J. Cent. South Univ. (2019) 26: 2623-2633

DOI: https://doi.org/10.1007/s11771-019-4199-z

Tribological behavior of Cu-15Ni-8Sn/graphite under sea water,distilled water and dry-sliding conditions

WANG Yan(王艳)¹, ZHANG Lei(张雷)², ZHAI Hong-fei(翟洪飞)¹,GAO Hong-xia(高红霞)¹, ZHOU Ke-chao(周科朝)²

1. Henan Key Laboratory of Intelligent Manufacturing of Mechanical Equipment, Institute of Mechanical and Electrical Engineering, Zhengzhou University of Light Industry, Zhengzhou 450002, China;

2. State Key Laboratory for Powder Metallurgy, Central South University, Changsha 410083, China

Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2019

Abstract: The tribological behaviors of Cu-15Ni-8Sn/graphite composites with the graphite content of 38 vol.% against AISI321 stainless steel under dry-sliding, deionized water and sea water were investigated on a block-on-ring configuration. The results indicated that the friction coefficient was the lowest under dry-sliding, and the highest in deionized water. The wear rate decreased to reach the minimum value of 1.39×10^-15 m³/(N·m) in sea water and in deionized water, it increased to the maximum value of 5.56×10^-15 m³/(N·m). The deionized water hindered the formation of tribo-oxide layer and lubricating film, which resulted in the largest friction coefficient and wear rate. In sea water, however, the corrosion products comprised of oxides, hydroxides and chlorides were found on the worn surface, and the compacted layer composed of corrosion products and graphite played an important role in keeping the excellent wear resistance. It was elucidated that the tribological behaviors of Cu-15Ni-8Sn/graphite composite were powerful influenced by the friction environments.

Key words: self-lubricating composites; tribological behavior; compacted layers; corrosion products; sea water

Cite this article as: WANG Yan, ZHANG Lei, ZHAI Hong-fei, GAO Hong-xia, ZHOU Ke-chao. Tribological behavior of Cu-15Ni-8Sn/graphite under sea water, distilled water and dry-sliding conditions [J]. Journal of Central South University, 2019, 26(10): 2623-2633. DOI: https://doi.org/10.1007/s11771-019-4199-z.

1 Introduction

Copper matrix alloys and their composites with good wear resistance [1-5], anti-friction [6-9] and corrosion resistance have been extensively used as sliding bearings. The Cu-15Ni-8Sn alloy attracted more attention in the trio-material due to its excellent performances, such as high hardness, high strength and exceptional bearing properties [10, 11]. The contained soft phase (Sn) will result in the self-lubricating of Cu-15Ni-8Sn alloy during the service process. However, its self-lubricating is insufficient generally. In previous research, the graphite particles were added in the Cu-15Ni-8Sn alloy and the Cu-15Ni-8Sn/graphite composites with different contents of graphite were obtained. The researches on the tribological and tribo- corrosion behavior of Cu-15Ni-8Sn/graphite composites are important from both scientific and technological points. Besides, understanding the synergistic effect of wear and corrosion on the tribological behavior is of more significance.

As well known, the mechanical wear and corrosion damage will affect the service life of materials distinctly. In some specific environments, for example, in acid rain, sea water or distilled water, the tribological properties of copper matrix composites had been studied [12-14]. CUI et al [15] found that the corrosion behavior resulted from sea water increased the wear rate of bronze-graphite composites. JIA et al [14] pointed out that the bronze/graphite composite showed better wear resistance in the distilled water than under dry-sliding. For the metal based self-lubricating composites, the synergistic effect of lubricant and corrosion product resulted in the obvious difference on the tribological behavior of friction systems. It is worth mentioning that the mixed layer composed by graphite, oxides and corrosion products will form due to the wear and corrosion during the process of sliding, which affected the wear property significantly. So there are an increasing number of researches on the synergistic effect of wear and corrosion on the tribological behavior [16, 17]. WANG et al [18] pointed out that the compacted layer resulted from the wear and corrosion during the sliding was beneficial to decreasing the friction coefficient and wear rate of Cu-9Ni-6Sn alloy in NaCl solution. CUI et al [19] indicated that the sea water showed the lubricating and corrosive effect during the sliding process of bronze-Al₂O₃/graphite composite. Unfortunately, the effect of corrosion behavior on the friction behavior of copper matrix alloys and its composites has not been well clarified and some results are contradictory. It was reported that the corrosion could either increase [18] or decrease [15] the wear resistance of materials. Additionally, the research about the influence of corrosion environment on the formation of compacted layer is quite limited and the study of tribo-corrosion behavior caused by corrosion and mechanical wear need to be clarified deeply. Therefore, the further research on the compacted layer formed by sliding in different environments and its role in the tribological behavior are benefit for the present work.

