Effect of annealing temperature on the structural and mechanical properties of coatings prepared by electrophoretic deposition of TiO2 nanoparticles

Accepted Manuscript Effect of annealing temperature on the structural and mechanical properties of coatings prepared by electrophoretic deposition of TiO2 nanoparticles

Hafedh Dhiflaoui, Nader Ben Jaber, Florica Simescu Lazar, Joel Faure, Ahmed Ben Cheikh Larbi, Hicham Benhayoune PII: DOI: Reference:

S0040-6090(17)30551-5 doi: 10.1016/j.tsf.2017.07.056 TSF 36122

To appear in:

Thin Solid Films

Received date: Revised date: Accepted date:

13 December 2016 20 July 2017 21 July 2017

Please cite this article as: Hafedh Dhiflaoui, Nader Ben Jaber, Florica Simescu Lazar, Joel Faure, Ahmed Ben Cheikh Larbi, Hicham Benhayoune , Effect of annealing temperature on the structural and mechanical properties of coatings prepared by electrophoretic deposition of TiO2 nanoparticles, Thin Solid Films (2017), doi: 10.1016/j.tsf.2017.07.056

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ACCEPTED MANUSCRIPT Effect of annealing temperature on the structural and mechanical properties of coatings prepared by electrophoretic deposition of TiO2 nanoparticles

Hafedh Dhiflaoui 1, Nader Ben Jaber 1, 2, Florica Simescu Lazar2, Joel Faure 2, Ahmed Ben Cheikh Larbi 1 and Hicham Benhayoune 2*

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Université de Tunis, LMMP, 5 Av. Taha HUSSIN Monfleury, 1008 Tunis, Tunisia

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Université de Reims Champagne-Ardenne, LISM EA 4695, Bat. 6, Moulin de la Housse, BP

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*Corresponding author: Tel.: 00 33 (0)3 26 91 36 60 [email protected]

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1039, 51687 Reims Cedex 2, France

Abstract

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In the present study, TiO2 nanoparticles coatings were prepared on 316L stainless steel substrate by electrophoretic deposition (EPD) process. The effect of a thermal treatment on the obtained

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coatings was studied. Indeed, after electrophoretic deposition, a thermal treatment is required

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to evaporate the solvent from the coating and to improve its cohesion and its adhesion to the substrate. Three temperatures were selected: 650°C, 750°C and 850°C. The TiO2 coatings were

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characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) combined with energy-dispersive X-ray spectroscopy (EDXS) and atomic force microscopy (AFM).

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Results of electron microscopy and atomic force microscopy observations showed that a smooth and uniform porous layer was provided with particle sizes of about 20-100 nm. XRD measurement indicated that TiO2 coating was single crystalline with a pure rutile structure after heating at 850°C during 2h. The mechanical properties of the TiO2 coatings were investigated by means of nano-indentation and scratch tests. It was observed that the increase of annealing temperature improves the hardness, the Young’s modulus as well as the coatings adhesion to the substrate. Moreover, a new scratch test mode called ‘wear mode’ was performed to evaluate 1

ACCEPTED MANUSCRIPT the wear resistance of the coatings. It was noticed that when increasing the annealing temperatures, the friction coefficient and the wear resistance of the coated samples were improved. Therefore, the best tribological properties were obtained at 850 °C regarding to the self-lubrication role induced by the rutile phase.

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Keywords: Annealing; Electrophoretic deposition; TiO2 nanoparticles; 316 L stainless steel;

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Nanoindentation; Scratch tests; Wear tests

1. Introduction

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Thin film coatings have recently been considered promising to a variety of industrial applications in order to improve wear resistance [1], corrosion resistance [2,3], biocompatibility

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[4,5] and photocatalytic activity [6,7]. For instance, nanostructured titanium dioxide (TiO2) films are widely used in these applications. Indeed, TiO2 is an important inorganic material

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because of its good physical properties, which make it appropriately used in coating

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applications. The influence of TiO2 coating on tribological properties of substrate material and the effects of process parameters on TiO2 oxide films properties have been studied in the

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scientific literature [8-11].

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Several methods, such as sol-gel process [12], vapor phase deposition [13-14], micro-arc oxidation [15], and electrophoretic deposition [16] were used to produce TiO2 coatings. Electrophoretic deposition is a simple and low cost technique, which consists in the migration of the charged particles powder in suspension under the effect of an electric field. The particles will agglomerate and form a homogeneous layer at the surface of the substrate used as an electrode. This process has numerous advantages like its short processing time as well as its ability to control the surface morphology and the thickness of the coatings [17]. 2

ACCEPTED MANUSCRIPT However, the electrophoretic deposition technique needs further heat treatment to remove volatile species from the films and to enhance their mechanical properties. These properties are essentially governed by the coating hardness, its Young’s modulus and its adhesion to the substrate. Initially, commercialized TiO2 has three distinct phases: rutile (tetragonal), anatase (tetragonal),

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and brookite (orthorhombic) [18]. Heat treatments can induce phase transformations. For

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example, H. Yaghoubi et al. [19] obtained the anatase to rutile transformation on TiO2 sol-gel

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films deposited on glass and annealed at 500°C.

On the other hand, wear resistance is considered as one of the most important characteristics of

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the TiO2 coatings. The parameters governing the wear resistance include both intrinsic parameters (rigidity, residual stress and hardness) and extrinsic ones such as the dependence of

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sliding velocity as a function of normal load. For example, P. Baghery et al. [20] showed that nanoparticles TiO2 coatings with high hardness prevents the dislocations movement during the

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deformation of the material and suppresses the formation or propagation of the cracks. To the best of our knowledge, the tribological behavior of TiO2 nano-particles coatings prepared by EPD on 316L stainless steel have not been carefully studied so far. For this reason, the

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objective of this work is to produce TiO2 nanoparticles coatings on 316L stainless steel by

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electrophoretic deposition with enhanced mechanical properties. First EPD deposition of TiO2 nanoparticles coatings were carried out, then we study the effect of heat treatment (over 500°C) on the composition, the particles size and the crystallinity of these coatings. The hardness, the Young’s modulus and adhesion to the substrate of the obtained coatings were evaluated by nano-indentation using the “Oliver and Pharr” method [21]. The scratch test was used to evaluate the adhesive limit of the coatings.

