The effects of Cr2O3 particles on the microstructure and wear-resistant properties of electrodeposited CoNiP coatings

The effects of Cr2O3 particles on the microstructure and wear-resistant properties of electrodeposited CoNiP coatings

Journal Pre-proof The effects of Cr2O3 particles on the microstructure and wearresistant properties of electrodeposited CoNiP coatings Wenjing Xiong,...

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Journal Pre-proof The effects of Cr2O3 particles on the microstructure and wearresistant properties of electrodeposited CoNiP coatings

Wenjing Xiong, Minyu Ma, Jin Zhang, Yong Lian PII:

S0257-8972(19)31157-0

DOI:

https://doi.org/10.1016/j.surfcoat.2019.125167

Reference:

SCT 125167

To appear in:

Surface & Coatings Technology

Received date:

21 August 2019

Revised date:

12 November 2019

Accepted date:

14 November 2019

Please cite this article as: W. Xiong, M. Ma, J. Zhang, et al., The effects of Cr2O3 particles on the microstructure and wear-resistant properties of electrodeposited CoNiP coatings, Surface & Coatings Technology (2019), https://doi.org/10.1016/j.surfcoat.2019.125167

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© 2019 Published by Elsevier.

Journal Pre-proof The effects of Cr2O3 particles on the microstructure and wear-resistant properties of electrodeposited CoNiP coatings Wenjing Xionga,b, Minyu Maa,b, Jin Zhanga,b, Yong Liana,b*, a

Institute for Advanced Materials and Technology, University of Science and

Technology Beijing, Beijing 100083, China b

Beijing Key Laboratory for Corrosion Erosion and Surface Technology,

Beijing 100083, China *Corresponding author: Yong Lian

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E-mail: [email protected]

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Abstract: In this paper, CoNiP and CoNiP/Cr2O3 composite coatings were successfully electrodeposited onto Cr-Ni-Mo-V steels substrate by using direct current

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(DC). The effects of Cr2O3 particle contents and heat treatment on the microstructures,

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coating compositions, microhardness and wear resistance properties of the coatings

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were investigated by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), vickers hardness tester and

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ball-on-disk tribometer. The results showed that the coatings transformed from amorphous to crystalline structures by heat treatment at 350℃, and their

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microhardness significantly increased. The contents of Cr2O3 particles in the coatings reached a stable value for the coatings deposited in the plating bath with concentration of Cr2O3 higher than 15 g/L, meanwhile the coating deposited in the plating bath of 15 g/L Cr2O3 (CoNiP-15 g/L Cr2O3) possessed the highest microhardness. Wear test results at room temperature, 200, 300, 400 and 500℃ showed that the wear resistance of the coatings were improved by the addition of Cr2O3 particles, and the CoNiP-15 g/L Cr2O3 coating had the lowest coefficient of friction and wear loss among all the samples. Key words : Electrodeposition, CoNiP/Cr2O3 coatings, Heat treatment, Wear resistance 1. Introduction Electrodeposited hard chrome coatings have been widely used in industrial to improve the service life of mechanical parts due to its high wear resistance and

Journal Pre-proof corrosion resistance [1]. However, the traditional process of electroplating hard chrome produced Cr6+, and was harmful to the environment [2]. In recent years, Co-based coatings, especially CoP have attracted much attentions because of their high deposition efficiency, excellent mechanical properties, and the plating process is environmentally friendly as compared to that of the chrome [3-7]. These coatings are considered to be the most promising alternative materials for plating chrome coatings [3,8,9]. Many researchers applied electrodeposited Co-based coating process for the modification and repair of aircraft and naval mechanical parts [5,8,9]. CoNiP coatings

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are commonly used as electrolytic materials of water electrocatalytic [10], magnetic

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materials [11], microwave absorbing materials [12]. Ma et al. [13] reported that the CoNiP coatings annealed at 400℃ have low friction and excellent wear resistance at

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room temperature, and it can be a potential substitute for the electroplated hard

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chrome. CoNiP coatings have the potentiality to be used at elevated temperature

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conditions, for example, on some parts of aero engine and fast-fire weapon for better high temperature wear resistance performance. However, few studies have been done

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on the tribological and wear properties of CoNiP at high temperatures. Therefore, it is essential and urgent to study the friction and wear behavior of CoNiP coatings at high

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temperatures.