In the previous researches, the Cu-15Ni-8Sn/ graphite composites with the different graphite contents had been obtained [20]. Further, it was indicated that the Cu-15Ni-8Sn/graphite composite with the graphite content of 38% contributed to the formation of a protective mechanical mixed layer, which showed the excellent friction property under dry-sliding. In this work, the tribo-corrosion behaviors of Cu-15Ni-8Sn/38% graphite (henceforth referred as Cu-15Ni-8Sn/graphite) composites was investigated. The sliding was proceeding under dry-sliding, deionized water and sea water, and the counterpart is the AISI321 stainless steel. Particularly, the synergism between lubricant and corrosion product and its role in the tribological behavior of Cu-15Ni-8Sn/graphite composites were analyzed. The morphologies of worn surfaces and wear debris, especially, the mixed layer composed by graphite, oxides and corrosion products, were performed.

2 Experimental procedures

2.1 Materials

The Cu-15Ni-8Sn/graphite composite with the graphite content of 38 vol.% were prepared by the powder metallurgy process. The Cu-15Ni-8Sn alloy powder (particle size<45 μm) and graphite powder (particle size<74μm) were mixed together for 24 h. Then the mixed powders were hot-pressing in a graphite mold and the Cu-15Ni-8Sn/graphite composite discs were obtained. The temperature of hot-pressing was 950 °C with the pressure of 25 MPa for 1 h and the hot-pressing process was carried out in the argon atmosphere. Finally, the Cu-15Ni-8Sn/graphite composites were cooled down to room temperature, and the details can be found elsewhere [20].

2.2 Friction and wear tests

The tribological tests were conducted on a MRH-3 trio-tester with a block-on-ring configuration under dry-sliding, deionized water and sea water. An AISI321 stainless steel ring (HV: 420 MPa) was used as counterpart, and the outer diameter, inner diameter and thickness were 49 mm, 43 mm and 13 mm, respectively. The size of all specimens used in the experiments is 12 mm×12 mm×19 mm and the 12 mm×19 mm face was contacted with the sliding rings. Prior to the tests, the specimen surface was polished using silicon carbide grinding papers, and then the samples and the ring were cleaned with acetone. All of the tests were performed at the applied load of 50 N with the sliding speed of 100 r/min and testing time of 2 h. Besides, the samples were weighted before and after the testing by a digital microbalance (0.1 mg precision). The wear rates were calculated by W=△m/(Pρs), and the △m, ρ, P and s are the wear mass loss, the density of composites, the normal load and the sliding distance, respectively. Three parallel tests were performed for each testing condition.

The sea water was prepared according to the standard ASTM 1141-98 (2013) as shown in Table 1. The PH value was adjusted to 8.2 by using the 0.1 mol/L NaOH or HCl. During the tests, the bottom of ring was immersed in the deionized water and sea water.

Table 1 Chemical composition of sea water (g·L^-1)

2.3 Characterization of composites

The morphologies of worn surfaces and wear debris were analyzed by scanning electron microscope (SEM) equipped with EDS. The compositions of worn surfaces under dry-sliding, deionized water and sea water were performed by X-ray photoelectron spectroscopy (XPS). The hardness and the density of Cu-15Ni-8Sn/graphite composites were determined by Brinell hardness tester and the method of Archimedes, which can be found elsewhere in details [20]. The bending strength tests were carried out on a 3369 electronic universal material testing machine (specimen dimensions of 3 mm×3 mm×25 mm, three-point bending test).

