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The influence of multiple fillers on friction and wear behavior of epoxy composite coatings
Accepted Manuscript The influence of multiple fillers on friction and wear behavior of epoxy composite coatings
Yan Hao, Xiying Zhou, Jiajia Shao, Yukun Zhu PII: DOI: Reference:
S0257-8972(19)30128-8 https://doi.org/10.1016/j.surfcoat.2019.01.110 SCT 24310
To appear in:
Surface & Coatings Technology
Received date: Revised date: Accepted date:
27 November 2018 28 January 2019 30 January 2019
Please cite this article as: Y. Hao, X. Zhou, J. Shao, et al., The influence of multiple fillers on friction and wear behavior of epoxy composite coatings, Surface & Coatings Technology, https://doi.org/10.1016/j.surfcoat.2019.01.110
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ACCEPTED MANUSCRIPT The influence of multiple fillers on friction and wear behavior of epoxy composite coatings Yan Haoa, Xiying Zhou*a, Jiajia Shaoa, Yukun Zhua
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School of Material Engineering, Shanghai University of Engineering Science, Shanghai
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201620, China
*Corresponding author at: School of Material Engineering, Shanghai University of
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Engineering Science, Shanghai 201620, China.
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E-mail: [email protected]
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ABSTRACT: Optimized design of polymeric composites that are comprised of
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polymers and commonly used fillers forms one of the key focuses in this community since it may enhance the feasibility of real applications in industries. In this work, we
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produced three different epoxy composite coatings through filling the diamond, SiC,
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MoS2 and graphite. Then, the influence of these fillers on friction and wear performance of the composite coating is investigated. Comparison of the net epoxy
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(EP), the fracture toughness and young’s modulus of the epoxy composite coatings
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(GME) can be 37.4 GPa and 4.3GPa, respectively, much higher than those of unfilled EP, i.e. 25.45 GPa and 3.75 GPa. More importantly, inclusion of multiple fillers can significantly reduce the wear rate and frictional coefficient of the GME. They are mainly because the graft treatment of the diamond and SiC dispersed uniformly in EP leads to a strong interface between the particles and matrix, making GME showing higher mechanical properties. Furthermore, due to the lubricant fillers-MoS2 and graphite, a continuous and thick lubricant film were observed on the worn surface of 1
ACCEPTED MANUSCRIPT the GME, which can effectively decrease the friction heating and further damage to the matrix. Therefore, the strategy presented here is a valid method to create positive synergetic effect of different fillers, which can serve as an important guidance for rational design of the epoxy composite coatings towards in further industrial
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applications.
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Key words: composite coatings; epoxy resin; frictional coefficient; wear rate
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1. Introduction
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Epoxy (EP) is one of the most commonly used industrial materials with numerous advantages, including superior temperature stability, high adhesive ability
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and considerable solvent resistance [1-3]. However, due to the three-dimensional
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network structure and poor surface characteristics, epoxy can’t be used as the wear resistant materials directly [3-4]. To improve its anti-friction and wear-resistant
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performance, combined with different fillers then acting as filler reinforced epoxy
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composites is an important way to solve these problem. In fact, many various fillers can be used to enhance the tribological properties of EP, especially by a combination of fibers, nanoparticles and internal lubricants. It has already demonstrated that particles such as SiO2, TiO2, Al2O3, ZnS, nanoclay, and lubricants such as the MoS2, graphite et al, can significantly decrease the friction coefficient and improve the wear performance as compared to net polymer [5-9]. From these researches, we notice that although many works have been carried out by filling nanoparticles to the polymer, 2
ACCEPTED MANUSCRIPT most of them have not reached their targets because of nanoparticles’ aggregation and poor interfacial interaction with the matrix [10-13]. However, combination of different particles across the length scale range from macro to nano, has proved to be a popular research to improve the mechanical and tribological properties of polymer
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composites. In particular, modification of polymer reinforced composites through
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incorporation of harder particles and solid lubricants is highly effective since the
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properties of the composite materials may be significantly changed by positive synergetic effect of these fillers [14]. In other words, it is worth to consider
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developing a new kind of epoxy composites containing macro, nano particles and
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lubricants, to encounter harsh operating conditions in practices [15]. In this work, we prepared different epoxy composite coatings containing
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diamond, SiC, MoS2 and graphite, aiming to design and fabricate special composite
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coating for numerous industrial applications. And the effects of various fillers on the mechanical and tribological properties of these composite coatings were investigated.
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To achieve these improvements, silane coupling agent KH550 has been utilized to
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modify the diamond and SiC, through which a strong interface between the fillers and epoxy matrix can be formed [16-17]. From the experimental investigation, it is apparent that the presence of these different fillers especially their positive synergetic effect can strongly improve the mechanical properties such as the fracture toughness and young’s modulus of the epoxy composite coating. The wear rate and frictional coefficient of the fabricated composite coatings have also been reduced effectively. This investigation presents an in-depth understanding of the synergetic effects of 3
ACCEPTED MANUSCRIPT different fillers, providing a more powerful and achievable approach to fabricate more useful epoxy composites used in industrial applications.
2. Experiment
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2.1 Materials
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The diglycidyl ether of bisphenol A (DGEBA) epoxy E51, E44, hardener and
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KH550 coupling agent were used in this study (Shanghai Resin factory co., ltd, China). Molybdenum disulphide (MoS2) (average diameter ≤2.5μm, 99.8% grad) and
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graphite (average diameter ≤3μm, 99.5% grad) were supplied by Shanghai Huayi
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Group Huayuan Chemical Industry co., ltd. Diamond (average diameter ≤5μm, 99.5% grad) and SiC (average diameter ≤5μm, 99.5% grad) were purchased from Henan
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Borui Science Industry co., ltd. China.
2.2 Composites preparation
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Epoxy composite coatings were prepared by adding the functionalized diamond
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and SiC, MoS2 and graphite into EP with mechanical stirring for 2 h and ultrasonication for 30 min at room temperature. Then, the hardener was added into the mixture with a ratio of 100:30 by weight with slowly stirring. Afterwards, the compounds were poured into agent-coated metallic and heated at 60℃ for 6 h, followed by 12 h at 120℃. Finally, three kinds of coatings were prepared, i.e. SCE (containing the SiC, 50 wt%), DOE (containing the SiC and diamond, 25 wt% and 25 wt%, respectively), and GME (containing the SiC, diamond, MoS2 and graphite, 25 4
ACCEPTED MANUSCRIPT wt%, 15 wt%, 5 wt%, 5 wt%, respectively). The thickness of these coatings was fixed at 2 mm and detailed information of the components is shown in Table 1.
2.3 Mechanical experiments
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Fracture toughness tests were carried out in accordance with GB/T 2567-2008,
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using dumbbell shaped and type Ⅱ specimens. Young modulus were calculated from
L0 P b h L
(1)
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Et
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the equation:
Where L0, b and h are respectively the original length, width and thickness of
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specimen; P is the load increment during sliding and ∆L is the incremental
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deformation. At least five specimens of each composition were measured.
