Effects of laser nanocrystallisation on the wear behaviour of electroless Ni–W–P coatings

An investigation into the relationships between the microstructure and wear behaviour of electroless Ni–W–P coatings with different phosphorus contents (i.e. Ni–4.1 W–11.3 P and Ni–4.9 W–5.9 P in wt.%) and under different thermal treatment processes (i.e. by a furnace and a laser) has been performed. The work shows that the microstructures and morphology of the coatings involving nanocrystallisation, phase transformation, porosity formation and grain growth could be controlled by changing the phosphorus content of the Ni–W–P matrix and by performing different thermal treatments. The best wear resistance for both coatings was achieved with the laser treatment. For laser treatment, the alternation of hard and soft zones resulting from overlapping for large area coverage is beneficial for wear resistance. The wear mechanism is mainly associated with the characteristic of nanocrystalline structure before and after heat treatments, in terms of the volume fraction of various phases, grain size of Ni3P phase and amount of porosity present in the coating.

► Quantitative XRD allowed investigation of nanocrystallinity (volume, size of each phase),
► Laser annealing demonstrated superior wear resistance to furnace treatment.
► Alternation of hard/soft zones by laser overlap benefited wear resistance.
► Wear mechanisms depended on nanocrystalline characteristics of the coatings.