TiC–Y2O3 nanocomposites by one-step electrodeposition at different duty cycle and evaluation of structural, surface and performance as protective coating

Journal Pre-proof Fabrication of Ni–B/TiC–Y2O3 nanocomposites by one-step electrodeposition at different duty cycle and evaluation of structural, surface and performance as protective coating Baosong Li, Weiwei Zhang, Tianyong Mei, Yicheng Miao PII:

S0925-8388(20)30251-6

DOI:

https://doi.org/10.1016/j.jallcom.2020.153888

Reference:

JALCOM 153888

To appear in:

Journal of Alloys and Compounds

Received Date: 29 September 2019 Revised Date:

9 January 2020

Accepted Date: 15 January 2020

Please cite this article as: B. Li, W. Zhang, T. Mei, Y. Miao, Fabrication of Ni–B/TiC–Y2O3 nanocomposites by one-step electrodeposition at different duty cycle and evaluation of structural, surface and performance as protective coating, Journal of Alloys and Compounds (2020), doi: https:// doi.org/10.1016/j.jallcom.2020.153888. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Credit Author Statement

Baosong Li: Conceptualization, Methodology, Resources, Supervision, Writing- Original Draft & Editing. Weiwei Zhang: Methodology. Tianyong Mei: Investigation. Yicheng Miao: Investigation.

Fabrication of Ni-B/TiC-Y2O3 nanocomposites by one-step electrodeposition at different duty cycle and evaluation of structural, surface and performance as protective coating Baosong Li a, *, Weiwei Zhang b, Tianyong Mei a, Yicheng Miao a a

College of Mechanics and Materials, Hohai University, Nanjing 211100, China

b

College of Mechanical and Electrical Engineering, Hohai University, Changzhou 213022,

China *

Corresponding author. E-mail address: [email protected] (B. Li)

Abstract A novel Ni-B/TiC-Y2O3 nanocomposites has been synthesized by one-step pulse electrodeposition at different duty cycle as protective coating. The effects of pulse duty cycle on its structural, surface, corrosion an wear behavior were evaluated. The coating exhibits compact and hill-valley like structure. The average roughness (Sa) was about 56-161 nm and duty cycle of 30% benefits low roughness and fine-grained structure. The crystallite size is 16-19 nm and slightly varied with process parameters. The coating exhibits the preferred orientation of Ni (111) texture. AFM and XPS were utilized to analyze the surface properties. Electrochemical impedance and wear studies illustrated that duty cycle of 30% was the optimal parameter for the best corrosion and wear resistance, exhibiting an excellent long-term performance stability in 3.5 wt% NaCl corrosive solution. This coating exhibits good potentiality for various industrial applications in aggressive medium.

Keywords: Nanocomposite coating; Ni-B/TiC-Y2O3; Pulse electrodeposition; Corrosion resistance; Electrochemical impedance spectroscopy

1. Introduction Recently, nanocomposite coating with specific structures and properties prepared by electrodeposition have attracted much attention. This is because electrodeposition has many unique advantages, such as simple process, flexible, easy controllable, inexpensive and high efficiency [1]. Furthermore, electrodeposition has remarkable superiority in the preparation of smooth surface, uniform structure and components, nanostructured surface and better bonding between coating and substrate [2, 3]. In recent years, ceramic nanoparticles (e.g., SiO2 [4], Al2O3 [5], TiO2 [6], TiN [7], ZrO2 [8], WC [9] and SiC [10, 11]) and rare earth oxide nanoparticles (e.g., CeO2, Y2O3, Tl2O3 and La2O3) have been introduced into metallic matrix to prepare metal matrix composite (MMC) coating due to their outstanding physical and chemical properties [12]. Usually, these particles have distinctive functional characteristics. The well-distributed nanoparticles in metal matrix not only improve its mechanical property (e.g., hardness, wear resistance), but also enhance the chemical stability (e.g., corrosion resistance, thermal stability), then expand its potential applications. Ni-B alloy is an essential protective coating and has been widely used in various fields due to its excellent mechanical and protective properties [13]. However, further improvement in performance is continuously desired to extend its service life in aggressive medium. To meet the individual requirements of practical application, Ni-B matrix has been reinforced by ceramic nanoparticles to enhance its wear and corrosion resistance [14]. Akbari [15] prepared Ni-B/SiC composite coatings and found that the coating presents excellent hardness and corrosion resistance. Karahan [16] revealed that the addition of hBN particles to