2.4 Tribological experiments
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The friction and wear rate values for all specimens were performed using a ball-on-plate machine with AISI 52100 bearing steel ball at room temperature, as shown in Fig. 1. The
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radius of the wear track is about 5 mm, the ball is with a diameter of 9.5 mm and a surface roughness Ra = 0.25 μm. The sliding tests were carried out under the load of 60 ~ 120 N with the sliding speed 200 r/min. The testing time was from 1800 s to 3600 s, allowing the system to reach a steady friction and wear process. The specimens were machined with a geometry of 6 mm × 6 mm × 2 mm. Besides, reported friction coefficients were obtained from the machine UTM3, and at least three tests were performed on each specimen. The wear was
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ACCEPTED MANUSCRIPT measured by the loss in weight, which was then converted into wear volume through the measured density data. The specific wear rate was calculated according to the equation:
K
V m3/Nm LD
(2)
where ΔV is the volume loss in m3, L is the load in New-tons and D is the distance in
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meters.
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2.5 Characterization
After sputtering with a thin layer of gold on the worn surface of specimens, they
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were characterized using a scanning electron micrograph (SEM). Distribution of
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chemical element on the worn surfaces of each epoxy composite coatings were tested by the energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction
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(XRD).
3. Results and discussion
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3.1 Mechanical properties
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As demonstrated in Fig. 2, we notice that the addition of different fillers can significantly improve the mechanical performance of the epoxy composite coatings. Young’s modulus of the GME increases by 14.7% from 3.75 GPa to 4.3GPa, and the fracture toughness increases by a fact of 147% from 15.1 MPa/m2 to 37.4 MPa/m2 compared with those of the net EP. The improvement of young’s modulus is mainly due to the strong interfacial interaction between epoxy matrix and fillers. M.R. Ayatollahi et al reported that when the content of nanodiamonds in epoxy matrix is 6
ACCEPTED MANUSCRIPT 0.1wt%, both the young’s modulus and tensile strength achieve their maximum values, while these properties decline consistently with the content of nanofillers increasing [18-19]. Compared with nanoparticles, microparticles can disperse more homogeneously within the epoxy matrix; but the former could lead to aggregation for
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minimizing their surface energy. On the other hand, the presence of macro and nano
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particles in epoxy may induce various fracture mechanisms, e.g. crack deflection and
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crack pinning, as depicted in the reference of [19]. For the crack deflection mechanism, the crack deviates from its initial part of propagation when reach the
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particles, and crack front can be pinned between these fillers and stopped to extend in
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a longer path. Thus, the addition of different fillers into the epoxy especially the formed strong interfical interaction can significantly enhance the mechanical
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characteristics of the epoxy composite coatings.
3.2 Friction coefficient and wear rate analysis
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The real-time coefficient of friction (COF) and related wear rate for the EP and
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other three different epoxy composite coatings under a load of 80 N are plotted in Fig. 3 and Fig. 4, respectively. It can be clearly observed that the COFs (in Fig. 3) can be divided into three working regions. The COF first increases quickly and then decreases until they are nearly invariable. When compared with the net EP, the COF of a composite coating GME stabilizes at a value of 0.24, which is the lowest one among the composite coatings. However, for the related wear rates, they exhibit a very different change, which decrease firstly and then almost no change take place as 7
ACCEPTED MANUSCRIPT the time goes on. We should notice that the larger initial fluctuations in friction coefficients and wear rate are related to the variation in topography before testing. When the test progresses, the friction coefficients and related wear rate decrease due to the formation of wear tracks on the contacting surfaces. Clearly, the smallest of the
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COF and wear rate belongs to the GME.
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When compared with the net EP, the higher COFs for SCE and DOE can be
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attributed to the addition of different fillers. Due to the added macro and nano particles, the generation of wear particles on the worn surfaces are much easier. Once
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wear particles are formed, the abrasiveness and shape will lead to the further increase
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of COF. As time goes on, the higher COFs for composite coatings (SCE and DOE) might originate from an uneven composite morphology even after plowing, where
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part of fillers such as functionalized SiC and diamond agglomerates stick out of the
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epoxy matrix. For the GME containing the MoS2 and graphite lubricant particles, continuous lubricant film could be formed between the contacting surface, resulting in
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the reducing of COF, which will be discussed in detail below. This is the reason why
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the GME has the lowest COF and wear rate at the stable state. To obtain more information about the wear performance of GME, the longer sliding time were performed.
Fig. 5 depicts the evolution of the friction coefficient and wear rate versus sliding time for GME, error bars represent the standard deviations. It is seen that these values for GME at the final state (3600s) are strongly similar to those of at the half sliding time. In other words, sliding distances have less effect on the wear performance of the 8
ACCEPTED MANUSCRIPT GME. The wear rate exhibits an abruptly drop but the COF changes opposite and then both of them remain insensitive to the sliding distance thereafter. That is because in the initial fluctuated stage the wear particles can form, and the contact is mainly between the counter body and epoxy material, thus the specific COF and wear rate
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increase. When wear particles accumulate, the lubricating film begin to form under
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the conditions of repeating sliding. These changes are essentially the same as the
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descriptions in the ref [20], where the produced transfer film can reduce the COF and wear rate significantly. Moreover, because of the generation of tribo-layer, a
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dramatically decrease of the COF and wear rate were found, as reported by Dhieb et
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al [21]. In addition, the lubricant film also effectively reduces the friction heating [20], leading to less damage to the matrix, fillers and their adhesion. So lubricant film
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performance of composites.
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formed on the counter surface plays an important role in the control of wear
In order to investigate the wear mechanism of GME more deeply especially
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under different load conditions, more tests were carried out. The changes of COF and
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wear rate under various applied loads are depicted in Fig. 6 and Fig. 7, respectively. It is apparent that the special COFs of GME seem to be the highest one under the load of 60 N. At stable stage, as the applied load increases to 100 N, the COF decreases; but it increases again when the load reaches to 120 N, as shown in Fig. 6. From the Fig. 7, we notice that the wear rate has a significantly increase with the applied load changes from 60 to 120 N. In particular, the wear rate obtained at 60 N is much
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ACCEPTED MANUSCRIPT smaller than that of at 120 N. Briefly, the lower the applied load is, the smaller the wear rate can be reached. This change is mainly because the functionalized diamond and other fillers have a uniform distribution in the EP matrix, which will lead to a strong interface between
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these fillers and the matrix and therefore the applied load could be transferred to the
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composites more efficiently. Hence, the added fillers such as the micro and nano
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particles can tolerate more loads and as a result, the wear load bearing capacity increases. Meanwhile, during the relative sliding, SiC and diamond particles
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embedded in the epoxy matrix can reduce the adhesion, due to physical interaction
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between the contact surfaces, generating the higher hardness of GME. In addition, as the applied load continuously increases, extra frictional heat are produced between the
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contact surfaces which makes the matrix soft, thus the lubricants MoS2 and graphite
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removed from the subsurface layer and transferred on to the contact surface forming a high quality lubricant film. When the applied load under 120 N exceeds one certain
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point (such as 1350 s), the lubricant film is destroyed. As the sliding time goes on, the
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fatigue wear takes place, and meanwhile the particles and debris accumulate on the counter surface, which lead to a sharply increase of the COF and wear rate.
3.3 Analysis of wear volume The variation in the specific wear volume and average COF of composite coatings at 10 N is shown in Fig. 8. It is obvious that the wear volume of coatings decreases with the increasing of the different fillers under same total weight
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ACCEPTED MANUSCRIPT percentage of added fillers; especially the wear volume strongly depends on the different kind of fillers. Wear volume of GME specimen is reduced by 73.8% in comparison with that of neat EP, and for DOE it decreases nearly 55% and this reduction for SCE is by 38%. In other words, the enhancement of epoxy with micro
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and nano particles can effectively improve the wear resistance; in particular, with the
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synergistic effect of the fillers, the wear resistance of composite coatings such as the
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GME specimen can be enhanced significantly. However, there is a distinct difference between the average COF behavior. Specific average COF decrease from 0.29 for net
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EP to 0.23 for the GME composite coatings. In contrast to the GME, average COFs
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for SCE and DOE exhibit an increasing trend, which are higher than that of EP. The obviously higher average COF for the composite coatings containing hard particles
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might originate from an uneven composite morphology and higher shear stress on the
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counter surface. The values of average COF and wear volume decrease significantly for GME composite, due to the synergistic effect of the hard particles and lubricants,
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which plays a key role in improving the tribological properties of EP composites.