3 Results and discussion

3.1 Material characteristic

The XRD patterns of Cu-15Ni-8Sn/graphite composite can be found elsewhere [20]. As seen, the main phase of composites was the copper and graphite phases. The results indicated that the Cu, Ni and Sn atoms were formed solid solutions. Additionally, the graphite was present in the elementary form in the matrix, which showed that the graphite did not react with other elements during the hot-pressed process. The SEM micrograph of Cu-15Ni-8Sn/graphite composite with 38 vol.% graphite is shown in Figure 1. It is observed that the graphite particles were distributed along the gap. The Brinell hardness, density and bending strength of Cu-15Ni-8Sn/graphite composite were 47.0 HB, 6.49 g/cm³ and 196.1 MPa, respectively.

Figure 1 SEM micrograph of Cu-15Ni-8Sn/graphite composite

3.2 Friction and wear properties

Figure 2 shows the average of friction coefficients and wear rates of composites under different media. As seen, the friction coefficient was the lowest under dry-sliding, and the highest in deionized water. The friction heat was released during the continuous sliding and it significantly promoted the formation of tribo-oxides layers and lubricating film. The layers avoided the direct contact and adhesion between friction pairs [21, 22]. Therefore, the friction coefficient was the lowest under dry-sliding. However, the distilled water and sea water obviously hindered the self-lubricity of Cu-15Ni-8Sn/graphite composites, which resulted in the higher friction coefficients in comparison with under dry-sliding. The formed corrosion products decreased the contact area of friction couple and it also showed a lubricating effect during the sliding in sea water. The similar trends in friction coefficient had been reported by CUI [23].

As shown in Figure 2, the wear rates of Cu-15Ni-8Sn/graphite composites were 1.97×10^-15 m³/(N·m), 5.56×10^-15 m³/(N·m) and 1.39×10^-15 m³/(N·m) under dry-sliding, deionized water and sea water, respectively. It indicated that the wear rate was the lowest in sea water and highest in deionized water. It was worth pointing out that the wear rate of samples under dry-sliding and sea water was very close. During the dry-sliding process, the released friction heat would improve the formation of tribo-oxides layers and lubricating films, so that a low wear rate material was kept [21]. During the process of sliding, the deionized water would take away the wear debris comprised of graphite and the oxides, which resulted in the higher wear rate than that under dry-sliding. Sliding in sea water, however, the oxides and graphite were fixed on the worn surface before being cut off due to the accelerating of oxidation reaction. Besides, the corrosion products were formed, and then it was compacted during the continuous sliding process [18]. The compacted corrosion products resulted in the reducing of friction between the substrate and counter-face, which decreased the wear rate of Cu-15Ni-8Sn/graphite composites. Therefore, the wear rate in deionized water was larger than others.

Figure 2 Average value of friction coefficients and wear rates of Cu-15Ni-8Sn/graphite composites under dry-sliding, deionized water and sea water

3.3 Evolution of worn surface

SEM micrographs of the worn surfaces for Cu-15Ni-8Sn/graphite composites with the EDS spectra of marked regions in different friction conditions are shown in Figures 3-5. As seen, the morphologies of worn surfaces were markedly different in different environments. Under dry-sliding, the grooves were parallel to the sliding direction. It indicated that the wear mechanism of Cu-15Ni-8Sn/graphite composite was abrasive wear [18]. It can be seen from Figure 3(a) that a large amount of compacted layers adhered to the worn surface of Cu-15Ni-8Sn/graphite composite. The corresponding BSED image is shown in Figure 3(b) and many gray regions were observed. Besides, the micro-cracks and peeling-off morphologies were found on the worn surface of Cu-15Ni-8Sn/graphite after dry sliding, as shown in Figure 3(a). During the repeated extrusion, the micro-cracks were formed easily at the interface of Cu-15Ni-8Sn and graphite due to the poor bonding strength, and subsequent propagated along the interface. Additionally, the depth of grooves on the worn surface of Cu-15Ni-8Sn/graphite composite under dry-sliding was deeper than other conditions.

Figure 3 SEM micrographs of worn surface of Cu-15Ni-8Sn/graphite composite under dry-sliding (a), corresponding backscattered SEM image (b), and EDS spectra of marked region (c)

Figure 4 SEM micrographs of worn surface of Cu-15Ni-8Sn/graphite composite in deionized water (a), corresponding backscattered SEM image (b), and EDS spectra of corresponding marked region (c)

The EDS spectra of marked region on the morphologies of worn surface are shown in Figure 3(c). It indicated the transfer of Fe element from the ring to the block surface. It was deduced that the adhered layers were primarily comprised of graphite, metal and metal oxides, which were excellent lubricating films, and decreased the friction coefficients of Cu-15Ni-8Sn/graphite composites during dry sliding [24, 25].