Ni-B alloy improve its corrosion resistance. Waware [17] fabricated Ni-B/AlN nanocomposite coating and demonstrated the enhancement in hardness and protective performance. Li [18] reported that the inclusion of Al2O3 nanoparticles into Ni-B matrix exhibits high corrosion and wear resistance. At the same time, rare earth oxide nanoparticles were also reported as an effective reinforcement phase to Ni-B alloy. Pancreciou [19] fabricated Ni-B-CeO2 composite coating and revealed that the embedded CeO2 enhanced the wear and corrosion resistance of Ni-B matrix. Waware [20] synthesized Ni-B-Tl2O3 composites and demonstrated the significant improvement in microhardness, elastic modulus and corrosion resistance as compared to Ni-B alloy. Cui [21] reported that the presence of La2O3 in Ni-B alloy could improve its thermal stability. Shakoor[22] revealed that the co-deposition of Y2O3 in Ni-B coating enhanced its mechanical and anticorrosion properties. As a promising ceramic material, TiC has excellent physical and chemical properties, such as high melting temperature (3150℃), high hardness (3000 kg/mm2), high antioxidation, superior thermal and chemical stability, excellent corrosion and wear resistance [23]. In recent years, TiC has been used as reinforcing particles for composite coating to enhance the wear and corrosion resistance for different applications [24]. Yazdian [24] fabricated Ni-TiC nanocomposite coating and reported that the embedding TiC in Ni matrix decreased its crystallite size. Kumaraguru [2] prepared Ni-TiO2-TiC coating and illustrated that the microhardness was enhanced when large amount of TiO2-TiC particles encapsulated in the coatings. To our knowledge, TiC ceramic particles reinforced Ni-B matrix coating have rarely been studied.

Rare earth yttrium oxide (Y2O3) nanoparticles reinforced nickel-based composites has been investigated by some researchers due to its higher hardness, better wear resistance, excellent corrosion resistance, and high-temperature stability. Xu [25] fabricated Ni-Y2O3 composites and optimized their microhardness and tribological properties. Jiang [26] investigated Ni-Al-Y2O3 composite coatings at different Y2O3 content. Therefore, it is well expected that TiC and Y2O3 nanoparticles are suitable reinforcements to improve the performance of nickel matrix. However, TiC and Y2O3 doped Ni-B matrix coating has not been investigated yet. Literature about the preparation process details and its corrosion resistance are not available. Therefore, this work aims to prepare Ni-B/TiC-Y2O3 nanocomposite coating via pulse electrodeposition to improve its structure and performance. The influences of duty cycle on its surface, structural and performance were investigated. This coating exhibits good potentiality for various industrial applications in aggressive medium. 2. Experimental 2.1 Preparation Fig. 1 was the schematic diagram of the electrodeposition system. The anode was nickel plate, which can replenish the reduced Ni2+ during the deposition process. A copper sheet was used as cathode with 3.0 cm distance from the anode. A one-way pulse current in square wave mode was applied in the experiment. Ni-B/TiC-Y2O3 nanocomposite coating were fabricated by pulse electroplating. The electrolyte formula and electrodeposition parameters are summarized in Table 1. Electrolyte was produced with analytic reagents and distilled water. NiSO4·6H2O and NiCl2·6H2O was the primary Ni2+ source during the deposition process. Cl-

ions could prevent the passivation of nickel electrode. H3BO3 acts as pH buffer of the plating bath. TiC and Y2O3 particles were commercially provided in diameter of 40 nm. Magnetic stirring was

conducted

to

suspend

nanoparticles

in

deposition

process.

Before

electrodeposition, the nanoparticles were sonicated for 30 min, then mechanically stirred for 2 h to guarantee the full suspension in solution.

Fig. 1. Schematic of the experimental device

The bath temperature was controlled at 45±1

by a constant temperature water bath.

The pH was controlled at 4.8±0.1 with dilute sulfuric acid or sodium hydroxide solution. The copper sheets were first cleaned in alkaline solution in the presence of surfactant, and then ultrasonic cleaning in alcohol for 5 min. It was immersed in a dilute hydrochloric acid solution for about 30 s and then vertically immersed in the electroplating bath. After

electrodeposition, the sample was taken out, treated by an ultrasonic cleaner to wash off the adsorbed particles.

Table 1 Bath formula and operating parameters of the composite coating.

Bath formula (g L-1)

Process parameters

NiSO4·6H2O

240 gL-1

pH

NiCl2·6H2O

45 gL-1

Temperature(T)

-1

4.8±0.1

H3BO3

30 gL

DMAB

3 gL-1

TiC

15 g L-1

Duty cycle

10%-90%

Y2O3 (50 nm)

9 g L-1

Frequency

100 Hz

Saccharine

0.5 gL-1

Stirring rate

400±50 rpm

Electrode spacing

3 cm

Sodium dodecyl sulfate (SDS)

Deposition time(t)

45±1

Peak

current

density (ip)

-1

0.01 gL

20 min 10 A dm-2

2.2 Characterization AFM (NT-MDT Prima) was adopted to evaluate the topography and roughness of the coating. The phase composition and crystallite size were measured by D8 advance-Bruker XRD using Cu Kα radiation (λ=0.15406 nm). Crystallite size was obtained according to the Scherrer Eq. (1). D=



(1)

In Eq.(1), the D represents the crystallite size, k is 0.94, λ is 0.15406 nm, β represents the FWHM in radian. The relative texture coefficient (RTC) was determined by Eq. (2) to represent the relative degree of preferred orientation.

