Trans. Nonferrous Met. Soc. China 23(2013) 2002-2010

Tribological behavior and mechanism of NiCrBSi-Y₂O₃ composite coatings

Bin CAI, Ye-fa TAN, Hua TAN, Qi-feng JING, Zhong-wei ZHANG

College of Field Engineering, PLA University of Science and Technology, Nanjing 210007, China

Received 5 June 2012; accepted 5 December 2012

Abstract: The NiCrBSi-Y₂O₃ composite coatings were prepared on the surface of 45 carbon steel by plasma spray, the microstructure and tribological properties of the coatings were investigated. The results show that the NiCrBSi-Y₂O₃ composite coatings are mainly composed of γ-Ni, CrB, Cr₇C₃ and Y₂O₃. With addition of Y₂O₃, hard phases such as CrB, Cr₇C₃ emerge in composite coating, and the density of the composite coatings also increases. The NiCrBSi-0.5Y₂O₃ composite coating presents excellent tribological properties. Its friction coefficient is 0.175, which is about 37% of that of the pure NiCrBSi coating. The mass wear loss is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. When the loads are 6-10 N, the NiCrBSi-0.5Y₂O₃ composite coating suffers from slight wear and the wear mechanisms are mainly adhesive wear accompany with slight micro-cutting wear and micro-fracture wear. As the load increases to 12 N, the wear mechanisms are adhesive wear and severe micro-cutting wear.

Key words: plasma spray; composite coating; NiCrBSi; Y₂O₃; friction; wear

1 Introduction

The parts used in metallurgical and construction machinery usually suffer from severe friction and wear, the anti-wear alloy coatings are widely applied to improving their wear resistance and prolong their sevice lives [1,2]. However, the values of friciton coefficients of the anti-wear alloy coatings are usually high, thus leading to high energy consumption [3,4]. As the mechanical equipments develop, the mechine parts are getting more demands on anti-friciton property. So, it becomes research hotspot to develope the surface coatings with both property of anti-wear and low friction coefficients.

Rare earth oxides such as CeO₂ and La₂O₃ are commonly used to improve mechanical property and wear resistance of surface coatings. For example, the microhardness and wear resistance of the laser clad TiC_p/Ni-base alloy composite coatings could be improved by adding 0.5% La₂O₃ (in mass fraction), and friction coefficient of the composite coatings was also reduced [5]. With addition of 1.5% Sm₂O₃ (in mass fraction), the microstructure of the laser cladded Ni-based alloy coating could be refined and the microhardness increased from HV_0.2 484 to HV_0.2 712. The wear rate of the composite coatings was reduced by 50% compared with the pure Ni-based alloy coatings [6]. WANG et al [7] found that the microhardness of the spray welded Ni-based alloy coating decreased with addition of 4%La₂O₃ (in mass fraction), and its mass wear loss was reduced by 20% compared with the coating without La₂O₃. That is because La₂O₃ can improve the uniformity of the coating microstructure and its resistance to micro-cutting. It can be concluded that rare earths not only improve wear resistance but also have the effects of anti-friction.

Wear resistance of surface coatings with rare earths increases because the microstructure of surface coatings is refined and purified, so their hardness and fracture toughness increase [8-10]. However, there are different views on the anti-friction mechanisms of rare earths in surface coatings. For example, ZHANG et al [11] considered that rare earth oxides have the character as solid lubricant. HAN and LU [12] attributed the anti-friction effects of CeO₂ not only to its hexagonal structure, but also to the reduction of micro-cutting force for the improved density of the composite coatings. HUANG et al [13] reckoned that rare earth refined the coating structure and improved the fracture toughness of the coating, so reduced the friction coefficients.