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The variation in wear volume and average COF for GME at applied load from 60 N to 120 N against sliding time is demonstrated in Fig. 9. The wear data of fabricated composite coatings reveal that the wear volume tends to increase with increasing the applied load. Wear volume of GME at 120 N is increased by 250% when compared with that of at 60 N. It should be noticed that a great deal of increasing is observed at 80 N, and only minor increase can be fund at 100 N and 120 N, that the wear volume values increase only by 5.1% and 13.1%, respectively. The variation is because when 11
ACCEPTED MANUSCRIPT a small load of 60N is applied, wear debris in the GME worn surface can not adhere to the counter surface. As the load increases at 80 N even 100 N, much more abrasive particles will penetrate into the matrix and lead to the generation of lubricant film, which can largely reduce the friction violent and provide protection to the worn
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surface. Therefore, the wear volume at higher load increases rather slowly as
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compared to at a lower load. When the applied load increasing to 120 N, the formed
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lubricant film could be destroyed, thus leading to the wear volume increasing largely. Furthermore, average COF of GME seems to be very small even under different
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applied load. It has a minimal value at 80 N and then rises again but not exceeds 0.25.
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This behavior mainly because of the special structure of graphite and MoS2 [22-23]. For graphite, its layer is loosely bonded together by Van der Waal’s forces, through
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which the layer can slide over one another, making graphite an ideal lubricant and
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resulting a reduced wear loss. The MoS2, because of the weak Van der Waal’s interactions between the sheets of sulfide atoms, it has a low COF and results its
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lubricating properties. The lower average COF of GME composites under various
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applied load can be attributed to the self-lubricating nature of graphite, MoS2 and GME’s inherent mechanical properties.
3.4 Worn surface morphology and EDS, XRD analysis In order to investigate the wear mechanism for filled and unfilled composites, the corresponding low and high magnification SEM images of the worn surfaces are demonstrated in Fig.10 (a–d, g, h). The worn surface of EP (Fig.10(a)) appears flaky, 12
ACCEPTED MANUSCRIPT micro-cracks and debris pulled-out leaving large pits on the surface (pitting); while the worn surface of SCE (Fig.10(b)) exhibits a combination of ductile smearing and flaky as well as the increase of surface grooving. For the DOE (Fig.10(c)) composites, it shows compact and slightly smooth with evidence of adhesive wear debris pullout.
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The texture of these surfaces agree with the elastic/plastic behavior from the micro
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scratch results. Base on the above results, we could conclude that the DOE has a
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much different deformation mechanism when compared with the EP and SCE, which is because the functionalized diamonds in DOE generate a strong interface between
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the particles and matrix, therefore the matrix stresses can be transferred to endure
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higher normal load. With the addition of the lubricants particles, the GME worn surface is covered with a nearly continuous and thick film, as shown in Fig.10 (d). It
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seems that the transfer film has a compact and smooth structure except for some
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microcracks, this can be seen clearly in a high SEM magnification (Fig.10 (g)). There exist less wear debris and damage on the one surface of GME, resulting in a improved
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wear resistance. So inclusion of lubricants such as the graphite and MoS2 can produce
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a distinctly different morphology than those of the EP and other hybrid composites just containing hard particles [24]. The improved mechanical properties of EP composites possibly alleviate stress transfer on SiC and functionalized diamond as well as the lubricant. Accordingly, with the normal load increases and exceeds the capacity of GME, the lubricant film will be destroyed and loss the wear resistance, as shown in Fig.10 (h), where many of debris pull out and loose structure as well as pitting producing a terrible worn surface. 13
ACCEPTED MANUSCRIPT To have further information about the mechanochemically induced changes in the surface layer during wear, EDS and XRD studies of the worn surfaces of DOE and GME were conducted, as shown in Fig.10 (E) and (F). A large number of elements coming from the chrome steel ball are observed on the worn surface of DOE,
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indicating the transfer of ball material to the epoxy composites. Further, more
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contents of Fe and Cr were found on the worn surface of DOE than that of GME from
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84.80%, 1.28% to 67.89%, 1.16% (by weight), respectively. Partial Fe and Cr and lot of Mo, S, and C can be obserced on the worn surface of GME, demonstrating that the
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wear powders from chrome ball also accumulate on the worn surface of GME.
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However, because of the lubricant film formed on the GME surface, it can largely reduce the friction violent and provide more protection to the contact surface. On the
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other hand, wear debris on the DOE and GME worn surface are also analyzed through
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the XRD to investigate the main mechanism. From the Fig.11 (a), (b), we can observe that the SiO2 is mainly from the debris of DOE but not the GME. This might be
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because the SiO2 can be produced by chemical reaction on the DOE surface during
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the sliding process especially on the badly wear behavior. This found can further explain the significantly differences in morphology and texture between the DOE and GME.
4. Conclusion In summary, three different epoxy composite coatings, i.e. SCE, DOE and GME, conatining diamond, SiC, MoS2 and graphite, were produced in this work; then we 14
ACCEPTED MANUSCRIPT investigated the various fillers on the mechanical and tribological properties of those composite coatings. On one hand, inclusion of different micro particles can significantly enhance the mechanical performance of the epoxy based coatings. For instance, Young’s modulus of EP increased about 14.7% from 3.75 GPa to 4.3 GPa
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(for GME), the fracture toughness increased by 147% to 37.4 GPa (for GME), and the
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tensile strength also had a evidently improved. On the other hand, the excellent wear
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resistance and friction coefficients were observed for the produced composite coatings. For instance, the wear volume of GME is reduced by a fact of 73.8% in
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comparison with that of neat EP, indicating the strongly increase in wear resistance of
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these coatings. They all could be attributed to a uniform distribution of microparticles in the EP matrix, formatting a strong interface between these particles and epoxy
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matrix, thus leading to a higher load bearing capacity to epoxy. Furthermore, it also
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depends on the lubricant film formed on the contact surface. Through the SEM magnification, a nearly continuous, thick lubricant film and a compact and smooth
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structure can be observed on the worn surface of GME. Through the EDS analysis, we
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can confirm that the much more C and Mo and less Fe and Cr elements are included in the lubricant film; especially the compound of SiO2 was obtained on the worn surface of DOE from XRD pattern. Therefore, the unique strategy proposed here can be used to deepen the understanding of the synergetic effects of different fillers in epoxy composite coatings, serving as an important guide for designing and fabricating high tribological performance polymer matrix composites.
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ACCEPTED MANUSCRIPT Acknowledgements The project was supported by the Leading Academic Discipline Project of Shanghai Education Committee, China (YLJX12-2) and the Research Foundation of
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Shanghai University Of Engineering Science, China (CS1205003).
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References
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[1] J. Abenojar, J. Tutor, Y. Ballesteros, J.C.D. Real, M.A. Martínez, Erosion-wear, mechanical and thermal properties of silica filled epoxy nanocomposites,
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Composites Part B Engineering. 120 (2017) 42-53.
