Effect of Rare Earth on the Corrosion Resistance of Electroless Ni-Mo-P Composite Coatings

Abstract

A kind of corrosion-resistant Ni-Mo-P composite coating was deposited on the surface of AZ91D magnesium alloy substrate by electroless plating method with different concentration of Ce(NO 3 ) 3 and Nd(NO 3 ) 3 . The deposition mechanism of Ni-Mo-P composite coating was explored. Furthermore, the effects of Ce(NO 3 ) 3 and Nd(NO 3 ) 3 concentration on the microstructure and properties of Ni-Mo-P composite coatings were studied. Results indicated that the Ni-Mo-P composite coatings prepared by adding the optimal concentration of Ce(NO 3 ) 3 and Nd(NO 3 ) 3 had few defects. Meanwhile, the deposition rate of the composite coatings and the adhesion between the coating and the magnesium alloy substrate were improved. When the concentration of Ce(NO 3 ) 3 and Nd(NO 3 ) 3 were 0.10 and 1.00 g/L, the Ni-Mo-P composite coatings had the minimum corrosion rate of 0.826 and 0.681 g/m 2 •h, respectively. Herein, compared with the addition of Ce(NO 3 ) 3 , the Nd(NO 3 ) 3 added Ni-Mo-P composite coating has the maximum arc radius of capacitive resistance and significant improvement corrosion resistance.

Effect of rare–earth (Ce, La) compounds on the microstructure, mechanical and electrochemical corrosion characteristics of electroplated Ni films

“…According to the Tafel linear extrapolation method, the fitted parameters of corrosion potential (E corr ) and corrosion current density (i corr ) for different RE compound modified Ni films were shown in figure 7(c). It was identified that the corrosion tendency and degree were represented by the E corr and i corr , and the stronger anti-corrosion resistance was indicated by a more positive E corr and lower i corr [10,24]. In comparison to those by DC-electrodeposition, the E corr of both RE compound modified Ni films by PC-electrodeposition moved positively and the i corr decreased at different degrees, which demonstrated the both decrease in thermodynamic corrosion tendency and dissolution rate.…”

“…(2)Owing to the large ionic radius and unique outer layer electronic structure, both RE ions tended to characteristically adsorb on the crystal activity sites of growth points, which impeded the preferential growth of Ni coarsening crystals subsequently [21,23,24,30]. Also, the adsorbed RE ions provided a large number of electron orbital holes or free electrons, which decreased the surface activation energy and increased the nucleation rate of the Ni2+ reduction [20,30,31].…”

“…For example, Liu et al [21] and Zhang et al [22] increased the corrosion resistance of electroless or DC-electrodeposited Ce-modified Ni-Cu layers by grain refinement, and Wang et al [23] optimized the surface consistency, microhardness, and corrosion property of Ni layer by La 3+ . Moreover, Li et al [20] revealed that Y 3+ had a more positive effect on bath stability and corrosion potential of nickel-phosphorus deposits than La 3+ , and Jia et al [24] further reported that the performance of Ni-Mo-P coatings could be better obtained by adding Nd 3+ rather than Ce 3+ at optimum concentration.…”

A comprehensive review of properties of the biocompatible thin films on biodegradable Mg alloys

“…The corrosion test results showed that the MAO coating, which was sealed in a Ce bath for 10 min, enhanced the corrosion resistance of the substrate significantly with lower porosity [72]. Jia et al [73] developed a composite coating of Ni-Mo-P by electroless plating with different Ce(NO 3 ) 3 and Nd(NO 3 ) 3 concentrations. With the increase in the concentration of Ce(NO 3 ) 3, the I corr of the composite coatings decreases to 0.10 g l −1 and later, the corrosion resistance gradually deteriorates due to the Ce(NO 3 ) 3 concentration exceeding 0.10 g l −1 [73].…”

“…Jia et al [73] developed a composite coating of Ni-Mo-P by electroless plating with different Ce(NO 3 ) 3 and Nd(NO 3 ) 3 concentrations. With the increase in the concentration of Ce(NO 3 ) 3, the I corr of the composite coatings decreases to 0.10 g l −1 and later, the corrosion resistance gradually deteriorates due to the Ce(NO 3 ) 3 concentration exceeding 0.10 g l −1 [73]. Jiang et al developed Ce-V coating on AZ31 Mg alloy by CC technique to improve corrosion resistance.…”