Efect Of Rare Earth On The Process And Corrosion Resistance Of Ni-P Alloy Gradient Coatings

The rare earth element has successfully been applied in surface treating techniques such aselectroplating, hot galvanization, conversion film and heat-treatment. Amorphous alloycoating has attracted great interest owing to its favorable physical and chemical properties. Asone of the promising materials, functionally graded materials(FGM) have been developedunder the high requirement of modern industry. In addition, the adhesive strength betweencoating and substrate as well as the corrosion resistance of the coatings can be improvedefficiently by its component and structure compatibility.Employing chemical plating method, amorphous Ni-P alloy coating using the differenttypes of rare earth as additives is prepared using the LY12alloy as substrate in this paper. Theinfluence of different type and content of rare earth on the composition, microstructure,micro-hardness and corrosion resistance of Ni-P amorphous alloy coatings were analysed bymeans of SEM, EDS, XRD and orther instruments.The results show that the microhardness and corrosion resistance of Ni-P coating areimproved by adding the rare earth which can be able to increase the content of totalphosphorus in the coating and enhance the extent of amorphization. The comprehensiveproperty of Ni-P coating with0.15g/L Y(NO3)3rare earth is the best. The microhardness is641HV and the corrosion resistances of Ni-P coating in neutral, acidic and alkaline solutionsare excellent.In addition, Ni-P alloy gradient coating was prepared. The internal structure of Ni-P alloygradient coating was changed from crystalline to crystalline and amorphous and then toamorphous by means of altering the P content. The results show that the cohesion between thecoating and substrate and the corrosion resistances of Ni-P gradient plating is better than that of the amorphous Ni-P alloy coating in neutral, acidic and alkaline solutions.