Researches on anti-wear and anti-friction effects of rare earths are mainly focused on coatings prepared by fused cladding technology such as laser cladding and induction cladding, but the mechanisms of rare earths in the plasma spray technology are different from those in the fused cladding technology, which need to be researched. The temperature of the substrate is low in plasma spray process and the solidification speed of the sprayed particles is higher than 10⁵ °C/s [14]. In addition, the Y₂O₃ particles may act as the better heterogeneous nucleation than La₂O₃ and CeO₂ particles, which may improve the uniformity of the hard phase and the microhardness of the coatings [15]. In this work, the NiCrBSi-Y₂O₃ composite coatings were prepared on the surface of 45 carbon steel by plasma spray technology, the microstructure, microhardness and tribological properties of the composite coatings were investigated to provide theory basis and experimental data for application of Y₂O₃ in the plasma spray coatings.

2 Experimental

2.1 Specimen preparation

The NiCrBSi-Y₂O₃ composite materials are composed of NiCrBSi powders and Y₂O₃ powders. The chemical composition of the NiCrBSi powders was 16Cr, 3.1B, 4.3Si, 4Fe, 0.65C and balance Ni (mass fraction, %) and its particle sizes were in the range of 55-128 μm. The purity of Y₂O₃ powders with sizes of 15-45 μm was 99.5%. The composite spray powders were made by the mixture of the Ni-based alloy powders and the Y₂O₃ powders in a ball mill equipment for 1 h.

The 45 carbon steel was chosen as the substrate, and was previously treated by surface degrease and sand spraying. The composite powders were respectively sprayed on the surface of 45 carbon steel by the plasma spray equipment of DH1080. The spray technological parameters were electric current of 600 A, voltage of 40 V and spray distance of 80 mm. The thickness of the spray coating was 400 μm with surface roughness of 0.5 μm after being ground by diamond wheel.

2.2 Tribological tests

The tribological tests were carried out in a ball-on-disc tribometer of HT-500. The upper specimen was GCr15 steel ball with the diameter of 4 mm and the surface roughness of 0.05 μm. The down ones were the composite coatings. Tribological tests were conducted at the speed of 0.1 m/s in room temperature, normal load was 6-12 N, and sliding distance was 360 m. The mass wear losses of the specimens were measured by the balance of TG328A with accuracy of 0.1 mg.

2.3 Surface analysis

The X-ray diffraction (XRD) of the composite coatings was performed on a D/max 2500 X-ray diffractometer. Porosity of the coatings was tested by the DM-3000 metallography analysis software. The microhardness of the coatings was measured using the DHV-1000 sclerometer under the load of 4.92 N with a dwell time of 15 s. The morphologies of the microstructure and the worn surface of the composite coatings were observed by the scanning electron microscope (SEM) of QUANTA 200. Chemical composition of the composite coatings was analyzed with the energy-dispersive analysis of X-ray (EDAX).

3 Results and discussion

3.1 Microstructure of NiCrBSi-Y₂O₃ composite coatings

The XRD patterns of the NiCrBSi-Y₂O₃ composite coatings are shown in Fig. 1. It can be found that the NiCrBSi-Y₂O₃ composite coatings are mainly composed of γ-Ni, CrB, Cr₇C₃ and Y₂O₃. Compared with the pure NiCrBSi coating, there are some new phases such as CrB and Cr₇C₃ emerge in the NiCrBSi-0.5Y₂O₃ composite coating. During the spraying process, the NiCrBSi powders and the Y₂O₃ powders were heated and fused by the plasma flame, and then the fused particles quickly solidified on the substrate of the carbon steel. It was reported that element C can promote the decomposition of rare earth oxides into rare earth elements during solidification process of the fused particles [16], so Y₂O₃ may react with C to produce Y:

Y₂O₃+3[C]=2[Y]+3CO                        (1)

The solid solubility of Y in NiCrBSi is low because the large radius of Y is 0.18 nm [17]. This may account for the segregation of Y at the dislocation and grain boundary area of the NiCrBSi coating, which leads to distortion area in the coating [18]. Y has a strong adsorptive action to elements C and B [19], so it causes segregation of elements C and B in the distortion area. As the concentrations of elements C and B increase to certain degree at the distortion area, CrB and Cr₇C₃ may precipitate. So, the diffraction peaks of CrB and Cr₇C₃ emerge in the NiCrBSi-0.5Y₂O₃ composite coating, which indicates that Y₂O₃ may promote the precipitation of CrB and Cr₇C₃ in the composite coatings. The hard phases of CrB and Cr₇C₃ can improve the wear resistance of the composite coatings.