In general, the incorporation of ceramic particles can further improve the performance of the coating, and this method can be applied onto the Co-based composite coatings to obtain excellent wear resistance properties [14,15]. Cr2O3 particles have been confirmed as a beneficial ceramic particles for improving the wear and corrosion resistance of electrodeposited coatings [16,17], and in this paper, Cr2O3 particles were incorporated in the electrodeposited CoNiP coatings, to further improve the properties. The aim of this paper is to investigate the wear properties at different temperatures of the CoNiP/Cr2O3 composite coatings after heat treatment, to study the effects of Cr2O3 particles contents on the microstructures and wear resistance of the electrodeposited CoNiP and CoNiP/Cr2O3 composite coatings.

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2. Materials and methods The CoNiP and CoNiP/Cr2O3 composite coatings were prepared by direct current (DC) electrodeposition in a sulfate system consisting 60~120 g/L CoSO4·7H2O, 40~80 g/L NiSO4·6H2O, 10~20 g/L NaH2PO2·H2O, 30~40 g/L H3BO4, 10~20 g/L H3PO4 and an appropriate amount of additives (Saccharin sodium). The contents of Cr2O3 particles (with average size of 5±2μm) in the solutions were 1, 5, 10, 15, and 20 g/L, respectively. The temperature of the electrodeposited solutions is about 50℃, and

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the pH of the solutions is between 2 and 3. The bath pH was adjusted by the addition of H2SO4 and NaOH. 25Cr3Mo2WNiVNb (C: 0.25, Cr: 2.8, Ni: 0.75, Mo: 1.8, V:

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0.75, W: 0.8, Nb: 0.05, Fe: balance in mass percentage; with size of 15×10×2 mm)

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was used as substrate for further improving its wear properties at room and high temperature. The samples were ground to 1500 and pickled for 5 min by 30% HCl.

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The coatings were prepared by DC electrodeposition at 6 A/dm2 and the

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electrodeposition time was 30 min. Heat treatment was carried out in a muffle furnace at a temperature of 350℃ for 30 min in order to obtain a certain degree of

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crystallization of the coatings (350℃ was selected based on the microhardness tests of coatings after heat treatment at different temperature).

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The phases of the coatings were studied by Smart Lab X-ray diffractometer using a copper target with wavelength of 1.5406 Ȧ, operating voltage of 40 kV, operating current of 150 mA, diffraction angle of 20° to 80°, and diffraction speed of 20 °/min. The mean grain size of the coatings was calculated by Debye-Scherer formula, D=kλ/βcosθ,where k is a Scherer constant, λ is wavelength of X-ray, β is FWHM, and θ is Bragg angle [18]. The surface and cross-section morphologies, wear tracks and chemical composition were characterized by FEI Quanta 250 scanning electron microscope (SEM) and energy dispersive spectrometer (EDS). The volume fractions of the particles in the coatings were calculated by Image J processing software. The vickers hardnesses of the coatings were tested by HXD-1000 microhardness tester on the coating surface under applied load of 100 g for 15 s, and each test was repeated 5 times. The friction and wear behavior of the coatings were tested on ball-on-disk

Journal Pre-proof tribometer (Lanzhou Chemical Physics Research, HT-600). The grinding material was Si3N4 ball (with diameter of 5 mm and microhardness of 1300 Hv). The load was 100 N, while the sliding speed was 400 r/min and the duration time was 20 min. The wear rate was calculated according to the following Archard’s formula: The wear rate was calculated according to the following Archard’s formula: Wr=ΔV/SP. ΔV is defined by: ΔV=Lh(3h2+4b2)/(6b), where ΔV relates to volume loss (mm-3), the S is sliding distance (m), and the P is the sliding load (N). L is the perimeter of the wear ring, h and b are the depth and width of the wear scars, respectively [19]. The depth and

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width of wear marks were measured by confocal laser three-dimensional (3D) surface

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profilometer. The schematic diagram of typical wear scar profile is shown in Fig. 1. In order to ensure the reproducibility, the wear test and measurement under each

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condition were performed by three times. The friction coefficient and wear rate

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reported in this work are the average of the tested values.