Figure 5 SEM morphology of worn surface of Cu-15Ni-8Sn/graphite composites in sea water (a), corresponding backscattered SEM image (b), and EDS spectra of marked region (c)

The worn surfaces morphologies of Cu-15Ni-8Sn/graphite composites after sliding in deionized water are shown in Figure 4. As seen, the worn surface of Cu-15Ni-8Sn/graphite composite in deionized water was clean except for some fine grooves and a small amount of wear debris. The distribution of graphite in the matrix was distinct compared with others. It was worth noting that the amount of grooves on the worn surface after sliding in deionized water was reduced compared with the dry-sliding. It indicated that the deionized water can take away the friction heat, and then reduce the softening of the material and improve the resistance of deformation [23]. Besides, it is obtained from Figure 4(b) that little gray region appeared on the worn surface of Cu-15Ni-8Sn/graphite composite, which proved that no tribo-oxide layer and lubricating film were formed on the worn surface during the sliding. The friction heat and the compacted wear debris were necessary for the formation of tribo-oxide layer and lubricating film. However, it was found that the deionized water took away a great amount of friction heat, at the same time, the scouring action of water also made it difficult for the wear debris to stay on the worn surface for a long time, which resulted in no formation of tribo-oxide layer and lubricating film on the worn surface. Figure 4(c) presents the EDS spectra of marked regions on the morphologies of worn surface. The EDS results of marked region indicated the contents of C and O element are less. It was confirmed that the deionized water hindered the formation of tribo-oxide layer and lubricating film, which resulted in the highest friction coefficient and wear rate as sliding in deionized water compared with others, as shown in Figure 2.

At last, the SEM morphologies of worn surfaces with the EDS spectra of the marked regions after sliding in sea water are presented in Figure 5. The fine grooves and micro-cracks were observed on the worn surface. The graphite and the gray regions were present on the worn surface of Cu-15Ni-8Sn/graphite composites as shown in Figure 5(b). It can be found that the worn surface morphologies of Cu-15Ni-8Sn/graphite composite in sea water and deionized water were obviously different. Compared with the worn morphologies in deionized water, the compacted layer adhered to the worn surface after sliding in sea water, which decreased the wear rate sharply. Additionally, Figure 5(c) shows the EDS spectra of marked regions. As seen, the Cl element peak was detected, which indicated the corrosion reaction was formed during the process of sliding in sea water. The peaks of Fe were also observed in the EDS spectra. It can be proved that the black region was primarily comprised of chloride, metal oxides and graphite, which was benefited to obtain the lower friction coefficient and wear rate during the sliding in sea water. Therefore, it was confirmed that the synergy of graphite lubrication and corrosion products decreased the wear rate of Cu-15Ni-8Sn/graphite composites.

During the dry-sliding, the friction heat was released and the oxidation and the plastic deformation of friction surface would be improved. Then, the released graphite and the oxides were compacted on the worn surface, which affected the tribological behavior of Cu-15Ni-8Sn/graphite composites. However, the deionized water would take away the friction heat and hinder the oxidation reaction of matrix. Moreover, the wear debris was carried away from the worn surface due to the scour of deionized water. Therefore, no tribo-oxide layer and lubricating film were formed on the worn surface during the process of sliding in deionized water, which resulted in the highest friction coefficients and wear rates compared with other sliding conditions. During sliding in sea water, the corrosion products comprised of chloride, metal oxides were formed on the worn surface. Due to the accelerating of oxidation reaction and the formation of corrosion products, the graphite and the corrosion products were fixed before being taken away. It indicated that the formation of compacted corrosion products decreased the contact area of friction couple, ultimately increasing the lubricity and wear resistance of composites. Besides, the wear mechanism of Cu-15Ni-8Sn/graphite composites was abrasive wear under dry-sliding and deionized water. The corrosive wear was main wear mechanism in sea water.