Fig. 1 XRD patterns of NiCrBSi-Y₂O₃ composite coatings

As Y₂O₃ increases to 1.0% (in mass fraction), CrB in the composite coating increases compared with the NiCrBSi-0.5Y₂O₃ composite coating. It also shows a little Y₂O₃ in the composite coating which indicates some unreacted Y₂O₃ particles retained in the composite coating. The CrB content is improved due to the heterogeneous nucleation effects of the unreacted Y₂O₃ particles.

When Y₂O₃ is 2.0%, the new phase of NiSi emerges in the composite coating. The unreacted Y₂O₃ particles retained in the composite coating increase as Y₂O₃ content increases, which enhances the heterogeneous nucleation effect and promotes the precipitation of brittle composites, such as NiSi. Therefore, the brittleness of the composite coating increases. It can be concluded that the optimum addition of 0.5% Y₂O₃ may improve the hard phases of CrB and Cr₇C₃ in the composite coating, but excess Y₂O₃ may induce brittle phases such as NiSi in the composite coatings and result in higher brittleness.

Figure 2 shows the metallographic pictures of the pure NiCrBSi coating and the NiCrBSi-0.5Y₂O₃ composite coating. The grain size of the latter is smaller than that of the former. This indicates that Y₂O₃ may refine the grain size of the NiCrBSi coating.

Figure 3 shows the porosity of the NiCrBSi-Y₂O₃ composite coatings as a function of Y₂O₃ content. The porosity initially decreases and then increases with increasing Y₂O₃ content. It is observed that the porosity of the composite coatings is much lower than that of the pure NiCrBSi coating (porosity of 2.96%). It is 0.92% when the Y₂O₃ content is 0.5%, and then reaches the lowest value (about 0.67%) as the Y₂O₃ content increases to 1.0-1.5%. It is well known that porosity of the sprayed coatings is closely related to the deformation degree of the fused particles. It was reported that the deformation degree of the fused particles during plasma spray can be demonstrated as Eq. (2) [20]:

                               (2)

where σ is the surface tension of the fused particles; ρ is density of the particles; d is the size of the particles; D/h is the ratio of size to height of the particles on the substrate. The higher the value of D/h is, the more flat the particles become.

Fig. 2 Metallographic pictures of pure NiCrBSi coating (a) and NiCrBSi-0.5Y₂O₃ composite coating (b)

Fig. 3　Porosity of NiCrBSi-Y₂O₃ composite coatings

Rare earths can improve the wettability of the NiCrBSi particles due to their high activity [21], so σ of the NiCrBSi powders decreases with addition of Y₂O₃, which means the value of D/h increases. Figure 4 shows the sprayed particles morphology of the pure NiCrBSi powders and the NiCrBSi-0.5Y₂O₃ composite powders. The spread particles in the composite powders with Y₂O₃ (as shown in Fig. 4(b)) are larger than those in the pure NiCrBSi powders (as shown in Fig. 4(a)), which indicates the fused particles of the NiCrBSi-Y₂O₃ composite coatings are more flat and compact than those of the coatings without Y₂O₃. This may account for the decreasing porosity of the NiCrBSi-Y₂O₃ composite coatings.

Fig. 4 OM images showing sprayed particles morphology of pure NiCrBSi powder (a) and NiCrBSi-0.5Y₂O₃ composite powders (b)

However, the porosity of the composite coatings increases to 1.16% when the Y₂O₃ content is 2.0% because the unreacted Y₂O₃ particles may induce defects such as voids and pores in the composite coating.

Microhardness of the NiCrBSi-Y₂O₃ composite coatings as a function of Y₂O₃ content is shown in Fig. 5. The average microhardness of the NiCrBSi-Y₂O₃ composite coatings is HV 700, which is found to dramatically increase compared with the pure NiCrBSi coating (HV 586). It can be attributed to the following reasons: 1) Plastic deformation of the composite coatings after microhardness test decreases because of the increased density due to the decrease of porosity with addition of Y₂O₃; 2) The hard phase precipitates such as CrB and Cr₇C₃ are improved by Y₂O₃, which can increase the microhardness of the composite coatings.

