Effect of electroless Ni-B, Ni-P/Ni-B ve Ni-B/Ni-P coatings on surface properties of AISI 316l stainless steel

The AISI 316L austenitic stainless steels are widely used in different industrial areas due to its very high corrosion resistance in many aqueous environments. However, their low hardness and low wear resistance are disadvantageous properties for possible industrial applications. Conventional nitriding and heat treatment processes improves the low hardness and wear resistance, but generally decreases the corrosion resistance due to affected very quickly from attack of chloride ion in aqueous solution. Electroless nickel alloy coatings are known for providing a hard, wear and corrosion resistant surface. Thus, the present study aimed to investigate the wear, corrosion and tribocorrosion behaviours of single layer Ni-B and duplex Ni-P/Ni-B and Ni-B/Ni-P coated on 316L steel in comparison with untreated 316L steel in dry and 0,9 wt.% NaCl solution environments. It was determined that the coatings had a mixture of crystal and amorphous structures with the results of XRD analysis. OM observations of cross-section showed that the duplex interfaces on the 316L were uniform and the compatibility between the layers were good. The coatings reached the highest hardness and surface roughness values by deposition of the Ni-B and Ni-P/Ni-B coatings. Ni-B coating due to its high hardness had the lowest wear volume and wear rate values in dry and corrosive wear environments compared to untreated 316L and other duplex coatings. SEM images of the Ni-B coating showed that it increased the resistance to plastic deformation and prevented the adhesion between the contact surfaces. Although the Ni-P/Ni-B coating had the highest corrosion potential, the Ni-B coating exhibited similar corrosion properties with this coating. All test results showed that the mechanical effect was more dominant than corrosion effect. The use of Ni-B can be suggested instead of duplex coatings for 316L steel in synergistic combination of mechanical (wear) and chemical (corrosion) processes.