Investigation on the lubrication performance of different carbon nanofluids for titanium alloy

Investigation on the lubrication performance of different carbon nanofluids for titanium alloy | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Investigation on the lubrication performance of different carbon nanofluids for titanium alloy Ye Yang, Hao Luan, Yaru Tian, Lina Si, Hongjuan Yan, Fengbin Liu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4001746/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Titanium alloys are difficult to machine and have poor tribological properties. This paper investigated the lubricating performance of different carbon nanoparticles in water-based lubrication for titanium alloys. The lubricating performance of four kinds of carbon nanofluids on titanium alloys were tested and the results showed that single-layer graphene had the smallest COF and wear volume. The interaction between nanoparticles and debris was an important factor that influenced the lubrication performance of nanoparticles for titanium alloy. The effect of length on the lubricating property of multi-walled carbon nanotubes (MWCNTs) was investigated. It was found that the shorter the length of the MWCNTs, the lower their friction coefficient and wear volume. Moreover, the hybrid nanofluid with graphene and spherical graphite in a ratio of 1:2 achieved a balance between lubricating performance and price, making it the optimal choice. The mechanisms of these nanoparticles were analyzed and the interaction between nanoparticles and debris was evaluated. carbon nanofluids water-based lubrication titanium alloy hybrid nanofluids Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 1 Introduction Titanium alloys are difficult to machine materials due to their low thermal conductivity, low elastic modulus, and high chemical reactivity. The resulting high cutting temperature and severe built-up edge formation during machining often lead to excessive tool wear and poor surface quality [1] . Traditional lubricants such as mineral oil, vegetable oil, and grease have proven ineffective in adequately lubricating titanium alloys [2] . Therefore, there is a pressing need to explore effective water-based lubricants for titanium alloys [3-4] . Castor oil sulfated sodium salt (CSS) solution which has shown potential in reducing friction coefficient and adhesive wear is a promising lubricant for titanium alloys [5] . However, further enhancements are required to optimize the lubricating and cooling performance of CSS solution for more efficient application. The incorporation of nanoparticles with lubricants has emerged as a promising approach, as these nanofluids exhibit excellent frictional properties and high load-carrying capacity. By enhancing thermal conductivity and thermal Brownian motion of nanoparticles, nanofluids have demonstrated significant improvements in heat transfer performance and been applied in metal processing [6] . Carbon-based nanomaterials which have exceptional mechanical, electrical, thermal, optical, and chemical properties, are particularly well-suited for tribological applications [7-10] . Various carbon-based nanomaterials including graphite, graphene, and nanotubes with different shapes and sizes have been extensively investigated about the tribological properties by researchers [11-16] . Graphite could penetrate into the concave zone between the contact surfaces to repair the damage and form a thin layer to separate the rubbing surface, thus friction can be reduced [11] . Mayur used different concentrations of graphite nanoparticles in sunflower oil to evaluate the machinability of chromium nickel iron alloy 625 and found that graphite effectively improved surface quality and tool wear [12] . Compared with graphite, graphene shows outstanding anti-wear characteristics [13] . With single layer structure, it is easier to form a lubricant layer between the rubbing surfaces. Graphene nanoparticles were added to rapeseed oil by Wang’s group and the lubrication and cooling performance were improved for the reason that the length of the chip-adhesion layer was shortened and the adhesion wear was reduced [17] . Wang added graphene nanoparticles to modified lithium-based oil and found that graphene exhibited excellent tribological behavior by providing the lowest coefficient of friction [18] . Due to the unique 1D structure, carbon nanotubes have been used as lubricant additives as well which possess a higher surface energy and tension [10,19, 20] . Under high contact pressure, carbon nanotubes can form nano-bearings between friction pairs which could reduce friction coefficient and wear rate [21] . Different concentrations of multi-walled carbon nanotubes were dispersed into coconut oil By Sarkar [22] . Compared with traditional cutting fluid, the nanofluid has better processing performance than traditional processing in cutting force, tool-tip temperature, and width of flank wear [22] . While most of the researches about nanoparticles are focused on ferrous metal or aluminum alloy, there are limited researches on difficult-to-cut metal such as titanium alloys. Gupta evaluated the performance of Al 2 O 3 , MoS 2 , and graphite nanoparticles in turning Ti alloys and found that graphite exhibited the lowest cutting force, cutting temperature and surface roughness [23] . Singh used graphene-enriched nanofluid in turning of titanium alloy and it was proved that with nanofluid lubrication, the tool life was the highest, the cutting force and the cutting temperature was the lowest [24] . However, these researches are usually investigated single carbon-based nanoparticles. There is lack of comparative study on different kinds of carbon-based nanoparticles used for metal cutting especially for titanium alloys. This paper aims to evaluate the lubrication differences between various carbon nanoparticles in water-based nanofluids for titanium alloys. The lubricating mechanism is further investigated. Finally, a new water-based nanofluid that exhibits excellent lubricity is developed to improve the working performance of cutting fluid for Ti-6Al-4V. 2 Experiment 2.1 Experimental setup and materials Castor oil sulfated sodium salt (CSS) solution was chosen as the lubricating base stock for titanium alloy. To enhance its performance, four types of carbon nanoparticles were incorporated into a 10wt% CSS solution: spherical graphite, flake graphite, graphene, and multi-walled carbon nanotubes (MWCNTs). Frictional tests were conducted in the laboratory using a ball-on-disc device (CFT-I, Licp, Lanzhou, China) to evaluate the lubricating properties of various solution. Figure 1 illustrates the schematic diagram and photograph of the experimental setup. The lower specimen was a Ti-6Al-4V disc with a hardness of HRC 35 and surface roughness (Sa) of less than 40 nm. The chemical composition of the Ti-6Al-4V titanium alloy was detailed in Table 1, while Table 2 presented its mechanical parameters. For machining Ti-6Al-4V, cemented carbide is the recommended tool material [4] . Therefore, the upper specimen was a YG8 (WC-Co) ball with a hardness of 89HRA, a diameter of 10 mm, and a surface roughness (Sa) of 25 nm. Each specimen were ultrasonic cleaned with acetone，ethanol and deionized water for 10 minutes. The upper ball was then reciprocated on the stationary disc with a 5 mm amplitude and a 5 Hz frequency for 10 minutes. Prior to the reciprocating motion, 0.2 mL of lubricant was applied to the disc surface. A normal load of 50 N was exerted, resulting in a maximum Hertz contact pressure of 7.5 GPa. Each experiment was repeated more than three times, and the friction coefficient curves represent the average of the collected data. The relative errors of the friction coefficients were within the range of ±1%. Table 1. Chemical compositions of Ti-6Al-4V titanium alloy (wt.