3.2 Effects of Y₂O₃ content on tribological behavior and mechanisms of composite coatings

The friction coefficients of the NiCrBSi-Y₂O₃ composite coatings with the increasing Y₂O₃ content are shown in Fig. 6. The friction coefficients initially decrease and then increase and lastly remain unchanged.

Fig. 5　Microhardness of NiCrBSi-Y₂O₃ composite coatings

Fig. 6 Friction coefficients of NiCrBSi-Y₂O₃ composite coatings (load=10 N)

Fig. 7 Wear mass loss of NiCrBSi-Y₂O₃ composite coatings under load of 10 N

Fig. 8 SEM image showing worn surface morphology (a) and EDAX spectrum (b) of pure NiCrBSi coating

The friction coefficient of NiCrBSi-0.5Y₂O₃ composite coating (0.175) is much lower than that of the pure NiCrBSi coating (0.47). As the Y₂O₃ content increases to 1.0%, the friction coefficient is 0.36, which is higher than that of the NiCrBSi-0.5Y₂O₃ composite coating. The friction coefficient remains at 0.37 when Y₂O₃ is 2.0%.

Figure 7 shows the wear mass loss of the NiCrBSi-Y₂O₃ composite coatings as a function of Y₂O₃ content. The wear mass losses of the composite coatings firstly decrease and then increase. The wear mass loss of the NiCrBSi-0.5Y₂O₃ composite coating is 1.2 mg, reduced by 43% compared with the pure NiCrBSi coating (2.1 mg). That is because the microhardness of the former is higher than the latter. The mass loss wear of the NiCrBSi-1.0Y₂O₃ composite coating is the lowest (0.9 mg). When Y₂O₃ exceeds 1.0%, the wear mass losses of the composite coatings increase. For example, the wear mass loss of the NiCrBSi-2.0Y₂O₃ is 1.6 mg.

Figure 8 shows the worn surface of the pure NiCrBSi coating with its EDAX spectrum. Some worn furrows emerge on the worn surface, as shown in Fig. 8(a), because the solid welding nodes in the contact area between the pure NiCrBSi coating and GCr15 steel ball suffer from shear damage and lead to plastic flow of the surface materials. The chemical composition of the worn surface is 1.22C, 8.50O, 4.01Si, 16.98Cr, 11.50Fe and 57.78Ni (mass fraction, %) according to Fig. 8(b). The content of element Fe is 11.50% on the worn surface, which is about 2.9 times that in the NiCrBSi powders because the GCr15 steel ball materials transfer to the worn surface of the pure NiCrBSi coating as a result of shear damage of the solid welding nodes. The friction coefficient of the pure NiCrBSi coating is relatively high because of severe adhesive friction. In addition, the grooves on the worn surface indicate micro-cutting wear of the composite coating, so the main wear mechanisms of the pure NiCrBSi coating are adhesive wear and micro-cutting wear.

Fig. 9 SEM image showing worn surface morphology (a) and EDAX spectrum (b) of NiCrBSi-0.5Y₂O₃ composite coating

The friction coefficients and wear mass loss of the NiCrBSi-0.5Y₂O₃ composite coating are greatly reduced compared with the pure NiCrBSi coating. Figure 9 shows the worn surface of the NiCrBSi-0.5Y₂O₃ composite coating and its EDAX spectrums. Figure 9(a) shows that a dark grey film emerges on the worn surface. The chemical composition of the film is 2.42C, 9.88O, 3.18Si, 15.99Cr, 7.36Fe and 61.18Ni (mass fraction, %) (Fig. 9(b)), which indicates Fe₂O₃, Fe₃O₄ and NiO in the film. The film may easily shear under the friction force and lead to greatly decrease of the shear strength at the friction interface. So, the friction coefficients of the NiCrBSi-0.5Y₂O₃ composite coating decrease. The vacancy density increases in the friction surface because of the increased temperature induced by friction heat. Then Y at the grain boundary is more apt to diffuse and segregate in the vacancies than other alloying elements for its low free energy. The segregated rare earth on the friction surface can reduce vacancies and voids between the oxide film and the substrate, which results in the increasing combined strength of the oxide film. As a result, the complete oxide film is developed on the worn surface.

