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Mechanical and corrosion resistance properties of TiO2nanoparticles reinforced Ni coating by electrodeposition

W Shao1, D Nabb

2, N Renevier

3, I Sherrington

3and J K Luo

1

1University of Bolton, UK

2MSC Copperflow Ltd,UK,3University of Central Lancashire,UK

Emails: W.Shao@bolton.ac.uk, J.Luo@bolton.ac.uk

Abstract. Coatings have been widely used in engineering and decoration to protect

components and products and enhance their life span. Nickel (Ni) is one of the most importanthard coatings. Improvement in its tribological and mechanical properties would greatly

enhance its use in industry. Nanocomposite coatings of metals with various reinforced

nanoparticles have been developed in last few decades. Titania (TiO2) exhibit excellent

mechanical properties. It is believed that TiO2 incorporation in Ni matrix will improve the

properties of Ni coatings significantly. The main purpose of the current work is to investigate

the mechanical and anti-corrosion properties of the electroplated nickel nanocomposite with asmall percentage of TiO2. The surface morphology of nanocomposite coating was

characterized by scanning electron microscopy (SEM). The hardness of the nanocoating was

carried out using micromaterials nanoplatform. The sliding wear rate of the coating at room

temperature in dry condition was assessed by a reciprocating ball-on-disk computer-controlled

oscillating tribotester. The results showed the nanocomposite coatings have a smoother andmore compact surface than the pure Ni layer and have higher hardness and lower wear rate

than the pure Ni coating. The anti-corrosion property of nanocomposite coating was carried out

in 3.5% NaCl and high concentrated 35% NaCl solution, respectively. The results also showed

that the nanocomposite coating improves the corrosion resistance significantly. This present

work reveals that incorporation of TiO2 in nickel nanocomposite coating can achieve improved

corrosion resistance and mechanical properties of both hardness and wear resistanceperformances, and the improvement becomes stronger as the content of TiO2is increased.

1. Introduction

Incorporation of ceramic, polymer and metal nanoparticles within metal matrix produces compositecoatings which have many attractive properties such as wear resistance, corrosion resistance,

particularly useful for engineering [1]. Majority of the work has been concentrated on nickel (Ni)coating. The reinforced particles could be SiC, Al2O3, titania (TiO2), carbon nanotubes (CNTs) andpolymers such as Polytetrafluoroethylene (PTFE) and Polyethylene (PE) [2-5]. Among thesereinforcements, TiO2 is one of the most important used in the engineering materials. The titanium-based material offers high strength, good corrosion and oxidation resistance [5], it is believed thatincorporation of nanoparticles can greatly improve the mechanical, tribological properties andcorrosion resistance, hence can be used in industry either in single layer or multilayer structure. In this

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paper, we will report the mechanical properties and corrosion resistance for the TiO2 nanoparticlesreinforced Ni coatings.

2. Experiments

2.1 Preparation of coatingsMild steel plates with the dimension of 20mm20mm1mm were used as the substrates. Beforeelectroplating, the steel substrates were cleaned by alkaline cleaning solution and followed by an acidetch process. De-ionized water was used to rinse after each step, and finally dried by dry N2gas. The

electrolyte used in this study is a standard Watts bath, containing up to 12 g/l TiO2 nanoparticles(Sigma, ~50nm) with suitable surfactant. Electrodeposition took place in the bath of 50

C and at a

current density of 3 A/dm2

for 1hr.

2.2 Characterization of the coatings

A Philips XL30 ESEM (SEM) operating at an accelerating voltage of 15 KV was used to observe thesurface morphologies of the coated samples.

Hardness tests were carried out using a three-sided flat pyramidal diamond flat tip with an angle of

104.3 at room temperature. The indenter was lowered at a rate of 50 nm/s to indent the matrix up to adepth of 500 nm and then to retrieve from the coating surface.

The wear tests were evaluated on a reciprocating ball-on-disk computer-controlled oscillatingtribotester. A tungsten carbide (WC) ball with diameter 6 mm was used as the counter body. All thewear tests were performed using a load of 12 N at 12 mm/s sliding speed in dry condition at roomtemperature.The total sliding distance is 10000 mm.