3.4 Wear debris

The morphologies of wear debris with the EDS spectra under dry-sliding, deionized water and sea water are shown in Figure 6. A little amount of flaky particles and many fine particles can be seen in Figure 6(a), and the size of flaky was less than 50 μm. The corresponding EDS spectra are displayed in Figure 6(d). As seen, the peaks of Fe and Cr were significant, which indicated that the counter-face materials were transferred and formed the wear debris. Besides, the peaks of oxygen and graphite were also seen in the EDS spectra. It was confirmed that the wear debris contained mainly graphite and metal oxides during the dry sliding. As sliding in deionized water, the wear debris was composed with fine particles and a little amount of flaky particles. The corresponding EDS spectra are displayed in Figure 6(e). Additionally, Figure 6(c) shows the morphology of wear debris obtained from the sea water and the corresponding EDS spectra are shown in Figure 6(f). The sizes of fine particles were less than 10 μm. It was indicated from the EDS spectra that the wear debris mainly contained graphite and metal oxides. The obvious peaks of Fe and Cr were observed in the EDS spectra, and the peaks of the Cl, Na and Mg were also seen in the EDS spectra of wear debris.

3.5 Effect of sliding environments on tribo- corrosion behaviors

XPS analyses of the wear surface of Cu-15Ni-8Sn/graphite composites after sliding in three different conditions were performed and the full XPS spectra curves are showed in Figure 7. It indicated the presence of copper, nickel, tin, graphite and oxygen under dry-sliding and deionized water. In sea water, however, the nickel peak was disappeared and a noticeable peak was proved as the chlorine. It was related to the formation of corrosion product film on the worn surface during the sliding in sea water. The Ni was easily gathered in the inner side of the corrosion product film, which resulted in the disappearance of nickel in the full XPS spectra curves. The similar conclusions were reported by STOTT [26].

Figure 6 SEM micrograghs and corresponding EDS spectra of wear debris obtained under dry-sliding (a, d), deionized water (b, e) and sea water (c, f)

Figure 7 Full XPS spectra of worn surface of Cu-15Ni-8Sn/graphite composites under dry-sliding, deionized water and sea water

XPS spectra of Cu 2p, Ni 2p, Sn 3d and Cl 2p of the Cu-15Ni-8Sn/graphite composite on the worn surface in sea water are given in Figure 8. It can be observed from Figure 8(a) that the copper Cu 2p_3/2 showed the main peak at (932.4±0.2) eV assigned to Cu or Cu⁺. It suggested that the Cu₂O was formed under dry-sliding and deionized water [27, 28], but the CuCl was also formed in sea water [29, 30]. Then there is a shoulder peak at (934.4±0.2) eV under dry-sliding and deionized water, which could be assigned to Cu²⁺ in Cu(OH)₂ [28]. However, the peak around (934.4±0.2) eV in sea water was attributed to Cu(OH)₂, CuCl₂ and Cu(OH)₂Cl [31]. In addition, the peak of (933.7±0.3) eV attributed to CuO was contained in the XPS spectrum of Cu2p under three different conditions. It was observed from the Figure 8(a) that the peak of Cu 2p_3/2 moved to the high binding energy dramatically under dry-sliding and deionized water due to the formation of Cu(OH)₂. In sea water, the amount of Cu²⁺ decreased and the peak of Cu 2p_3/2 was mainly composed by Cu⁺. It was speculated that the percentage of Cu⁺ increased distinctly due to the reduction reaction of Cu²⁺, which resulted from the standard electrode potentials of Ni²⁺/Ni, Sn²⁺/Sn and Cu²⁺/Cu⁺ are -0.25 V, -0.13 V and 0.15 V respectively. Figure 8(b) gives the XPS spectra of Ni 2p under dry-sliding and deionized water. The peaks of Ni 2p around (856.4±0.2) eV and (861.4±0.3) eV were attributed to Ni(OH)₂ and NiO, respectively. XPS spectra of Sn 3d under different conditions are shown in Figure 8(c). As seen, the similar results were obtained under dry-sliding and deionized water. It was confirmed that the peaks of Sn 3d_5/2 around (486.3±0.4) eV and (486.8±0.3) eV were attributed to SnO and SnO₂ [32]. The peak of Sn 3d in sea water was obviously different. ROBBIOLA et al [33] reported that the positive shift of Sn3d_3/2 core level could be no related to the Sn chemical environment (such as Cl^－). Therefore, the peak of Sn 3d was affected by the Na Auger peak. Figure 8(d) shows the XPS spectra of Cl 2p in sea water. It indicated the formation of metal chlorides and other compounds except the NaCl [29, 33, 34].