The content of element Fe on the worn surface is 7.46%, much less than that in the worn surface of the pure NiCrBSi coating. This suggests that the adhesive action is alleviated because of less GCr15 steel transferred to the worn surface. It can be concluded that the oxide film on the worn surface of the NiCrBSi- 0.5Y₂O₃ composite coating can not only reduce friction coefficients, but also reduce adhesive wear. Besides, the lump wear debris are found on the worn surface of the composite coating as shown in Fig. 9(a), which indicates certain extent brittle fracture of the coating. It shows that the wear mechanisms of the NiCrBSi- 0.5Y₂O₃ composite coating are mainly slight adhesive wear accompany with slight micro-fracture wear.

The wear behavior and mechanisms of the NiCrBSi-Y₂O₃ composite coatings change with the further increase of Y₂O₃ content. The worn surface of the NiCrBSi-1.0Y₂O₃ composite coating and its EDAX spectrum are shown in Fig. 10. It is obvious that many black point-like structures distribute on the smooth worn surface with little oxide film as shown in Fig. 10(a). The chemical composition of the point-like structures is 1.15% C, 9.64% O, 0.76% Si, 82.16% Cr, 1.63% Fe, 3.59% Ni and 1.08% Y (Fig. 10(b)). It shows that the point-like structures are rich in Cr, indicating that the point-like structures are mainly CrB and Cr₇C₃. These hard phases are exposed on the worn surface and support the GCr15 steel ball after the alloy matrix around the hard phases wears off during friction process. Thus the hard phases bear main load and induce great decrease in pressure on the Ni-based alloy matrix, which results in reduction of the friction heat by plastic deformation. Therefore, friction oxidation reaction of the Ni-based alloy matrix is too little to produce oxide film which can account for the increase in friction coefficient of the NiCrBSi-1.0Y₂O₃ composite coating.

Fig. 10 SEM image showing worn surface morphology (a) and EDAX spectrum (b) of NiCrBSi-1.0Y₂O₃ composite coating

The wear mass loss of the NiCrBSi-1.0Y₂O₃ composite coating is lower than that of the NiCrBSi-0.5Y₂O₃ composite coating, because the former coating is more resistant to plastic deformation than the latter due to its higher microhardness than the latter. Some micro-cracks and fracture pits emerge on the worn surface of the composite coating (Fig. 10(a)). These micro-cracks can be attributed to the stress concentration in the combine region between the hard phases and the Ni-based alloy matrix as a result of high shear force on the hard phases during friction. This suggests that the main wear mechanisms of the NiCrBSi-1.0Y₂O₃ composite coating are mainly adhesive wear and micro-fracture wear.

Figure 11 shows the worn surface of the NiCrBSi-1.5Y₂O₃ composite coating and there are more micro-cracks on its worn surface than on the NiCrBSi-1.0Y₂O₃ composite coating, and some micro-cutting grooves are produced on the worn surface. Due to the increasing brittleness phases in the NiCrBSi-1.5Y₂O₃ composite coating, there are the micro-cracks and micro-fracture in the composite coating caused by the shear force increase. The micro-cutting grooves are plough by wear debris on the worn surface and lead to increase of wear mass loss. Main wear mechanisms of the NiCrBSi-1.5Y₂O₃ composite coating are micro-fracture wear and micro-cutting wear.

As the Y₂O₃ content increases to 2.0%, many micro-cracks and micro-cutting grooves emerge on the worn surface of the composite coating (Fig. 12). The increased porosity of the composite coating causes more defects in the coating. These defects develop to micro-cracks under cyclic load, and lead to fracture of the worn surface materials which act as wear debris. The wear debris induces three-body abrasive wear, so the micro-cutting grooves increase in Fig. 12. As a result, micro-fracture wear and micro-cutting wear of the NiCrBSi-2.0Y₂O₃ composite coating increase compared with the NiCrBSi-1.5Y₂O₃ composite coating.