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ACCEPTED MANUSCRIPT Moreover, to investigate the wear resistance and tribological properties of the coatings as a function of the annealing temperature, a new scratch test mode called ‘wear mode’ was developed. This process is based on dissipated energy friction quantification. 2. EXPERIMENTAL SECTION

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2.1.Materials and methods

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2.1.1. Electrophoretic deposition (EPD)

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EPD was carried out in a suspension prepared by dispersing 6g of TiO2 nano-powder in 1 L of absolute ethanol (0.75% weight). The nano-powder (particle size lower than 21 nm) was provided by Sigma-

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Aldrich. The TiO2 suspension was prepared into ethanol by using an ultrasonic dispersion (50 kHz) during 15 min. These experimental conditions are similar to those used by D. Schiemann and al.

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[22] and T. Moskalewicz and al. [23] who determine a zeta potential value of the TiO2 nanoparticles around + 40 mV. This positive value of the zeta potential indicates that the

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nanoparticles in contact with ethanol became positively charged leading to cathodic EPD (Fig. 1).

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Fig. 1. Sketch of the electrophoretic deposition process.

316L stainless steel disks having a diameter of 15 mm and a thickness of 3mm were used as metallic electrodes. They were cleaned by ultra-sonication with acetone then with water before using. The cathode surface of the studied 316L stainless steel was mechanically polished using silicon carbide (SiC) papers of 120, 1000, 2400 and 4000 grit followed by a diamond pastes to get mirror finish. The distance between the two metallic electrodes was set at 10 mm. Optimized EPD was performed at an applied voltage of 30 V, during 5 min at room temperature. Finally the deposited coatings were air dried for 24 hours. 4

ACCEPTED MANUSCRIPT 2.1.2. Thermal treatment in air The coated 316L stainless steel disks were thermally treated after EPD in air flow (21% O 2). The furnace temperature was increased with a rate equal to 2.5°C/min until it reached the selected temperature. Afterwards, it was held at this temperature for 2 h. The air flow was maintained during the whole thermal treatment until the complete cooling to room temperature.

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To study the effect of anatase or rutile phase on the mechanical properties of TiO 2 coatings

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deposited by EPD, three temperatures were selected: 650°C, 750°C and 850°C [24,25] . The

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temperature was limited at 850°C because this value is considered in several works as an optimal temperature for TiO2. Indeed, if this temperature is exceeded, the cracks formation into

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the coating during thermal treatment increases which further degrade its adhesive and

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tribological properties [26,27].

2.1.3. Scanning electron microscopy and energy dispersive X-ray spectroscopy (SEM-

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EDXS)

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The coatings surface morphologies were examined with a LaB6 scanning electron microscope (JEOL JSM 6460 LV) functioning at 0-30 keV. To carry out the energy dispersive X-ray

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analysis, this microscope was linked to an ultra-thin window Si (Li) detector. Indeed, the acquisition of X-ray spectra was achieved at primary beam energy equal to 20 keV during 120

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s. To quantitatively analyze the coatings composition and thickness, commercial software (PGT, France) together with a quantitative procedure developed in our laboratory called “TFQuantif” [28] were used. It consists to use standards samples with known thicknesses taking into account the matrix effects on the coating (ZAF : atomic number, Absorption and Fluorescence). The precision on the calculated thickness using this method is about 10%. 2.1.4. X-ray Diffraction (XRD)

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ACCEPTED MANUSCRIPT The samples phase composition was studied by an X-ray diffractometer (Bruker D8 Advance). Using a monochromatic CuKα radiation with a step of 0.02° every 2 s, the X-ray pattern data were collected from 2θ = 20° to 70°. The XRD analysis was carried out before and after each thermal treatment. The phase identification was achieved using the Powder Diffraction Files

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(PDF) of the International Center for Diffraction Data (ICDD).

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2.1.5. Atomic force microscopy (AFM)

The surface morphology and average surface roughness of TiO2 coatings were analyzed by

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atomic force microscopy (AFM, Model Nanoscope III). Tapping mode images were obtained

to 10 nm and a spring constant k = 42 N/m.

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2.2.Mechanical study

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in air using Silicon Nitride tips (TESP, Nanosensors) with a maximum radius of curvature equal

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2.2.1. Nanoindentation

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The Nanoindentation was carried out using a Nanoindenter XP (CSM Instruments, Switzerland). The experiments were performed using a Berkovich three-sided pyramidal

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diamond indenter having a nominal angle equal to 65.3° and a nominal radius curvature of 20 nm at a normal load of 80 mN and a sliding velocity of 1 mm.s-1. At least, 5 tests were carried

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out on each sample. The Poisson coefficient chosen was equal to 0.28 because it corresponds to that of commercial TiO2. Load-displacement curves were obtained by the Oliver and Pharr method to estimate the TiO2 coatings mechanical properties (Young’s modulus and Hardness). The first part of the loadingunloading curve shows the evolution of the penetration depth as a function of the applied load (Fig. 2). The plastic deformation energy corresponding to the maximum load (Pmax) can be related to the maximum penetration depth (hmax). From the load–penetration curves, elastic and 6

ACCEPTED MANUSCRIPT plastic deformation energies, surface hardness (H), and Young’s modulus (E) were calculated using integrated software.

The hardness is obtained by:

H

Pmax Ac

Where Pmax represents the maximum applied load and Ac is the projected contact area of the

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indenter tip.

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2 1 2 1 1 i   E Eeff Ei

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The Young modulus E of the coating is calculated using:

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Where i and  are respectively the Poisson coefficients of the indenter and the coating.

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Ei and E and are respectively the Young’s modulus of the indenter and the coating.

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Eeff corresponds to the measured value by the Nanoindenter.

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Fig. 2. Schematic of a typical load versus indenter displacement data hc = contact depth (the height of contact between the tip and the sample); hf = final depth of

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contact impression after unloading.