%) N C H Fe O Al V Ti 0.05 0.08 0.015 0.4 0.2 5.5-6.75 3.5-4.5 Remaining Table 2. The mechanical parameters of Ti-6Al-4V titanium alloy Tensile strength (MPa) Yield Strength (MPa) Hardness (VHN) Young’s Modulus (GPa at 20 ◦C) Poisson’s Ratio 1230 1060 315 113.8 0.34 After the completion of the frictional tests, the worn specimens underwent a 30-minute cleaning process with acetone followed by drying. The wear volume was determined using the LEXT™OLS5100 laser scanning confocal microscope (Olympus, Tokyo, Japan). Each test was repeated three times and the average value was calculated. The microtopography of the worn surface was examined using a scanning electron microscope equipped with Energy-dispersive X-ray spectroscopy (FEI, Hillsboro, OR, USA). The chemical compositions of the worn surfaces were analyzed using an X-ray photoelectron spectrometer (XPS, EscaLab 250Xi, TFS, USA). The contact angle was measured using a contact angle meter (JY-82B KRUSS DSA, KRüSS Company, Germany). 2.2 Nanofluids preparation Spherical graphite, flake graphite, graphene and multi-walled carbon nanotubes were selected as nano-additives for lubricating titanium alloys. The microtopography of these four types of nanoparticles was examined through SEM shown in Figure 2. Detailed parameters of these nanoparticles were provided in Table 3. The diameter of spherical graphite is 20 nm. The diameter of flake graphite is about 3-6 μm and the thickness is 40 nm. Graphene has a diameter of 10 μm and a thickness of three carbon atoms. The diameter of multi-walled carbon nanotubes is 50 nm and the length is 10-30 μm. The preparation of nanofluids involved a two-step process to disperse the nanoparticles into the CSS aqueous solution. The nanoparticle fraction used was 1 wt%. Prior to the frictional tests, the mixture underwent 20 minutes of ultrasonic vibration for effective dispersion. Table 3. Properties of the nanoparticles provided by the manufacturer Property spherical graphite flake graphite graphene multi-walled carbon nanotube Purity 99% 99% 99% 99% Average particle size 20nm 3-6μm 10μm 50nm Length/thickness \ 40nm Thickness of three carbon atoms 10-30μm Specific surface area (m 2 /g) 150 400 2600 40 Crystal structure cubic flaky flaky siphonate 3. Results and Discussion 3.1 Lubricating properties of the nanoparticles with different shapes The friction coefficient curves for the four types of nanofluids and a control group (CSS aqueous solution without nanoparticles) were illustrated in Figure 3(a). During the initial running-in period, the friction coefficients of the nanofluids rose to 0.4 before exhibiting fluctuations caused by factors such as lubricating film rupture and adhesive wear. Subsequently, the friction coefficients stabilized at a constant level. Comparative analysis with the control group revealed that all nanofluids were able to reduce friction coefficients at various stages for titanium alloy. The average friction coefficients for spherical graphite, flake graphite, graphene, and multi-walled carbon nanotubes were approximately 0.158, 0.154, 0.130, and 0.175, respectively. In comparison to the control group, these nanofluids demonstrated reductions in friction coefficients of up to 20.2%, 22.2%, 34.3%, and 11.6%. Notably, graphene nanofluid exhibited the lowest friction coefficient, while multi-walled carbon nanotubes displayed the least effective lubrication performance with the highest COF. The worn surfaces of the titanium discs were tested and the wear volume was calculated in Figure 3(b). It can be seen that graphene with single layer structure exhibited best anti-wear property with the smallest wear volume 1.06×10 8 μm 3 which is 44.8% smaller than that of CSS solution without nanoparticles. Spherical graphite can also reduce the wear of titanium alloy effectively with a decrease of 26.6%. While flake graphite and MWCNTs did not show obvious anti-wear effect. The wear volume of flake graphite is almost similar with the control group. MWCNTs even promoted the wear of titanium alloy to some extent with the largest wear volume 1.98×10 8 μm 3 which is slightly higher than the control group. Considering both the friction coefficients and wear lubricated by the four kinds of carbon-based nanofluids, graphene exhibits the best lubrication effect with the smallest COF and wear volume. It is speculated that the single layer structure is more prone to adhere on titanium alloy surface thus forming a lubricative layer. Spherical graphite ranked the second while the tubular carbon nanotubes had the poorest lubrication effect on titanium alloy. Scanning electron microscopy (SEM) was employed to observe the microtopography of the worn titanium discs. As shown in Figure 4(b), adhesive wear and deposition can be observed on the worn surfaces with flake graphite lubrication. The surface lubricated by MWCNTs was slightly better than that of flake graphite. But there was some adhesive wear as well seen from Figure 4(d). By contrast, the surfaces lubricated by spherical graphite and graphene were much smoother without obvious grooves and scratches shown in Figure 4(a) and (c). Generally, smaller friction coefficients and wear result in higher surface quality. When lubricated by graphene, adhesive wear and furrow wear was greatly reduced for the good lubricating condition. Meanwhile, the surface lubricated by spherical graphite was fairly good as well. The size dimension of MWCNTs was different from other nanoparticles, and their poor lubrication performance may be not only due to their shape, but also their length. Therefore, the length needed to be taken into consideration. 3.2 Lubricating properties of MWCNTs with different length In order to further investigate the impact of morphology on nanoparticle’s lubrication performance, three kinds of MWCNTs with different length were selected to detect the effect of length on the lubricating property. The length of MWCNTs ranging from 0.5-2μm is named short，the length 10-30μm is long and the length 40-60μm is the longest. The specific parameters of the nanoparticles were listed in Table 4. Table 4 . Properties of MWCNTs with different length provided by the manufacturer. Property multi-walled carbon nanotube(short) multi-walled carbon nanotube(Long) multi-walled carbon nanotube(Longest) Purity 99% 99% 99% Diameter 50nm 50nm 50nm Length 0.5-2μm 10-30μm 40-60μm Specific surface area (m 2 /g) 40 40 40 Crystal structure siphonate siphonate siphonate The friction coefficient of these MWCNTs were presented in Figure 5(a). The COF of the longest MWCNTs was not stable and obvious fluctuation was observed during the frictional test. To the end of the test, the friction coefficient dropped to 0.185. When lubricated by the long MWCNTs, COF kept stable at 0.179 after the running-in period. The short MWCNTs demonstrated best lubricating property with the smallest COF 0.163. The worn surface of the titanium discs after frictional tests was observed and the wear volume was shown in Figure 5(b). The wear volume lubricated by the short MWCNTs was the smallest, followed by the long MWCNTs and the longest MWCNTs had the biggest wear volume. It can be seen that shorter MWCNTs exhibit better lubricating property. The SEM images of the titanium discs lubricated by different length of MWCNTs were shown in Figure 6. It can be seen that titanium surface lubricated with shorter MWCNTs was smoother with fewer grooves and adhesive wear, indicating better surface quality. As shown in Figure 6 (c), adhesive wear and spalling can be observed, suggesting that longer multi-walled carbon nanotubes often resulted in poorer surface quality. It can be concluded that smaller nanoparticles have a greater advantage in lubricating titanium alloys. However, the lubrication performance of the shortest MWCNTs nanofluid on titanium alloy was still inferior to that of graphene. 