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Ni brush plated composite coatings
Surface & Coatings Technology 192 (2005) 311 – 316 www.elsevier.com/locate/surfcoat
Preparation, microstructure and tribological properties of nano-Al2O3/Ni brush plated composite coatings Lingzhong Dua,b,*, Binshi Xua,b, Shiyun Dongb, Hua Yangb, Yixiong Wua a
College of Material Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, PR China b National Key Laboratory for Remanufacturing, Beijing 100072, PR China Received 30 November 2003; accepted in revised form 3 June 2004 Available online 4 August 2004
Abstract Nano-Al2O3/Ni brush plated composite coatings were prepared by co-deposition of Al2O3 nanoparticles with Ni metal matrix during brush plating. In this process nanocrystalline ceramic powders with grain sizes below 40 nm were suspended in the plating solution and deposited with the metal to produce nanoparticle strengthened metal matrix composite coatings. The microstructure, composition, microhardness and wear properties of the coating in abrasive contaminant lubrication were examined. The results show that the nanoparticles are uniformly distributed in the composite coating, and the microstructure of the composite coating is much finer and denser compared with the pure nickel plating coating. Moreover, the microhardness and tribological properties of the composite coating are higher than that of the pure nickel coating. D 2004 Elsevier B.V. All rights reserved. Keywords: Brush plating; Composite coating; Microhardness; Tribological property
1. Introduction In desert areas, fine sand particles are attracted into machine lubricating systems through the air or fuel filters [1]. This condition causes serious wear problems for the sliding components in lubrication and, under extreme circumstances, a total failure of the equipments [2–4]. Consequently, improving the abrasive resistance of the components becomes a research subject of top priority and great industrial importance. Composite coatings are prepared by co-depositing fine particles of metallic or nonmetallic compounds with the metal matrix. With a newly developed nanopowder, ranging in size from 1 to 100 nm available, the nanoparticles strengthened composite coatings are increasingly attracting scientific and technological interest by virtue of their high hardness, low friction * Corresponding author. Department of Materials Science and Engineering, 21 Dujiakan, Changxindian, Fengtai District, Beijing 100072, PR China. Tel.: +86 10 66719225; fax: +86 10 66717144. E-mail address: [email protected] (L. Du). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.06.008
coefficient and total inertness to any acid or other chemical attack [5,6]. Mqller and Hahn [7], Wun-Hsing Lee et al. [8] and Mqller and Ferkel’s [9] works have shown that nano-ZrO2, nano-diamond and nano-Al2O3 significantly increase the hardness of the Ni plating coating. The higher content of nanoceramic in the deposit, the higher hardness is of the composite coating. Ferkel et al. [10] reported that the Al2O3 nanoparticles could effectively hinder the decreasing of the hardness even when the coating was heated at the temperature of 850 8C for 20 h. Benea et al. [11] found that the friction coefficient of the nano-SiC/Ni plating coating is smaller and the wear corrosion resistance is higher than that of the pure nickel coating in Na2SO4 solution. The brush plating technique, different from conventional vat plating, is an electrochemical process conducted with an electrolyte applied to the substrate by a so-called brush to form the adherent deposit [12]. Nanoparticle strengthened brush plated composite coating combines the advantages of the brush plating technique (cost effectiveness, simple operation and selective area plating) and the composite coating [13]. Jiang et al.’s [14]
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L. Du et al. / Surface & Coatings Technology 192 (2005) 311–316
study has shown that the contact fatigue life of the nanoSiO2/Ni brush plated composite coating was 20% higher than that of nickel coating. Ma et al. [15] found that the unlubricated wear losses of nano-Al2O3/Ni brush plated coating are only 50% of the pure nickel coating. In the current research, the nano-Al2O3/Ni brush plated composite coating is prepared and its tribological properties in abrasive contaminant lubrication are studied. Our purpose is to verify the feasibility of nanoparticle strengthened brush plated composite coating being candidate wear protective materials for the machine components used in desert area. For comparison, the current pure nickel coating is selected. Fig. 2. Schematic diagram of T-11 test rig.