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2.2.2. Scratch test

The TiO2 coatings were submitted to a series of adhesion strength measurements using a scratch-tester type MST (CSM instruments, Switzerland) which was equipped with a Rockwell spherical diamond tip with a radius of 100 nm. The scratch tests were performed by increasing continuously the normal load from 30 mN to 10 N. The loading speed was 0.5 N.s-1 and the track length was 5 mm. The critical load is determined at the first moment of layer spallation and delamination then confirmed by SEM micrographs. 7

ACCEPTED MANUSCRIPT 2.2.3. Wear test Wear tests were performed with a CSM micro-scratch tester schematically illustrated in Fig. 3a. The indenters consist of spherical diamond Rockwell with a tip radius R = 100 µm and a cone angle  = 60° (Fig. 3b). The number of cycles, the applied load and the sliding speed were

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fixed during the “Wear mode”. The sensor system measures the normal and tangential forces in real time. For these tests, the

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normal force Fn, the sliding speed (V), the number of cycles and the sliding distance (L) can be

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controlled. The normal loads were 1, 1.5, 2, 2.5 and 3 N. The sliding velocities were 100, 200, and 300 µm/s. Each test was conducted for 500 cycles of repeat passages and the sliding

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amplitude L = 3 mm with a temperature of 22°C and relative humidity of 46%. The wear volume

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from the coating was evaluated by measuring the surface profile across the wear track. The obtained value was then normalized with the sliding distance and the applied load to obtain the wear rate. The frictional force was divided by the applied load to calculate the coefficient of

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friction.

the indenters.

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Fig. 3. A schematic drawing of the scratch test (a) the test configuration and (b) the shape of

3. RESULTS and DISCUSSION 8

ACCEPTED MANUSCRIPT 3.1.Elaboration and characterization of TiO2 coating 3.1.1. Morphology and composition of the TiO2 coating SEM images of Fig. 4 show the morphology of the optimised coating before and after thermal treatment in air at 650°C, 750°C and 850°C. One may observe that this thermal treatment

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promotes the generation of several small surface cracks caused by evaporation of solvent

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expansion coefficients of the substrate and the coating [30].

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trapped within the coating during EPD [29] and by the difference between the thermal

Fig. 4. SEM micrograph of the TiO2 coating (a) before and after thermal treatment in air at (b)

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650°C, (c) 750°C and (d) 850°C.

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At 650°C, the SEM micrographs (Fig. 4b) reveal that the coating is porous with small pores inside its structures. As the annealing temperature rises to 750 °C (Fig. 4c), the coating morphology is made of agglomerated spheroids. By further increasing the annealing

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temperature to 850 °C (Fig. 4d), the particles size increased and the coating porosity decreased

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leading to a densification and homogenization of the TiO2 coating [31, 32]. Fig. 5 presents the EDXS spectra associated to the SEM micrographs of Fig. 4. They show that the characteristic peak of oxygen (OK) increase as a function of the temperature. Indeed, the calculated Ti/O atomic ratio significantly decreases at 850°C, indicating an oxidation of the coated samples. Concurrently, the estimated coating thickness by TF-Quantif procedure [28] is reduced from about 8.3± 0.9 µm to about 3.5 µm ± 0.4 µm. Many works showed that the coating thickness is reduced when the sample is submitted to a post- deposition thermal 9

ACCEPTED MANUSCRIPT treatment [33-35]. This result proves that the coating compactness increase with the thermal treatment temperature.

Fig. 5. EDXS spectra of the TiO2 coating (a) before and after thermal treatment at (a) 650°C,

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(b) 750°C, and (c) 850°C.

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3.1.2. X-Ray Diffraction Analysis

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Fig. 6 presents the X-ray diffraction patterns of the coatings before and after thermal treatment at 650°C, 750°C and 850°C. The diffraction peaks at 2θ = 25.28, 36.95, 48.05 and 55.07 deg.

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corresponds to (101), (103), (200) and (211) planes of the anatase phase. The diffraction peaks

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at 2θ = 27.4, 36.2, 39.4, 41.28, 44.15, 54.3, 56.6, 62.7, 64.1 and 69.1 deg. corresponds to (110), (101), (200), (111), (210), (211) , (220), (002), (310) and (301) planes of the rutile phase. The

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peaks at 2θ = 43.6 and 50.7 correspond to 316L substrate. One may clearly observe that at

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750°C and 850°C, the (101) peak of anatase completely disappeared while the (110) peak of rutile appeared suggesting that the coating structure is pure monophasic rutile from 750°C

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In general, the anatase to rutile transformation may be conducted in a wide range of temperatures and the transformation is influenced by parameters such as preparation method

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and particle size [36].

Fig. 6. The X-ray diffraction pattern of TiO2 (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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ACCEPTED MANUSCRIPT The average grain size D was calculated by using Debye-Scherer’s formula [37-39] from the full-width at half maximum (FWHM) of the (101) peak for anatase and (110) for rutile :

D = (0.89* cos(

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where  is the X-ray wavelength,  represents the diffraction angle and B corresponds to the

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full width at the diffraction peak half maximum.

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The precision of the grain size D calculating is related to the full width B and estimated to 10%. Fig. 7 shows that the average grain size presents an increasing trend with annealing temperature.

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While its value is about 21.0 ± 2.1 nm before thermal treatment, it increases from 31.5 ± 3.2 nm to 71 ± 7.2 nm when the annealing temperature passes from 650 °C to 850 °C. Obviously,

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the grain size and the sintering of TiO2 nanoparticles are determined by the increase of annealing

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temperature. This result confirms the SEM observations.

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Fig. 7. The average grain size for TiO2 coating as a function of annealing temperature.

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3.1.3. Atomic force microscopy (AFM) Fig. 8 shows typical AFM three-dimensional representations (0.1 µm x 0.1 µm surface plots) of TiO2 coated samples before and after thermal temperatures. They reveal a rough surface texture consisting of particles fused together at the inter-particle contacts and deep valleys. As can be observed from Table 1, the thermal treatment has a direct impact on the grain size and the deposited films topography. The grain size and the roughness increased respectively from

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ACCEPTED MANUSCRIPT (21 and 21.6 nm) to 71 nm and 50 nm when the temperature increased from ambient temperature to 850°C. These values are in good agreement with those deduced from XRD patterns.

Fig. 8. Topography of TiO2 coating (a) before and after thermal treatment at (b) 650°C, (c)

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750°C and (d) 850°C.

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Table 1

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Grain size and roughness of the TiO2 coating before and after thermal treatment at different

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temperatures.