MA
[2] Q.B. Guo, K.T. Lau, M.Z. Rong, M.Q. Zhang, Optimization of tribological and mechanical properties of epoxy through hybrid filling, Wear. 269 (2010) 13-20.
D
[3] S.V. Sosnovskii, A.S. Mikhnevich, V.P. Sel’Kin, Effect of reinforcing epoxy
PT E
coatings with carbon cloth on their wear under great loads, Journal of Friction & Wear. 35 (2014) 465-469.
CE
[4] A. Dasari, Z.Z. Yu, Y.W. Mai, Fundamental aspects and recent progress on
AC
wear/scratch damage in polymer nanocomposites, Materials Science & Engineering R Reports. 63 (2009) 31-80. [5] B.R. Raju, B. Suresha, R.P. Swamy, B.S.G. Kanthraju, Investigations on Mechanical and Tribological Behaviour of Particulate Filled Glass Fabric Reinforced Epoxy Composites, Journal of Minerals and Materials Characterization and Engineering. 01 (2013) 160-167. [6] B. Shivamurthy, K.U. Bhat, S. Anandhan, Mechanical and sliding wear properties 16
ACCEPTED MANUSCRIPT of multi-layered laminates from glass fabric/graphite/epoxy composites, Materials & Design. 44 (2013) 136-143. [7] A. Yasmin, I.M. Daniel, Mechanical and thermal properties of graphite platelet/epoxy composites, Polymer. 45 (2004) 8211-8219.
PT
[8] W. Jiao, Y. Liu, G. Qi, Studies on mechanical properties of epoxy composites
RI
filled with the grafted particles PGMA/Al2O3, Composites Science & Technology.
SC
69 (2009) 391-395.
[9] Z.B. Xu, X.L. Tang, J.Y. Zheng, Thermal Stability and Flame Retardancy of Rigid
NU
Polyurethane Foams/Organoclay Nanocomposites, Journal of Macromolecular
MA
Science: Part D-Reviews in Polymer Processing. 47 (2008) 1136-1141. [10] Z.Z. Wang, P. Gu, X.P. Wu, H. Zhang, Z. Zhang, M.Y.M. Chiang,
D
Micro/nano-wear studies on epoxy/silica nanocomposites, Composites Science &
PT E
Technology. 79 (2013) 49-57.
[11] I. Neitzel, V. Mochalin, I. Knoke, G.R. Palmese, Y. Gogotsi, Mechanical
CE
properties of epoxy composites with high contents of nanodiamond, Composites
AC
Science & Technology. 71 (2011) 710-716. [12] J. Zhang, L. Chang, S. Deng, L. Ye, Z. Zhang, Some insights into effects of nanoparticles on sliding wear performance of epoxy nanocomposites, Wear. 304 (2013) 138-143. [13] G. Pan, Q. Guo, J. Ding, W. Zhang, X. Wang, Tribological behaviors of graphite/epoxy two-phase composite coatings, Tribology International. 43 (2010) 1318-1325. 17
ACCEPTED MANUSCRIPT [14] I. Neitzel, V. Mochalin, J.A. Bares, R.W. Carpick, A. Erdemir, Y. Gogotsi, Tribological Properties of Nanodiamond-Epoxy Composites, Tribology Letters. 47 (2012) 195-202. [15] R. Baptista, A. Mendão, F. Rodrigues, C.G. Figueiredo-Pina, M. Guedes, R.
PT
Marat-Mendes, Effect of high graphite filler contents on the mechanical and
RI
tribological failure behavior of epoxy matrix composites, Theoretical & Applied
SC
Fracture Mechanics. 85 (2016) 113-124.
[16] F. Ahangaran, A. Hassanzadeh, S. Nouri, Surface modification of Fe3O4@SiO2
NU
microsphere by silane coupling agent, International Nano Letters. 3 (2013) 1-5.
MA
[17] T. Shengnian, L.I. Xing, Surface Modification of SiC Powder with Silane Coupling Agent, Journal of the Chinese Ceramic Society. 39 (2011) 409-413(405).
D
[18] B. Wetzel, P. Rosso, F. Haupert, K. Friedrich, Epoxy nanocomposites – fracture
2375-2398.
PT E
and toughening mechanisms, Engineering Fracture Mechanics. 73 (2006)
CE
[19] M.R. Ayatollahi, E. Alishahi, S. Doagou-R, S. Shadlou, Tribological and
AC
mechanical properties of low content nanodiamond/epoxy nanocomposites, Composites Part B Engineering. 43 (2012) 3425-3430. [20] S. Basavarajappa, S. Ellangovan, Dry sliding wear characteristics of glass–epoxy composite filled with silicon carbide and graphite particles, Wear. 296 (2012) 491-496. [21] H. Dhieb, J.G. Buijnsters, F. Eddoumy, J.P. Celis, Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating 18
ACCEPTED MANUSCRIPT sliding in ambient air, Composites Science & Technology. 71 (2011) 1769-1776. [22] B. Suresha, Siddaramaiah, Kishore, S. Seetharamu, P.S. Kumaran, Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites, Wear. 267 (2009) 1405-1414.
PT
[23] H. Li, Y. Ma, Z. Li, Y. Cui, H. Wang, Synthesis of novel multilayer composite
RI
microcapsules and their application in self-lubricating polymer composites,
SC
Composites Science and Technology. 164 (2018) 120-128.
[24] Z. Jiang, L.A. Gyurova, A.K. Schlarb, K. Friedrich, Z. Zhang, Study on friction
NU
and wear behavior of polyphenylene sulfide composites reinforced by short carbon
MA
fibers and sub-micro TiO2 particles, Composites Science & Technology. 68 (2008)
AC
CE
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D
734-742.
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Fig.1 Ball-on-disc wear test apparatus. Fig.2 Fracture toughness and young’s modulus for net EP and epoxy composite coatings.
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Fig.3. Development of coefficient of friction (COF) over testing time for EP, SCE, DOE and GME composite coatings at 80 N.
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Fig.4. Development of wear rate over testing time for EP, SCE, DOE and GME composite coatings at
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80 N.
Fig.5. Development of COF and wear rate over testing time for GME composite coating at 80 N.
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Fig.6. Development of COF over testing time for GME composite coating at different applied loads. Fig.7. Development of wear rate over testing time for GME composite coating at different applied loads.
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Fig.8. Average COF and wear volume for EP, SCE, DOE and GME composite coatings at 80 N. Fig.9. Average COF and wear volume of GME composite coating at different applied loads. Fig.10. SEM micrographs of EP (a), SCE (b), DOE (c) and GME (d, g, h); and EDS analysis (E), (F)
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from the related specimens of DOE (e) and GME (f). Note that the worn surface of (h) is obtained at
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120 N, while others at 80 N.
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Fig.11. XRD patterns of the wear debris from DOE (a) and GME (b) at 80 N.
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Table 1 Physico-properties of EP and epoxy composite coatings. Material
Fillers /wt.%
EP /wt.%
SiC
Diamond
Graphite
MoS2
EP
0
0
0
0
100
SCE
50
0
0
0
50
DOE
25
25
0
0
50
GME
25
15
5
5
50
20
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The followings are the highlights:
The coatings have wear-resisting anti-friction properties under larger stress.
Multiple particles can be well dispersed and have synergistic effects after surface
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modification, including diamond, silicon carbide, molybdenum disulfide and
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CE
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D
MA
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SC
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graphite.
