Evaluation of residual stress and corrosion behaviour of electroless plated Ni-P/Ni-Mo-P coatings
(1. School of Mechanical and Automotive Engineering, Qilu University of Technology (Shandong Academy of Sciences), Ji’nan 250353, China;
2. Corrosion and Protection Centre, School of Materials, The University of Manchester, Manchester, M13 9PL, UK)
2. Corrosion and Protection Centre, School of Materials, The University of Manchester, Manchester, M13 9PL, UK)
Abstract: Single Ni-P and Ni-Mo-P coatings as well as duplex Ni-P/Ni-Mo-P coatings with the same compositions were prepared by electroless plating. The residual stresses of the coatings on the surface and cross sections were measured by nanoindentation and AFM analysis, and the corrosion behaviour of the coatings in 10% HCl solution was evaluated by electrochemical methods, to establish the correlation between the residual stresses and corrosion behaviour of the coatings. The results showed that the single Ni-P and duplex Ni-P/Ni-Mo-P coatings presented residual compressive stresses of 241 and 206 MPa respectively, while the single Ni-Mo-P coating exhibited a residual tensile stress of 257 MPa. The residual compressive stress impeded the growth of the pre-existing porosity in the coatings, protecting the integrity of the coating. The duplex Ni-P/Ni-Mo-P coatings had better corrosion resistance than their respective single coating. In addition, the stress states affect the corrosive form of coatings.
Key words: electroless plating; Ni-P/Ni-Mo-P duplex coatings; residual stress; nano indentation; corrosion resistance