=∑

× 100%;

=

(2)

Where Is(hkl) and Ip(hkl) represent the diffraction intensities of the produced samples and standard Ni powder sample (PDF No. 04-0850), respectively. The surface element was analyzed by XPS (ESCALAB 250XI). Wear test was measured using a UMT-3 friction and wear tester at frequency 5 Hz and amplitude 5 mm under 10 N for dry-sliding. Counterparts were SiC balls with a diameter of 3 mm. A surface profiler (Alpha-Step IQ) was used to measure the wear track profile. Electrochemical properties were measured in a classic three-electrode cell by an electrochemical workstation (CHI660E, Chenhua Instruments Co.) in a 3.5wt% NaCl corrosive medium without agitation at room temperature. The reference electrode was SCE, and the auxiliary electrode was platinum. The as-deposited sample with 1 cm2 exposed area was acted as research electrode. The sample was soaked for 30 min to reach open circuit potential (Eocp). EIS was measured from Eocp under 10 mV disturbance amplitude in the frequency of 105-10-2 Hz. 3. Results and discussion 3.1 Phase composition and crystallite size Fig. 2 shows the XRD patterns of the nanocomposites deposited at different duty cycle. It indicated that the duty cycle does not affect the phase composition, but slight changes in peak intensity were observed. The peak intensity and width are respectively related to crystallinity and crystallite size, which is affected by the embedded nanoparticles and B content. The B peak was not found because of the generation of a single solid solution of Ni-B matrix. The three peaks at about 44.6°, 51.6° and 76.5° correspond to Ni (111), Ni (200) and Ni (220) texture, respectively (PDF No. 04-0850). All coatings present a face-centered

cubic structure. The preferred orientation is (111) planes. The small peak at about 36.1 ° is ascribed to TiC particles distributed in the coating. The small peak at 29.2° belongs to Y2O3 nanoparticles. The nanoparticle peak in the X-ray diffraction pattern is small due to their low content in the composite coating. In Fig. 2a, Cu peaks attributing to substrate were also observed due to the thin thickness. Fig. 2b shows the local enlarged view of the nanoparticles and Ni (111) diffraction peak.

Fig. 2. (a) XRD patterns of the composite coating; (b) Partially enlarged details.

The RTC and crystallite size were listed in Table 2. The crystallite size was 16.2 nm-18.6 nm depending on different duty cycle. The crystallite size slightly varied with the duty cycle. Table 2 shows that the RTC value also varied with the duty cycle. The Ni (111) texture was the primary preferred orientation and Ni (200) texture was the secondary preferred orientation with the RTC larger than 30%. According to our previous studies, the usual operating range of duty cycle is 30%-70%. As seen in Table 2, increasing duty cycle from 30% to 70%, the RTC

value of (111) plane slightly increases from 40.62% up to 42.77 %, and the RTC value of (200) texture slightly decreased from 38.68% down to 35.03%. It suggested that the preferred orientation of (111) texture slightly increased and (200) texture decreased with the increases of duty cycle from 30% to 70%. In the co-deposition process, the grain will be refined if the nucleation rate was faster than the grain growth rate. Pavlatou et al. [27] proposed that the grain refinement was ascribed to the embedded nanoparticles, which could provide a large number of nucleation sites, immobilizes the grain boundary, and then hinders crystal growth.

Table 2 RTC and crystallite size of the composite coating developed at different duty cycle.

RTC (%)

Crystallite size (nm)

Samples (111)

(200)

(220)

(111)

(200)

(220)

10%

45.11

42.86

12.03

18.6

12.7

12.9

30%

40.62

38.68

20.70

16.7

11.4

12.1

50%

42.30

36.35

21.35

16.6

11.7

12.0

70%

42.77

35.03

22.20

16.2

11.4

11.4

90%

41.22

37.19

21.59

17.8

12.2

11.9

3.2 Cross-sectional observation Fig. 3 presents the cross-sectional images of the nanocomposite coating. The interface between the coating and substrate, thickness, the embedded nanoparticles were examined. The coating thickness is 5-10 µm. The bulk of the coating is uniform and compact. Defects such as cracks, gaps, delaminating has not been detected in the interface between the coating and substrate, indicating a satisfactory adhesion. Fig. 3b shows the enlarged view of the local

region marked with a red rectangle in Fig.3a. The local enlarged details demonstrated that these nanoparticles in dimension about 40 nm have been uniformly distributed in the electrodeposited Ni-B matrix. No defects was noticed at the interface between the particles and matrix, indicating the good bonding.

Fig. 3. (a) Cross-sectional images of the nanocomposites; (b) Partial enlarged details.