3.3 Lubricating properties of hybrid nanofluids The experiments in section 3.1 shows that graphene and spherical graphite exhibit good lubrication performanc e on titanium alloys. In this part, graphene and spherical graphite were mixed forming a hybrid nanofluid to see the mutual effect of the nanoparticles. Compared with single nanofluids, hybrid nanofluids often demonstrate superior lubrication performance [25-28] . The mass fraction of graphene and spherical graphite was denoted by mix(x:y). Seven groups of hybrid nanofluids were prepared to investigate the impacts of the nanoparticles' content ratio. These groups encompassed pure graphene, pure spherical graphite, mix(1:1), mix(1:2), mix(2:1), mix(1:4), and mix(4:1). The friction coefficient curves for seven groups of nanofluids were presented in Figure 7 (a). The friction curve under stable state was shown to be more clearly. The average friction coefficients of various nanofluids were listed in Table 5. It can been that mix(1:2) had lower friction coefficients compared to pure nanofluids. The friction coefficients of all hybrid nanofluids were lower than those of pure spherical graphite. Mix(1:1) and mix(1:2) even had lower friction coefficients than pure graphene in a stable state. In addition, compared with the COF lubricated by single spherical graphite or graphene nanofluid, the fluctuation amplitude of the friction curve of the hybrid nanofluid was also smaller. The wear volume of the titanium disc was shown in Figure 7(b). It can be seen that all the hybrid nanofluids had reduced wear volume to a certain extent compared to pure spherical graphite nanofluids. Similar to the friction coefficient curve, among several hybrid nanofluids, mix(1:1) and mix(1:2) had relatively smaller wear volumes. Compared with the control group, their wear volumes were reduced by 48.2% and 51.8%, respectively. Table 5 . Average friction coefficient of seven nanofluids. Time/Min Pure graphene Mix(4:1) Mix(2:1) Mix(1:1) Mix(1:2) Mix(1:4) Pure spherical graphite 10 wt% CSS Solution 1 0.249 0.253 0.170 0.198 0.184 0.198 0.194 0.247 2 0.152 0.154 0.142 0.144 0.139 0.164 0.151 0.227 3 0.144 0.146 0.150 0.145 0.149 0.163 0.158 0.200 4 0.163 0.140 0.151 0.146 0.152 0.160 0.192 0.192 5 0.138 0.137 0.156 0.137 0.152 0.154 0.167 0.194 6 0.136 0.137 0.150 0.137 0.150 0.148 0.161 0.187 7 0.133 0.138 0.147 0.135 0.140 0.140 0.164 0.185 8 0.130 0.141 0.144 0.127 0.135 0.138 0.162 0.183 9 0.129 0.143 0.139 0.123 0.128 0.135 0.154 0.182 10 0.127 0.138 0.134 0.121 0.124 0.135 0.150 0.185 Average 0.150 0.153 0.148 0.141 0.145 0.153 0.165 0.198 Average in steady 0.130 0.140 0.141 0.127 0.132 0.137 0.158 0.184 The microtopography of the worn titanium discs was observed and presented in Figure 8. As evident from Figure 8(a)(d)(e), the surfaces lubricated by mix(1:1), mix(1:2), and pure graphene nanofluid exhibited the smoothest surfaces devoid of conspicuous grooves and scratches. Notably, the worn surface under mix(1:2) lubrication demonstrated an exceptionally excellent surface quality which is attributed to the synergistic effect of the hybrid nanofluid. Figure 8(f) illustrated that the worn surface under mix(1:4) lubrication appeared relatively smooth with only a small amount of deposition. In contrast, Figure 8(b)(c) highlighted clear scratches and plow furrows on the worn surfaces with mix(4:1) and mix(2:1) lubrication. These surfaces exhibited more debris and relatively rougher surface quality compared to other experimental groups. The surface roughness (Ra) of the wear marks was measured and presented in Table 6. It was apparent that the surface roughness aligned with the surface quality observed in the SEM images. Specifically, the mix(1:1) and mix(1:2) demonstrated the best surface roughness values of 0.692 µm and 0.723 µm, respectively, while the mix(4:1) exhibited relatively poorer surface roughness (1.037 µm). Due to the limited heat transfer capabilities of titanium alloys, adhesive wear often occurs during frictional processes. Previous studies have explored oil-based lubricants for titanium alloys, but achieving satisfactory machined surface quality has proven challenging with surface roughness ranging from 1.14 µm to 1.328 µm [28-29] . In this experiment, the surfaces after frictional tests appeared smooth and flat, with fewer adhesive wear scars, indicating that the hybrid aqueous nanofluid exhibited superior lubricating and anti-friction effects compared to pure nanofluids for titanium alloys. Table 6 . Average surface roughness of the worn surfaces. Lubricant Mix(1:0) Mix(4:1) Mix(2:1) Mix(1:1) Mix(1:2) Mix(1:4) Mix(0:1) CSS Solution Surface roughness (Ra/µm ) 0.712 1.037 0.825 0.692 0.723 0.905 1.199 1.359 Compared to pure graphene nanofluids, the use of hybrid nanofluids can achieve similar or even superior coefficients of friction and wear volume. The mix(1:1) and mix(1:2) demonstrated the lowest friction coefficients. Considering the high price of graphene, the addition of graphite reduces the cost of lubricant greatly. As a result, nanofluid with graphene and spherical graphite in a ratio of 1:2 achieves a balance between lubricating performance and price, making it the optimal choice of cutting fluid for titanium alloys. 3.4. Lubrication Mechanisms To further characterize the frictional properties of different carbon nanoparticles, the wettability of the nanofluids on titanium alloys were tested. The contact angles of the four types of nanofluids (circular graphite, flake graphite, graphene, and multi-walled carbon nanotube) on titanium alloy substrates were shown in Figure 9. The contact angle of 10wt% CSS aqueous solution without any nanoparticles was 10.03. The addition of spherical graphite and flake graphite could increase the contact angle to 10.93 and 12.43 separately. The contact angle of MWCNTs nanofluid reached to 22.61, which was more than that of pure CSS solution. The wettability of MWCNTs was the worst among the four kinds of nanofluids. While the graphene nanofluid with the smallest contact angle 8.66 showed the best wettability. Combining the lubricating performance of the four types of nanofluids shown in Figure 3, it can be summarized that graphene with the smallest contact angle had the best lubricating ability. MWCNTs with the largest contact angle had the worst lubricating performance. The lubricants which could spread on titanium alloy surface more easily can form lubricating film more effectively. In order to clarify how the nanoparticles acting with titanium surface and reveal the lubricating mechanism, XPS analysis was used to investigate the elemental states and binding modes of the worn titanium surface. Detailed high resolution XPS scans of C1s and Ti2p were recorded and shown in Figure 10. The binding energy peaks of C1s appeared at approximately 284.8 eV, 285.8 eV indicating the presence of C-C, C-O. The peaks at 454.3 eV, 458.8 eV, and 464.6 eV corresponded to Ti and TiO2. The peak with a binding energy of 288.8 eV indicated O-C=O. By contrast, there were no significant differences between the peaks of the four kinds of nanofluids. Furthermore, no C-Ti peak at 281.7 eV was observed in Figure 10 (a1), (b1), (c1), and (d1), indicating that carbon-based nanoparticles do not directly undergo frictional chemical reactions with titanium which was very different with ferrous metals. The interfacial C-Fe bonds could passivate the surface of ferrous metals during friction which played a significant role in friction reduction and anti-wear ability [30][31] . On the contrary, no chemical reaction film formed on titanium alloy surface and the main wear was a combination of abrasive wear and adhesive wear. The accumulated debris generated during friction process caused surface damage of titanium alloys [32] . It can be suggested that the differences in the lubricating performance are not primarily caused by frictional chemical reactions but their inherent low shear strength. As seen in the Ti2p