Preparation And Properties Of Ni-Mo-P/MoS₂ Coating On Steel Substrate With Ultrasonic–Assisted

In this paper,Ni-Mo-P ternary alloy coating and Ni-Mo-P/MoS2 composite coating were successfully prepared on low carbon steel by electroless plating.Ultrasonic,sodium molybdate content in the bath,high temperature heat treatment and the effect of MoS2 particles on the morphology,structure and properties of the coating were investigated.The main analytical methods used are:field emission scanning electron microscopy?SEM?,X-ray diffractometry?XRD?,transmission electron microscopy?TEM?,atomic force microscopy?AFM?,X-ray photoelectron spectroscopy?XPS?,microhardness tester.Wait.The results are as follows:As the content of sodium molybdate in the plating solution increases,the content of Mo and P in the coating also increases,but the content is too high and the inhibition effect is also observed.It was found that with the addition of Mo metal,the corrosion resistance and hardness of the plating layer can be improved.0.6 g/L sodium molybdate gives the best corrosion resistance(7.06?A cm^-2).The best hardness?698 HV?was obtained with 0.4 g/L sodium molybdate.Ultrasonic assist can increase the deposition rate,make the coating smoother and more uniform,and the structure is more compact.The corrosion resistance(5.81?A cm^-2)and hardness?886 HV?of the coating were further improved.The coating was annealed at 300?,400? and 600?,respectively.It was found that the heat treatment caused the plating layer to change from an amorphous state to a crystalline state,and a precipitation of the Ni₃P phase,which greatly enhanced the hardness of the plating layer?1042.6 HV?.However,the heat treatment causes P in the plating layer to be precipitated outward,and defects such as grain boundaries and dislocations appear inside.Causes a decrease in the corrosion resistance of the coating.In the Ni-Mo-P/MoS₂ composite coating,the MoS₂ particles act only as impurities and become the core of the Ni-Mo-P alloy nucleation or randomly dispersed in the coating.The presence of MoS₂ particles increases the porosity and surface roughness of the coating,and due to the non-uniformity of the coating structure,micro-cells are formed,causing galvanic corrosion,resulting in a decrease in corrosion resistance of the Ni-Mo-P/MoS₂ coating.However,MoS2 particles can increase the hardness of the coating.