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3. Results and discussion

3.1 Morphology of the as-deposited coating

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Fig. 2 shows the surface morphologies of the electrodeposited CoNiP and CoNiP/Cr2O3 coatings. It can be seen that the coatings are composed of spherical

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bump with a size of 5-10 μm (Fig. 2a). Each bump consists of individual nanocrystals aggregation which is consistent with the result of the reference [20]. The coatings reveal typical “cauliflower” morphology for CoNiP coatings. Cr2O3 particles are dispersed in the surface of the coatings evenly. As reported in the literature [21], the incorporation of the particles into the plating bath can reduce the growth rate of the nucleus, and result in the formation of refined microstructure, so the concentration of Cr2O3 in the plating bath indirectly determined the morphology of the coatings. Besides, the particle contents on the coating surface increase as the particle concentrations in the plating bath increase. The cross-sectional scanning electron micrographs of the coatings deposited in the plating bath with different concentrations of Cr2O3 are shown in Fig. 3. As clearly seen, the coatings are closely bonded to the substrates, and Cr2O3 particles are embedded in the coatings. The thickness of coatings for different samples are shown

Journal Pre-proof in Fig.3. From the graphs, it is found that for the coatings deposited in the plating bath with higher Cr2O3 concentrations, a higher contents of Cr2O3 particles in the coatings can be obtained. When the concentration of Cr2O3 in the plating bath reaches a critical level (15 g/L), the particle contents in the coatings come to almost saturated. This is consistent with the results of the calculated weight fractions by the EDS (Fig. 4) and volume fractions by the Image J software from the cross-section graphs of the coatings (Fig.5). The particle contents in the coatings were determined by EDS coupled to the SEM as an average of three areas measurements. The chrome oxide

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concentration was determined by the stoichiometric ratio of oxygen to chromium in

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Cr2O3. It is considered that the contents of Cr2O3 particles in the coatings are related to the amounts of Cr2O3 particles adsorbed on the cathode, and is determined by two

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factors. The first factor is the content of Cr2O3 particles in the plating bath, the higher

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the content of Cr2O3 particles in the plating bath, the greater the probability that the

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Cr2O3 particles move to the cathode material. The other factor is related to the properties of the cathode, thus the amount of particles that can be adsorbed by the

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cathode is limited. When the concentration of Cr2O3 particles in the plating bath reach a critical value, the particles adsorbed on the cathode are saturated, thus the particle

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contents of the coatings hardly change. 3.2 XRD studies

Fig. 6a shows the XRD patterns of the electrodeposited CoNiP and CoNiP/Cr2O3 coatings deposited in the plating bath with different Cr2O3 particles concentrations before heat treatment. It can be seen from the XRD patterns that the CoNiP coating has an amorphous structure before heat treatment with no sharp diffraction peak. The patterns of the CoNiP/Cr2O3 coatings shows typical peaks corresponding to (012), (104), (110), and (116) crystallographic planes of Cr2O3 phase. For the coatings deposited in the plating bath with higher Cr2O3 concentrations, a higher contents of Cr2O3 in the coatings are obtained, and it is consistent with the slightly increasing intensities of these crystallographic planes of the coatings . The XRD patterns of CoNiP and CoNiP/Cr2O3 composite coatings after 350℃ heat treatment are shown in Fig. 6b. It can be obviously seen that the CoNiP and

Journal Pre-proof CoNiP/Cr2O3 coatings are transformed from amorphous to crystalline structures during the heat treatment. The hcp-Co peaks, fcc-Co peaks and peaks related to Co2P phase are identified in the XRD patterns of the annealed CoNiP and CoNiP/Cr2O3 coatings, and the diffraction peaks of Cr2O3 are the same as those of the coatings without heat treatment. The peaks at 40.95° and 53.11°correspond to Co2P, whereas the peak at 44.45° and 47.19° are related to hcp-Co(Ni), fcc-Co(Ni), respectively. The formation of the fcc phase can be attributed to the phase transformation during the heat treatment [22]. It can be seen from Fig.6b, the diffraction peaks of fcc-Co(Ni)