21
Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11
Yan Hao, Xiying Zhou, Jiajia Shao, Yukun Zhu PII: DOI: Reference:
S0257-8972(19)30128-8 https://doi.org/10.1016/j.surfcoat.2019.01.110 SCT 24310
To appear in:
Surface & Coatings Technology
Received date: Revised date: Accepted date:
27 November 2018 28 January 2019 30 January 2019
Please cite this article as: Y. Hao, X. Zhou, J. Shao, et al., The influence of multiple fillers on friction and wear behavior of epoxy composite coatings, Surface & Coatings Technology, https://doi.org/10.1016/j.surfcoat.2019.01.110
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
ACCEPTED MANUSCRIPT The influence of multiple fillers on friction and wear behavior of epoxy composite coatings Yan Haoa, Xiying Zhou*a, Jiajia Shaoa, Yukun Zhua
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School of Material Engineering, Shanghai University of Engineering Science, Shanghai
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201620, China
*Corresponding author at: School of Material Engineering, Shanghai University of
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Engineering Science, Shanghai 201620, China.
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E-mail: [email protected]
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ABSTRACT: Optimized design of polymeric composites that are comprised of
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polymers and commonly used fillers forms one of the key focuses in this community since it may enhance the feasibility of real applications in industries. In this work, we
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produced three different epoxy composite coatings through filling the diamond, SiC,
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MoS2 and graphite. Then, the influence of these fillers on friction and wear performance of the composite coating is investigated. Comparison of the net epoxy
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(EP), the fracture toughness and young’s modulus of the epoxy composite coatings
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(GME) can be 37.4 GPa and 4.3GPa, respectively, much higher than those of unfilled EP, i.e. 25.45 GPa and 3.75 GPa. More importantly, inclusion of multiple fillers can significantly reduce the wear rate and frictional coefficient of the GME. They are mainly because the graft treatment of the diamond and SiC dispersed uniformly in EP leads to a strong interface between the particles and matrix, making GME showing higher mechanical properties. Furthermore, due to the lubricant fillers-MoS2 and graphite, a continuous and thick lubricant film were observed on the worn surface of 1
ACCEPTED MANUSCRIPT the GME, which can effectively decrease the friction heating and further damage to the matrix. Therefore, the strategy presented here is a valid method to create positive synergetic effect of different fillers, which can serve as an important guidance for rational design of the epoxy composite coatings towards in further industrial
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applications.
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Key words: composite coatings; epoxy resin; frictional coefficient; wear rate
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1. Introduction
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Epoxy (EP) is one of the most commonly used industrial materials with numerous advantages, including superior temperature stability, high adhesive ability
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and considerable solvent resistance [1-3]. However, due to the three-dimensional
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network structure and poor surface characteristics, epoxy can’t be used as the wear resistant materials directly [3-4]. To improve its anti-friction and wear-resistant
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performance, combined with different fillers then acting as filler reinforced epoxy
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composites is an important way to solve these problem. In fact, many various fillers can be used to enhance the tribological properties of EP, especially by a combination of fibers, nanoparticles and internal lubricants. It has already demonstrated that particles such as SiO2, TiO2, Al2O3, ZnS, nanoclay, and lubricants such as the MoS2, graphite et al, can significantly decrease the friction coefficient and improve the wear performance as compared to net polymer [5-9]. From these researches, we notice that although many works have been carried out by filling nanoparticles to the polymer, 2
ACCEPTED MANUSCRIPT most of them have not reached their targets because of nanoparticles’ aggregation and poor interfacial interaction with the matrix [10-13]. However, combination of different particles across the length scale range from macro to nano, has proved to be a popular research to improve the mechanical and tribological properties of polymer
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composites. In particular, modification of polymer reinforced composites through
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incorporation of harder particles and solid lubricants is highly effective since the
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properties of the composite materials may be significantly changed by positive synergetic effect of these fillers [14]. In other words, it is worth to consider
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developing a new kind of epoxy composites containing macro, nano particles and
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lubricants, to encounter harsh operating conditions in practices [15]. In this work, we prepared different epoxy composite coatings containing
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diamond, SiC, MoS2 and graphite, aiming to design and fabricate special composite
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coating for numerous industrial applications. And the effects of various fillers on the mechanical and tribological properties of these composite coatings were investigated.
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To achieve these improvements, silane coupling agent KH550 has been utilized to
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modify the diamond and SiC, through which a strong interface between the fillers and epoxy matrix can be formed [16-17]. From the experimental investigation, it is apparent that the presence of these different fillers especially their positive synergetic effect can strongly improve the mechanical properties such as the fracture toughness and young’s modulus of the epoxy composite coating. The wear rate and frictional coefficient of the fabricated composite coatings have also been reduced effectively. This investigation presents an in-depth understanding of the synergetic effects of 3
ACCEPTED MANUSCRIPT different fillers, providing a more powerful and achievable approach to fabricate more useful epoxy composites used in industrial applications.
2. Experiment
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2.1 Materials
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The diglycidyl ether of bisphenol A (DGEBA) epoxy E51, E44, hardener and
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KH550 coupling agent were used in this study (Shanghai Resin factory co., ltd, China). Molybdenum disulphide (MoS2) (average diameter ≤2.5μm, 99.8% grad) and
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graphite (average diameter ≤3μm, 99.5% grad) were supplied by Shanghai Huayi
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Group Huayuan Chemical Industry co., ltd. Diamond (average diameter ≤5μm, 99.5% grad) and SiC (average diameter ≤5μm, 99.5% grad) were purchased from Henan
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Borui Science Industry co., ltd. China.
2.2 Composites preparation
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Epoxy composite coatings were prepared by adding the functionalized diamond
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and SiC, MoS2 and graphite into EP with mechanical stirring for 2 h and ultrasonication for 30 min at room temperature. Then, the hardener was added into the mixture with a ratio of 100:30 by weight with slowly stirring. Afterwards, the compounds were poured into agent-coated metallic and heated at 60℃ for 6 h, followed by 12 h at 120℃. Finally, three kinds of coatings were prepared, i.e. SCE (containing the SiC, 50 wt%), DOE (containing the SiC and diamond, 25 wt% and 25 wt%, respectively), and GME (containing the SiC, diamond, MoS2 and graphite, 25 4
ACCEPTED MANUSCRIPT wt%, 15 wt%, 5 wt%, 5 wt%, respectively). The thickness of these coatings was fixed at 2 mm and detailed information of the components is shown in Table 1.
2.3 Mechanical experiments
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Fracture toughness tests were carried out in accordance with GB/T 2567-2008,
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using dumbbell shaped and type Ⅱ specimens. Young modulus were calculated from
L0 P b h L
(1)
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Et
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the equation:
Where L0, b and h are respectively the original length, width and thickness of
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specimen; P is the load increment during sliding and ∆L is the incremental
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deformation. At least five specimens of each composition were measured.
2.4 Tribological experiments
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The friction and wear rate values for all specimens were performed using a ball-on-plate machine with AISI 52100 bearing steel ball at room temperature, as shown in Fig. 1. The
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radius of the wear track is about 5 mm, the ball is with a diameter of 9.5 mm and a surface roughness Ra = 0.25 μm. The sliding tests were carried out under the load of 60 ~ 120 N with the sliding speed 200 r/min. The testing time was from 1800 s to 3600 s, allowing the system to reach a steady friction and wear process. The specimens were machined with a geometry of 6 mm × 6 mm × 2 mm. Besides, reported friction coefficients were obtained from the machine UTM3, and at least three tests were performed on each specimen. The wear was
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ACCEPTED MANUSCRIPT measured by the loss in weight, which was then converted into wear volume through the measured density data. The specific wear rate was calculated according to the equation:
K
V m3/Nm LD
(2)
where ΔV is the volume loss in m3, L is the load in New-tons and D is the distance in
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meters.
