J. Cent. South Univ. (2020) 27: 311-324
DOI: https://doi.org/10.1007/s11771-020-4297-y
Wear map for sliding wear behavior of Cu-15Ni-8Sn alloy against bearing steel under oil-lubricated condition
CHENG Jin-juan(成金娟)1, GAN Xue-ping(甘雪萍)1, LI Zhou(李周)2,LEI Qian(雷前)1, ZHOU Ke-chao(周科朝)1
1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China;
2. School of Materials Science and Engineering, Central South University, Changsha 410083, China
Central South University Press and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract:
Wear behaviors of a peak-aged Cu-15Ni-8Sn alloy fabricated by powder metallurgy were investigated. The results indicated that the friction coefficients and the wear rates of Cu-15Ni-8Sn alloy within a normal load range of 50-700 N and a sliding speed range of 0.05-2.58 m/s were less than 0.14 and 2.8×10-6 mm3/mm, respectively. Stribeck-like curve and wear map were developed to describe the oil-lubrication mechanism and wear behavior. The equation of the dividing line between zones of safe and unsafe wear life was determined. Lubricating oil was squeezed into micro-cracks under severe wear conditions. In addition, the lubricating oil reacted with Cu-15Ni-8Sn alloy to generate the corresponding sulfides, which hindered the repair of micro-cracks, promoted cracks growth, and led to delamination. This work has established guidelines for the application of the Cu-15Ni-8Sn alloy under oil-lubricated conditions through developing wear map.
Key words:
Cu-15Ni-8Sn alloy; oil lubrication; wear behavior; wear map；
Cite this article as:
CHENG Jin-juan, GAN Xue-ping, LI Zhou, LEI Qian, ZHOU Ke-chao. Wear map for sliding wear behavior of Cu-15Ni-8Sn alloy against bearing steel under oil-lubricated condition [J]. Journal of Central South University, 2020, 27(2): 311-324.
DOI:https://dx.doi.org/https://doi.org/10.1007/s11771-020-4297-y1 Introduction
Cu-Ni-Sn alloys have gained widespread attentions since 1970s since they were fabricated by Bell Telephone Laboratory. The mechanical and wear-resistant properties of Cu-Ni-Sn alloy are close to those of Cu-Be alloys [1]. Therefore, Cu-Ni-Sn alloys are considered substitutes for Cu-Be alloys in wear materials recently [2]. Cu-Ni-Sn alloys were regarded as a series of bearing material with great application prospects in automotive, aircrafts, drilling and mining equipment and machine tools industries [3, 4]. Lots of studies were conducted on Cu-Ni-Sn alloys, which included designing of alloy composition [5, 6], preparation methods [7], optimization of aging temperature and aging time [8], microstructure evolutions [9-12], and properties [13-16]. The Cu-15Ni-8Sn alloy (C72900) possesses excellent performances after heat treatment, such as high strength and hardness, good wear and corrosion resistance, and it is very suitable to make bearings with high-performance for rollers, aircraft landing gear and heavy duty mobile industrial equipment [17-20].
Wear resistance for a given material is primarily affected by the contact conditions, such as the normal load, the sliding speed, the contact medium, and the electrical simulation [21]. Wear map is an effective approach to study the wear resistance of materials under various operating conditions. WILSON and ALPAS [22] have established wear maps for metal matrix composites in dry sliding contact against SAE (AISI) 52100 bearing steel, RASOOL and STACK for TiC composite based coatings deposited on 303 stainless steel in dry sliding contact against alumina [23], and so on [24-26]. Wear maps based on sliding speed, normal load, friction coefficient and wear rate can intuitively show the type and severity of friction or wear for a wide range of operating conditions. They can be used as design guidelines for the use of materials in different industrial applications.