spectrum, a large amount of TiO2 was generated during friction for the heat effect. If the debris cannot be smoothly removed, adhesive wear is more likely to occur. The friction coefficient of spherical graphite is similar to that of flake graphite nanoparticles, but the wear volume and surface quality are significantly different. It can be attributed to the shape of the nanoparticles. As shown in Figure 11(a), the contact area between spherical graphite nanoparticles and frictional debris is small, making it difficult to adhere to the debris. The spherical nanoparticles do not affect the motion of the debris during the friction process but act as bearings to reduce friction. This is reflected in the SEM image (Figure 4a), where the titanium alloy surface lubricated with spherical graphite nanoparticles showed few debris and slight adhesive wear. Compared with spherical nanoparticles, flake nanoparticles were more favorable for forming a lubricating film in the early stages due to their structure. As friction progresses, the flake nanoparticles were more prone to aggregation and ultimately adhered to the friction pair (Figure 11b). The contact area between the layered nanoparticles and the frictional debris was large, hindering the flow of debris. The accumulated debris on the contact surface prevented the formation of effective lubricating film and eventually lead to adhesive wear on the contact surface which was demonstrated in Figure 4(b). Graphene has a large specific surface area and ultrahigh thermal conductivity. Even if graphene adheres to the surface of debris, it is difficult to impede the flow of debris for the extremely thin thickness, excellent thermal conductivity, and outstanding ductility. Moreover, it is easy to spread and form a lubricating film due to the layered structure. When lubricated with graphene nanofluid, almost no adhesive wear was observed (Figure 4c). Graphene exhibited the best lubrication performance. As to MWCNTs, when passing through titanium alloy surface, they may wrap and adhere onto the debris which promoted grain fracture and made debris difficult to go out. So adhesive wear and spalling can be observed in Figure 6. This action is similar to a non-slip chain. With the increasing of length, the interaction of the particles with the debris became stronger, resulting in higher friction coefficient and wear volume. 4. Conclusions The lubrication performance of different forms of carbon nanoparticles in water-based lubrication for titanium alloys was investigated, and several conclusions were drawn as follows: The lubricating performance of four kinds of carbon-based nanofluids on titanium alloys were tested and the results showed that single-layer graphene had the smallest COF and wear volume, which reduce by 34.3% and 44.8% compared with the solution without any nanoparticles. The interaction between nanoparticles and debris is an important factor that influences the lubrication performance of nanoparticles for titanium alloy. The surface of the titanium alloy lubricated by sheet-like nanoparticles is more prone to adhesion and aggregation, resulting in significant differences in surface quality between spherical and sheet-like graphite. The effect of length on the lubricating property of MWCNTs was investigated. It was found that the shorter the length of the MWCNTs, the lower their friction coefficient and wear volume. Smaller nanoparticles usually had better lubrication performance. For graphene/spherical graphite hybrid nanofluids, mix(1:1) and mix(1:2) showed the most significant anti-friction effect on titanium alloy. The hybrid nanofluid with graphene and spherical graphite in a ratio of 1:2 achieved a balance between lubricating performance and price, making it the optimal choice. 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Wang P, Duan F., Tribochemistry of graphene oxide/graphene confined between iron oxide sSubstrates: implications for graphene-based lubricants. ACS Appl. Nano Mater. 2022, 5(9), 12817–12825. Restuccia P, Righi M C., Tribochemistry of graphene on iron and its possible role in lubrication of steel. Carbon, 2016, 106, 118–124. Song Z., Fanyue M., Bingli F., Yu D., Jibo W., Xiaowen Q., Evaluation of wear mechanism between TC4 titanium alloys and self-lubricating fabrics, Wear. 2023, 512–513. Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4001746","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":275729971,"identity":"e1f39db3-2262-48c3-8696-a9ccca788cce","order_by":0,"name":"Ye Yang","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAzUlEQVRIiWNgGAWjYPACGyjNRryWNCBmJk3LYRK0GBw/e/g1T8X5PP4Z+QcYPpQdZuCf3UBAy5m8NGueM7eLJW4kMzDOOHeYQeLOAQJaDuSYGfO23U7cIJHMwMzbdpjBQCKBgJbzb4Ba/p2DaPlLlJYbOcaPeRsOQLQwEqNF8sYbM8Y5x5ITZ5x5bHCw51w6j8QNAlr4zucYf3hTY5fY35748MGPMms5/hkEtCgcYGCT4oFyDgAxDx7FECDfwMD88QdBZaNgFIyCUTCiAQB+D0Vp6EsSLwAAAABJRU5ErkJggg==","orcid":"","institution":"North China University of Technology","correspondingAuthor":true,"prefix":"","firstName":"Ye","middleName":"","lastName":"Yang","suffix":""},{"id":275729972,"identity":"9cc15486-73b7-4a22-945d-d7e831b440e4","order_by":1,"name":"Hao Luan","email":"","orcid":"","institution":"North China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Hao","middleName":"","lastName":"Luan","suffix":""},{"id":275729973,"identity":"3fbbd8d4-45c2-4c62-b27e-ed5e1e48a888","order_by":2,"name":"Yaru Tian","email":"","orcid":"","institution":"North China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Yaru","middleName":"","lastName":"Tian","suffix":""},{"id":275729974,"identity":"dacf1001-e2b9-400f-b719-2e31b30426db","order_by":3,"name":"Lina Si","email":"","orcid":"","institution":"North China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Lina","middleName":"","lastName":"Si","suffix":""},{"id":275729975,"identity":"78dc21bf-e38c-4ed8-b3bb-b3011c6d8bad","order_by":4,"name":"Hongjuan Yan","email":"","orcid":"","institution":"North China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Hongjuan","middleName":"","lastName":"Yan","suffix":""},{"id":275729976,"identity":"c954964e-b996-44b1-9dc3-5e16531171ee","order_by":5,"name":"Fengbin Liu","email":"","orcid":"","institution":"North China University of Technology","correspondingAuthor":false,"prefix":"","firstName":"Fengbin","middleName":"","lastName":"Liu","suffix":""}],"badges":[],"createdAt":"2024-03-01 02:21:46","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4001746/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4001746/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":52108310,"identity":"ec6c43a0-211a-4f7e-9586-20355771429a","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":260553,"visible":true,"origin":"","legend":"\u003cp\u003e(a) The schematic diagram and (b) the photo of CFT-I tribo-tester.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/3bed5dd4679e7757fa623b39.png"},{"id":52108313,"identity":"5f651b1e-9158-4ef5-8d35-9b8b88b971fa","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":472912,"visible":true,"origin":"","legend":"\u003cp\u003eThe microtopography of the nanoparticles (a) spherical graphite (b) flake graphite\u003c/p\u003e\n\u003cp\u003e(c) graphene (d) multi-walled carbon nanotube.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/97db502963d1a09eb7002bb8.png"},{"id":52108309,"identity":"75012ed2-6215-46a1-80a7-1af358eca099","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":124266,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient (a) and wear volume (b)of different nanofluids and control group.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/4e7fbf73a2e9aaec7d4606f2.png"},{"id":52108311,"identity":"4d8c2081-8deb-4d4c-9692-8fa42210961e","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":268622,"visible":true,"origin":"","legend":"\u003cp\u003eSEM morphology of the tracks on Ti-6Al-4V lubricated by (a) spherical graphite (b) flake graphite (c) graphene (d) multi-walled carbon nanotube.