 4 mm, and 0.8 m/s, respectively. The microstructure and elemental composition of the deposited layers were analysed using optical and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) and in addition the electrochemical characteristics were determined. The laser alloyed layer was 1.8 mm thick, hard, non-porous, and crack free layer that formed a dendritic, non-uniform elemental distribution, and an inhomogeneous microstructure. The microstructure of the layers depended on the composition of the powder used. The sample alloyed with 100wt% Ru powder showed mainly a columnar dendritic structure, while the sample alloyed with 100wt% Ni powder showed an equiaxed dendritic structure. The sample treated with 100wt% Ru had the most noble corrosion potential at −50 mV and the lowest current density at 25 µA/cm2 in 60wt% sulphuric acid solution at 45 °C.