3.3 Surface topography and roughness Fig. 4 shows the 2D surface micrograph of the coating fabricated at duty cycle of 30%, ip=10 A dm-2 and 90%, ip=5 A dm-2. As shown in Fig. 4, the surface is composed of large granular grains which were stacked to a compact coating. The size of the large granular grains is about 1-5 µm. Some gaps or pits were found on the surface. Careful observation found that many clusters in size of several hundred nanometers were distributed on the coating. The clusters and protrusions were sparsely dispersed on the relatively flat coating. These clusters were composed of nanoparticles and cellular grains. Partial granules are the nanoparticles

coated with fine Ni-B grains. Many granules were dispersed on the surface of the clusters and also on the dense coating. Some gullies were noticed. The formation of these clusters and gullies are mainly attributed to the “tip discharge effect” and the aggregation of nanoparticles. Due to the “tip discharge effect”, the metallic ions are preferentially adsorbed on the “tip” sites and reduced to metal atom, forming large protrusion structure.

Fig. 4. 2D topography of the composite coating prepared at (a, b) 30%, ip=10 A dm-2, (c, d) 90%, ip=5 A dm-2 in as-prepared form.

Fig. 5 shows the 3D surface topography of the nanocomposite coating. It shows that the

coating exhibits hill-valley like structure. The large granular grains observed in 2D images are the large protrusions in 3D topography. The pits were the gullies surrounding the protrusions. Fine granules and particles are distributed on the coating. Table 3 shows the average roughness (Sa) and root mean square roughness (Sq) of these coatings. It shows that the coating deposited at duty cycle of 30% has the Sa, Sq of 56.7-88.9 nm, 71.9-117.1 nm, respectively. The coating deposited at 90% owns the Sa, Sq of 135.1-161.5m, 175.5-214.1 nm, respectively. The coating electrodeposited at 30% exhibited finer grains and smaller hill-like protrusions with the max height 768-1064 nm. When duty cycle is 90%, granules size was enlarged and the height is 1661-2239 nm, presenting a rougher surface. It indicated that the roughness increased when duty cycle is 90%. It suggested that the duty cycle of 30% benefits smooth and fine-grained structure.

Fig. 5. 3D topography of the nanocomposites prepared at (a, b) 30%, ip=10 A dm-2, (c, d) 90%, ip=5 A dm-2 in as-prepared form.

Table 3 The average roughness (Sa) and root mean square roughness (Sq) of the composite coating.

samples

Sa (nm)

Sq (nm)

Max height (nm)

a (30%, ip 10 A dm-2)

88.9

117.1

1064

b (30%, ip 10 A dm-)

56.7

71.9

768

c (90%, ip 5 A dm-2)

135.1

175.5

1661

d (90%, ip 5 A dm-2)

161.5

214.1

2239

In the initial stage of electrodeposition, the coating formed was relatively flat, but not absolutely flat. Due to the “tip discharge effect”, the growth rate at the raised regions is fast, forming cellular bulges. Continue to deposition, the bulges become bigger and bigger. Finally, the hill-valley like structure was formed. The small cellular bulges like seeds. With the extending of deposition time, seeds grew continuously and formed protrusion clusters. Defects such as pinholes, pitting, cellular bulges, impurities (dust, hydroxide, anode muds) on cathode surface, promoted the formation of large protuberance and clusters. Fig. 6 shows the distribution of granule size. For coating obtained at 30%, the average granule size is 330-510 nm, and is distributed between 200 nm and 710 nm. However, for coating prepared at 90%, the average granule size is about 970 nm, and is distributed in range from 700 nm to 1260 nm. Fig. 7. presents the bearing ratio distribution of the composite coating with granule size. It

suggests that more than 95% granules are less than 680 nm in dimension for coating of 30%, indicating the fine-grained structure. However, more than 95% granules are larger than 630 nm and less than 1300 nm. It indicated that the coating of 30% has finer structure and low roughness.

Fig. 6. Granule size distribution of the nanocomposites.

Fig. 7. Bearing ratio distribution of the nanocomposites with granule size.

3.4 Formation mechanism Fig. 8 shows the formation mechanism of the nano- or micro-scale protrusion clusters and gullies structure of the nanocomposite coating. When the surface was relatively flat, the growth rate over the substrate is almost the same, and the crystal cells grew uniformly. At this stage, the coating was composed of crystal grains in similar size. Due to the “tip discharge effect”, the growth rate on bulges is faster than in other areas [28]. Therefore, the Ni2+ ions were preferentially reduced at the bulges, providing a number of nucleation sites. Thus, the coating is more likely to grow at the bulges. As a result, large protrusions formed. Besides, the protrusions were charged in electric field with the same electric charge. Then, the repulsive force was generated between them to ensure vertical growth. Finally, larger protrusion clusters were formed [29]. Because certain distance exists between these protrusions, it is easy to form gullies or pits surrounding these protrusions.

Fig. 8. Formation mechanism of the protrusion cluster and gully structure.