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can be obviously found in the patterns of CoNiP and CoNiP with low Cr2O3 content

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(CoNiP -1g/L Cr2O3), but no obvious fcc-Co(Ni) peaks can be found in the patterns of CoNiP with high Cr2O3 content, so we concluded that the addition of the Cr2O3

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particles can inhibit the formation of the fcc-Co(Ni) during the heat treatment. It is

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beneficial to improve the wear resistance of the coating since the hcp structure

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exhibits lower friction coefficient and wear rate than the fcc structure [23]. In addition, the diffraction peaks of Co2P become higher and sharper, and the Co(Ni) peaks of hcp

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phase broadened to some extent, indicating that the crystallinity of Co2P becomes larger and the grains of Co(Ni) are refined. Fig. 6 shows the mean grain size of the

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coatings deposited in the plating baths with different Cr2O3 contents, which were calculated using Debye-Scherrer formula. It can be seen from the figure that Cr2O3 particles have an effect on the grain size of the coatings. The grain size of the coating is defined by the competition between nucleation and crystal growth, the presence of Cr2O3 particles provides more nucleation sites by increasing the surface area of cathode, and consequently results in finer grain size [24]. 3.3 Microhardness Microhardness is an important performance characteristic of coatings, especially for the tribological performance. As reported that the electroplated CoP and CoNiP coatings have high hardness (more than 600 Hv) and further reach 900 Hv after heat treatment at 350~400℃ due to the precipitation strengthening (Co2P), which resulted in improved mechanical properties [3,25,26]. Fig. 8 shows the microhardness of the substrate, CoNiP coating and CoNiP/Cr2O3 composite coatings with different Cr2O3

Journal Pre-proof contents before and after heat treatment at 350℃. It can be seen that the microhardness of the coatings increase after the heat treatment due to the precipitation of Co2P, and the microhardness of the composite coatings increase as the Cr2O3 contents in the coatings increase. The precipitated strengthen phase and adding particles synergistically increase the hardness of the coatings. The CoNiP-15 g/L Cr2O3 composite coating possesses the highest microhardness, which is 800±10 Hv and 1100±18 Hv before and after heat treatment. Furthermore, when the content of Cr2O3 in the plating bath reaches 15g/L, the hardness of the coating tends to be stable,

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and even if the content of Cr2O3 is increased, the hardness of the coating will not

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change significantly, fluctuating within a certain error. The effects of Cr2O3 particles incorporation on the microhardness improvement can be attributed to: (i) the high

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hardness of the Cr2O3 particles; (ii) the dispersion strengthening of particles in the

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coatings; (iii) Cr2O3 particles nucleate on the matrix, which results in the refinement

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of the coating structure. The grain refinement can increase the dislocation barrier and improve the deformation resistance of the material. Nevertheless, the hardness of the

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coating decreases with the further increase of particle concentration in the bath. It may be related to the formation of the agglomerated particles in the coating.

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3.4 Tribological properties

Since the amorphous structures of the coatings are changed to a crystalline CoNiP phase and the microhardness of the coatings increase after the heat treatment, the wear test was carried out on the samples with heat treatment at 350℃.Moreover, among the CoNiP/Cr2O3 composite coatings, only CoNiP-15g/L Cr2O3 coating was tested since it has the highest microhardness among these composite coatings. 3.4.1 Wear surface The wear track is an important evidence to demonstrate the tribological mechanism. The worn surface morphologies of the substrate, CoNiP and CoNiP-15g/L Cr2O3 composite coatings at different testing temperatures are shown in Fig. 9. At room temperature (RT), plastic deformation occurs on the surface of the substrate, and repeated shear stress caused by friction causes fatigue peeling of the contact bumps under high-speed sliding, there are some grooves and pit , a bit of wear