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3.2.Mechanical Study

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3.2.1. Nanoindentation

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The tests of nano-indentation were performed in order to determine the layer intrinsic mechanical characteristics without the substrate influence. The output obtained from a nano-

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indentation test is a graph relating the applied load and the corresponding indenter displacement during the loading and unloading phases. The load and the displacement were recorded

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continuously during the indentation process. During unloading, the penetration depth (hmax) decreased with the applied load. However, when the indenter was completely removed, the residual depth hf was obtained. The experimental hardness values obtained are presented in Table 2. These results include the unloading data from which TiO2 Young’s modulus can be calculated. Fig. 9 shows the evolution of the normal force as a function of the penetration depth obtained by nano-indentation at the surface of TiO2 coatings before and after the thermal treatment. 12

ACCEPTED MANUSCRIPT Results show a similar trend where the maximum displacement decreases with increased annealing temperature. Increasing annealing temperature from 650°C to 850°C results in the hardness increase from 0.56 GPa to 0.97 GPa and Young’s modulus rise from 20.33 GPa to 25.48 GPa. These values are of the same order of magnitude as those obtained by other authors in the case of TiO2 coatings [40,41]. The increase of the indentation parameters is due to the

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phase transformation (anatase to rutile). Anatase has a tetragonal crystal structure where the Ti–

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O octahedra share four corners. Rutile has a crystal structure similar to that of anatase with the

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exception that the octahedra share four edges instead of four corners. This leads to the formation of chains, which are subsequently arranged in a four-fold symmetry. In comparison, the rutile

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structure is more densely packed than anatase [36].

The resistance to elastic deformation is related to the ratio of the hardness and the modulus H/E,

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while the resistance to plastic deformation is related to H3/E2 [42,43]. Higher values of H3/E2 and H/E are obtained at 850°C, which indicates the high coating resistance to elastic/plastic

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deformation. This result is expected from a coating exhibiting high hardness and Young’s

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modulus.

The charge-discharge curve shape demonstrates that the TiO2 coating is characterized by an

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elastic-plastic behavior. This finding is proved by the ratios of plastic deformation energy (Wp) and the elastic deformation energy (We) with the total energy (Wt) presented in Table 2. This

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table reveals that the temperature rise over the layer behavior is plastic, which shows the effect of the rutile phase plastic deformation energy.

Fig. 9. Load-displacement curves carried out on the electrophoretically deposited TiO2 coating (a) before and after thermal treatment at (b) 650°C, (c) 750°C and (d) 850°C.

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ACCEPTED MANUSCRIPT Table 2 Mechanical properties of the TiO2 coating before and after thermal treatment at different annealing temperatures.

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3.2.2. Scratch Test

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When performing scratch tests, the chipping increases with increasing the normal load

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alongside the scratch track. Critical loads have been determined from the load-displacement profile. LC1 is characterized by an initial part of plastic deformation followed by the appearance

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of small cracks within the scratch track. LC2 is the upper critical load at which the first delaminating at the edge of the scratch track occurred (adhesion failure) [44] and the LC3 is

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recorded when the damage of the film exceeded 50% [45]. Fig. 10 presents the graph of the friction force versus the normal force for the sample before

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thermal treatment. One can observe a faster increase of the friction force at a critical load around 4.4 N . This critical load refers to the load at which the coating first delaminates and is a measure of the adhesion of the coating [46]. M. Laamari et al. [47, 48] used this procedure to estimate

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the adhesion of TiO2 coatings obtained by EPD on metallic substrates.

Fig. 10. Scratch-test study of the electrophoretically deposited TiO2 coating at ambient temperature.

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ACCEPTED MANUSCRIPT The scratch tests graphs associated to the scratch length and tracks of the thermal treated coatings are presented in Figs. 11-13. The three critical load LC1, LC2 and LC3 are identified. Their values as a function of annealing temperature are summarized in Table 3.

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Fig. 11. Scratch-test study of the electrophoretically deposited TiO2 coating at 650°C.

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Fig. 12. Scratch-test study of the electrophoretically deposited TiO2 coating at 750°C.

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Fig. 13. Scratch-test study of the electrophoretically deposited TiO2 coating at 850°C.

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Table 3

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Critical loads obtained by scratch test of the TiO2 coatings.

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The increase of the critical load LC1 with the three treatment conditions (650°C, 750°C and 850°C during 2 hours) clearly demonstrates that heat treatment in air improves the cohesion of the TiO2 coating. This improvement indicates the presence of a better covalent bond within the obtained coating [49, 50]. The increase of the critical load LC2 with the annealing temperature reveals that the start of the spallation of the bonded adhesive coating is improved. The spallation of thermal treated coating 15

ACCEPTED MANUSCRIPT is linked to its adhesive limit. The LC2 increase is due to the appearance of the rutile phase which becomes more intense at high temperatures (over 750°C). Furthermore, EDXS analyses show that after thermal treatment at 850°C the TiO2 coating is still detected on the substrate. We also note that the coating treated at 850°C has the higher critical load (LC3), which

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corresponds to the total delamination of the layer. It seems that this higher temperature can improve the formation of chemical bonds at the interface between the coating and the substrate.

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the coating adhesion to the 316L stainless steel substrate.

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The increase of the critical load LC3 clearly demonstrates that the thermal treatment enhances

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3.2.3. Wear mode

In this study, we have chosen to run wear tests with loads between 1 and 3 N. We have used

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low loads to avoid plastic deformation and the formation of smooth and thick tribolayer. Measurement of the tangential force during the wear tests allowed us to study the evolution of

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the friction coefficient. Fig. 14 represents the friction coefficient evolution as a function of time

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for the samples before and after thermal treatment. The mean friction coefficient of the untreated sample is about 0.3 while it is equal to 0.2, 0.17 and 0.15 respectively for annealing

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temperatures of 650, 750 and 850°C. We note that the friction coefficient values decreased with increasing annealing temperature. Indeed, the increase of annealing temperature promote the

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rutile-TiO2 phase which play a role like solid lubricant, changing the interfacial contact area and bearing behavior. The self-lubricant nature of rutile TiO2 thin films induces the reduction of friction coefficient [26,51]. We also notice that the change in the friction coefficient was related to the properties of samples. It decreased when hardness and elastic modulus increased [52,53].

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ACCEPTED MANUSCRIPT Y. Sun et al. [54] showed in their study that rutile TiO2 films have low friction coefficient due to their stability structure, high hardness and elastic modulus.