Simulation of operating conditions is an important topic in the design and application of the tribo-tests for friction and wear assessment and material, which includes simulative tribo-testing, material and lubricant medium selection [27]. The operating conditions of Cu-15Ni-8Sn alloy were simulated as a kind of high-speed and heavy-duty diesel engine sliding bearing used in large vehicles and mining equipment. According to Refs. [18, 20], peak-aged Cu-15Ni-8Sn alloy would possess good wear resistance.
In this work, the Cu-15Ni-8Sn alloy fabricated by powder metallurgy and hot extrusion is selected as the investigation subject, and then treated with peak-aging. CD5W-40 engine oil (Sinopec Lubricant Co., Ltd., China) can be used not only in automobiles but also in mining equipment, so it is selected as lubricant medium. Wear tests for the peak-aged Cu-15Ni-8Sn alloy against GCr15 bearing steel under oil lubrication were performed using a block-on-ring tester, varying normal load (50-700 N) and sliding speed (0.05-2.58 m/s) condition. The goal is to investigate its wear behavior through developing corresponding wear regime and wear mechanism map. The dividing line between zones of safe and unsafe wear life is also discussed.
2 Experimental procedures
Cu-15Ni-8Sn-0.21Nb alloy powders (15.1 Ni, 8.04 Sn, 0.21 Nb, and the balance copper in wt. %; detected by ICP-OES) with the particle size less than 150 μm were prepared using gas (N2) atomization method. Cu-15Ni-8Sn alloy rod was fabricated by hot isostatic pressing (HIP) at 850 °C and 150 MPa for 1.5 h, followed by furnace cooling. The dimensions of the alloy rods after removing the wrap were d123 mm×190 mm. The alloy rods were solid solution-treated at 850 °C for 2 h and then hot-extruded at 850 °C using backward extrusion method with an extrusion speed of 30 mm/s and an extrusion ratio of 15:1. The as-extruded alloy was solid solution-treated at 850 °C for 1 h in H2 atmosphere and rapidly quenched in water. The solid solution-treated samples were aged at 400 °C under H2 atmosphere for different periods of time and then quenched in water quickly. The hardness of the aged sample was measured using a MicroMet 5104 tester (BUEHLER, USA) to determine the optimum hardness value of the alloy. The hardness of the alloy aged for different periods of time is listed in Table 1. The hardness values were derived from the average of 10 times random measurements. The wear behaviors of the alloy aged at 400 °C for 60 min were investigated in detail.
Table 1 Hardness of Cu-15Ni-8Sn alloy aged for different periods of time at 400 °C
Wear tests were carried out under oil lubrication condition at room temperature, using a block-on-ring tester (MRH-1, Yihua Tribology Testing Technology Co., Ltd., China), within a normal load range of 50-700 N, a sliding speed range of 0.05-2.58 m/s (20-1000 r/min) and a constant friction time of 60 min. The representative schematic of the test configuration is shown in Figure 1. The peak-aged Cu-15Ni-8Sn alloy strip was cut into blocks of 12.30 mm×12.30 mm×19.05 mm using wire electrical discharge machine. Wear specimens were prepared by grinding on SiC abrasive paper, followed by polishing with diamond paste. GCr15 bearing steel (HV 746) with an outer diameter of 49.22 mm was used as counterface rings. The GCr15 bearing steel ring always contacted with lubricating oil during wear test. Prior to weighing and testing, specimens and rings were cleaned in acetone for 15 min. An analytical balance with accuracy of 0.01 mg was used to evaluate mass loss of specimens. The friction coefficient was continually recorded during the test and the average friction coefficient was calculated for each test within 60 min. The wear rate was calculated by an equation of w=△m/ρL, where w is the wear rate (mm3/mm), △m is the wear mass loss (g), ρ is the density of the specimen (g/cm3) and L is the total sliding distance (m). Each test was repeated five times, and the average of tests was reported.