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/6e5539c7b696776f757fcae9.png"},{"id":52108315,"identity":"002d8da8-dbbb-4f74-8254-8a96eab26ef3","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":124862,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient (a) and wear volume (b) of different nanofluids.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/252cfae8d4d9bd42a3393cbc.png"},{"id":52108495,"identity":"b513f984-6c2a-4263-9632-41d9b0b6778b","added_by":"auto","created_at":"2024-03-06 20:19:55","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":490595,"visible":true,"origin":"","legend":"\u003cp\u003eSEM morphology of the tracks on Ti-6Al-4V lubricated by multi-walled carbon nanotube with a length of (a) 0.5-2μm (b) 10-30μm (c) 40-60μm.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/87daac4bcf0f3ce96844d78a.png"},{"id":52108318,"identity":"35495934-5025-43f5-806d-da6da482123c","added_by":"auto","created_at":"2024-03-06 20:11:56","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":214922,"visible":true,"origin":"","legend":"\u003cp\u003eFriction coefficient (a) and wear volume (b)of seven nanofluids.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/60f9d78bf005319119764eec.png"},{"id":52108316,"identity":"914a027f-1e9b-42cb-8499-c960a66e8f16","added_by":"auto","created_at":"2024-03-06 20:11:56","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":421781,"visible":true,"origin":"","legend":"\u003cp\u003eSEM morphology of the tracks on Ti-6Al-4V lubricated by (a) Pure graphene (b) mix(4:1) (c) mix(2:1) (d) mix(1:1) (e) mix(1:2) (f) mix(1:4) (g) pure spherical graphite.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/929b9171f00c37fcee459687.png"},{"id":52108312,"identity":"903688bb-95e9-4c96-83ca-4dce93ea41ba","added_by":"auto","created_at":"2024-03-06 20:11:55","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":23507,"visible":true,"origin":"","legend":"\u003cp\u003eContact angle of different nanofluids and control group.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/bb180fdde5d096f07b50a723.png"},{"id":52108320,"identity":"26aaf0a5-380f-4762-bc0f-61f61060bd07","added_by":"auto","created_at":"2024-03-06 20:11:56","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":215650,"visible":true,"origin":"","legend":"\u003cp\u003eXPS spectrograms C1s and Ti2p after lubrication with (a1) (a2) spherical graphite (b1) (b2) flake graphite (c1) (c2) multi-walled carbon nanotube and (d1) (d2) graphene.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/8d4ec647d1cf343c7d1d60d2.png"},{"id":52108319,"identity":"3cbee12c-00f4-4bab-8487-840548c64117","added_by":"auto","created_at":"2024-03-06 20:11:56","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":58116,"visible":true,"origin":"","legend":"\u003cp\u003eLubrication Mechanisms of (a) spherical graphite (b) flake graphite (c) graphene (d) multi-walled carbon nanotube.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/66d2787dc4580cda621ca646.png"},{"id":52109222,"identity":"df2cfc13-4500-48b8-9e1d-489fee4c2c0b","added_by":"auto","created_at":"2024-03-06 20:35:59","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2730814,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4001746/v1/cc88d97f-d3d7-4215-972c-d8417b88e06c.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Investigation on the lubrication performance of different carbon nanofluids for titanium alloy","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eTitanium alloys are difficult to machine materials due to their low thermal conductivity, low elastic modulus, and high chemical reactivity. The resulting high cutting temperature and severe built-up edge formation during machining often lead to excessive tool wear and poor surface quality \u003csup\u003e[1]\u003c/sup\u003e. Traditional lubricants such as mineral oil, vegetable oil, and grease have proven ineffective in adequately lubricating titanium alloys \u003csup\u003e[2]\u003c/sup\u003e. Therefore, there is a pressing need to explore effective water-based lubricants for titanium alloys \u003csup\u003e[3-4]\u003c/sup\u003e. Castor oil sulfated sodium salt (CSS) solution which has shown potential in reducing friction coefficient and adhesive wear is a promising lubricant for titanium alloys \u003csup\u003e[5]\u003c/sup\u003e. However, further enhancements are required to optimize the lubricating and cooling performance of CSS solution for more efficient application.\u003c/p\u003e\n\u003cp\u003eThe incorporation of nanoparticles with lubricants has emerged as a promising approach, as these nanofluids exhibit excellent frictional properties and high load-carrying capacity. By enhancing thermal conductivity and thermal Brownian motion of nanoparticles, nanofluids have demonstrated significant improvements in heat transfer performance and been applied in metal processing \u003csup\u003e[6]\u003c/sup\u003e. Carbon-based nanomaterials which have exceptional mechanical, electrical, thermal, optical, and chemical properties, are particularly well-suited for tribological applications \u003csup\u003e[7-10]\u003c/sup\u003e. Various carbon-based nanomaterials including graphite, graphene, and nanotubes with different shapes and sizes have been extensively investigated about the tribological properties by researchers \u003csup\u003e[11-16]\u003c/sup\u003e. Graphite could penetrate into the concave zone between the contact surfaces to repair the damage and form a thin layer to separate the rubbing surface, thus friction can be reduced \u003csup\u003e[11]\u003c/sup\u003e. Mayur used different concentrations of graphite nanoparticles in sunflower oil to evaluate the machinability of chromium nickel iron alloy 625 and found that graphite effectively improved surface quality and tool wear \u003csup\u003e[12]\u003c/sup\u003e. Compared with graphite, graphene shows outstanding anti-wear characteristics \u003csup\u003e[13]\u003c/sup\u003e. With single layer structure, it is easier to form a lubricant layer between the rubbing surfaces. Graphene nanoparticles were added to rapeseed oil by Wang\u0026rsquo;s group and the lubrication and cooling performance were improved for the reason that the length of the chip-adhesion layer was shortened and the adhesion wear was reduced \u003csup\u003e[17]\u003c/sup\u003e. Wang added graphene nanoparticles to modified \u0026nbsp; lithium-based oil and found that graphene exhibited excellent tribological behavior by providing the lowest coefficient of friction \u003csup\u003e[18]\u003c/sup\u003e. Due to the unique 1D structure, carbon nanotubes have been used as lubricant additives as well which possess a higher surface energy and tension \u003csup\u003e[10,19, 20]\u003c/sup\u003e. Under high contact pressure, carbon nanotubes can form nano-bearings between friction pairs which could reduce friction coefficient and wear rate \u003csup\u003e[21]\u003c/sup\u003e. Different concentrations of multi-walled carbon nanotubes were dispersed into coconut oil By Sarkar \u003csup\u003e[22]\u003c/sup\u003e. Compared with traditional cutting fluid, the nanofluid has better processing performance than traditional processing in cutting force, tool-tip temperature, and width of flank wear \u003csup\u003e[22]\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eWhile most of the researches about nanoparticles are focused on ferrous metal or aluminum alloy, there are limited researches on difficult-to-cut metal such as titanium alloys. Gupta evaluated the performance of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, MoS\u003csub\u003e2\u003c/sub\u003e, and graphite nanoparticles in turning Ti alloys and found that graphite exhibited the lowest cutting force, cutting temperature and surface roughness \u003csup\u003e[23]\u003c/sup\u003e. Singh used graphene-enriched nanofluid in turning of titanium alloy and it was proved that with nanofluid lubrication, the tool life was the highest, the cutting force and the cutting temperature was the lowest \u003csup\u003e[24]\u003c/sup\u003e. However, these researches are usually investigated single carbon-based nanoparticles. There is lack of comparative study on different kinds of carbon-based nanoparticles used for metal cutting especially for titanium alloys. This paper aims to evaluate the lubrication differences between various carbon nanoparticles in water-based nanofluids for titanium alloys. The lubricating mechanism is further investigated. Finally, a new water-based nanofluid that exhibits excellent lubricity is developed to improve the working performance of cutting fluid for Ti-6Al-4V.