Figure 8 XPS spectra of Cu 2p, Ni 2p, Sn 3d and Cl 2p of Cu-15Ni-8Sn/graphite composites worn surface

The morphologies of corrosion products and the corresponding EDS spectrum are shown in Figure 9. As seen, the partly compacted layer was formed on the worn surface of Cu-15Ni-8Sn/ graphite composite in sea water. As displayed in Figure 9(b), the peaks of Cu, Ni, Sn, Cl, O and C etc. were detected. Thus, the corrosion products were consisted of metal oxides, chlorides and hydroxides, which decreased the contact area of friction couple during the sliding process. Furthermore, the formation of oxides and corrosion products hindered the departure of graphite, ultimately increasing the lubrication and wear resistance of composites. In this research, the synergy effect of graphite and corrosion products played an important role in keeping the excellent tribological behavior in sea water.

Figure 9 SEM morphologies of corrosion products on worn surface of Cu-15Ni-8Sn/graphite composites in sea water (a), and EDS spectrum of corresponding region (b)

4 Conclusions

From the present study on the tribo-corrosion behaviors of Cu-15Ni-8Sn/graphite composite against AISI321 stainless steel under dry-sliding, deionized water and sea water, the main results are summarized as follows:

1) The friction environments affected the tribological properties of Cu-15Ni-8Sn/graphite composites considerably. The friction coefficient was the lowest under dry-sliding, and the highest in deionized water. Besides, the wear rate of Cu-15Ni-8Sn/graphite in sea water decreased to reach the minimum value of 1.39×10^-15 m³/(N·m) and it increased to the maximum value of 5.56×10^-15 m³/(N·m) during sliding in deionized water. The wear mechanism of Cu-15Ni-8Sn/graphite composite was abrasive wear under dry-sliding and deionized water, and the corrosive wear was the main wear mechanism in sea water.

2) The XPS analyses of worn surfaces showed that the metal oxides and hydroxides were formed under dry-sliding and deionized water. As sliding in sea water, however, the chlorides (CuCl₂ and Cu(OH)₂Cl ) were also found on the worn surfaces of Cu-15Ni-8Sn/graphite composites.

3) The deionized water hindered the formation of tribo-oxide layer and lubricating film, which resulted in the largest friction coefficient and wear rate. In sea water, however, the compacted layers comprised of corrosion products and graphite played an important role in keeping the excellent wear resistance.

References

[1] RAJKUMAR K, ARAVINDAN S. Tribological behavior of microwave processed copper-nanographite composites [J]. Tribology International, 2013, 57: 282-296.

[2] JIN K J, QIAO Z H, ZHU S Y, CHENG J, YIN B, YANG J. Friction and wear properties and mechanism of bronze-Cr- Ag composites under dry-sliding conditions [J]. Tribology International, 2016, 96: 132-140.

[3] SINGH M K, GAUTAM R K. Mechanical and tribological properties of plastically deformed copper metal matrix nano composite [J]. Materials Today: Proceedings, 2018, 5: 5727-5736.

[4] HUANG Z X, ZHENG Z, ZHAO S, DONG S J, LUO P, CHEN L. Copper matrix composites reinforced by aligned carbon nanotubes: Mechanical and tribological properties [J]. Materials & Design, 2017, 133: 570-578.

[5] ZHOU J, MA C, KANG X, ZHANG L, LIU X L. Effect of WS₂ particle size on mechanical properties and tribological behaviors of Cu-WS₂ composites sintered by SPS [J]. Transactions of Nonferrous Metals Society of China, 2018, 28: 1176-1185.

[6] CUI G J, BI Q L, NIU M Y, YANG J, LIU W M. The tribological properties of bronze-SiC-graphite composites under sea water condition [J]. Tribology International, 2013, 60: 25-35.