Figure 1 Schematic of friction pairs
The peak-aged samples were examined using transmission electron microscope (TEM, JEM-2100F, JEOL, Japan). TEM samples were prepared by mechanical polishing coupons to a thickness of 60 μm. Then thin foils with 3 mm in diameter were punched from the coupons. Finally, the thin foils were thinned using dual-jet electro-polishing with a mixture of 30% HNO3 and 70% methanol. The temperature of electro- polishing was (-34±2) °C and the work voltage was 6-8 V. The phases in the alloy were determined by X-ray diffraction (XRD, TTRIII, Rigaku, Japan) using a Cu Kα radiation. A 2θ scanning rate was 4°/min and a distribution was 10°-110°.
The peak-aged sample, worn surface and worn cross-section were studied with scanning electron microscope (SEM, FEI, USA) equipped with an energy dispersive X-ray spectrometer (EDS). In order to observe the grain boundaries and precipitates, the peak-aged sample was etched using a mixture solution consisting of 100 mL ethanol,5 g FeCl3 and 25 mL HCl solution. Wear debris was analyzed with transmission electron microscope. The chemical states of the elements on worn tracks were examined by X-ray photoelectron spectroscopy (XPS-Escalab210). The XPS analysis used Al Kα radiation as the excitation source, and the binding energy of contaminated carbon (C 1s=284.8 eV) was used as a reference.
3 Results and discussion
3.1 Microstructure of peak-aged Cu-15Ni-8Sn alloy
SEM and bright-field (BF) TEM images and the corresponding selected-area diffraction patterns (SAED) of the peak-aged Cu-15Ni-8Sn alloy are shown in Figure 2. According to the schematic [100] zone diffraction pattern provided by ZHAO and NOTIS [10], L12 and DO22 diffraction spots were detected in the SAED pattern, indicating the presence of the ordered L12 and DO22 phases in the alloy. Cellular precipitates (discontinuous γ DO3 phase) along grain boundaries can be also captured in the alloy.
Figure 3 shows an X-ray diffraction pattern of the peak-aged Cu-15Ni-8Sn alloy. The peaks located at 43.107°, 50.363°, 73.946°, 89.970° and 95.261° were associated with the planes of (111), (200), (220), (311) and (222) in α-Cu (PDF card 04-0836), respectively. These peaks located at 25.949°, 29.858°, 42.732° and 78.253° were associated with the planes of (111), (200), (220) and (422) in γ phase [12], respectively. γ is an ordered DO3 phase (Fm-3m) with (CuxNi1-x)3Sn composition phases.
3.2 Effects of sliding speed and normal load on friction coefficient
To depict the stability (i.e., the change in amplitude of friction coefficient with sliding time) of friction behavior, the friction coefficient curves of Cu-15Ni-8Sn alloy at the smallest, middle and largest sliding speed under different normal loads, respectively, are presented in Figure 4. The figures show that the friction behavior of Cu-15Ni-8Sn alloy under different friction conditions was stable after running-in period. This could be related to the lubrication and wear regime of the alloy, which would be analyzed in more detail later. It can be observed that the wear test lasted for about 6 min under a normal load of 700 N and a sliding speed of 2.32 m/s condition was forced to stop because the instantaneous frictional torque reached the maximum friction torque of the wear tester (4000 N·m). The friction and wear behavior of the alloy under this case was not investigated.
Figure 2 SEM (a, b) and TEM (c) images of peak-aged Cu-15Ni-8Sn alloy and corresponding SAED pattern along [100] crystal zone axis (d)
Figure 3 XRD pattern of peak-aged Cu-15Ni-8Sn alloy
Figure 5 shows the average friction coefficients of the Cu-15Ni-8Sn alloy with different loads and sliding speeds under oil-lubricated condition. Both at 50 N and 100 N, the friction coefficients decreased initially with the increase of sliding speed and then increased slowly when the sliding speed reached 1.8 m/s. When the load was larger than 148 N obtained by mathematical method, the friction coefficient decreased with the increase of the sliding speed. The friction coefficient exhibited increasing trend with increasing normal load irrespective of sliding speed.