Fig. 14. Friction coefficient evolution as a function of number of cycles for the TiO2 coating

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(a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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3.2.3.a. Wear variation with sliding velocities

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The wear volume evolution as a function of sliding velocities and normal force of the samples before and after thermal treatment is shown in Fig. 15. For all samples, the wear volume

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increases with sliding velocities regardless of the applied normal load levels. The wear volume of untreated sample was higher than that of treated samples. These results reveal that the TiO 2

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coating, treated at 850°C, show the best wear behavior, due the presence of rutile phase at this

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elastic modulus [55,56].

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temperature. Indeed, the rutile phase has a stable structure and higher hardness as well as higher

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Fig. 15. Wear volume as a function of sliding velocities at various normal loads for the TiO2 coating (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

3.2.3.b. Dissipated energy variation with sliding velocities Fig. 16 shows the dissipated energy evolution as a function of sliding velocities and normal load of the samples before and after thermal treatment. One may observe that the dissipated 17

ACCEPTED MANUSCRIPT energy tended to decrease when the sliding velocities increased regardless of the applied load. Dissipated energy of treated samples was higher than that of the untreated one. This behavior can be explained by the improvement of mechanical properties after heat treatment.

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Fig. 16. Energy as a function of sliding velocities at various normal loads for the TiO2 coating

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(a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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3.2.3.c. Energy wear factor

The volume loss is related to the energy dissipated during wear. Fig. 17 represents the relation

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between the lost volume and dissipated energy obtained after 500 cycles. This relation is linear for all studied surface states. The associated slope is the energetic wear coefficient and

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represents the resistance capacity of the surface to wear in fretting. The energetic wear

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Table 4

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coefficients of all samples are reported in Table 4.

coatings.

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Energetic wear coefficients and associated correlation parameter (R2) values for studied

This result shows that the energetic wear coefficient of untreated sample was higher than that of treated ones. It also reveal that the energetic wear coefficient decrease with increasing the annealing temperature. This result confirms the good wear resistance of the treated coating at

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ACCEPTED MANUSCRIPT 850 °C. Indeed, when the mechanical properties, such as hardness and elastic modulus increase the coating wear decreases resulting in a lower energetic wear coefficient.

Fig. 17. Variation of the wear volume as a function of dissipated energy for the TiO2 coating

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(a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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The examination of the wear trace of TiO2 coating treated at 850°C using SEM images obviously indicates the mechanism of wear (Fig. 18). It is observed that the wear track is smooth

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and has a width of about 75 µm. It was also observed that a thin TiO2 film is still present at the

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surface (presence of TiK and Ok peaks in the EDXS spectrum of Figure 19), which confirms

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that the substrate is not achieved after 500 cycles.

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Fig. 18. SEM image of worn surface thermal treated at 850°C for an applied load of 3 N and a

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sliding velocity of 300 µm/s.

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Fig. 19. EDXS spectrum of worn surface of the sample treated at 850°C.

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ACCEPTED MANUSCRIPT 4. Conclusions In this study, TiO2 coatings were successfully deposited on 316L stainless steel substrate by electrophoretic process. To improve their mechanical properties, they were thermally treated in air. It was observed that electrophoretic TiO2 coatings exhibited optimal mechanical properties

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for heat treatment temperature of 850°C. Surface observations and nano-indentation analysis demonstrated that the agglomerate

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spheroids/porous morphology play a dominant role in improving the TiO2 coating mechanical

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properties such as hardness and Young’s modulus. XRD results showed that the structure of the coating changes with the heat treatment temperature. Rutile phase was obtained at 850°C while

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initially TiO2 coatings are composed of rutile and anatase phases.

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ACCEPTED MANUSCRIPT Acknowledgments: This work was financially supported by Tunis University. The Laboratory of Engineering and Materials Science (LISM), University of Reims Champagne Ardennes, French, has provided access to SEM and XRD equipment and the technical support. Author contributions: In this work Hafedh Dhiflaoui has performed part of the electrophoretic deposition runs and the mechanical characterization of the TiO2 nano-particles coatings; Nader

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Ben Jaber has optimized wear tests; Florica Simescu Lazar has performed SEM and XRD

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characterizations; Joel Faure has supervised the electrophoretic deposition program; Ahmed

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Ben Cheikh Larbi has contributed to the implementation, organization and funding of the mechanical characterizations activities at LMMP lab; Hicham Benhayoune supervised the SEM

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he is corresponding author of this paper.

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and DRX studies and also contributed to the organization of LMMP/LISM collaboration and

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Conflicts of Interest: The authors declare no conflict of interest.

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ACCEPTED MANUSCRIPT References

[1] D. Siva Rama Krishna, Y.L. Brama, Y. Sun, Thick rutile layer on titanium for tribological applications, Tribol. Int. 40 (2007) 329-334.

PT

[2] M. Herrmann, Corrosion of silicon nitride materials in aqueous solutions, J. Am. Ceram. Soc. 96 (2013) 3009-3022.

RI

[3] A. Ghasemi, V.S. Raja, C. Blawert, W. Dietzel, K.U. Kainer, Study of the structure and

SC

corrosion behavior of PEO coatings on AM50 magnesium alloy by electrochemical impedance

NU

spectroscopy, Surf. Coat. Technol. 202 (2008) 3513-3518.

[4] F. Samanipour, M.R. Bayati, H.R. Zargar, F. Golestani-Fard, T. Troczynski, M.Taheri,

MA

Electrophoretic enhanced micro arc oxidation of ZrO2-Hap-TiO2 nanostructured porous layers,

D

J. Alloys Compd. 509 (2011) 9351-9355.

PT E

[5] F. Samanipour, M.R. Bayati, F. Golestani-Fard, H.R. Zargar, A.R. Mirhabibi, V.ShoaeiRad, S. Abbasi, Innovative fabrication of ZrO2–HAp–TiO2 nano/micro-structured composites

CE

through MAO/EPD combined method, Mater. Lett. 65 (2011) 926-928. [6] M.R. Bayati, F. Golestani-Fard, A.Z. Moshfegh, How photocatalytic activity of the MAO-

AC

grown TiO2 nano/micro-porous films is influenced by growth parameters? Appl. Surf. Sci. 256 (2010) 4253-4259.