PG581 potentiostat system was used for electrochemical measurements with three standardelectrodes. The measurements were carried out in a 250 ml cell in 3.5 % NaCl solution at roomtemperature. All the potentials were recorded with respect to saturated calomel electrode (SCE). Prior

to Tafel polarization, the specimens were allowed to immerse in the electrolyte while the open circuitpotential (OCP) was measured until it reached a stable value. Potentiodynamic polarization curveswere recorded from a starting potential of 500 mV below the OCP and were scanned towards thepositive direction at a scan rate of 1 mVs-1, until the potential reached 500 mV. Weight loss methodwas used to assess the corrosion resistance of coatings. The specimens were immersion into 35 %NaCl solution at room temperature in order to accelerate the corrosion rates. The weight differenceswere recorded after 10 days and 20 days immersion.

3. Results and discussion

3.1 Characterization of Ni nanocomposite coatingsFigure 1 shows the SEM morphologies of Ni coating and Ni-TiO2nanocoating containing 12 g/l TiO2nanoparticles. The microstructures between pure Ni coating and Ni-TiO2 nanocoating are differentsignificantly. The Ni coating has a rather regular structure with large grain size in the range of 2~4 m(Figure 1a). The Ni-TiO2 nanocoating shows smaller gain sizes of 0.1~1 m (Figure 1b), whichindicates that the co-deposited TiO2 nanoparticles are much uniformly distributed in the Ni matrix. Itshows that Ni-TiO2nanocoating has fairly uniform, continuous and compact morphology.

3.2 Hardness of Ni nanocomposite coatingsFigure 2 shows the microhardness of Ni coating and Ni-TiO 2nanocoatings with the different contentsof TiO2 nanoparticles. It can be seen that the hardness of Ni-TiO2 nanocoating increases withincreasing the content of TiO2nanoparticles, and that with 12 g/l TiO2nanoparticles has the maximumhardness of 387 HV, clearly demonstrated its significant effect. This is because the co-deposited TiO2nanoparticles in the Ni matrix can restrain the growth of the Ni grains resulting in the very fine grain

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attributed to contribute to the improvement of anti-corrosion property. Figure 6 shows the weight lossresults for different Ni based coatings immersed in 35 % NaCl solution for 10 days and 20 days,

respectively. It is evident that TiO2 nanoparticles reinforced Ni has a good tendency for corrosionresistance compared with pure Ni coatings.

(a) (b)Figure 4.SEM of worn surfaces (a) pure Ni coating, (b) Ni-TiO2nanocoating.

Figure 5.Tafel curves of Ni andNi-TiO2nanocoatings.

Figure 6.Weight loss results after 10 days and20 days in 35 % NaCl solution.

Table 1.Electrochemical parameters and calculated corrosion rates for tested coatings.

Samples Ecorr [mV] Icorr[A] Rcorr[mpy]

Ni coating

Ni-TiO2(4 g/l)

Ni-TiO2(8 g/l)

Ni-TiO2(12 g/l)

-755

-742

-733

-727

333

314

296

258

15.3

14.4

13.6

11.5

4. Conclusions

TiO2 nanoparticles reinforced Ni nanocomposite coatings revealed a much smoother surface

microstructure with excellent mechanical properties. The Ni-TiO2 nanocomposite coatings exhibitedhigher hardness and higher wear resistance in comparison with pure Ni coating. Meanwhile, thecorrosion resistance has been enhanced significantly.

5. Acknowledgement

The authors would like to acknowledge the financial support by Knowledge Transfer Partnership and

TSB (KTP007867) and The Knowledge Centre for Materials Chemistry under Grant No. of X00680PR.

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[5] A.A.Aal: Mater. Sci. Eng., A, vol.474 (2008), p181[6] L. Shi, C. Sun,P. Gao, F. Zhou and W. Liu: Appl. Surf. Sci., vol. 252 (2006), p. 3591

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