Friction behavior under oil-lubricated condition depends upon a complex relationship between interacting surfaces together with the lubricant. It can be explained using the Stribeck curve [28]. The variation of friction coefficient of the peak-aged Cu-15Ni-8Sn alloy in oil, μ, versus S0 is shown in Figure 6, where S0 is the Sommerfeld number (S0=ηv/P) [29, 30]. The relationship between friction coefficient and Sommerfeld number was almost parabola, which could be expressed as follows:
μ=Α+Β(ηv/P)+C(ηv/P)2 (1)
where μ is friction coefficient; η is dynamic viscosity of this kind of oil (20 °C: 0.15 Pa·s, detected by rheology); P is normal load in N; v is sliding speed in m/s; A, B, and C are constants that could be calculated from experimental data. By non-linear fitting, values of A, B, and C were obtained as 0.1115, -4.7×10-3 and 4.957×10-5, respectively. According to friction theory [28], with an increase in Sommerfeld number, the lubrication regime changed from boundary lubrication (BL) to mixed lubrication (ML) which contained both BL and fluid lubrication (FL), then changed from ML to FL. In BL, the friction coefficient is between 0.1 and 0.15 [31]. The boundary between ML and FL is determined by above non-liner fitting, S0=47.41× 10-4.
Figure 4 Friction coefficient curves of Cu-15Ni-8Sn alloy under different friction conditions:
Figure 5 Effect of normal load on friction coefficient at various sliding speed
Figure 6 Friction coefficient of Cu-15Ni-8Sn alloy as function of ηv/P
The relationship between friction coefficient and Sommerfeld number is related to the characteristics of lubrication film between friction pairs. The Sommerfeld number is lower, the spacing between friction pairs is smaller, the lubrication film is more easily broken, and the direct solid- solid contact is more easily established, so the friction coefficient is increased and the lubrication regime is BL [28]. With the increase in Sommerfeld number, the oil lubrication film is more unbroken, the friction coefficient decreases and the lubrication regime would change from BL to ML or FL. The lubrication regime for the Cu-15Ni-8Sn alloy sliding against GCr15 bearing steel under oil-lubricated condition is shown in Figure 6.
3.3 Effects of sliding speed and normal load on wear rate
Figure 7 shows the effects of sliding speed and normal load on wear rate of the Cu-15Ni-8Sn alloy sliding against GCr15 bearing steel under oil-lubricated condition. The wear rate decreased with the increase of sliding speed; furthermore, the wear rate at 0.05 m/s was almost one order of magnitude larger than that at 2.58 m/s under the normal load of 50-500 N. As the normal load increased, the wear rate also increased. The wear rate at 700 N is one order of magnitude larger than that at 50 N at the same sliding speed. It could be explained detailedly as follows. First, both the real contact area and embedded depth increase as the normal load increases, causing the increase of adhesive wear. Second, the plastic deformation work would increase due to the increase of normal load, so that the surface damage is more serious, resulting in accelerating the wear.
Figure 7 Effect of sliding speed on wear rate at various normal loads
Figure 7 shows that the wear rate of the Cu-15Ni-8Sn alloy varied approximately from 1.2×10-8 to 2.767×10-6 mm3/mm, which might imply the transition of wear regime. A wear regime map is important to present the correlation among wear regime, wear rate, normal load, and sliding speed. In general, boundaries between wear regimes were determined by the sudden change in wear rate of at least one order of magnitude [32-34]. It was generally considered that the boundary between mild and severe wear regime was w=10-6 mm3/mm [29]. For smaller w values, wear was mild. For larger w values, wear was severe. On the basis of the obtained wear rate data from experiments, the different wear regimes were identified as ultra-mild wear (w≤10-7 mm3/mm), mild wear (10-7
P=C1+C2v (2)
where P is the transition normal load; v is the transition sliding speed; C1 and C2 are constant. According to the experimental data, C1 and C2 are 303.83 and 316.41, respectively. The establishment of the boundary equation could help us to select appropriate test parameters in applications.