Fig. 11 SEM image showing worn surface morphology of NiCrBSi-1.5Y₂O₃ composite coating

Fig. 12 SEM image showing worn surface morphology of NiCrBSi-2.0Y₂O₃ composite coating

It can be concluded that the NiCrBSi-0.5Y₂O₃ composite coating presents excellent tribological properties, whose friction coefficient is 0.175 which is 37% of that of the pure NiCrBSi coating. The wear mass loss of the composite coating is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. The decreased friction coefficient of the composite coating can be attributed to the solid lubrication effect of the oxide film on the worn surface.

3.3 Effects of load on tribological properties of NiCrBSi-Y₂O₃ composite coatings

The effects of load on tribological properties of the NiCrBSi-0.5Y₂O₃ composite coating are researched in consideration of its excellent tribological properties. Figure 13 shows the friction coefficients and wear mass losses of the NiCrBSi-0.5Y₂O₃ composite coating as a function of load. Its friction coefficients take on a slight decrease trend as the load increases, which is in the range of 0.173 and 0.18. The wear mass losses of the composite coating increase with the increasing load.

Fig. 13 Friction coefficients and wear mass loss of NiCrBSi-0.5Y₂O₃ composite coating vs load

Under at the loads of 6-10 N, the composite coating suffers from slight wear and the wear mass losses are between 0.7 mg and 1.2 mg. As the load exceeds 10 N, the mass wear loss increases to 2.7 mg, indicating severe wear of the composite coating.

Fig. 14 SEM image showing worn surface morphology (a) and EDAX spectrum (b) of NiCrBSi-0.5Y₂O₃ composite coating under load of 6 N

The worn surface of the NiCrBSi-0.5Y₂O₃ composite coating under the load of 6 N is shown in Fig. 14 with its EDAX spectrum. It can be observed that some slight micro-cutting grooves develop on the worn surface accompanied with a little oxide (Fig. 14(a)). The plough action of the wear debris is slight at low load due to the small depth of indention of the wear debris. The worn surface is composed of 4.96O, 3.44Si, 17.55Cr, 6.92Fe and 67.13Ni (Fig. 14(b)). It can be found that element O is much less under load of 6 N than at the load of 10 N (9.17%), which indicates less oxide at low load than at high load. This is because the friction oxidation reaction caused by friction heat is reduced at a low load. The wear mechanisms of the NiCrBSi-Y₂O₃ composite coating at a low load are adhesive wear and slight micro-cutting wear.

Figure 15 shows the worn surface and EDAX spectrum of the NiCrBSi-0.5Y₂O₃ composite coating at high load of 12 N. The worn surface is covered by the oxide film with the chemical composition of 1.51C, 11.23O, 3.70Si, 16.94Cr, 6.89Fe and 59.73Ni. The worn surface is severely oxidized with O content of 11.23% due to the severe friction heat in the shear process as a result of high contact stress at high loads. In addition, many plough grooves can be found in Fig. 15(a), indicating severe micro-cutting wear of the composite coating at high loads. It shows that the main wear mechanisms of the NiCrBSi-0.5Y₂O₃ composite coatings at high loads are adhesive wear and severe micro-cutting wear.

Fig. 15 SEM image showing worn surface morphology (a) and EDAX spectrum (b) of NiCrBSi-0.5Y₂O₃ composite coating under load of 12 N

4 Conclusions

1) The plasma sprayed NiCrBSi-Y₂O₃ composite coatings are mainly composed of γ-Ni, CrB, Cr₇C₃ and Y₂O₃. With addition of Y₂O₃, hard phases such as CrB, Cr₇C₃ emerge in the composite coating, the density of the composite coatings also increases. The porosity of the NiCrBSi-Y₂O₃ composite coatings is less than 1%, much less than that of the pure NiCrBSi coating. The microhardness of the NiCrBSi-0.5Y₂O₃ composite coatings is about 1.2 times that of the pure NiCrBSi coating.