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2.5 Characterization
After sputtering with a thin layer of gold on the worn surface of specimens, they
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were characterized using a scanning electron micrograph (SEM). Distribution of
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chemical element on the worn surfaces of each epoxy composite coatings were tested by the energy-dispersive X-ray spectroscopy (EDS) and X-ray powder diffraction
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(XRD).
3. Results and discussion
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3.1 Mechanical properties
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As demonstrated in Fig. 2, we notice that the addition of different fillers can significantly improve the mechanical performance of the epoxy composite coatings. Young’s modulus of the GME increases by 14.7% from 3.75 GPa to 4.3GPa, and the fracture toughness increases by a fact of 147% from 15.1 MPa/m2 to 37.4 MPa/m2 compared with those of the net EP. The improvement of young’s modulus is mainly due to the strong interfacial interaction between epoxy matrix and fillers. M.R. Ayatollahi et al reported that when the content of nanodiamonds in epoxy matrix is 6
ACCEPTED MANUSCRIPT 0.1wt%, both the young’s modulus and tensile strength achieve their maximum values, while these properties decline consistently with the content of nanofillers increasing [18-19]. Compared with nanoparticles, microparticles can disperse more homogeneously within the epoxy matrix; but the former could lead to aggregation for
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minimizing their surface energy. On the other hand, the presence of macro and nano
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particles in epoxy may induce various fracture mechanisms, e.g. crack deflection and
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crack pinning, as depicted in the reference of [19]. For the crack deflection mechanism, the crack deviates from its initial part of propagation when reach the
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particles, and crack front can be pinned between these fillers and stopped to extend in
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a longer path. Thus, the addition of different fillers into the epoxy especially the formed strong interfical interaction can significantly enhance the mechanical
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characteristics of the epoxy composite coatings.
3.2 Friction coefficient and wear rate analysis
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The real-time coefficient of friction (COF) and related wear rate for the EP and
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other three different epoxy composite coatings under a load of 80 N are plotted in Fig. 3 and Fig. 4, respectively. It can be clearly observed that the COFs (in Fig. 3) can be divided into three working regions. The COF first increases quickly and then decreases until they are nearly invariable. When compared with the net EP, the COF of a composite coating GME stabilizes at a value of 0.24, which is the lowest one among the composite coatings. However, for the related wear rates, they exhibit a very different change, which decrease firstly and then almost no change take place as 7
ACCEPTED MANUSCRIPT the time goes on. We should notice that the larger initial fluctuations in friction coefficients and wear rate are related to the variation in topography before testing. When the test progresses, the friction coefficients and related wear rate decrease due to the formation of wear tracks on the contacting surfaces. Clearly, the smallest of the
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COF and wear rate belongs to the GME.
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When compared with the net EP, the higher COFs for SCE and DOE can be
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attributed to the addition of different fillers. Due to the added macro and nano particles, the generation of wear particles on the worn surfaces are much easier. Once
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wear particles are formed, the abrasiveness and shape will lead to the further increase
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of COF. As time goes on, the higher COFs for composite coatings (SCE and DOE) might originate from an uneven composite morphology even after plowing, where
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part of fillers such as functionalized SiC and diamond agglomerates stick out of the
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epoxy matrix. For the GME containing the MoS2 and graphite lubricant particles, continuous lubricant film could be formed between the contacting surface, resulting in
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the reducing of COF, which will be discussed in detail below. This is the reason why
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the GME has the lowest COF and wear rate at the stable state. To obtain more information about the wear performance of GME, the longer sliding time were performed.
Fig. 5 depicts the evolution of the friction coefficient and wear rate versus sliding time for GME, error bars represent the standard deviations. It is seen that these values for GME at the final state (3600s) are strongly similar to those of at the half sliding time. In other words, sliding distances have less effect on the wear performance of the 8
ACCEPTED MANUSCRIPT GME. The wear rate exhibits an abruptly drop but the COF changes opposite and then both of them remain insensitive to the sliding distance thereafter. That is because in the initial fluctuated stage the wear particles can form, and the contact is mainly between the counter body and epoxy material, thus the specific COF and wear rate
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increase. When wear particles accumulate, the lubricating film begin to form under
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the conditions of repeating sliding. These changes are essentially the same as the
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descriptions in the ref [20], where the produced transfer film can reduce the COF and wear rate significantly. Moreover, because of the generation of tribo-layer, a
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dramatically decrease of the COF and wear rate were found, as reported by Dhieb et
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al [21]. In addition, the lubricant film also effectively reduces the friction heating [20], leading to less damage to the matrix, fillers and their adhesion. So lubricant film
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performance of composites.
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formed on the counter surface plays an important role in the control of wear
In order to investigate the wear mechanism of GME more deeply especially
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under different load conditions, more tests were carried out. The changes of COF and
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wear rate under various applied loads are depicted in Fig. 6 and Fig. 7, respectively. It is apparent that the special COFs of GME seem to be the highest one under the load of 60 N. At stable stage, as the applied load increases to 100 N, the COF decreases; but it increases again when the load reaches to 120 N, as shown in Fig. 6. From the Fig. 7, we notice that the wear rate has a significantly increase with the applied load changes from 60 to 120 N. In particular, the wear rate obtained at 60 N is much
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ACCEPTED MANUSCRIPT smaller than that of at 120 N. Briefly, the lower the applied load is, the smaller the wear rate can be reached. This change is mainly because the functionalized diamond and other fillers have a uniform distribution in the EP matrix, which will lead to a strong interface between
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these fillers and the matrix and therefore the applied load could be transferred to the
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composites more efficiently. Hence, the added fillers such as the micro and nano
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particles can tolerate more loads and as a result, the wear load bearing capacity increases. Meanwhile, during the relative sliding, SiC and diamond particles
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embedded in the epoxy matrix can reduce the adhesion, due to physical interaction
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between the contact surfaces, generating the higher hardness of GME. In addition, as the applied load continuously increases, extra frictional heat are produced between the
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contact surfaces which makes the matrix soft, thus the lubricants MoS2 and graphite
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removed from the subsurface layer and transferred on to the contact surface forming a high quality lubricant film. When the applied load under 120 N exceeds one certain
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point (such as 1350 s), the lubricant film is destroyed. As the sliding time goes on, the
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fatigue wear takes place, and meanwhile the particles and debris accumulate on the counter surface, which lead to a sharply increase of the COF and wear rate.
3.3 Analysis of wear volume The variation in the specific wear volume and average COF of composite coatings at 10 N is shown in Fig. 8. It is obvious that the wear volume of coatings decreases with the increasing of the different fillers under same total weight
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ACCEPTED MANUSCRIPT percentage of added fillers; especially the wear volume strongly depends on the different kind of fillers. Wear volume of GME specimen is reduced by 73.8% in comparison with that of neat EP, and for DOE it decreases nearly 55% and this reduction for SCE is by 38%. In other words, the enhancement of epoxy with micro
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and nano particles can effectively improve the wear resistance; in particular, with the
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synergistic effect of the fillers, the wear resistance of composite coatings such as the
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GME specimen can be enhanced significantly. However, there is a distinct difference between the average COF behavior. Specific average COF decrease from 0.29 for net
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EP to 0.23 for the GME composite coatings. In contrast to the GME, average COFs
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for SCE and DOE exhibit an increasing trend, which are higher than that of EP. The obviously higher average COF for the composite coatings containing hard particles
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might originate from an uneven composite morphology and higher shear stress on the
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counter surface. The values of average COF and wear volume decrease significantly for GME composite, due to the synergistic effect of the hard particles and lubricants,
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which plays a key role in improving the tribological properties of EP composites.