\u003c/p\u003e"},{"header":"2 Experiment","content":"\u003cp\u003e\u003cstrong\u003e2.1 Experimental setup and materials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCastor oil sulfated sodium salt (CSS) solution was chosen as the lubricating base stock for titanium alloy. To enhance its performance, four types of carbon nanoparticles were incorporated into a 10wt% CSS solution: spherical graphite, flake graphite, graphene, and multi-walled carbon nanotubes (MWCNTs).\u003c/p\u003e\n\u003cp\u003eFrictional tests were conducted in the laboratory using a ball-on-disc device (CFT-I, Licp, Lanzhou, China) to evaluate the lubricating properties of various solution. Figure 1 illustrates the schematic diagram and photograph of the experimental setup. The lower specimen was a Ti-6Al-4V disc with a hardness of HRC 35 and surface roughness (Sa) of less than 40 nm. The chemical composition of the Ti-6Al-4V titanium alloy was detailed in Table 1, while Table 2 presented its mechanical parameters. For machining Ti-6Al-4V, cemented carbide is the recommended tool material \u003csup\u003e[4]\u003c/sup\u003e. Therefore, the upper specimen was a YG8 (WC-Co) ball with a hardness of 89HRA, a diameter of 10 mm, and a surface roughness (Sa) of 25 nm. Each specimen were ultrasonic cleaned with acetone，ethanol and deionized water for 10 minutes. The upper ball was then reciprocated on the stationary disc with a 5 mm amplitude and a 5 Hz frequency for 10 minutes. Prior to the reciprocating motion, 0.2 mL of lubricant was applied to the disc surface. A normal load of 50 N was exerted, resulting in a maximum Hertz contact pressure of 7.5 GPa. Each experiment was repeated more than three times, and the friction coefficient curves represent the average of the collected data. The relative errors of the friction coefficients were within the range of \u0026plusmn;1%.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1.\u0026nbsp;\u003c/strong\u003eChemical compositions of Ti-6Al-4V titanium alloy (wt.%)\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"524\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eH\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eV\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e0.08\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e0.015\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.452107279693486%\"\u003e\n \u003cp\u003e5.5-6.75\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003e3.5-4.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.64367816091954%\"\u003e\n \u003cp\u003eRemaining\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003eThe mechanical parameters of Ti-6Al-4V titanium alloy\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"524\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.46938775510204%\"\u003e\n \u003cp\u003eTensile strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003eYield Strength (MPa)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.367346938775512%\"\u003e\n \u003cp\u003eHardness (VHN)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.387755102040817%\"\u003e\n \u003cp\u003eYoung\u0026rsquo;s Modulus\u003c/p\u003e\n \u003cp\u003e(GPa at 20\u0026nbsp;◦C)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.346938775510203%\"\u003e\n \u003cp\u003ePoisson\u0026rsquo;s Ratio\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"23.46938775510204%\"\u003e\n \u003cp\u003e1230\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.428571428571427%\"\u003e\n \u003cp\u003e1060\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.367346938775512%\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.387755102040817%\"\u003e\n \u003cp\u003e113.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.346938775510203%\"\u003e\n \u003cp\u003e0.34\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eAfter the completion of the frictional tests, the worn specimens underwent a 30-minute cleaning process with acetone followed by drying. The wear volume was determined using the LEXT\u0026trade;OLS5100 laser scanning confocal microscope (Olympus, Tokyo, Japan). Each test was repeated three times and the average value was calculated. The microtopography of the worn surface was examined using a scanning electron microscope equipped with Energy-dispersive X-ray spectroscopy (FEI, Hillsboro, OR, USA). The chemical compositions of the worn surfaces were analyzed using an X-ray photoelectron spectrometer (XPS, EscaLab 250Xi, TFS, USA). The contact angle was measured using a contact angle meter (JY-82B KRUSS DSA, KR\u0026uuml;SS Company, Germany).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e2.2 Nanofluids preparation\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSpherical graphite, flake graphite, graphene and multi-walled carbon nanotubes were selected as nano-additives for lubricating titanium alloys. The microtopography of these four types of nanoparticles was examined through SEM shown in Figure 2. Detailed parameters of these nanoparticles were provided in Table 3. The diameter of spherical graphite is 20 nm. The diameter of flake graphite is about 3-6 \u0026mu;m and the thickness is 40 nm. Graphene has a diameter of 10 \u0026mu;m and a thickness of three carbon atoms. The diameter of multi-walled carbon nanotubes is 50 nm and the length is 10-30 \u0026mu;m. The preparation of nanofluids involved a two-step process to disperse the nanoparticles into the CSS aqueous solution. The nanoparticle fraction used was 1 wt%. Prior to the frictional tests, the mixture underwent 20 minutes of ultrasonic vibration for effective dispersion.\u003c/p\u003e\n\u003cp\u003eTable 3. Properties of the nanoparticles provided by the manufacturer\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"103%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003eProperty\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003espherical graphite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eflake graphite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003egraphene\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003emulti-walled carbon nanotube\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003ePurity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003eAverage particle size\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e20nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e3-6\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e10\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e50nm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003eLength/thickness\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e\\\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e40nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003eThickness of three carbon atoms\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e10-30\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003eSpecific surface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003e150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003e400\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003e2600\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"28.8659793814433%\"\u003e\n \u003cp\u003eCrystal structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.52577319587629%\"\u003e\n \u003cp\u003ecubic\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.463917525773196%\"\u003e\n \u003cp\u003eflaky\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.556701030927837%\"\u003e\n \u003cp\u003eflaky\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.587628865979383%\"\u003e\n \u003cp\u003esiphonate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"3. Results and Discussion","content":"\u003cp\u003e\u003cstrong\u003e3.1 Lubricating properties of the nanoparticles with different shapes\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe friction coefficient curves for the four types of nanofluids and a control group (CSS aqueous solution without nanoparticles) were illustrated in Figure 3(a). During the initial running-in period, the friction coefficients of the nanofluids rose to 0.4 before exhibiting fluctuations caused by factors such as lubricating film rupture and adhesive wear. Subsequently, the friction coefficients stabilized at a constant level. Comparative analysis with the control group revealed that all nanofluids were able to reduce friction coefficients at various stages for titanium alloy. The average friction coefficients for spherical graphite, flake graphite, graphene, and multi-walled carbon nanotubes were approximately 0.158, 0.154, 0.130, and 0.175, respectively. In comparison to the control group, these nanofluids demonstrated reductions in friction coefficients of up to 20.2%, 22.2%, 34.3%, and 11.6%. Notably, graphene nanofluid exhibited the lowest friction coefficient, while multi-walled carbon nanotubes displayed the least effective lubrication performance with the highest COF. The worn surfaces of the titanium discs were tested and the wear volume was calculated in Figure 3(b). It can be seen that graphene with single layer structure exhibited best anti-wear property with the smallest wear volume 1.06\u0026times;10\u003csup\u003e8\u003c/sup\u003e \u0026mu;m\u003csup\u003e3\u0026nbsp;\u003c/sup\u003ewhich is 44.8% smaller than that of CSS solution without nanoparticles. Spherical graphite can also reduce the wear of titanium alloy effectively with a decrease of 26.6%. While flake graphite and MWCNTs did not show obvious anti-wear effect. The wear volume of flake graphite is almost similar with the control group. MWCNTs even promoted the wear of titanium alloy to some extent with the largest wear volume 1.98\u0026times;10\u003csup\u003e8\u003c/sup\u003e \u0026mu;m\u003csup\u003e3\u0026nbsp;\u003c/sup\u003ewhich is slightly higher than the control group.\u003c/p\u003e\n\u003cp\u003eConsidering both the friction coefficients and wear lubricated by the four kinds of carbon-based nanofluids, graphene exhibits the best lubrication effect with the smallest COF and wear volume. It is speculated that the single layer structure is more prone to adhere on titanium alloy surface thus forming a lubricative layer. Spherical graphite ranked the second while the tubular carbon nanotubes had the poorest lubrication effect on titanium alloy.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eScanning electron microscopy (SEM) was employed to observe the microtopography of the worn titanium discs. As shown in Figure 4(b), adhesive wear and deposition can be observed on the worn surfaces with flake graphite lubrication. The surface lubricated by MWCNTs was slightly better than that of flake graphite. But there was some adhesive wear as well seen from Figure 4(d). By contrast, the surfaces lubricated by spherical graphite and graphene were much smoother without obvious grooves and scratches shown in Figure 4(a) and (c). Generally, smaller friction coefficients and wear result in higher surface quality. When lubricated by graphene, adhesive wear and furrow wear was greatly reduced for the good lubricating condition. Meanwhile, the surface lubricated by spherical graphite was fairly good as well. The size dimension of MWCNTs was different from other nanoparticles, and their poor lubrication performance may be not only due to their shape, but also their length. Therefore, the length needed to be taken into consideration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.2 Lubricating properties of MWCNTs with different length\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn order to further investigate the impact of morphology on nanoparticle\u0026rsquo;s lubrication performance, three kinds of MWCNTs with different length were selected to detect the effect of length on the lubricating property. The length of MWCNTs ranging from 0.5-2\u0026mu;m\u0026nbsp;is named short，the length\u0026nbsp;10-30\u0026mu;m is long and the length 40-60\u0026mu;m is the longest.\u0026nbsp;The specific parameters of the nanoparticles were listed in Table 4.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e4\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eProperties of MWCNTs\u0026nbsp;with different length provided by the manufacturer.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"99%\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003eProperty\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003emulti-walled carbon nanotube(short)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003emulti-walled carbon nanotube(Long)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003emulti-walled carbon nanotube(Longest)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003ePurity\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e99%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003eDiameter\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e50nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e50nm\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e50nm\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003eLength\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e0.5-2\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e10-30\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e40-60\u0026mu;m\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003eSpecific surface area (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003e40\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"35.05154639175258%\"\u003e\n \u003cp\u003eCrystal structure\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003esiphonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003esiphonate\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.649484536082475%\"\u003e\n \u003cp\u003esiphonate\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe friction coefficient of these MWCNTs were presented in Figure 5(a). The COF of the longest MWCNTs was not stable and obvious fluctuation was observed during the frictional test. To the end of the test, the friction coefficient dropped to 0.185. When lubricated by the long MWCNTs, COF kept stable at 0.179 after the running-in period. The short MWCNTs demonstrated best lubricating property with the smallest COF 0.163. The worn surface of the titanium discs after frictional tests was observed and the wear volume was shown in Figure 5(b). The wear volume lubricated by the short MWCNTs was the smallest, followed by the long MWCNTs and the longest MWCNTs had the biggest wear volume. It can be seen that shorter MWCNTs exhibit better lubricating property.\u003c/p\u003e\n\u003cp\u003eThe SEM images of the titanium discs lubricated by different length of MWCNTs were shown in Figure 6. It can be seen that titanium surface lubricated with shorter MWCNTs was smoother with fewer grooves and adhesive wear, indicating better surface quality. As shown in Figure 6 (c), adhesive wear and spalling can be observed, suggesting that longer multi-walled carbon nanotubes often resulted in poorer surface quality. It can be concluded that smaller nanoparticles have a greater advantage in lubricating titanium alloys. However, the lubrication performance of the shortest MWCNTs nanofluid on titanium alloy was still inferior to that of graphene.