2) The NiCrBSi-0.5Y₂O₃ composite coating presents excellent tribological properties, whose friction coefficient is 0.175, 37% of the pure NiCrBSi coating. The wear mass loss of the composite coating is 1.2 mg, which is reduced by 43% compared with the pure NiCrBSi coating. The decreased friction coefficient of the composite coating can be attributed to the solid lubrication effect of the oxide film on the worn surface. At the loads of 6-10 N, the composite coating suffers from slight wear and the wear mechanisms are mainly adhesive wear accompany with slight micro-cutting wear and micro-fracture wear. As the load increases to 12 N, the wear of the composite coating becomes severe and the wear mechanisms are adhesive wear and severe micro-cutting wear.

References

[1]  I, CADENAS M,  B A, FELGUEROSO D. Microstructural study of NiCrBSi coatings obtained by different processes [J]. Wear, 2007, 263(1-6): 619-624.

[2] LIU Sheng-lin, ZHENG Xue-ping, GENG Gang-qiang. Dry sliding wear behavior and corrosion resistance of NiCrBSi coating deposited by activated combustion-high velocity air fuel spray process [J]. Materials and Design, 2010, 31(2): 913-917.

[3] PAN Jiao-liang, WANG Yin-zhen, LI Fang-po, GAO Hai-jun. Effect of MoS₂ coated with nickel on tribological properties of Ni-based coating [J]. Tribology, 2008, 28(3): 225-229. (in Chinese)

[4] CAI Bin, TAN Ye-fa, TU Yi-qiang, WANG Xiao-long, XU Ting. Effects of graphite content on microstructure and tribological properties of graphite/TiC/Ni-base alloy composite coatings [J]. Transactions of Nonferrous Metals Society of China, 2011, 21(8): 1741-1749.

[5] WANG Xin-hong, ZHANG Min, ZOU Zeng-da, QU Shi-yao. Microstructure and properties of laser clad TiCp/Ni-based alloys composite coating [J]. Chinese Journal of Mechanical Engineering, 2003, 39(2): 37-41. (in Chinese)

[6] ZHANG Shi-hong, LI Ming-xi, YOON J H, CHU T Y. Characterization on the coatings of Ni-base alloy with nano- and micron-size Sm₂O₃ addition prepared by laser deposition [J]. Materials Chemistry and Physics, 2008, 112(2): 668-674.

[7] WANG Hong-yu, XU Xiao-jing, CHEN Kang-min, ZHANG Xue-feng, LIU Xi. Effect of La₂O₃ on microstructure and properties of Ni-based spray-welding coating on titanium alloys substrate [J]. Journal of the Chinese Rare Earth Society, 2005, 23(3): 339-344. (in Chinese)

[8] LI An-min, XU Bo-fan, PAN Ying-jun. Effects of La₂O₃ on microstructure and property of TiC/Ni-based composite coating [J]. Journal of Iron and Steel Research, 2003, 15(1): 57-61. (in Chinese)

[9] SHARMA S P, DWIVEDI D K, JAIN P K. Effect of La₂O₃ addition on the microstructure, hardness and abrasive wear behavior of flame sprayed Ni based coatings [J]. Wear, 2009, 267(2): 853-859.

[10] LI Jian-liang, XIONG Dang-sheng, HUANG Zhong-jia, KONG Jian, DAI Ji-hui. Effect of Ag and CeO₂ on friction and wear properties of Ni-base composite at high temperature [J]. Wear, 2008, 267(1): 576-584.

[11] ZHANG Zhen-yu, WANG Zhi-ping, LIANG Bu-nü. Microstructure and dry-sliding wear behavior of thermal sprayed and fused Ni-based coatings with the addition of La₂O₃ [J]. Tribology Letters, 2010, 37(2): 141-148.

[12] HAN Bao-lei, LU Xin-chun. Tribological and anti-corrosion properties of Ni-W-CeO₂ coatings against molten glass [J]. Surface & Coatings Technology, 2008, 202(14): 3251-3256.