2. Experimental In this investigation, the composite coating was obtained by brush plating nanosized Al2O3 particles with nickel metal on 1045 steel substrate. The employed nanoparticles were provided by the Institute of Processes of the Chinese Academy of Sciences. TEM image (Fig. 1) shows that nanoparticles are spherical with diameters between 20 and 40 nm. Before brush plating, the suspension slurry was prepared by adding the nanoparticles to the typical nickel electrolyte and sufficiently stirred by high-energy mechanical and chemical dispersion method [16]. The brush plating was carried out with a voltage of 12 V and a relative velocity between the negative and positive pole of 10 m/min. The distribution of nanoparticles in the electrolyte was measured using Mastersizer S granularity analysis instruments. The microstructures of surface were examined by scanning electron microscopy (SEM). Transmission electron microscope (TEM) was used to determine the size and
Fig. 1. TEM image of Al2O3 nanoparticles.
distribution of the ceramic particles in the metal matrix. The content of ceramic particle in the metal matrix was analyzed by energy dispersive spectroscopy (EDS). Microhardness indentations were made into the crosssection to avoid the effect of the substrate. The measurements were performed on E¨MT-3 hardness tester at a load of 0.5 N for 15 s. The friction and wear tests in abrasive contaminant lubrication were conducted on a bball-on-diskQ wear tester (T-11). Fig. 2 shows the schematic diagram of the test machine. The lower disk specimen brush plated made from 1045 steel was rotating, with a dimension of U 25.46.1 mm (coating thickness is 0.1 mm) and surface roughness R a=0.065 Am. The upper ball specimen, made from Si3N4 ceramic, was stationary, with a diameter of U=6.35 mm, surface roughness R a=0.012 Am. All the tests were conducted at a normal load of 30 N, a rotating radius of 10 mm and a slide speed of 0.4 m/s. The contaminant was the sand with the major constituent of SiO2 (74–76%) and Al2O3 (14–16%). Particles sizing was carried out in the laboratory using standard sieving procedures. Only those grits that passed through a 300-mesh sieve (nominal
Fig. 3. Size distribution of nanoparticles in the solution with 20 g/l nanoparticle content in the electrolyte.
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opening, 50 Am) were used. The cyclic lubrication mode with 50cc diesel oil was adopted and the contaminant level was 400 mg/l. Prior to performing a test, the oil was stirred immediately in order to scatter the sand evenly. The wear volume was calculated by measuring the wear trace using an optical microscope (with precision of 0.01 mm). Each test was repeated three times and the average was adopted as the experimental data.
3. Results and discussion 3.1. Distribution of nanoparticles in the electrolyte Fig. 3 shows the distribution of nanoparticles in the electrolyte. It is obviously that most of nanoparticle size is
Fig. 5. EDS spectrum of nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
less than 100 nm. The agglomeration of nanoparticles in the solution is to some degree solved by our dispersion method. 3.2. Microstructure and composition of the composite coating
Fig. 4. Surface micrographs (a) pure nickel coating, (b) composite coating with 20 g/l nano-Al2O3 content in the electrolyte.
Fig. 4 depicts a typical scanning electron surface micrograph of the pure nickel and composite coating with 20 g/l nano-Al2O3 in the electrolyte. Nodular units composed of many crystal grains characterize the surface morphology of the composite coating and the pure nickel coating. It is clear that the microstructure of the composite coating is largely improved, more fine, compact and uniform than that of the pure nickel coating. An electrodeposited layer is a competitive step between crystal nucleation and growth. During co-deposition, the higher nucleation [9], due to nanoparticles incorporation, perturbs the growth of nickel matrix and results in a smaller grain size. The Al2O3 content of composite coatings was measured using a SEM with EDS on cross-section of the coating. Fig. 5 presents the general analysis of the coating and it reveals the presence of Ni, Al in the surface deposits. The relatively lower intensity of Al peaks compared to those of Ni suggests that the former is present in the low fraction. The total amount of nano-Al2O3 particles inside the deposit was about 2.6 wt.% calculated from the Al content in the coating. SEM and TEM investigations of co-deposited surface have been conducted to reveal the distribution of the codeposited particles on the surface of the substrates. From the Al element distribution in the composite coating by SEM (Fig. 6), it can be seen that the Al2O3 nanoparticles are uniformly distributed in the Ni metal matrix. A TEM image (Fig. 7) reveals that Al2O3 nanoparticles are mostly deposited along the boundaries of electrodeposited Ni
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Fig. 7. TEM micrograph of nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
co-deposition. It is apparent that the microhardness of the co-deposited layer increases with increasing nanoparticle concentration in the plating solution. The microhardness value of the specimen treated with 20 g/l Al2O3 powder concentration reaches 692 HV, which is 60% higher than that of the pure Ni substrate (440 HV). The striking increase in the hardness of the composite coating can be explained by the hardening effect of the dispersoids (pinning of dislocations and also of grain boundaries [5,8]). Nanoparticles scatter uniformly in the composite coating, so even the low fraction of ceramic phase is sufficient to significantly affect the mechanical properties of the nickel deposit. Further increasing the nanoparticle content in the solution leads to decrease of the hardness, because too many nanoparticles in the solution result in the agglomeration, which reduces the strengthening effect of the nanoparticles.