Journal Pre-proof debris on the worn track of the sample of the substrate, indicating that the wear mechanism is fatigue wear (Fig. 9a ). The substrate is directly contacted with the silicon nitride ball of the upper friction pairs, thus plastic deformation on the substrate surface occurs due to high-speed sliding. The wear mechanism of CoNiP coating is adhesive wear at RT due to its slight solid-phase bond, uneven micro-structure and plough groove (Fig. 9b). The worn surface of CoNiP-15 g/L Cr2O3 composite coating (Fig. 9c), is much smoother with less wear debris and plastic deformation, indicating that the coating has excellent wear resistance properties. With the addition of ceramic

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particles, the wear mechanisms are changed from adhesive to abrasive because of the

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underlying properties of the particles [27]. The protruding Cr2O3 particles are firstly rubbed against the grinding pair, and ground or peeled off before the matrix of CoNiP

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is rubbed. The hard Cr2O3 particles in the CoNiP/Cr2O3 composite coatings play a

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roles of dispersion strengthening and supporting, makeing the coatings less

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susceptible to fracture and plastic deformation.

At 200℃ and 300℃,the wear track can be observed on the worn surface of the

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substrate, as shown in Fig. 9d and Fig. 9g. The wear surface morphologies are similar. Compared with the surface morphology of the substrate at room temperature, there

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are more wear debris, and plastic deformation on the surface. Moreover, the worn surface has a disk-shape of delamination. It is indicated that the wear failure mechanism of steel at this condition is that the material is oxidized under the external heating and friction heat, and the oxide layer gradually exfoliates due to the friction force. For the coated samples (CoNiP and CoNiP-15g/L Cr2O3 composite coatings) tested at 200℃ and 300℃, the wear tracks become slighter and smoother as compared with the surface morphology of that at room temperature, and only a few narrow and shallow grooves parallel to the sliding direction can be found (Fig. 9e、9f and Fig. 9h、 9i). Fig. 9j shows the surface morphology of the bare substrate tested at temperature of 400℃. It can be seen that as the wear progresses, the plastic deformation accumulates on the surface of substrate, and the crack is generated and propagates until it is stripped into wear debris. The worn surface is more serious than that of the

Journal Pre-proof substrate tested at RT, 200℃and 300℃, is covered by the oxidized friction layer confirmed by the morphology and EDS results of different regions shown in Table 1. Consequently, the wear mechanisms of the substrate are oxidation wear and fatigue wear. The CoNiP coatings produced fewer traces of plastic deformation and the worn surface of the CoNiP/Cr2O3 composite coatings emerged scaly-like adhesion. In comparison, the wear degree of the coated samples is lighter than that of the bare substrate, suggesting that the CoNiP and CoNiP/Cr2O3 composite coatings have excellent wear resistance at high temperature.

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As presented in Fig. 9m, when the test temperature reached 500℃, the surface

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oxidation of substrate is further intensified due to friction heat and high environment temperature, a lot of cracks and oxide debris are produced. In contrast, the worn

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surface of CoNiP and CoNiP/Cr2O3 is relatively smooth, only some narrow and

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shallow grooves parallel to the sliding direction can be observed. Similarly, the EDS

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results of different regions of CoNiP and CoNiP/Cr2O3 composite coatings are shown in Table 2 and Table 3. It can be obtained that the oxidation of the coating at different

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temperatures is lighter than that of the substrate. It also can be found that the wear mechanisms at high temperatures are the same, and the CoNiP and CoNiP/Cr2O3

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composite coatings always have better high temperature stability and wear resistance than the substrate.