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The variation in wear volume and average COF for GME at applied load from 60 N to 120 N against sliding time is demonstrated in Fig. 9. The wear data of fabricated composite coatings reveal that the wear volume tends to increase with increasing the applied load. Wear volume of GME at 120 N is increased by 250% when compared with that of at 60 N. It should be noticed that a great deal of increasing is observed at 80 N, and only minor increase can be fund at 100 N and 120 N, that the wear volume values increase only by 5.1% and 13.1%, respectively. The variation is because when 11
ACCEPTED MANUSCRIPT a small load of 60N is applied, wear debris in the GME worn surface can not adhere to the counter surface. As the load increases at 80 N even 100 N, much more abrasive particles will penetrate into the matrix and lead to the generation of lubricant film, which can largely reduce the friction violent and provide protection to the worn
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surface. Therefore, the wear volume at higher load increases rather slowly as
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compared to at a lower load. When the applied load increasing to 120 N, the formed
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lubricant film could be destroyed, thus leading to the wear volume increasing largely. Furthermore, average COF of GME seems to be very small even under different
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applied load. It has a minimal value at 80 N and then rises again but not exceeds 0.25.
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This behavior mainly because of the special structure of graphite and MoS2 [22-23]. For graphite, its layer is loosely bonded together by Van der Waal’s forces, through
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which the layer can slide over one another, making graphite an ideal lubricant and
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resulting a reduced wear loss. The MoS2, because of the weak Van der Waal’s interactions between the sheets of sulfide atoms, it has a low COF and results its
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lubricating properties. The lower average COF of GME composites under various
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applied load can be attributed to the self-lubricating nature of graphite, MoS2 and GME’s inherent mechanical properties.
3.4 Worn surface morphology and EDS, XRD analysis In order to investigate the wear mechanism for filled and unfilled composites, the corresponding low and high magnification SEM images of the worn surfaces are demonstrated in Fig.10 (a–d, g, h). The worn surface of EP (Fig.10(a)) appears flaky, 12
ACCEPTED MANUSCRIPT micro-cracks and debris pulled-out leaving large pits on the surface (pitting); while the worn surface of SCE (Fig.10(b)) exhibits a combination of ductile smearing and flaky as well as the increase of surface grooving. For the DOE (Fig.10(c)) composites, it shows compact and slightly smooth with evidence of adhesive wear debris pullout.
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The texture of these surfaces agree with the elastic/plastic behavior from the micro
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scratch results. Base on the above results, we could conclude that the DOE has a
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much different deformation mechanism when compared with the EP and SCE, which is because the functionalized diamonds in DOE generate a strong interface between
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the particles and matrix, therefore the matrix stresses can be transferred to endure
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higher normal load. With the addition of the lubricants particles, the GME worn surface is covered with a nearly continuous and thick film, as shown in Fig.10 (d). It
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seems that the transfer film has a compact and smooth structure except for some
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microcracks, this can be seen clearly in a high SEM magnification (Fig.10 (g)). There exist less wear debris and damage on the one surface of GME, resulting in a improved
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wear resistance. So inclusion of lubricants such as the graphite and MoS2 can produce
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a distinctly different morphology than those of the EP and other hybrid composites just containing hard particles [24]. The improved mechanical properties of EP composites possibly alleviate stress transfer on SiC and functionalized diamond as well as the lubricant. Accordingly, with the normal load increases and exceeds the capacity of GME, the lubricant film will be destroyed and loss the wear resistance, as shown in Fig.10 (h), where many of debris pull out and loose structure as well as pitting producing a terrible worn surface. 13
ACCEPTED MANUSCRIPT To have further information about the mechanochemically induced changes in the surface layer during wear, EDS and XRD studies of the worn surfaces of DOE and GME were conducted, as shown in Fig.10 (E) and (F). A large number of elements coming from the chrome steel ball are observed on the worn surface of DOE,
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indicating the transfer of ball material to the epoxy composites. Further, more
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contents of Fe and Cr were found on the worn surface of DOE than that of GME from
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84.80%, 1.28% to 67.89%, 1.16% (by weight), respectively. Partial Fe and Cr and lot of Mo, S, and C can be obserced on the worn surface of GME, demonstrating that the
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wear powders from chrome ball also accumulate on the worn surface of GME.
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However, because of the lubricant film formed on the GME surface, it can largely reduce the friction violent and provide more protection to the contact surface. On the
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other hand, wear debris on the DOE and GME worn surface are also analyzed through
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the XRD to investigate the main mechanism. From the Fig.11 (a), (b), we can observe that the SiO2 is mainly from the debris of DOE but not the GME. This might be
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because the SiO2 can be produced by chemical reaction on the DOE surface during
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the sliding process especially on the badly wear behavior. This found can further explain the significantly differences in morphology and texture between the DOE and GME.
4. Conclusion In summary, three different epoxy composite coatings, i.e. SCE, DOE and GME, conatining diamond, SiC, MoS2 and graphite, were produced in this work; then we 14
ACCEPTED MANUSCRIPT investigated the various fillers on the mechanical and tribological properties of those composite coatings. On one hand, inclusion of different micro particles can significantly enhance the mechanical performance of the epoxy based coatings. For instance, Young’s modulus of EP increased about 14.7% from 3.75 GPa to 4.3 GPa
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(for GME), the fracture toughness increased by 147% to 37.4 GPa (for GME), and the
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tensile strength also had a evidently improved. On the other hand, the excellent wear
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resistance and friction coefficients were observed for the produced composite coatings. For instance, the wear volume of GME is reduced by a fact of 73.8% in
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comparison with that of neat EP, indicating the strongly increase in wear resistance of
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these coatings. They all could be attributed to a uniform distribution of microparticles in the EP matrix, formatting a strong interface between these particles and epoxy
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matrix, thus leading to a higher load bearing capacity to epoxy. Furthermore, it also
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depends on the lubricant film formed on the contact surface. Through the SEM magnification, a nearly continuous, thick lubricant film and a compact and smooth
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structure can be observed on the worn surface of GME. Through the EDS analysis, we
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can confirm that the much more C and Mo and less Fe and Cr elements are included in the lubricant film; especially the compound of SiO2 was obtained on the worn surface of DOE from XRD pattern. Therefore, the unique strategy proposed here can be used to deepen the understanding of the synergetic effects of different fillers in epoxy composite coatings, serving as an important guide for designing and fabricating high tribological performance polymer matrix composites.
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ACCEPTED MANUSCRIPT Acknowledgements The project was supported by the Leading Academic Discipline Project of Shanghai Education Committee, China (YLJX12-2) and the Research Foundation of
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Shanghai University Of Engineering Science, China (CS1205003).
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References
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[1] J. Abenojar, J. Tutor, Y. Ballesteros, J.C.D. Real, M.A. Martínez, Erosion-wear, mechanical and thermal properties of silica filled epoxy nanocomposites,
NU
Composites Part B Engineering. 120 (2017) 42-53.
MA
[2] Q.B. Guo, K.T. Lau, M.Z. Rong, M.Q. Zhang, Optimization of tribological and mechanical properties of epoxy through hybrid filling, Wear. 269 (2010) 13-20.