Fig. 6. Element surface distribution of the composite coating (a) surface micrograph, (b) Al element distribution, (c) Ni element distribution.
grains and well compatible with the nickel matrix, and any of noticeable defects is devoid. 3.3. Microhardness of the composite coating Fig. 8 shows the microhardness of the surface deposits for different density of dispersion in the electrolyte during
Fig. 8. Variation of microhardness with nanoparticle content in the electrolyte.
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3.4. Wear resistance of the composite coating The variations of wear volume and friction coefficient with sliding distance are displayed in Fig. 9. It can be found that after a short running-in stage at the beginning of the test, the friction coefficient enters a steady-state period. The friction coefficient of the composite coating is lower than that of the pure nickel coating. As to the wear resistance, it can be seen that the wear volume of nanoAl2O3/Ni and pure nickel coating increase linearly with sliding distance. However, the wear volume of nanoAl2O3/Ni composite coating is only 60% of that of the pure nickel coating under the same testing condition. Fig. 10 shows the worn surface of the composite coating and pure nickel coating. The fine striations along the sliding direction, probably from the sands plowing its way forward can be seen on the surface. The striations of the composite coating are found milder than that of the pure nickel coating, which is consistent with the wear data. When the nanoparticles co-deposited with the matrix metal, the fine surface morphology of the composite coating will increase the load-carrying area and reduce the stress between the friction couples. On the other hand, uniformly
Fig. 10. Morphologies of worn surfaces with sliding distance of 2880 m (a) pure nickel coating, (b) nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
Fig. 9. Variation of wear volume and friction coefficient with sliding distance (a) wear volume, (b) friction coefficient.
distributed nanoparticles should also serve as obstacles to dislocation movement, thus increasing the hardness over the pure nickel coating. High microhardness prevents abrasive from deeply penetrating the substrate and plowing the coating surface, as a result the wear resistance of the composite coating is improved. The lower friction coefficient of the composite coating can be explained by the bmicro-ball bearingQ effect of the nanoparticles during the sliding. Nano-Al2O3/Ni brush plated composite coating shows an improved tribological property compared with the pure nickel coating in abrasive contaminant lubrication. And it is probably a promising way of utilizing nanocrystals to develop a superficial composite coating on engineering components to enhance wear resistance in crucial environment.
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4. Conclusions
Acknowledgements
From the experiments and analyses performed, some conclusions can be drawn:
Financial support from the Key Project of National Nature Science Foundation of China (No. 50235030), the National 973 Planning Project (No. G1999065009) and the UK/China Science and Technology Collaboration Project in 2002 (No. 2002M3) are gratefully acknowledgement.