[7] CHEN B M, BI Q L, YANG J, XIA Y Q, HAO J C. Tribological properties of solid lubricants (graphite, h-BN) for Cu-based P/M friction composites [J]. Tribology International, 2008, 41: 1145-1152.

[8] MAI Y J, CHEN F X, LIAN W Q, ZHANG L Y, LIU C S, JIE X H. Preparation and tribological behavior of copper matrix composites reinforced with nickel nanoparticles anchored graphene nanosheets [J]. Journal of Alloys and Compounds, 2018, 756: 1-7.

[9] GAO X, YUE H Y, GUO E J, ZHANG S L, YAO L H, LIN X Y, WANG B, GUAN E H. Tribological properties of copper matrix composites reinforced with homogeneously dispersed graphene nanosheets [J]. Journal of Materials Science & Technology, 2018, 34: 1925-1931.

[10] CRIBB W R, RATKA J O. Copper spinodal alloys [J]. Advanced Materials & Processes, 2002, 160: 27-30.

[11] ZHANG S H, GAN X P, CHENG J J, JIANG Y X, LI Z, ZHOU K C. Effect of applied load on the transition behavior of wear mechanism in the Cu-15Ni-8Sn alloy under oil lubrication [J]. Journal of Central South University, 2017, 24(8): 1754-1761.

[12] KESTURSATYA M, KIM J K, ROHATGI P K. Wear performance of copper-graphite composite and a leaded copper alloy [J]. Materials Science & Engineering A, 2003, 339: 150-158.

[13] KATO H, TAKAMA M, IWAI Y, WASHIDA K, SASAKI Y. Wear and mechanical properties of sintered copper-tin composites containing graphite or molybdenum disulfide [J]. Wear, 2003, 255: 573-578.

[14] JIA J H, CHEN J M, ZHOU H D, WANG J B, ZHOU H. Friction and wear properties of bronze-graphite composite under water lubrication [J]. Tribology International, 2004, 37: 423-429.

[15] CUI G J, BI Q L, ZHU S Y, YANG J, LIU W M. Tribological properties of bronze-graphite composites under sea water condition [J]. Tribology International, 2012, 53: 76-86.

[16] CHEN J, WANG J Z, CHEN B B, YAN F Y. Tribocorrosion behaviors of inconel 625 alloy sliding against 316 steel in sea water [J]. Tribology Transactions, 2011, 54: 514-522.

[17] TAO S, LI D Y. Investigation of corrosion-wear synergistic attack on nano-crystalline Cu deposits [J]. Wear, 2007, 263: 363-370.

[18] WANG Y, ZHANG L, XIAO J K, CHEN W, FENG C F, GAN X P, ZHOU K C. The tribo-corrosion behavior of Cu-9wt%Ni-6wt%Sn alloy [J]. Tribology International, 2016, 94: 260-268.

[19] CUI G J, BI Q L, ZHU S Y, FU L C, YANG J, QIAO Z H, LIU W M. Synergistic effect of alumina and graphite on bronze matrix composites: Tribological behaviors in sea water [J]. Wear, 2013, 303: 216-224.

[20] FENG C F, WANG Y, CHEN W, ZHANG L, ZHOU K C. The mechanical mixed layer and its role in Cu-15Ni-8Sn/graphite composites [J]. Tribology Transactions, 2017, 60: 135-145.

[21] ZHANG L, XIAO J K, ZHOU K C. Sliding wear behavior of silver-molybdenum disulfide composite [J]. Tribology Transactions, 2012, 55(4): 473-480.

[22] LI X Q, GAO Y M, SONG L C, YANG Q X, WEI S Z, YOU L, ZHOU Y C, ZHANG G S, XU L J, YANG B. Influences of hBN content and test mode on dry sliding tribological characteristics of B₄C-hBN ceramics against bearing steel [J]. Ceramics International, 2018, 44: 6443-6450.

[23] CUI G J, BI Q L, ZHU S Y, YANG J, LIU W M. Tribological behavior of Cu-6Sn-6Zn-3Pb under sea water, distilled water and dry-sliding conditions [J]. Tribology International, 2012, 55: 126-134.

[24] LI X Q, GAO Y M, WEI S Z, YANG Q X. Tribological behaviors of B₄C-hBN ceramic composites used as pins or discs coupled with B₄C ceramic under dry sliding condition [J]. Ceramics International, 2017, 43: 1578-1583.

