Microstructural characterisation and corrosion behaviour of electroless Ni-W-P deposits of mixed nanocrystalline/amorphous structures

An investigation has been undertaken of the influence of the mixed nanocrystalline and amorphous microstructure on the corrosion behaviour of electroless Ni-5.5W-6.5P (wt-%) deposits on steel substrates. The effects of annealing temperature on microstructure evolution were investigated. The corrosion behaviour of the deposits was evaluated by potentiodynamic polarisation in 0.5M H2SO4 solution and EIS measurements in 3.5%NaCl solution. Relationships between the microstructure and corrosion mechanisms of the as plated and the annealed deposits were considered by reference to microstructural information, including degree of crystallisation, grain sizes of both nickel and Ni3P phases, porosity development, microstrains and residual stresses.