The detailed growing process for the coating was proposed in Fig. 9. Firstly, after dispersed in the electrolyte, the nanoparticles were absorbed with some metal ions and positively charged in electrolyte. When current is on, the electric field was simultaneously

formed. Then, metal ions and positively charged particles were transported to cathode under the influence of electric field and agitation [28]. Subsequently, they were loosely absorbed on the cathode surface. As well known, nanoparticles are larger than Ni2+ ions, and it is hard to adhere to the cathode surface [30]. At this “weak adsorption” stage, most of the nanoparticles could be removed under the scouring of the solution. Soon, the nickel ions both in solution and covered on nanoparticles were quickly reduced to metal atoms on the cathode surface, which produces strong adsorption force. In this “strong adsorption” stage, the nanoparticles were strongly adsorbed onto the newly formed coating matrix. With the increase of deposition time, the strongly adsorbed particles were incorporated into Ni-B matrix, forming particles doped Ni-B matrix nanocomposite coating [28].

Fig. 9. Schematic diagram of the detailed growing process for the nanocomposites.

3.5 XPS analysis The XPS patterns of the composite coating fabricated at 30% were shown in Fig. 10. The survey spectrum (Fig. 10a) illustrated the presence of Ni, B, Ti, Y, O and C elements in the coating. Fig. 10b shows the Ni 2p XPS spectra. The three peaks at 851.75 eV, 855.10 eV and 860.48 eV are attributed to Ni 2p3/2, and the three peaks at 868.99 eV, 872.92 eV and 878.96 eV correspond to Ni 2p1/2. The peak at 851.75 eV with the area of 4.00×104 belongs to nickel atom (Ni0). The peak at 855.10 eV with the area of 7.72×104 corresponds to Ni2+ species such as NiO, Ni(OH)2. The oxidation of nickel formed nickel oxide [31]. During electrodeposition, hydrogen evolution (2H++2e=H2↑) is inevitable, leading to high amount of hydroxyl (OH-) at the cathode interface. Finally, nickel hydroxide might be formed and co-deposited in the coating. The peak at 860.48 eV with the area of 8.92×103 is related to satellite nickel in the form of Ni3+ species, such as NiOOH. The B 1s XPS spectra were presented in Fig. 10c, which comprises of two peaks. The peak at 186.95 eV with the area of 6.42×102 is ascribed to boron atom (B0). The peak at 191.71 eV with area of 2.7×103 corresponds to oxidized boron, especially B3+ ions. Ti 2p XPS patterns were shown in Fig. 10d., which has four peaks, including two peaks of Ti2p3/2 at 455.65 eV and 457.37 eV, and two peaks of Ti2p1/2 at 461.64 eV and 465.94 eV. It indicated that titanium oxide was formed with the binding energies shifting to a higher value. Fig. 10e displays the Y 3d XPS patterns which has four fitted peaks. The peaks at 156.07 eV, 159.60 eV belong to Y3d5/2, and the peaks at 157.87 eV, 161.52 eV correspond to Y3d3/2. The peaks at 156.07 eV, 157.87 eV correspond to Y2O3. Peaks at 159.60 eV, 161.52 eV are related to Y2O3-x species. Y come from the Y2O3 nanoparticles embedded in the coating. Fig. 10f

presents C 1s XPS pattern with four decomposed peaks, belonging to C-Ti (283.93 eV), C-C (284.27 eV), C-O (284.79 eV) and COx (288.05 eV), with the area of 9.46×103, 3.50×104, 1.09×104 and 1.15×104, respectively. The source of carbon is organic additives (SDS, saccharine, etc.), TiC particles, and carbon contamination.

Fig. 10. XPS spectra of (a) survey spectra, (b) Ni 2p, (c) B 1s, (d) Ti2p, (e) Y3d and (f) C1s of the composite coating in as-prepared form (r=30%)

3.6 Corrosion and wear resistance The stability of the nanocomposite coating is crucial to their applications in industrial field, especially the corrosion and wear behavior. Fig. 11 presents the effect of immersion time (1 h and 2 days) on the Nyquist and Bode diagram of the coating obtained at different duty cycle. Fig. 12 presents the equivalent electrical circuits (EEC). In the EEC model, the Rs, Rct and CPEdl were the solution resistance, charge transfer resistance and double-layer capacitance, respectively. Rc and CPEc are coating resistance and coating capacitance, respectively. All Nyquist curves could be well fitted by one-time constant EEC model (a) in Fig. 12. To to simplify the fitting process, the Rs(RctCPEdl) EEC model was used to fit the EIS curves. Fig. 11(a, b) shows that when immersed 1 h, all Nyquist plots exhibit a depressed capacitive loop in different radius. The corrosion data were provided in Table 4. It shows that the coating of 30% owns the largest Rct of 49.42 kΩ·cm2, and the coating of 90% exhibits the smallest Rct of 37.95 kΩ·cm2. The capacitance loop radius of 30% was the largest. In the initial stage of immersion, the coating obtained at 30% has the maximum Rct, revealing the best corrosion resistance [32]. When immersed for 2 days, Fig. 11 (c, d) indicated that all the radius of the capacitive loops increased, but in different amplitude. The coating obtained at 30% exhibited the highest corrosion resistance with maximum Rct of 190.28 kΩ·cm2. In this stage (2 days), the Rct of the coating obtained at 30% and 90% are larger than 180 kΩ·cm2, while the coating of 50% is less than 50 kΩ·cm2. This indicated that the coating of 30% exhibits better performance in this stage.