D
[3] S.V. Sosnovskii, A.S. Mikhnevich, V.P. Sel’Kin, Effect of reinforcing epoxy
PT E
coatings with carbon cloth on their wear under great loads, Journal of Friction & Wear. 35 (2014) 465-469.
CE
[4] A. Dasari, Z.Z. Yu, Y.W. Mai, Fundamental aspects and recent progress on
AC
wear/scratch damage in polymer nanocomposites, Materials Science & Engineering R Reports. 63 (2009) 31-80. [5] B.R. Raju, B. Suresha, R.P. Swamy, B.S.G. Kanthraju, Investigations on Mechanical and Tribological Behaviour of Particulate Filled Glass Fabric Reinforced Epoxy Composites, Journal of Minerals and Materials Characterization and Engineering. 01 (2013) 160-167. [6] B. Shivamurthy, K.U. Bhat, S. Anandhan, Mechanical and sliding wear properties 16
ACCEPTED MANUSCRIPT of multi-layered laminates from glass fabric/graphite/epoxy composites, Materials & Design. 44 (2013) 136-143. [7] A. Yasmin, I.M. Daniel, Mechanical and thermal properties of graphite platelet/epoxy composites, Polymer. 45 (2004) 8211-8219.
PT
[8] W. Jiao, Y. Liu, G. Qi, Studies on mechanical properties of epoxy composites
RI
filled with the grafted particles PGMA/Al2O3, Composites Science & Technology.
SC
69 (2009) 391-395.
[9] Z.B. Xu, X.L. Tang, J.Y. Zheng, Thermal Stability and Flame Retardancy of Rigid
NU
Polyurethane Foams/Organoclay Nanocomposites, Journal of Macromolecular
MA
Science: Part D-Reviews in Polymer Processing. 47 (2008) 1136-1141. [10] Z.Z. Wang, P. Gu, X.P. Wu, H. Zhang, Z. Zhang, M.Y.M. Chiang,
D
Micro/nano-wear studies on epoxy/silica nanocomposites, Composites Science &
PT E
Technology. 79 (2013) 49-57.
[11] I. Neitzel, V. Mochalin, I. Knoke, G.R. Palmese, Y. Gogotsi, Mechanical
CE
properties of epoxy composites with high contents of nanodiamond, Composites
AC
Science & Technology. 71 (2011) 710-716. [12] J. Zhang, L. Chang, S. Deng, L. Ye, Z. Zhang, Some insights into effects of nanoparticles on sliding wear performance of epoxy nanocomposites, Wear. 304 (2013) 138-143. [13] G. Pan, Q. Guo, J. Ding, W. Zhang, X. Wang, Tribological behaviors of graphite/epoxy two-phase composite coatings, Tribology International. 43 (2010) 1318-1325. 17
ACCEPTED MANUSCRIPT [14] I. Neitzel, V. Mochalin, J.A. Bares, R.W. Carpick, A. Erdemir, Y. Gogotsi, Tribological Properties of Nanodiamond-Epoxy Composites, Tribology Letters. 47 (2012) 195-202. [15] R. Baptista, A. Mendão, F. Rodrigues, C.G. Figueiredo-Pina, M. Guedes, R.
PT
Marat-Mendes, Effect of high graphite filler contents on the mechanical and
RI
tribological failure behavior of epoxy matrix composites, Theoretical & Applied
SC
Fracture Mechanics. 85 (2016) 113-124.
[16] F. Ahangaran, A. Hassanzadeh, S. Nouri, Surface modification of Fe3O4@SiO2
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microsphere by silane coupling agent, International Nano Letters. 3 (2013) 1-5.
MA
[17] T. Shengnian, L.I. Xing, Surface Modification of SiC Powder with Silane Coupling Agent, Journal of the Chinese Ceramic Society. 39 (2011) 409-413(405).
D
[18] B. Wetzel, P. Rosso, F. Haupert, K. Friedrich, Epoxy nanocomposites – fracture
2375-2398.
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and toughening mechanisms, Engineering Fracture Mechanics. 73 (2006)
CE
[19] M.R. Ayatollahi, E. Alishahi, S. Doagou-R, S. Shadlou, Tribological and
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mechanical properties of low content nanodiamond/epoxy nanocomposites, Composites Part B Engineering. 43 (2012) 3425-3430. [20] S. Basavarajappa, S. Ellangovan, Dry sliding wear characteristics of glass–epoxy composite filled with silicon carbide and graphite particles, Wear. 296 (2012) 491-496. [21] H. Dhieb, J.G. Buijnsters, F. Eddoumy, J.P. Celis, Surface damage of unidirectional carbon fiber reinforced epoxy composites under reciprocating 18
ACCEPTED MANUSCRIPT sliding in ambient air, Composites Science & Technology. 71 (2011) 1769-1776. [22] B. Suresha, Siddaramaiah, Kishore, S. Seetharamu, P.S. Kumaran, Investigations on the influence of graphite filler on dry sliding wear and abrasive wear behaviour of carbon fabric reinforced epoxy composites, Wear. 267 (2009) 1405-1414.
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[23] H. Li, Y. Ma, Z. Li, Y. Cui, H. Wang, Synthesis of novel multilayer composite
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microcapsules and their application in self-lubricating polymer composites,
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Composites Science and Technology. 164 (2018) 120-128.
[24] Z. Jiang, L.A. Gyurova, A.K. Schlarb, K. Friedrich, Z. Zhang, Study on friction
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and wear behavior of polyphenylene sulfide composites reinforced by short carbon
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fibers and sub-micro TiO2 particles, Composites Science & Technology. 68 (2008)
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734-742.
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Fig.1 Ball-on-disc wear test apparatus. Fig.2 Fracture toughness and young’s modulus for net EP and epoxy composite coatings.
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Fig.3. Development of coefficient of friction (COF) over testing time for EP, SCE, DOE and GME composite coatings at 80 N.
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Fig.4. Development of wear rate over testing time for EP, SCE, DOE and GME composite coatings at
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80 N.
Fig.5. Development of COF and wear rate over testing time for GME composite coating at 80 N.
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Fig.6. Development of COF over testing time for GME composite coating at different applied loads. Fig.7. Development of wear rate over testing time for GME composite coating at different applied loads.
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Fig.8. Average COF and wear volume for EP, SCE, DOE and GME composite coatings at 80 N. Fig.9. Average COF and wear volume of GME composite coating at different applied loads. Fig.10. SEM micrographs of EP (a), SCE (b), DOE (c) and GME (d, g, h); and EDS analysis (E), (F)
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from the related specimens of DOE (e) and GME (f). Note that the worn surface of (h) is obtained at
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120 N, while others at 80 N.
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Fig.11. XRD patterns of the wear debris from DOE (a) and GME (b) at 80 N.
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Table 1 Physico-properties of EP and epoxy composite coatings. Material
Fillers /wt.%
EP /wt.%
SiC
Diamond
Graphite
MoS2
EP
0
0
0
0
100
SCE
50
0
0
0
50
DOE
25
25
0
0
50
GME
25
15
5
5
50
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The followings are the highlights:
The coatings have wear-resisting anti-friction properties under larger stress.
Multiple particles can be well dispersed and have synergistic effects after surface
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modification, including diamond, silicon carbide, molybdenum disulfide and
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graphite.
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Figure 1
Figure 2
Figure 3
Figure 4
Figure 5
Figure 6
Figure 7
Figure 8
Figure 9
Figure 10
Figure 11