[7] M.R. Bayati, F. Golestani-Fard, A.Z. Moshfegh, Visible photodecomposition of methylene blue over micro arc oxidized WO3–loaded TiO2 nano-porous layers, Appl. Catal. A 382 (2010) 322-331.

22

ACCEPTED MANUSCRIPT [8] D. Wang, Gordon P. Bierwagen, Sol-gel coatings on metals for corrosion protection, Prog. Org. Coat. 64 (2009) 327-338. [9] T. Fu, C.S. Wen, J. Lu, Y.M. Zhou, S.G. Ma, B. H. Dong, B.G. Liu, Sol-gel derived TiO2 coating on plasma nitrided 316L stainless steel, Vacuum 86 (2012) 1402-1407.

PT

[10] R. Mechiakh, N. Ben Sedrine, R. Chtourou, R. Bensaha, Correlation between microstructure and optical properties of nano-crystalline TiO2 thin films prepared by sol-gel dip

RI

coating, Appl. Surf. Sci. 257 (2010) 670-676.

SC

[11] B. Surowska, J. Bieniaś, Composite layers on titanium and Ti6Al4V alloy for medical

NU

applications, Journal of Achievements in Materials and Manufacturing Engineering, 43 (2010) 162-169.

MA

[12] M.R. Bayati, H.R. Zargar, A. Talimian, A. Ziaee, R. Molaei, Characterization of Al2O3– TiO2 nano porous solar absorbers derived via MAO/sol-gel hybrid process, Surf. Coat. Technol.

PT E

D

205 (2010) 2483-2489.

[13] Z. Xu, J. Dai, J. Niu, N. Li, G. Huang, L. He, Thermal shock behavior of platinum

CE

aluminide bond coat/electron beam-physical vapor deposited thermal barrier coatings, J. Alloys Compd. 617 (2014) 185-191.

AC

[14] R. Ali, E. Alkhateeb, F. Kellner, S. Virtanen, N. Popovska-Leipertz, Chemical vapor deposition of titanium based ceramic coatings on low carbon steel: Characterization and electrochemical evaluation, Surf. Coat. Technol. 205 (2011) 5454-5463. [15] Y.K. Pan, C.Z. Chen, D.G.Wang, Z.Q. Lin, Preparation and bioactivity of micro-arc oxidized calcium phosphate coatings, Mater. Chem. Phys. 141 (2013) 842-849.

23

ACCEPTED MANUSCRIPT [16] M.F. De Riccardis, D. Carbone, E. Piscopiello, M.V. Antisari, Electron beam treatments of electrophoretic ceramic coatings, Appl. Surf. Sci. 254 (2008) 1830-1836. [17] R. Drevet, N. Ben Jaber, J.Faure, A. Tara, A BEN Cheikh Larbi, H. Benhayoune, Electrophoretic deposition (EPD) of nano-hydroxyapatite coatings with improved mechanical

PT

properties on prosthetic Ti6Al4V substrates, Surf. Coat. Technol. 301 (2016) 94-99. [18] M. Landmann, E. Rauls, W.G. Schmidt, The electronic structure and optical response of

SC

RI

rutile, anatase and brookite TiO2, J. Phys. Condens. Matter 24 (2012) 195503-195508. [19] H. Yaghoubi, N. Taghavinia, E. Keshavarz Alamdari and Alex A. Volinsky,

NU

Nanomechanical Properties of TiO2 Granular Thin Films, App. Mat. Inter. 02 (2010) 2629-

MA

2636.

[20] P. Baghery, M. Farzam, A.B. Mousavi, M. Hosseini, Ni–TiO2 nanocomposite coating with

D

high resistance to corrosion and wear, Surf. Coat. Tech. 204 (2010) 3804–3810.

PT E

[21] W.C. Oliver, G.M. Pharr, An improved technique for determining hardness and elastic modulus using load and displacement sensing indentation experiments, J. Mater. Res. 7 (1992)

CE

1564-1582.

AC

[22] D. Schiemann, P. Alphonse, P.L. Taberna, Synthesis of high surface area TiO2 coatings on stainless steel by electrophoretic deposition, J. Mater. Res. 28 (2013) 2023-2030.

[23] T. Moskalewicz, A. Czyrska-Filemonowicz, A.R. Boccacini, Microstructure of nanocrystalline TiO2 films produced by electrophoretic deposition on Ti–6Al–7Nb alloy, Surf. Coat. Technol. 201 (2007) 7467-7471.

24

ACCEPTED MANUSCRIPT [24] A. S. Attar, Z. Hassani, Fabrication and Growth Mechanism of Single-crystalline Rutile TiO2, Nanowires by Liquid-phase Deposition Process in a Porous Alumina Template, J. Mater. Sci. Technol. 31 (2015) 828-833.

[25] J. Hamagami, Y. Ato, K. Kanamura, Macroporous Hydroxyapatite Ceramic Coating by

PT

Using Electrophoretic Deposition and then Heat Treatment, J. Ceram. Soc. Jpn. 114 (2006) 51-

RI

54.

SC

[26] O. Çomaklı, T. Yetim, A. Çelik, The effect of calcination temperatures on wear properties

NU

of TiO2 coated CP-TiO, Surf. Coat. Tech. 246 (2014) 34-39.

MA

[27] C. K. Lin, T. J. Yang, Y. C. Feng, T. T. Tsung, C. Y. Su, Characterization of electrophoretically deposited nanocrystalline titanium dioxide films, Surf. Coat. Tech. 200

PT E

D

(2006) 3184-3189.

[28] N. Dumelie, H. Benhayoune, G. Balossier, TF_Quantif: a procedure for quantitative

CE

mapping of thin films on heterogeneous substrates in electron probe microanalysis (EPMA), J.

AC

Phys. D: Appl. Phys. 40 (2007) 2124-2131.

[29] M. Fanoki-Rad, T. Shahrabi, Effect of suspension medium on the electrophoretic deposition of hydroxyapatite nanoparticles and properties of obtained coatings, Ceram. Int. 40 (2014) 3031-3039. [30] X. Wang, P. Xiao, Residual stress and constrained sintering of YSZ/Al2O3 composite coatings, Acta Mater. 52 (2004) 2591-2603.