Fig. 11. Nyquist and Bode diagrams of the composite coating prepared at different duty cycle after immersed (a, b) 1 h, (c, d) 2 days.

Fig. 12. Equivalent electrical circuit (EEC) model.

After immersed 7 days, as shown in Fig. 13(a, b), the coatings exhibit a similar tendency in corrosion resistance to 2 days. Compared to other samples, the coating prepared at 30%

still has the Rct value of more than 130 kΩ·cm2 and presents excellent corrosion resistance during the long-term immersion in 3.5 wt.% NaCl corrosive medium. The coating of 50% has the smallest Rct of 65.8 kΩ·cm2. After immersed 15 days, as shown in Fig. 13(c, d), the coating prepared at 30% still has the maximum Rct value of more than 150 kΩ·cm2 and presents excellent corrosion resistance. It was observed that when immersed for 7 days, the coating of 70% shows the maximum Rct of 1.95.47 kΩ·cm2. However, taking into account the performance in the whole immersion period, the properties of the coating prepared at 70% are not stable and is not the best choice.

Fig. 13. Nyquist and Bode diagrams of the composite coating prepared at different duty cycle after immersed (a, b) 7 days, (c, d) 15 days.

As well known, many factors could influence the result of electrochemical tests. We believe that the best performance in statistics is more practical and valuable. Although the corrosion resistance varied with immersion time and duty cycle, the Rct for all coatings is still higher than 77 kΩ·cm2 after immersed 15 days, indicating that the samples still have excellent anti-corrosion performance and long-term service stability in corrosive medium.

Table 4 Corrosion data of the composite coating deposited at different duty cycle with immersion time.

Time

Samples

Rs

Rct

(Ω·cm2) (kΩ·cm2)

CPEdl (µF cm−2)

n

30%

4.76

49.42

21.31

0.91

50%

4.40

38.73

27.89

0.93

70%

5.40

44.66

21.54

0.89

90%

4.96

37.95

25.22

0.92

30%

4.92

190.28

21.22

0.91

50%

4.33

47.83

31.22

0.92

70%

4.76

132.07

22.28

0.88

90%

3.55

188.18

24.46

0.93

30%

4.68

131.36

20.37

0.92

50%

3.46

65.80

24.39

0.93

70%

5.82

195.47

22.88

0.89

90%

4.32

111.32

25.95

0.93

30%

5.66

154.71

24.69

0.92

50%

4.17

77.99

25.55

0.93

70%

5.37

98.06

25.66

0.90

90%

4.30

111.21

27.58

0.93

1 hour

2 days

7 days

15 days

Fig. 14 shows the change curve of the Rct value with immersion time. It displays that all the coating has similar trend that the Rct first increases and then decreases, then step into a relatively stable period. Take into account the performance in the whole service period, the coating prepared at duty cycle of 30% has the best corrosion resistance and the stability than other coatings.

Fig. 14. The change of Rct value with immersion time of the composite coating prepared at different duty cycle.

Fig. 15 presents wear track profile of the nanocomposites prepared at different duty cycle under dry-sliding condition (10 N, 5 Hz). The wear track profiles are intuitive way to compare the wear rates of different samples. Deeper depth and larger area of the wear track profiles indicates the more wear volume loss and high wear rate. It indicated that the depth and area of the wear track profiles for the coating obtained at 30% was the smallest. It indicated that under the dry-sliding condition, the nanocomposites prepared at 30% has the best wear resistance, which has the least volume loss in the wear tests. As well known, many factors

could affect the wear resistance, such as structure, phase composition, nanoparticles, roughness, grain size, etc. Therefore, many influencing factors and mechanism about the wear behavior of the nanocomposites have not been fully clarified yet, and further research is still needed in the future works.

Fig. 15. Wear track profiles of the samples at duty cycle under dry-sliding condition (10 N, 5 Hz).