(1)
(2)
(3)
(4)
Granularity analysis shows the size of most nanoparticles in the electrolyte is less than 100 nm, thus the agglomeration of nanoparticles in the solution is solved by our dispersion method to some degree. The Al2O3 nanoparticles are homogeneously distributed in the nickel metal matrix and deposited along the boundaries of electrodeposited Ni grains. The higher nucleation, due to nanoparticles incorporation, leads to fine and dense microstructure of the composite coating. The hardness of the composite coating increases when increasing the nanoparticle concentration in the electrolyte. The value of the specimen treated with 20 g/l Al2O3 powder concentration can reach 60% higher than that of the pure Ni coating. When the concentration exceeds a critical amount, the mechanical property of the composite coating decreases because of nanoparticles agglomeration. Due to the nanoparticle strengthening and frictionreducing effect, the nanoparticle strengthened brush plated composite coating shows a better tribological property compared with the pure nickel coating in abrasive contaminant lubrication, and it is a suitable candidate to improve the surface properties of materials in crucial environment.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
E.A. Khorshid, A.M. Nawwar, Wear 141 (1991) 349. H. Wang, W. Xia, Y. Jin, Wear 195 (1996) 47. R.S. Dwyer-joyce, Wear 233–235 (1999) 692. J. Sep, A. Kucaba-Pietal, Wear 249 (2001) 1090. I. Bakonyi, E. Toth-Kadar, L. Pogany, Surface and Coatings Technology 78 (1996) 124. U. Erb, Canadian Metallurgical Quarterly 34 (1995) 275. A. Mqller, H. Hahn, NanoStructured Materials 12 (1999) 259. W.-H. Lee, S.-C. Tang, K.-C. Chung, Surface and Coatings Technology 120–121 (1999) 607. B. Mqller, H. Ferkel, NanoStructured Materials 10 (8) (1998) 1285. H. Ferkel, B. Mqller, W. Riehemann, Materials Science and Engineering A 234–236 (1997) 474. L. Benea, P.L. Bonora, A. Borello, S. Martelli, Wear 249 (2002) 995. Y.-S. Ma, J.-J. Liu, B.-J. Zhu, G.-J. Zhai, L.-Q. Zheng, Wear 165 (1993) 63. S. Dong, B.D. Beake, R. Parkinson, B. Xu, Z. Hu, T. Bell, Surface Engineering 19 (3) (2003) 195. B. Jiang, B. Xu, P. Ding, Journal of Southwest Jiaotong University 11 (1) (2003) 46. Y. Ma, Z. Zhu, L. Ding, Journal of Tsinghua University (Chinese) 42 (1) (2002) 498. B. XU: China patent, No. 02101196.6, 2003.
Preparation, microstructure and tribological properties of nano-Al2O3/Ni brush plated composite coatings Lingzhong Dua,b,*, Binshi Xua,b, Shiyun Dongb, Hua Yangb, Yixiong Wua a
College of Material Science and Engineering, Shanghai Jiaotong University, Shanghai 200030, PR China b National Key Laboratory for Remanufacturing, Beijing 100072, PR China Received 30 November 2003; accepted in revised form 3 June 2004 Available online 4 August 2004
Abstract Nano-Al2O3/Ni brush plated composite coatings were prepared by co-deposition of Al2O3 nanoparticles with Ni metal matrix during brush plating. In this process nanocrystalline ceramic powders with grain sizes below 40 nm were suspended in the plating solution and deposited with the metal to produce nanoparticle strengthened metal matrix composite coatings. The microstructure, composition, microhardness and wear properties of the coating in abrasive contaminant lubrication were examined. The results show that the nanoparticles are uniformly distributed in the composite coating, and the microstructure of the composite coating is much finer and denser compared with the pure nickel plating coating. Moreover, the microhardness and tribological properties of the composite coating are higher than that of the pure nickel coating. D 2004 Elsevier B.V. All rights reserved. Keywords: Brush plating; Composite coating; Microhardness; Tribological property
1. Introduction In desert areas, fine sand particles are attracted into machine lubricating systems through the air or fuel filters [1]. This condition causes serious wear problems for the sliding components in lubrication and, under extreme circumstances, a total failure of the equipments [2–4]. Consequently, improving the abrasive resistance of the components becomes a research subject of top priority and great industrial importance. Composite coatings are prepared by co-depositing fine particles of metallic or nonmetallic compounds with the metal matrix. With a newly developed nanopowder, ranging in size from 1 to 100 nm available, the nanoparticles strengthened composite coatings are increasingly attracting scientific and technological interest by virtue of their high hardness, low friction * Corresponding author. Department of Materials Science and Engineering, 21 Dujiakan, Changxindian, Fengtai District, Beijing 100072, PR China. Tel.: +86 10 66719225; fax: +86 10 66717144. E-mail address: [email protected] (L. Du). 0257-8972/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2004.06.008