Figure 8 Wear map for sliding wear of a peak-aged Cu-15Ni-8Sn alloy against GCr15 bearing steel under oil-lubricated condition
3.4 Wear mechanism
Figure 9 shows SEM images and the corresponding EDS spectra of worn tracks for the peak-aged Cu-15Ni-8Sn alloy under different friction conditions. More complex information on the wear behavior of the alloy could be derived from Figure 9. The wear mechanisms of the Cu-15Ni-8Sn alloy sliding against GCr15 bearing steel in lubricating oil under ultra-mild wear, mild wear and severe wear conditions were further studied by analyzing the characterization of worn surface, worn sub-surface and wear debris.
Under ultra-mild wear condition, that is, low normal load and high sliding speed, such as 100 N and 1.8 m/s, the worn surface was smooth, and some micro-ploughings were observed in a direction parallel to the sliding direction, indicating that the alloy was subjected to slight wear. The oil was spread onto the worn surface to form a continuous and thick lubrication film, which effectively prevents solid-solid contact. The frictional heat increased rapidly with increase in sliding time at high sliding speed to cause the decrease of viscosity of lubricating oil, thus the lubrication film is hard to be damaged under low normal load condition. The lubrication film between friction pairs is still continuous, which could reduce the interaction between asperities, protecting worn surface and decreasing wear extent. As Cu alloys have a strong tendency to be oxidized [35, 36], the oxygen element which came from atmosphere was detected under different wear regime conditions, which indicated that the sample was suffered oxidative wear. Thus, the main wear mechanism in ultra-mild wear regime was the combination of micro-ploughing and oxidative wear.
Under mild wear condition, such as the normal load of 300 N and sliding speed of 0.78 m/s, some pits and deep grooves could be observed on the worn surface, as shown in Figure 9. The gap between friction pairs decreased with increase in normal load, and friction between asperities is easy to occur. What is more, the embedded depth of hard asperities increased as normal load increased, leading to the appearance of deep grooves. The viscosity of the lubricating oil would lower with increase in sliding time owing to the generation of frictional heat, resulting in thin lubrication film. Wear debris generated by rubbing and micro-cutting of hard asperities might be adhered to lubrication film to form new abrasive particles, causing the further abrasive wear. Under high normal load condition, the worn surface would undergo plastic deformation when the asperity from the Cu-15Ni- 8Sn alloy was suffered pressure larger than its yield strength, the real contact surface would be increased to bear the external load. The lubrication film might be broken and some cold- welding points formed. The formed cold-welding points would be cut off and some pits were left on the worn surface during friction. In general, groove, and pit were considered the direct evidence of abrasive wear and adhesive wear, respectively.
Figure 9 SEM images and corresponding EDS spectra of worn tracks for peak-aged Cu-15Ni-8Sn alloy under different friction conditions:
In severe wear regime, such as 500 N and 0.26 m/s, the worn surface was much rougher than that in mild wear regime, as shown in Figure 9. What is more, delamination appeared on the worn surface in addition to grooves, which indicated that the alloy is subjected to serious damage. Figures 10 and 11 show SEM images of worn cross-section and wear debris under mild wear and severe wear conditions, respectively. Non-peeling flake wear debris on the worn cross-section and flake debris could be found when the normal load was 500 N and sliding speed was 0.26 m/s, which once again confirmed the existence of delamination wear. It could be explained from the following aspects. First, the lubricating oil is very difficult to spread on the worn surface when the sliding speed is very low. On the other hand, the temperature, friction force and contact pressure between contact surfaces would increase due to high normal load, such as 500 N or 700 N, which made the formed lubrication film be easily destroyed, leading to solid-solid contact.