[13] HUANG Jin-liang, TIAN Bao-hong, CHANG Lian-zhi. Effect of rare earth CeO₂ on the microstructure and tribological properties of laser remelted NiCrBSi-WC alloy coating [J]. Hot Working Technology, 1999(4): 3-6. (in Chinese)

[14] DAI Da-huang, ZHOU Ke-song, YUAN Zhen-hai. Surface technology science of modern materials [M]. Beijing: Metallurgical Industry Press, 2004. (in Chinese)

[15] KANG Rui-quan, LIU Wen-jin, MA Ming-xing, ZHONG Min-lin, ZHANG Wei-ming, ZHANG Hong-jun. The Effect of rare earth oxides oil particles distribution in laser cladding particles reinforced Ni-base composite coatings [J]. Applied Laser, 2009, 29(5): 374-378. (in Chinese)

[16] YANG Qing-xiang, ZHAO Yan-hui, LI Yan-li, YAO Mei. Thermodynamics of modifying effect of rare earth oxide on inclusions in hardfacing metal of medium-high carbon steel [J]. Journal of Rare Metals, 2002, 20(4): 291-294.

[17] LIU Guang-hua. Rare earth materials and their application technology [M]. Beijing: Chemistry Industry Press, 2005. (in Chinese)

[18] PAN Xiao-lin, SUN Wen-ru, YANG Shlin, GUO Shou-ren, LI Zhan, YANG Hong-cai, HU Zhuang-qi. Solidification and segregation behavior of GH742y alloy [J]. The Chinese Journal of Nonferrous Metals, 2008, 18(12): 2158-2165. (in Chinese)

[19] ZHOU Yong-jun, ZHANG Guo-ying. Study on electronic theory of the interaction between rare earth elements and impurities at grain boundaries in Ni-base superalloy [J]. Rare Metal Materials and Engineering, 2007, 36(12): 2160-2162. (in Chinese)

[20] WU Jian-jun, CAO Xiao-ming, WEN Ming. Modern technology of metallic thermal spray [M]. Beijing: Chemistry Industry Press, 2007. (in Chinese)

[21] LIU Xiu-bo, YU Rong-li. Effects of La₂O₃ on microstructure and wear properties of laser clad γ/Cr₇C₃/TiC composite coatings on TiAl intermatallic alloy [J]. Materials Chemistry and Physics, 2007, 101 (2-3): 448-454.

NiCrBSi-Y₂O₃复合涂层的摩擦学行为与机理

蔡 滨，谭业发，谭 华，敬奇锋，张中威

解放军理工大学 野战工程学院，南京 210007

摘  要：运用等离子喷涂技术在45钢表面制备了NiCrBSi-Y₂O₃复合涂层，研究了其微观组织和摩擦学性能。结果表明：等离子喷涂NiCrBSi-Y₂O₃复合涂层主要由γ-Ni、CrB、Cr₇C₃和Y₂O₃等物相组成。在复合涂层中添加适量的Y₂O₃可增加CrB和Cr₇C₃等硬质相的含量，并提高复合涂层的致密度。当Y₂O₃含量(质量分数)为0.5%时，NiCrBSi-Y₂O₃复合涂层具有优异的摩擦学性能，其摩擦因数为0.175，仅为纯NiCrBSi涂层的37%；其磨损质量为1.2 mg，比纯NiCrBSi涂层的降低了43%。当载荷为6~10 N时，NiCrBSi-Y₂O₃复合涂层呈轻微磨损，其磨损机理主要为粘着磨损，并伴有轻微的微观切削和微观断裂磨损；当载荷达到12 N时，复合涂层产生严重磨损，其磨损机制转变为粘着磨损和严重的微观切削磨损。

关键词：等离子喷涂；复合涂层；NiCrBSi；Y₂O₃；摩擦；磨损

(Edited by Hua YANG)

Corresponding author: Ye-fa TAN; Tel: +86-25-80821055; E-mail: tanyefa7651@163.com

DOI: 10.1016/S1003-6326(13)62689-8