[25] LI X Q, GAO Y M, WEI S Z, YANG Q X, ZHONG Z C. Dry sliding tribological properties of self-mated couples of B₄C-hBN ceramic composites [J]. Ceramics International, 2017, 43: 162-166.

[26] STOTT F H. The role of oxidation in the wear of alloys [J]. Tribology International, 1998, 31: 61-71.

[27] MCINTYRE N S, COOK M G. X-ray photoelectron studies on some oxides and hydroxides of cobalt, nickel, and copper [J]. Analytical Chemistry, 1975, 47: 2208-2213.

[28] POULSTON S, PARLETT P M, STONE P, BOWKER M. Surface oxidation and reduction of CuO and Cu₂O studied using XPS and XAES [J]. Surface & Interface Analysis, 1996, 24: 811-820.

[29] LIU T, CHEN S G, CHENG S, TIAN J T, CHANG X T, YIN Y S. Corrosion behavior of super-hydrophobic surface on copper in seawater [J]. Electrochimica Acta, 2007, 52: 8003-8007.

[30] KEAR G, BARKER B D, WALSH F C. Electrochemical corrosion of unalloyed copper in chloride media-A critical review [J]. Corrosion Science, 2004, 46: 109-135.

[31] SANDBERG J, WALLINDER I O, LEYGRAF C, BOZEC N L. Corrosion-induced copper run off from naturally and pre-patinated copper in a marine environment [J]. Corrosion Science, 2006, 48: 4316-4338.

[32] TAYLOR J A, LANCASTER G M, RABALAIS J W. Chemical reactions of N²⁺ ion beams with group IV elements and their oxides [J]. Journal of Electron Spectroscopy & Related Phenomena, 1978, 13: 435-444.

[33] ROBBIOLA L, TRAN T T M, DUBOT P, MAJERUS O, RAHMOUNI K. Characterization of anodic layers on Cu-10Sn bronze (RDE) in aerated NaCl solution [J]. Corrosion Science, 2008, 50: 2205-2215.

[34] ANTONIJEVIC M M, MILIC S M, PETROVIC M B. Films formed on copper surface in chloride media in the presence of azoles [J]. Corrosion Science, 2009, 51: 1228-1237.

(Edited by HE Yun-bin)

中文导读

Cu-15Ni-8Sn/石墨复合材料在海水、去离子水和干摩擦中的摩擦学行为研究

摘要：本文选取AISI321不锈钢作为对偶材料，研究Cu-15Ni-8Sn/石墨复合材料(石墨含量为38 vol%)在干摩擦、去离子水与海水三种环境中的摩擦学行为，该实验在环块式摩擦试验机上进行。结果表明：Cu-15Ni-8Sn/石墨复合材料的摩擦系数在干摩擦时最小，在去离子水中最大；此外，海水中该复合材料的磨损率达到最小值，即1.39×10^-15 m³/(N·m)，在去离子水中，其磨损率增加到5.56×10^-15 m³/(N·m)，达到最大值。这表明去离子水阻碍了摩擦氧化层与润滑膜的形成，导致Cu-15Ni- 8Sn/石墨复合材料表现出较大的摩擦系数与磨损率。在海水环境中该复合材料磨损表面形成的腐蚀产物主要包括氧化物、氢氧化物与氯化物，且该腐蚀产物与石墨构成的压实层在保持优异的耐磨性能方面具有至关重要的作用。研究结果表明，摩擦环境显著影响Cu-15Ni-8Sn/石墨复合材料的摩擦学行为。

关键词：自润滑复合材料；摩擦学行为；压实层；腐蚀产物；海水

Foundation item: Project(51674304) supported by the National Natural Science Foundation of China; Project(19B430013) supported by the Key Scientific Research Projects of Higher Education Institutions in Henan Province, China; Project(2017BSJJ013) supported by the Doctor Research Foundation of Zhengzhou University of Light Industry, China

Received date: 2018-10-08; Accepted date: 2019-03-25

Corresponding author: ZHANG Lei, PhD, Professor; Tel: +86-731-88836303; E-mail: zhanglei@csu.edu.cn; ORCID: 0000-0003-4998- 3389