Electroless Ni-P-MoS₂ Composite Coating on TC4 Titanium Alloy

The effects of stirring ways,types and concentrations of surfactants on deposition rate and MoS2 concentration of electroless Ni-P-MoS2 composite coating were studied,the morphology and element distribution were tested using 3D video microscopy,SEM and EDS,the activation status and deposition ways of MoS2 were also studied.The experiment results indicated that fast deposition rate,high MoS2 particle content and uniform distribution were all achieved by using interval stirring since it could make all the ions and MoS2 particles well dispersed in the bath,as well as reduce the falling off of MoS2 particles.Under the combined action of specific adsorption and steric hindrance,the deposition rate and MoS2 content of electroless Ni-P-MoS2 composite coating were both guaranteed by adding single cationic surfactant to the bath.On account of the intense interaction of cationic and anionic surfactants,MoS2 particles were equally distributed in the coexistence of cationic and anionic surfactant.Activated MoS2 particles in bath were delivered to the surface of Ni-P coatings by stirring and electric force,while unactivated MoS2 particles in bath reached the surface of Ni-P coatings only by stirring.After catalysis,the MoS2 particles which were completely or partly activated in bath were completely or partly packed by nickel coatings,while the MoS2 particles which were not activated in bath were adhered to the surface of Ni-P coatings.