3.4.2 Friction coefficient and wear rate The average friction coefficients of the coatings as a function of the temperature under dry sliding wear conditions are present in Fig. 10. It can be seen that for all the samples, when the wear temperature increases, the friction coefficient decreases firstly (before 300℃)and then increases. It is considered to be that the decrease is related to an oxide film formed on the surface of the material at high temperatures, and producing a lubricating effect. Due to the oxide film, the interatomic bonding force between the friction pairs is replaced by the weaker van der Waals force, resulting in reduced adhesion between friction pairs, and reduced friction coefficient as well [19]. When the wear temperature further increases (to 400℃ and 500℃), the surface oxide film is broken under the continuous load of the extrusion, and a large

Journal Pre-proof amount of wear debris is generated in the wear scar, thus the friction coefficient increases. The friction coefficient of the substrate without coating is 0.58 at room temperature, and the friction coefficient of the sample coated with CoNiP coating decreases to 0.35, which is very close to that reported in the literature [13]. For the sample coated with CoNiP-15g/L Cr2O3 coating, the friction coefficient further decreases, which reach to 0.23. Similar trend can be found for the samples at other temperatures. In addition, the friction coefficients of CoNiP and CoNiP-15g/L Cr2O3 coatings at high temperatures are slightly decreased but not obvious, there is also no

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significant increase at high temperatures of 400℃ and 500°C. It may be attributed to

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the fact that the oxide film formed at high temperatures is not destroyed under continuous load, which can be observed from Fig.9. The CoNiP and CoNiP-15g/L

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Cr2O3 composite coatings show lower friction coefficients as compared to the bare

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substrate, and the CoNiP-15g/L Cr2O3 composite coatings have the lowest average

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friction coefficients.

Wear rate is usually used to evaluate wear resistance of the material. A smaller

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wear rate means a greater wear resistance. The wear rates of all the samples are shown in Fig. 11. It is noticed that overall the wear rates of the substrate increase as the test

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temperatures increase. It can be seen from the figure that the wear rate of substrate without coating is 4.7×10-6 mm3/Nm at room temperature, and the wear rate of sample coated with CoNiP is 2.6×10-6 mm3/Nm which is also close to that reported in the literature [13]. By incorporating the Cr2O3 paticles into CoNiP coating, the wear rate further decreases, which is 1.6×10-6 mm3/Nm. The CoNiP-15g/L Cr2O3 also exhibits the lowest wear rates at other temperatures (200, 300, 400 and 500℃), indicating that the composite coatings possess the best wear resistance. Especially at high temperature of 500℃, the wear rates of the coatings decrease from 14.6×10-6 mm3/Nm to 2.99×10-6 mm3/Nm, which is only 1/5 of that of the substrate material. The reason for this phenomenon is considered to be caused by two aspects. On the one hand, the Cr2O3 particles incorporate into the coatings, and result in a high hardness, on the other hand, the Cr2O3 particles are dispersed and distributed in the coatings, and play a supporting role, so that the contact area between the coatings and

Journal Pre-proof the grinding material is reduced, thus and the friction and wear weaken effectively, and the wear resistance of the coatings are improved, the similar mechanism can be found in the related literature [28,29]. The wear rates of substrate, CoNiP and CoNiP-15g/L Cr2O3 composite coatings increase overall, when the test temperatures increase from RT to 500 ℃. This phenomenon may be attributed to the high temperature softening of the material. 4. Conclusions The present work evaluated the effects of Cr2O3 particles on the microstructure,

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microhardness, tribological properties of CoNiP/Cr2O3 composite coatings at different

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temperatures. The conclusions are as follows:

(1) The CoNiP coating was transformed from amorphous to crystalline structure

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after heat treatment at 350°C, and its microhardness increased due to the

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precipitation strengthening of Co2P phase.

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(2) When the concentration of Cr2O3 reached 15 g/L, the content of particles in the coating was almost saturated, and hardly changed When the Cr2O3 concentration in the bath increased.