Figure 10 SEM images of worn cross-section under different friction conditions:
Figure 11 SEM images of wear debris under different friction conditions:
Second, when the hard asperities mainly come from the hard surface of GCr15 bearing steel repeatedly slid on the soft surface of the Cu-15Ni-8Sn alloy under relatively high normal load condition, dislocation easily accumulated in the sub-surface of the soft alloy and micro-cracks might be initiated at defects in the region of the maximum of inner stress. The micro-cracks extended and chipped off along sliding direction due to high shear stress, leading to the generation of flake wear debris. What is more, according to friction theory [28], the lubricating oil would be easily squeezed into the micro-cracks under high normal load condition and impact the crack wall. The coupling effect of the contact surface might seal the crack, which would further increase the lubricating oil pressure inside the cracks and cause the cracks extension rapidly. The spalling of a small piece of the metal occurs under high normal load condition when the crack extends to the surface or the root of the small piece of the alloy. The schematic diagram of this delamination wear mechanism is illustrated in Figure 12. According to EDS spectra, as shown in Figure 9, the S element might come from lubricating oil, which indicated that chemical interactions between lubricating oil and friction pairs might occur.
TEM was employed to investigate the wear debris obtained under different wear regime conditions, as shown in Figure 13. The existence of CuS phase, Fe2O3 phase, and CuO phase could be revealed when the normal load was 500 N and the sliding speed was 0.26 m/s, indicating the occurrence of sulfidation reaction. It should be emphasized that none of the phases observed was pure phase. For instance, the CuO phase was not pure CuO, but rather a (Cu, Ni, Sn)O oxide [15, 19]. The Fe2O3 phase was a (Fe, Cr)2O3 oxide. The CuS phase was a (Cu, Ni, Sn, Fe)S sulfide as well.
Figure 12 Schematic diagram of delamination wear resulting from lubricating oil effect under severe wear condition:
X-ray photoelectron spectroscopy (XPS) analysis was performed on the worn track ofCu-15Ni-8Sn alloy sliding against GCr15 bearing steel in lubricating oil under mild wear and severe wear conditions. The full XPS spectra curves and spectra of Cu 2p, Ni 2p, Sn 3d, O 1s and S 2p of specimens on the worn tracks by XPS peak-fitting method (XPS Peak Fit V4.1 software) are shown in Figures 14 and 15, respectively. CuS, NiS, SnS and FeS2 were detected by peak-fitting method in the worn track under 500 N and 0.26 m/s condition, besides CuO, Cu2O, Ni2O3, NiO, Sn and SnO2. Based on the results of TEM and XPS analyses, it could be ascertained that the penetrated lubricating oil remained into micro-cracks and reacted with the alloy to form corresponding sulfides. The formed sulfides inside the cracks would prevent the repair of cracks, which could lead to the cracks propagation and produce delamination wear [37]. The schematic diagram of this mechanism is given in Figure 12(b). Owing to the existence of sulfides, it could be confirmed that there was corrosive wear in the Cu-15Ni-8Sn alloy under severe wear condition, which would increase wear. Therefore, the dominant wear mechanisms in severe wear regime included abrasive wear, oxidative wear, corrosive wear, and delamination.
The predominant wear mechanisms and lubrication regime in ultra-mild wear, mild wear and severe wear were summarized as follows:micro-ploughing and oxidative wear, fluid lubrication; abrasive wear, adhesive wear andoxidative wear, mixed lubrication; abrasive wear, oxidative wear, corrosive wear and delamination, boundary lubrication.
Figure 13 Bright field TEM images of wear debris under different friction conditions and corresponding EDS spectra and SAED pattern:
Figure 14 Full XPS spectra of blocks on worn track under different conditions
4 Conclusions
In this work, a wear mechanism map for the oil-lubricated sliding of a peak-aged Cu-15Ni-8Sn alloy against bearing steel was developed. Following conclusions could be drawn:
1) With increase of the sliding speed, the friction coefficient tends to decline firstly and then increase when the normal load is 50 N and 100 N.When the normal load exceeds 148 N, the friction coefficient reduces as the sliding speed increases. Wear rate of Cu-15Ni-8Sn alloy increases with the increase of normal load but decreases with increase in sliding speed.