coefficient and total inertness to any acid or other chemical attack [5,6]. Mqller and Hahn [7], Wun-Hsing Lee et al. [8] and Mqller and Ferkel’s [9] works have shown that nano-ZrO2, nano-diamond and nano-Al2O3 significantly increase the hardness of the Ni plating coating. The higher content of nanoceramic in the deposit, the higher hardness is of the composite coating. Ferkel et al. [10] reported that the Al2O3 nanoparticles could effectively hinder the decreasing of the hardness even when the coating was heated at the temperature of 850 8C for 20 h. Benea et al. [11] found that the friction coefficient of the nano-SiC/Ni plating coating is smaller and the wear corrosion resistance is higher than that of the pure nickel coating in Na2SO4 solution. The brush plating technique, different from conventional vat plating, is an electrochemical process conducted with an electrolyte applied to the substrate by a so-called brush to form the adherent deposit [12]. Nanoparticle strengthened brush plated composite coating combines the advantages of the brush plating technique (cost effectiveness, simple operation and selective area plating) and the composite coating [13]. Jiang et al.’s [14]
312
L. Du et al. / Surface & Coatings Technology 192 (2005) 311–316
study has shown that the contact fatigue life of the nanoSiO2/Ni brush plated composite coating was 20% higher than that of nickel coating. Ma et al. [15] found that the unlubricated wear losses of nano-Al2O3/Ni brush plated coating are only 50% of the pure nickel coating. In the current research, the nano-Al2O3/Ni brush plated composite coating is prepared and its tribological properties in abrasive contaminant lubrication are studied. Our purpose is to verify the feasibility of nanoparticle strengthened brush plated composite coating being candidate wear protective materials for the machine components used in desert area. For comparison, the current pure nickel coating is selected. Fig. 2. Schematic diagram of T-11 test rig.
2. Experimental In this investigation, the composite coating was obtained by brush plating nanosized Al2O3 particles with nickel metal on 1045 steel substrate. The employed nanoparticles were provided by the Institute of Processes of the Chinese Academy of Sciences. TEM image (Fig. 1) shows that nanoparticles are spherical with diameters between 20 and 40 nm. Before brush plating, the suspension slurry was prepared by adding the nanoparticles to the typical nickel electrolyte and sufficiently stirred by high-energy mechanical and chemical dispersion method [16]. The brush plating was carried out with a voltage of 12 V and a relative velocity between the negative and positive pole of 10 m/min. The distribution of nanoparticles in the electrolyte was measured using Mastersizer S granularity analysis instruments. The microstructures of surface were examined by scanning electron microscopy (SEM). Transmission electron microscope (TEM) was used to determine the size and
Fig. 1. TEM image of Al2O3 nanoparticles.
distribution of the ceramic particles in the metal matrix. The content of ceramic particle in the metal matrix was analyzed by energy dispersive spectroscopy (EDS). Microhardness indentations were made into the crosssection to avoid the effect of the substrate. The measurements were performed on E¨MT-3 hardness tester at a load of 0.5 N for 15 s. The friction and wear tests in abrasive contaminant lubrication were conducted on a bball-on-diskQ wear tester (T-11). Fig. 2 shows the schematic diagram of the test machine. The lower disk specimen brush plated made from 1045 steel was rotating, with a dimension of U 25.46.1 mm (coating thickness is 0.1 mm) and surface roughness R a=0.065 Am. The upper ball specimen, made from Si3N4 ceramic, was stationary, with a diameter of U=6.35 mm, surface roughness R a=0.012 Am. All the tests were conducted at a normal load of 30 N, a rotating radius of 10 mm and a slide speed of 0.4 m/s. The contaminant was the sand with the major constituent of SiO2 (74–76%) and Al2O3 (14–16%). Particles sizing was carried out in the laboratory using standard sieving procedures. Only those grits that passed through a 300-mesh sieve (nominal
Fig. 3. Size distribution of nanoparticles in the solution with 20 g/l nanoparticle content in the electrolyte.
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313
opening, 50 Am) were used. The cyclic lubrication mode with 50cc diesel oil was adopted and the contaminant level was 400 mg/l. Prior to performing a test, the oil was stirred immediately in order to scatter the sand evenly. The wear volume was calculated by measuring the wear trace using an optical microscope (with precision of 0.01 mm). Each test was repeated three times and the average was adopted as the experimental data.