The improvement in performance is associated with many factors. First, the addition of TiC and Y2O3 nanoparticles provided many nucleating sites for crystal growing and refined the grains, leading to homogeneous and compact structure. Moreover, nanoparticles could be effectively absorbed in the defects, playing a role in filling micropores and microcracks. Then,

the compactness of the coating was improved. This prevents the corrosion media from permeating the coating and the corrosion resistance was enhanced. Besides, the doped TiC and Y2O3 particles also enhanced the physical shielding effect due to its stable chemical properties. Furthermore, the optimization of the microstructure and the improvement in mechanical properties also have a positive effect on its corrosion and wear resistance. 4. Conclusions Ni-B/TiC-Y2O3 nanocomposite protective coating has been synthesized by one-step pulse current electrodeposition method. The influences of duty cycle on structural, surface, corrosion and wear behaviors were investigated. The coating is compact with hill-valley like morphology. The average roughness (Sa) was about 56-161 nm and the duty cycle of 30% benefits low roughness and fine-grained structure. The crystallite size is 16-19 nm. The coating exhibits nanocrystalline structure and the preferred orientation was Ni (111) texture. Due to the “tip discharge effect”, the metal ions were preferentially reduced at the raised regions, forming the nano- or micro-scale protrusion clusters. Electrochemical and wear measurements illustrated that the electrodeposition parameters significantly affect the corrosion and wear behavior of the nanocomposites. Duty cycle of 30% was the optimal parameter for the best corrosion and wear resistance, exhibiting a desirable electrochemical stability in the long-term service in hash environment. Acknowledgements This work was supported by the National Natural Science Foundation of China (51679076), the Fundamental Research Funds for the Central Universities (2019B15914).

References [1] B. Li, T. Mei, D. Li, S. Du, Ultrasonic-assisted electrodeposition of Ni-Cu/TiN composite coating from sulphate-citrate bath: Structural and electrochemical properties, Ultrason. Sonochem. , 58 (2019) 104680. [2] S. Kumaraguru, G.G. Kumar, S. Raghu, R.M. Gnanamuthu, Fabrication of ternary Ni-TiO2-TiC composite coatings and their enhanced microhardness for metal finishing application, Appl. Surf. Sci. , 447 (2018) 463-470. [3] H. Li, Y. He, T. He, Y. Fan, Q. Yang, Y. Zhan, The influence of pulse plating parameters on microstructure and properties of Ni–W–Si3N4 nanocomposite coatings, Ceram. Int. , 42 (2016) 18380-18392. [4] R.A. Shakoor, U.S. Waware, R. Kahraman, A. Popelka, M.M. Yusuf, Corrosion behavior of electrodeposited Ni-B coating modified with SiO2 particles, Int. J. Electrochem. Sci. , 12 (2017) 4384-4391. [5] M. Alizadeh, A. Cheshmpish, Electrodeposition of Ni-Mo/Al2O3 nano-composite coatings at various deposition current densities, Appl. Surf. Sci. , 466 (2019) 433-440. [6] H. Krawiec, V. Vignal, A. Krystianiak, Y. Gaillard, S. Zimowski, Mechanical properties and corrosion behaviour after scratch and tribological tests of electrodeposited Co-Mo/TiO2 nano-composite coatings, Appl. Surf. Sci. , 475 (2019) 162-174. [7] W. Zhang, B. Li, C. Ji, Synthesis and characterization of Ni-W/TiN nanocomposite coating with enhanced wear and corrosion resistance deposited by pulse electrodeposition, Ceram. Int. , 45 (2019) 14015-14028. [8] B. Li, T. Mei, D. Li, S. Du, W. Zhang, Structural and corrosion behavior of Ni-Cu and

Ni-Cu/ZrO2 composite coating electrodeposited from sulphate-citrate bath at low Cu concentration with additives, J. Alloys Compd. , 804 (2019) 192-201. [9] N. Elkhoshkhany, A. Hafnway, A. Khaled, Electrodeposition and corrosion behavior of nano-structured Ni-WC and Ni-Co-WC composite coating, J. Alloys Compd. , 695 (2017) 1505-1514. [10] B. Li, W. Zhang, W. Zhang, Y. Huan, Preparation of Ni–W/SiC nanocomposite coatings by electrochemical deposition, J. Alloys Compd. , 702 (2017) 38-50. [11] W. Jiang, L. Shen, M. Xu, Z. Wang, Z. Tian, Mechanical properties and corrosion resistance of Ni-Co-SiC composite coatings by magnetic field-induced jet electrodeposition, J. Alloys Compd. , 791 (2019) 847-855. [12] H.J. Cho, Y.J. Kim, U. Erb, Thermal conductivity of copper-diamond composite materials produced by electrodeposition and the effect of TiC coatings on diamond particles, Composites Part B-Engineering, 155 (2018) 197-203. [13] L. Shen, M. Fan, M. Qiu, W. Jiang, Z. Wang, Superhydrophobic nickel coating fabricated by scanning electrodeposition, Appl. Surf. Sci. , 483 (2019) 706-712. [14] A. Rasooli, M.S. Safavi, M. Kasbkar Hokmabad, Cr2O3 nanoparticles: A promising candidate to improve the mechanical properties and corrosion resistance of Ni-Co alloy coatings, Ceram. Int. , 44 (2018) 6466-6473. [15] M. Salari Mehr, A. Akbari, E. Damerchi, Electrodeposited Ni-B/SiC micro- and nano-composite coatings: A comparative study, J. Alloys Compd. , 782 (2019) 477-487. [16] E. Ünal, İ.H. Karahan, Production and characterization of electrodeposited Ni–B/hBN composite coatings, Surf. Coat. Technol. , 333 (2018) 125-137.