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(3) The incorporation of Cr2O3 particles into the CoNiP coatings enhance their

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microhardness. The composite coating of CoNiP-15 g/L Cr2O3 exhibited the highest microhardness, and excessive increase of Cr2O3 concentration in the plating bath decreased the microhardness of the composite coatings. (4) The wear mechanisms were fatigue wear and adhesive wear for substrate and CoNiP coating repectively. The CoNiP-15 g/LCr2O3 coating exhibited the lowest frictions and wear rates at RT, 200, 300,400 and 500℃, suggesting that the wear resistance of the CoNiP-15 g/LCr2O3 composite coatings were better than that of the others. (5) The incorporation of Cr2O3 particles contributed to the enhancement of the mechanical and tribological properties of CoNiP/Cr2O3 composite coatings through: (i) Cr2O3 nanoparticles possess high hardness by themselves; (ii) Cr2O3 particles increased nucleation sites, resulting in grain refinement of the coating (iii) the CoNiP and the Cr2O3 particles were simultaneously subjected

Journal Pre-proof to a load, thereby inhibiting the plastic deformation of the coatings, thus the coatings were strengthened. References [1] Z. X. Zeng, L. P. Wang, L. Chen, J. Y. Zhang, The correlation between the hardness and tribological behaviour of electroplated chromium coatings sliding against ceramic and steel counterparts, Surf. Coat. Technol. 201(2006) 2282-2288. [2] M. Srivastava, C. Anandan, V. K. W. Grips, Ni–Mo–Co ternary alloy as a replacement for hard chrome, Appl. Sur. Sci. 285(2013)167-174.

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[18] R. Karslioglu, H. Akbulut, Comparison microstructure and sliding wear properties of nickel–cobalt/CNT composite coatings by DC, PC and PRC current electrodeposition, Appl. Surf. Sci. 353(2015)615–627. [19] L. M. Du, L.W. Lan, S. Zhu, Effects of temperature on the tribological behavior of Al0.25CoCrFeNi high-entropy alloy, J.Mater. Sci.Technol. 35(2019)917–925. [20] R. M. Zeinali, S. R. Allahkaram, S. Mahdavi, Effect of pH, Surfactant, and Heat Treatment on Morphology, Structure, and Hardness of Electrodeposited Co-P Coatings, J. Mater. Eng. Perform. 24(2015)3209-3217.

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[22] I. Kosta, A. Vicenzo, C. Müller, M. Sarret, Mixed amorphous-nanocrystalline cobalt phosphorous by pulse plating, Surf. Coat. Technol. 207(2012)443-449. [23] D. H. E. Persson, S. Jacobson, S. Hogmark, Effect of temperature on friction and galling of laser processed Norem 02 and Stellite 21, Wear. 255(2003)498–503. [24] S. R. Allahkaram, S. Golroh, M. Mohammadalipour, Properties of Al2O3

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nano-particle reinforced copper matrix composite coatings prepared by pulse and

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direct current electroplating, Mater.Design. 32(2011)4478-4484.

[25] A. E. Edward, S. Natarajan, Influence of carbon nanotube addition on sliding

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Phys. A-Mater. 120(2015)1653-1658.

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wear behaviour of pulse electrodeposited cobalt (Co)–phosphorus (P) coatings, Appl.

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[26] R. Tarozaitė, Z. Sukackienė, A. Sudavičius, R. kėnas, A. Selskis, A. Jagminienė, E. Norkus, Application of glycine containing solutions for electroless deposition of

117(2009)117-124.

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Co–P and Co–W–P films and their behavior as barrier layers, Mater. Chem. Phys.

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[27] B. Bostani, N. P. Ahmadi, S. Yazdani, R. Arghavanian, Co-electrodeposition and properties evaluation of functionally gradient nickel coated ZrO2 composite coating, Transact. Nonferr. Metal. Soc. 28(2018)66-76. [28] M.H. Allahyarzadeh, M. Aliofkhazraei, A.R. Sabour Rouhaghdam, V. Torabinejad,

Electrochemical tailoring of ternary Ni-W-Co(Al2O3) nanocomposite using pulse reverse technique, J. Alloy. Compd. 705(2017)788-800. [29] K.H. Hou, Y.C. Chen, Preparation and wear resistance of pulse electrodeposited Ni–W/Al2O3 composite coatings, Appl. Surf. Sci. 257(2011)6340–6346.