3. Results and discussion 3.1. Distribution of nanoparticles in the electrolyte Fig. 3 shows the distribution of nanoparticles in the electrolyte. It is obviously that most of nanoparticle size is
Fig. 5. EDS spectrum of nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
less than 100 nm. The agglomeration of nanoparticles in the solution is to some degree solved by our dispersion method. 3.2. Microstructure and composition of the composite coating
Fig. 4. Surface micrographs (a) pure nickel coating, (b) composite coating with 20 g/l nano-Al2O3 content in the electrolyte.
Fig. 4 depicts a typical scanning electron surface micrograph of the pure nickel and composite coating with 20 g/l nano-Al2O3 in the electrolyte. Nodular units composed of many crystal grains characterize the surface morphology of the composite coating and the pure nickel coating. It is clear that the microstructure of the composite coating is largely improved, more fine, compact and uniform than that of the pure nickel coating. An electrodeposited layer is a competitive step between crystal nucleation and growth. During co-deposition, the higher nucleation [9], due to nanoparticles incorporation, perturbs the growth of nickel matrix and results in a smaller grain size. The Al2O3 content of composite coatings was measured using a SEM with EDS on cross-section of the coating. Fig. 5 presents the general analysis of the coating and it reveals the presence of Ni, Al in the surface deposits. The relatively lower intensity of Al peaks compared to those of Ni suggests that the former is present in the low fraction. The total amount of nano-Al2O3 particles inside the deposit was about 2.6 wt.% calculated from the Al content in the coating. SEM and TEM investigations of co-deposited surface have been conducted to reveal the distribution of the codeposited particles on the surface of the substrates. From the Al element distribution in the composite coating by SEM (Fig. 6), it can be seen that the Al2O3 nanoparticles are uniformly distributed in the Ni metal matrix. A TEM image (Fig. 7) reveals that Al2O3 nanoparticles are mostly deposited along the boundaries of electrodeposited Ni
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Fig. 7. TEM micrograph of nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
co-deposition. It is apparent that the microhardness of the co-deposited layer increases with increasing nanoparticle concentration in the plating solution. The microhardness value of the specimen treated with 20 g/l Al2O3 powder concentration reaches 692 HV, which is 60% higher than that of the pure Ni substrate (440 HV). The striking increase in the hardness of the composite coating can be explained by the hardening effect of the dispersoids (pinning of dislocations and also of grain boundaries [5,8]). Nanoparticles scatter uniformly in the composite coating, so even the low fraction of ceramic phase is sufficient to significantly affect the mechanical properties of the nickel deposit. Further increasing the nanoparticle content in the solution leads to decrease of the hardness, because too many nanoparticles in the solution result in the agglomeration, which reduces the strengthening effect of the nanoparticles.
Fig. 6. Element surface distribution of the composite coating (a) surface micrograph, (b) Al element distribution, (c) Ni element distribution.
grains and well compatible with the nickel matrix, and any of noticeable defects is devoid. 3.3. Microhardness of the composite coating Fig. 8 shows the microhardness of the surface deposits for different density of dispersion in the electrolyte during
Fig. 8. Variation of microhardness with nanoparticle content in the electrolyte.
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3.4. Wear resistance of the composite coating The variations of wear volume and friction coefficient with sliding distance are displayed in Fig. 9. It can be found that after a short running-in stage at the beginning of the test, the friction coefficient enters a steady-state period. The friction coefficient of the composite coating is lower than that of the pure nickel coating. As to the wear resistance, it can be seen that the wear volume of nanoAl2O3/Ni and pure nickel coating increase linearly with sliding distance. However, the wear volume of nanoAl2O3/Ni composite coating is only 60% of that of the pure nickel coating under the same testing condition. Fig. 10 shows the worn surface of the composite coating and pure nickel coating. The fine striations along the sliding direction, probably from the sands plowing its way forward can be seen on the surface. The striations of the composite coating are found milder than that of the pure nickel coating, which is consistent with the wear data. When the nanoparticles co-deposited with the matrix metal, the fine surface morphology of the composite coating will increase the load-carrying area and reduce the stress between the friction couples. On the other hand, uniformly
Fig. 10. Morphologies of worn surfaces with sliding distance of 2880 m (a) pure nickel coating, (b) nano-Al2O3/Ni composite coating with 20 g/l nanoparticle content in the electrolyte.