[17] U.S. Waware, A.M.S. Hamouda, N.P. Wasekar, Mechanical properties, thermal stability and corrosion behavior of electrodeposited Ni-B/AlN nanocomposite coating, Surf. Coat. Technol. , 337 (2018) 335-341. [18] B. Li, W. Zhang, Y. Huan, J. Dong, Synthesis and characterization of Ni–B/Al2O3 nanocomposite coating by electrodeposition using trimethylamine borane as boron precursor, Surf. Coat. Technol., 337 (2018) 186-197. [19] J.K. Pancrecious, J.P. Deepa, V. Jayan, U.S. Bill, T.P.D. Rajan, B.C. Pai, Nanoceria induced grain refinement in electroless Ni-B-CeO2 composite coating for enhanced wear and corrosion resistance of Aluminium alloy, Surf. Coat. Technol. , 356 (2018) 29-37. [20] U.S. Waware, A.M.S. Hamouda, B. Bajaj, T. Borkar, A.K. Pradhan, Synthesis and characterization of electrodeposited Ni-B-Tl2O3 composite coatings, J. Alloys Compd. , 769 (2018) 353-359. [21] D. Zhang, X. Cui, G. Jin, Z. Cai, M. Dong, Thermal stability of Ni-B/La2O3 coatings by electro-brush plating technique, Surf. Coat. Technol. , 349 (2018) 1042-1047. [22] R. Shakoor, U. Waware, K. Ali, R. Kahraman, A. Popelka, M. Yusuf, A. Hasan, Novel electrodeposited Ni–B/Y2O3 composite coatings with improved properties, Coatings, 7 (2017) 161. [23] D. Zhang, J. Li, J. Zheng, Synthesis and electrochemical properties of PANI–TiC nanocomposite and its electrocatalytic behavior, Mater. Lett. , 93 (2013) 99-102. [24] M. Karbasi, N. Yazdian, A. Vahidian, Development of electro-co-deposited Ni–TiC nano-particle reinforced nanocomposite coatings, Surf. Coat. Technol. , 207 (2012) 587-593. [25] L.L. Tian, J.C. Xu, Electrodeposition and characterization of Ni-Y2O3 composite, Appl.

Surf. Sci. , 257 (2011) 7615-7620. [26] F. Cai, C. Jiang, Z. Zhang, V. Ji, Synthesis and characterization of Ni-Al-Y2O3 composite coatings with different Y2O3 particle content, Ceram. Int. , 40 (2014) 15105-15111. [27] E.A. Pavlatou, M. Stroumbouli, P. Gyftou, N. Spyrellis, Hardening effect induced by incorporation of SiC particles in nickel electrodeposits, J. Appl. Electrochem. , 36 (2005) 385-394. [28] I. Tudela, Y. Zhang, M. Pal, I. Kerr, A.J. Cobley, Ultrasound-assisted electrodeposition of thin nickel-based composite coatings with lubricant particles, Surf. Coat. Technol., 276 (2015) 89-105. [29] Z. Wang, L. Shen, W. Jiang, M. Fan, D. Liu, J. Zhao, Superhydrophobic nickel coatings fabricated by scanning electrodeposition on stainless steel formed by selective laser melting, Surf. Coat. Technol. , 377 (2019) 124886. [30] A. Mukhopadhyay, T.K. Barman, P. Sahoo, Friction and Wear Performance of Electroless Ni-B Coatings at Different Operating Temperatures, Silicon, 11 (2018) 721-731. [31] J. Winiarski, B. Cieślikowska, W. Tylus, P. Kunicki, B. Szczygieł, Corrosion of nanocrystalline nickel coatings electrodeposited from choline chloride:ethylene glycol deep eutectic solvent exposed in 0.05 M NaCl solution, Appl. Surf. Sci. , 470 (2019) 331-339. [32] T. He, Y. He, H. Li, Z. Su, Y. Fan, Z. He, Fabrication of Ni-W-B4C composite coatings and evaluation of its micro-hardness and corrosion resistance properties, Ceram. Int. , 44 (2018) 9188-9193.

Highlights

A novel Ni-B/TiC-Y2O3 nanocomposite coating has been fabricated by electrodeposition Effects of duty cycle on structure, surface and performance were invstigated Surface properties and formation mechanism were analyzed Corrosion and wear resistance of the nanocomposites was optimized and enhanced The sample prepared at duty cycle of 30% has the best corrosion and wear resistance

Declaration of interest Statement

I would like to declare on behalf of my co-authors that no conflict of interest exists in the submission of this manuscript. There have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Baosong Li Jan. 9, 2020