Figures:

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Fig.1. The schematic diagram of typical wear scar profile

Fig.2. SEM micrographs of surface of electrodeposited CoNiP/Cr2O3 coatings with different particles concentration:(a) 0g/L,(b) 1g/L,(c) 5g/L,(d)10g/L,(e) 15g/L,(f) 20g/L

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Fig.3. SEM micrographs of cross-section of the coatings with different particles concentrations of

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Cr2O3:(a) 0g/L,(b) 1g/L,(c) 5g/L,(d)10g/L,(e) 15g/L,(f) 20g/L

Fig.4. Effect of Cr2O3 particles concentration in plating bath on particle contents in composite coatings

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Fig.5. Effect of Cr2O3 particles concentration in plating bath on particles volume fraction in

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composite coatings

Fig.6. XRD patterns of CoNiP and CoNiP/Cr2O3 coatings (a) before and (b) after 350℃ heat treatment

Fig.7. Mean grain size of the coatings as a function of Cr2O3 particles concentration in the plating bath.

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Fig.8. Vickers microhardness of the samples with different concentration of Cr2O3 particles

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before and after 350℃ heat treatment.

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Fig.9. Worn surface morphologies of (a, d, g, j, m) substrate, (b, e, h, k, n) as-deposited CoNiP and (c, f, i, l, o) CoNiP-15g/L Cr2O3 coating at different temperature:(a, b, c) RT; (d, e, f) 200℃; (g, h, i) 300℃; (j, k, l) 400℃; (m, n, o) 500℃.

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Fig.10. Average friction coefficient of substrate, CoNiP and CoNiP/Cr2O3 composite coating at

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Fig.11. Wear rate of substrate, CoNiP and CoNiP/Cr2O3 composite coating at different temperature

Tabel 1 EDS analysis of element (at. %) in different regions (marked in Fig. 9) of the worn surface for substrate at different temperatures.

Temperature RT 200℃ 300℃ 400℃ 500℃

region

O

Fe

Cr

Mo

V

1 2 3 4

3.32 12.33 6.54 20.37

92.34 82.68 89.04 74.88

2.36 2.58 2.27 2.53

1.48 1.83 1.67 1.49

0.50 0.58 0.48 0.73

5

10.54

84.57

2.32

1.73

0.84

6

24.68

70.76

2.01

1.69

0.86

7 8

30.62 40.31

64.63 54.83

2.76 2.56

1.50 1.78

0.49 0.52

9

52.82

42.99

2.07

1.51

0.61

10

57.26

38.73

1.89

1.45

0.67

Journal Pre-proof Tabel 2 EDS analysis of element (at. %) in different regions (marked in Fig. 9) of the worn surface for CoNiP at different temperatures.

Temperature

region

Co

Ni

P

O

RT

1

71.13

14.36

10.82

3.69

200℃

2

66.21

13.54

11.46

8.79

300℃

3

60.79

13.89

10.65

14.67

400℃

4

58.94

12.76

12.32

15.98

500℃

5

57.45

12.26

10.54

19.75

Tabel 3 EDS analysis of element (at. %) in different regions (marked in Fig. 9) of the worn surface for

Co

Ni

RT

1

62.57

13.37

200℃

2

59.69

14.32

300℃

3

58.16

12.76

400℃

4

53.84

12.35

500℃

5

51.97

12.94

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P

Cr

O

10.27

8.14

5.65

11.48

8.28

6.23

10.85

7.89

10.34

12.03

7.91

13.87

11.57

8.06

15.46

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CoNiP/Cr2O3 at different temperatures.

Journal Pre-proof Author contributions

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Wenjing Xiong conducted all the experimental work and wrote the manuscript with the guidance of Yong Lian and Jin Zhang. Minyu Ma guided the sensing part of this work and corrected the manuscript.

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Declaration of Interest Statement The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of

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interest in connection with the work submitted.

Journal Pre-proof Highlights 1. The CoNiP/Cr2O3 composite coatings were prepared on the steel substrate. 2. The effect of heat treatment on the microstructure and microhardness of the coatings were studied. 3. The effects of Cr2O3 particle contents on the microstructures, compositions, and wear resistance properties of the coatings were investigated.

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4. The wear of the substrate and coatings at different wear temperatures were studied.