25

ACCEPTED MANUSCRIPT [31] Yuh-fan Su, Mong-chieh Lee, Guan-bo Wang, Yang-hsin Shih, An innovative method to quickly and simply prepare TiO2 nanorod arrays and improve their performance in photo water splitting, Chem. Eng. J. 253 (2014) 274-280.

[32] M. A. Butt, S. A. Fomchenkov, Thermal Effect on the Optical and Morphological

PT

Properties of TiO2 Thin Films Obtained by Annealing a Ti Metal Layer, J. Kor. Phys. Soc. 70

SC

RI

(2017) 169-172.

[33] A. Morteza Ali, S. Ramezani Sani, Study of the effect of annealing temperature on structure

NU

of TiO2 nanowires by oxidation annealing, Thin Solid Films 534 (2013) 183-185.

MA

[34] R. Drevet, J. Fauré and H. Benhayoune, Thermal treatment optimization of electrodeposited hydroxyapatite coatings on Ti6Al4V substrate, Adv.Eng. Mater. 14 (2012),

PT E

D

377-382.

[35] N Ben Jaber, R Drevet, J Fauré , C Demangel, S Potiron, A Tara, A Ben Cheikh Larbi and

CE

H Benhayoune, A new process for the thermal treatment of calcium phosphate coatings

AC

electrodeposited on Ti6Al4V substrate, Adv. Eng. Mater. 17(2015) 1608-1615.

[36] M. Lazzeri, A. Vittadini, A. Selloni, Structure and energetics of stoichiometric TiO2 anatase surfaces, Phys. Rev. B 63 (2001) 155409, 1-9.

[37] H. Yaghoubi, N. Taghavinia, E.K.Alamdari, Self-cleaning TiO2 coating on polycarbonate: Surface treatment, photocatalytic and nanomechanical properties, Surf. Coat. Technol. 204 (2010) 1562-1568. 26

ACCEPTED MANUSCRIPT [38] B.D. Cullity, Elements of X-Ray Diffraction, 2nd edn. Addison-Wesley Publishing Company Inc., London, 1978.

[39] P. Bilik, G. Plesch, Mechanochemical synthesis of anatase and rutile nano-powders from

PT

TiOSO4, Mater. Lett. 61 (2007) 1183-1186.

RI

[40] Meriem Laamari, Adel Ben Youssef, Latifa Bousselmi, TiO2 Photoanodes Developed by

SC

Cathodic Electrophoretic Deposition in Aqueous Media: Effect of the Applied Voltage, J. Adv.

NU

Oxid. Technol. 19 (2016) 165-170.

[41] Y. N. Xu, M. N. Liu,M. C. Wang, A. Oloyede, J. M. Bell, and C. Yan, Nanoindentation

MA

study of the mechanical behavior of TiO2 nanotube arrays, J.App.Phys.118 (2015)145301,1-7.

D

[42] F. Lu, S.P. Wen, R.L. Zong, F. Zeng, Y. Gao, F. Pan, Nanoindentation Study of

PT E

Amorphous-Co79Zr13Nb8/Cr Multilayers, Surf. Coat. Technol. 202 (2008) 3239-3245.

CE

[43] H.C. Barshilia, N. Selvakumar, B. Deepthi, K.S. Rajam, A comparative study of reactive

2193-2201.

AC

direct current magnetron sputtered CrAlN and CrN coatings, Surf. Coat. Technol. 201 (2006)

[44] L. Ipaz, J.C. Caicedo, J. Esteve, F.J. Espinoza-Beltran, G. Zambrano, Improvement of mechanical and tribological properties in steel surfaces by using titanium–aluminum/ titanium– aluminum nitride multilayered system, Appl. Surf. Sci. 258 (2012) 3805-3814.

27

ACCEPTED MANUSCRIPT [45] F. Vaz, P. Machado, L. Rebouta, P. Cerqueira, Ph. Goudeau, J.P. Rivière, E. Alves, K. Pischow, J. Rijk, Mechanical characterization of reactively magnetron-sputtered TiN films, Surf. Coat. Technol. 174-175 (2003) 375-382.

[46] Besim Ben-Nissan, Andy H. Choi, Avi Bendavid, Mechanical properties of inorganic

PT

biomedical thin films and their corresponding testing methods, Surf. Coat. Tech. 233 (2013)

SC

RI

39-48.

[47] M. Laamari, A. Ben Youssef, L. Bousselmi, Adhesion behavior of hydrophilic TiO2 films,

NU

Mater. Res. Innov. (2017) DOI: 10.1080/14328917.2017.1312745.

MA

[48] M. Laamari, A. B. Youssef, L. Bousselmi, Electrophoretic deposition of titanium dioxide

D

films on copper in aqueous media, Water Sci. Tech. 74 (2016) 424-430.

PT E

[49] E. Mohseni, E. Zalnezhad, A. R. Bushroa, Comparative investigation on the dhesion of ydroxyapatite coating on Ti–6Al–4V implant: A review paper, Int. J. Adhes. & Adhes. 48

CE

(2014) 238-257.

AC

[50] Y. C. Yang, E. Chang, Influence of residual stress on bonding strength and fracture of plasma-sprayed hydroxyapatite coatings on Ti-6Al-4V substrate, Biomaterials 22 (2001) 18271836.

[51] K. Dejun, G. Haoyuan, W. Wenchang Effects of Loadings on Friction and Wear Behaviors of Cathodic Arc Ion Plating AlTiN Coating at High Temperature, Tribology Transactions 59 (2016) 604-612. 28

ACCEPTED MANUSCRIPT [52] A. Alsaran, C. Albayrak, Effect of single and duplex surface treatments on wear properties of CP-Ti, Surf. Eng. 27 (2011) 205-210.

[53] I. A. Ovid'ko, A. G. Sheinerman, Plastic deformation and fracture processes in metallic

PT

and ceramic nanomaterials with bimodal sttructures, Rev. Adv. Mater. Sci. 16 (2007) 1-9.

RI

[54] Y. Sun, Tribological rutile-TiO2 coating on aluminium alloy, Appl. Surf. Sci. 233 (2004)

SC

328-335.