Fig. 9. Variation of wear volume and friction coefficient with sliding distance (a) wear volume, (b) friction coefficient.
distributed nanoparticles should also serve as obstacles to dislocation movement, thus increasing the hardness over the pure nickel coating. High microhardness prevents abrasive from deeply penetrating the substrate and plowing the coating surface, as a result the wear resistance of the composite coating is improved. The lower friction coefficient of the composite coating can be explained by the bmicro-ball bearingQ effect of the nanoparticles during the sliding. Nano-Al2O3/Ni brush plated composite coating shows an improved tribological property compared with the pure nickel coating in abrasive contaminant lubrication. And it is probably a promising way of utilizing nanocrystals to develop a superficial composite coating on engineering components to enhance wear resistance in crucial environment.
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L. Du et al. / Surface & Coatings Technology 192 (2005) 311–316
4. Conclusions
Acknowledgements
From the experiments and analyses performed, some conclusions can be drawn:
Financial support from the Key Project of National Nature Science Foundation of China (No. 50235030), the National 973 Planning Project (No. G1999065009) and the UK/China Science and Technology Collaboration Project in 2002 (No. 2002M3) are gratefully acknowledgement.
(1)
(2)
(3)
(4)
Granularity analysis shows the size of most nanoparticles in the electrolyte is less than 100 nm, thus the agglomeration of nanoparticles in the solution is solved by our dispersion method to some degree. The Al2O3 nanoparticles are homogeneously distributed in the nickel metal matrix and deposited along the boundaries of electrodeposited Ni grains. The higher nucleation, due to nanoparticles incorporation, leads to fine and dense microstructure of the composite coating. The hardness of the composite coating increases when increasing the nanoparticle concentration in the electrolyte. The value of the specimen treated with 20 g/l Al2O3 powder concentration can reach 60% higher than that of the pure Ni coating. When the concentration exceeds a critical amount, the mechanical property of the composite coating decreases because of nanoparticles agglomeration. Due to the nanoparticle strengthening and frictionreducing effect, the nanoparticle strengthened brush plated composite coating shows a better tribological property compared with the pure nickel coating in abrasive contaminant lubrication, and it is a suitable candidate to improve the surface properties of materials in crucial environment.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16]
E.A. Khorshid, A.M. Nawwar, Wear 141 (1991) 349. H. Wang, W. Xia, Y. Jin, Wear 195 (1996) 47. R.S. Dwyer-joyce, Wear 233–235 (1999) 692. J. Sep, A. Kucaba-Pietal, Wear 249 (2001) 1090. I. Bakonyi, E. Toth-Kadar, L. Pogany, Surface and Coatings Technology 78 (1996) 124. U. Erb, Canadian Metallurgical Quarterly 34 (1995) 275. A. Mqller, H. Hahn, NanoStructured Materials 12 (1999) 259. W.-H. Lee, S.-C. Tang, K.-C. Chung, Surface and Coatings Technology 120–121 (1999) 607. B. Mqller, H. Ferkel, NanoStructured Materials 10 (8) (1998) 1285. H. Ferkel, B. Mqller, W. Riehemann, Materials Science and Engineering A 234–236 (1997) 474. L. Benea, P.L. Bonora, A. Borello, S. Martelli, Wear 249 (2002) 995. Y.-S. Ma, J.-J. Liu, B.-J. Zhu, G.-J. Zhai, L.-Q. Zheng, Wear 165 (1993) 63. S. Dong, B.D. Beake, R. Parkinson, B. Xu, Z. Hu, T. Bell, Surface Engineering 19 (3) (2003) 195. B. Jiang, B. Xu, P. Ding, Journal of Southwest Jiaotong University 11 (1) (2003) 46. Y. Ma, Z. Zhu, L. Ding, Journal of Tsinghua University (Chinese) 42 (1) (2002) 498. B. XU: China patent, No. 02101196.6, 2003.