Figure 15 Spectra of Cu 2p, Ni 2p, Sn 3d, O 1s and S 2p of specimens on worn track under different friction conditions by XPS peak-fitting method
2) Wear map of the peak-aged Cu-15Ni-8Sn alloy against bearing steel under oil-lubricated condition was constructed using the axes of normal load and sliding speed, where three different characteristic wear regimes were clearly identified such as ultra-mild wear (safe zone), mild wear (safe zone) and severe wear (unsafe zone).
3) The dominant wear mechanisms in different wear regimes were determined by the characterization of worn surface, worn sub-surface and wear debris. The wear mechanisms in ultra-mild wear included micro-ploughing and oxidative wear. Abrasive wear, adhesive wear and oxidative wear occurred in the mild wear regime, and abrasive wear, delamination, corrosive wear and oxidative wear were involved in the severe wear regime.
4) Under severe wear regime, chemical reaction between oil and the alloy occurs and generates the corresponding sulfides. The presence of sulfides in the crack will hinder the repair of the micro-crack and force its growth, accelerating the delamination wear of Cu-15Ni-8Sn alloy.
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(Edited by YANG Hua)
中文导读
Cu-15Ni-8Sn合金在油润滑条件下与轴承钢滑动磨损行为的磨损图
摘要：本文研究了粉末冶金法制备的峰时效态Cu-15Ni-8Sn合金的磨损行为。结果表明：Cu-15Ni-8Sn合金在50~700 N的载荷和0.05~2.58 m/s的滑动速度下进行摩擦磨损试验时，其平均摩擦系数均小于0.14、磨损率均小于2.8×10-6 mm3/mm。通过绘制Stribeck-like曲线分析了润滑油的润滑机理。为了研究合金的磨损行为，研制了磨损图。此外，还确定了安全磨损与严重磨损区域的分界线。在严重磨损条件下，润滑油被挤压进入表面微裂纹，在裂纹壁上发生化学反应，生成相应的硫化物，阻止裂纹修复，促进裂纹扩展，导致剥层。通过研制磨损图，为Cu-15Ni-8Sn合金在油润滑条件下的应用提供了指导。
关键词：Cu-15Ni-8Sn合金；油润滑；磨损行为；磨损图
Foundation item: Projects(2017YFB0306105, 2018YFE0306100) supported by the National Key Research and Development Program of China
Received date: 2019-07-03; Accepted date: 2019-09-17
Corresponding author: GAN Xue-ping, PhD, Professor; Tel/Fax: +86-731-88836303; E-mail: ganxueping@csu.edu.cn; ORCID: 0000- 0001-8096-8799; LEI Qian, PhD, Associated Professor; Tel/Fax: +86-731-88830264; E-mail: leiqian@csu.edu. cn; ORCID: 0000-0002-5160-749X
Abstract: Wear behaviors of a peak-aged Cu-15Ni-8Sn alloy fabricated by powder metallurgy were investigated. The results indicated that the friction coefficients and the wear rates of Cu-15Ni-8Sn alloy within a normal load range of 50-700 N and a sliding speed range of 0.05-2.58 m/s were less than 0.14 and 2.8×10-6 mm3/mm, respectively. Stribeck-like curve and wear map were developed to describe the oil-lubrication mechanism and wear behavior. The equation of the dividing line between zones of safe and unsafe wear life was determined. Lubricating oil was squeezed into micro-cracks under severe wear conditions. In addition, the lubricating oil reacted with Cu-15Ni-8Sn alloy to generate the corresponding sulfides, which hindered the repair of micro-cracks, promoted cracks growth, and led to delamination. This work has established guidelines for the application of the Cu-15Ni-8Sn alloy under oil-lubricated conditions through developing wear map.