NU

[55] I. Jouanny, S. Labdi, P. Aubert, C. Buscema, O. Maciejak, M.H. Berger, V. Guipont, M. Jeandin, Structural and mechanical properties of titanium oxide thin films for biomedical

MA

application, Thin Solid Films 518 (2010) 3212-3217.

D

[56] D. Kaczmarek, J. Domaradzki, D. Wojcieszak, E. Prociow, M. Mazur, F. Placido,

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S. Lapp, Hardness of nanocrystalline TiO2 Thin Films, Journal of Nano Research 18-19 (2012)

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CE

195-200.

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ACCEPTED MANUSCRIPT Figures Captions :

Fig. 1. Sketch of the electrophoretic deposition process.

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Fig. 2. Schematic of a typical load versus indenter displacement data

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hc = contact depth (the height of contact between the tip and the sample); hf = final depth of contact impression after unloading.

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Fig. 3. A schematic drawing of the scratch test (a) the test configuration and (b) the shape of the indenters.

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Fig. 4. SEM micrograph of the TiO2 coating (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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Fig. 5. EDXS spectra of the TiO2 coating (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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Fig. 6. The X-ray diffraction pattern of TiO2 (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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Fig. 7. The average grain size for TiO2 coating as a function of annealing temperature.

Fig. 8 Topography of TiO2 coating (a) before and after thermal treatment at (b) 650°C, (c) 750°C and (d) 850°C.

Fig. 9. Load-displacement curves carried out on the electrophoretically deposited TiO2 coating (a) before and after thermal treatment at (b) 650°C, (c) 750°C and (d) 850°C.

Fig. 10. Scratch-test study of the electrophoretically deposited TiO2 coating at ambient temperature. 30

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Fig. 11. Scratch-test study of the electrophoretically deposited TiO2 coating at 650°C.

Fig. 12. Scratch-test study of the electrophoretically deposited TiO2 coating at 750°C.

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Fig. 13. Scratch-test study of the electrophoretically deposited TiO2 coating at 850°C.

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Fig. 14. Friction coefficient evolution as a function of cycles number for the TiO2 coating (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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Fig. 15. Wear volume as a function of sliding velocities at various normal loads for the TiO2 coatings (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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Fig. 16. Energy as a function of sliding velocities at various normal loads for the TiO2 coating (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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Fig. 17. Variation of the wear volume as a function of dissipated energy for the TiO2 coating (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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Fig. 18. SEM image of worn surface thermal treated at 850°C for an applied load of 3 N and a sliding velocity of 300 µm/s.

Fig. 19. EDXS spectrum of worn surface of the sample treated at 850°C.

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ACCEPTED MANUSCRIPT Table 1 Grain size and roughness of the TiO2 coating before and after thermal treatment at different temperatures.

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Table 2

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Mechanical properties of the TiO2 coating before and after thermal treatment at different

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annealing temperatures.

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Table 3

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Critical loads obtained by scratch test of the TiO2 coatings.

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Energetic wear coefficients and associated correlation parameter (R2) values for studied

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coatings.

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Fig. 1. Sketch of the electrophoretic deposition process.

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Fig. 2. Schematic of a typical load versus indenter displacement data

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impression after unloading.

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Fig. 3. A schematic drawing of the scratch test (a) the test configuration and (b) the shape of the indenters.

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Fig. 4. SEM micrograph of the TiO2 coating (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C. 36

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(a) (a) (b) (b) (c) (c) (d) (d)

Ti / O = 0.75 ± 0.01 Ti / O = 0.75 ± 0.01

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Ti / O = 0.63 ± 0.01 Ti Ti / O = 0.63 ± 0.01 Ti

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Ti / O = 0.84 ± 0.02 Ti / O = 0.84 ± 0.02

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Intensity Intensity(counts) (counts)

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Fig. 5. EDXS spectra of the TiO2 coating (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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Fig. 6. The X-ray diffraction pattern of TiO2 (a) before and after thermal treatment in air at (b) 650°C, (c) 750°C and (d) 850°C.

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Fig. 17. Variation of the wear volume as a function of dissipated energy for the TiO2 coating (a) before and after thermal treatment at (b) 650 °C, (c) 750 °C and (d) 850 °C.

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Grooves EDS

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650

750

850

Grain size (nm)

21.0±2.1

31.5±3.2

58.2±5.9

71.1±7.2

Roughness (nm)

21.6

41.7

43.7

50.3

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ACCEPTED MANUSCRIPT Table 2 Mechanical properties of the TiO2 coating before and after thermal treatment at different annealing temperatures. plastic

H3/E*2

deformation

deformation

(GPa)

energy

energy

We/Wt

Wp/Wt

0.45 x 10-4

0.017

0.983

0.027

4.24 x 10-4

0.137

0.862

21.15

0.031

6.70 x 10-4

0.1

0.899

25.48

0.038

14 x 10-4

0.053

0.946

temperature

depth

(°C)

(µm)

ambient

14.6

0.16

9.46

0.016

650

9.58

0.56

20.33

750

8.11

0.67

850

7.52

0.97

Hardness

H/E

(GPa)

AC

CE

PT E

D

MA

NU

SC

(GPa)

modulus

RI

Max

PT

elastic

Young’s

Annealing

54

ACCEPTED MANUSCRIPT Table 3 Critical loads obtained by scratch test of the TiO2 coatings. Annealing temperature Critical load

ambient

650°C

750°C

850°C

LC1

4.4

1.73

2.8

3.22

LC2

-

3.57

4

5.08

LC3

-

4.52

5.91

7.99

AC

CE

PT E

D

MA

NU

SC

RI

PT

(N)

55

ACCEPTED MANUSCRIPT Table 4 Energetic wear coefficients and associated correlation parameter (R2) values for studied coatings.

AC

CE

PT E

D

MA

NU

SC

RI

untreated 650°C 750°C 850°C

Correlation parameter R2 0.986 0.982 0.986 0.982

PT

Energetic wear coefficient µm3/J 105970 75400 57810 51240

56

ACCEPTED MANUSCRIPT Highlights Annealing induce the phase transformation of electrophoretic deposited TiO2 coating



Air heating at 850°C for 2h induce a single crystalline rutile phase in the coating



Increasing of heating temperature improves the coating mechanical properties



Wear resistance of the coating was evaluated by a new scratch test named: wear mode

AC

CE

PT E

D

MA

NU

SC

RI

PT



57