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.3 Lubricating properties of hybrid nanofluids\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe experiments in section 3.1 shows that graphene and spherical graphite exhibit good lubrication performanc e on titanium alloys. In this part, graphene and spherical graphite were mixed forming a hybrid nanofluid to see the mutual effect of the nanoparticles. Compared with single nanofluids, hybrid nanofluids often demonstrate superior lubrication performance \u003csup\u003e[25-28]\u003c/sup\u003e. The mass fraction of graphene and spherical graphite was denoted by mix(x:y). Seven groups of hybrid nanofluids were prepared to investigate the impacts of the nanoparticles\u0026apos; content ratio. These groups encompassed pure graphene, pure spherical graphite, mix(1:1), mix(1:2), mix(2:1), mix(1:4), and mix(4:1).\u003c/p\u003e\n\u003cp\u003eThe friction coefficient curves for seven groups of nanofluids were presented in Figure 7 (a). The friction curve under stable state was shown to be more clearly. The average friction coefficients of various nanofluids were listed in Table 5. It can been that mix(1:2) had lower friction coefficients compared to pure nanofluids. The friction coefficients of all hybrid nanofluids were lower than those of pure spherical graphite. Mix(1:1) and mix(1:2) even had lower friction coefficients than pure graphene in a stable state. In addition, compared with the COF lubricated by single spherical graphite or graphene nanofluid, the fluctuation amplitude of the friction curve of the hybrid nanofluid was also smaller. The wear volume of the titanium disc was shown in Figure 7(b). It can be seen that all the hybrid nanofluids had reduced wear volume to a certain extent compared to pure spherical graphite nanofluids. Similar to the friction coefficient curve, among several hybrid nanofluids, mix(1:1) and mix(1:2) had relatively smaller wear volumes. Compared with the control group, their wear volumes were reduced by 48.2% and 51.8%, respectively.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e5\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eAverage friction coefficient\u0026nbsp;of seven nanofluids.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"524\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003eTime/Min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003ePure\u0026nbsp;graphene\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(4:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(2:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003ePure\u0026nbsp;spherical graphite\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e10 wt% CSS Solution\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.249\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.253\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.170\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.198\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.184\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.198\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.194\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.247\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.152\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.142\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.139\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.164\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.151\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.227\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.146\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.149\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.163\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.158\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.200\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.163\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.151\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.146\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.152\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.160\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.192\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.192\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.156\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.152\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.167\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.194\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.136\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.148\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.161\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.187\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.133\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.147\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.135\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.164\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.185\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.144\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.127\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.135\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.162\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.183\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.129\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.143\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.139\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.123\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.128\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.135\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.154\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.182\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003e10\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.127\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.138\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.134\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.121\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.124\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.135\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.185\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003eAverage\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.150\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.153\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.148\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.145\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.153\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.165\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.198\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003eAverage in steady\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.130\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.140\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.141\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.127\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.132\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.137\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.158\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.184\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eThe microtopography of the worn titanium discs was observed and presented in Figure 8. As evident from Figure 8(a)(d)(e), the surfaces lubricated by mix(1:1), mix(1:2), and pure graphene nanofluid exhibited the smoothest surfaces devoid of conspicuous grooves and scratches. Notably, the worn surface under mix(1:2) lubrication demonstrated an exceptionally excellent surface quality which is attributed to the synergistic effect of the hybrid nanofluid. Figure 8(f) illustrated that the worn surface under mix(1:4) lubrication appeared relatively smooth with only a small amount of deposition. In contrast, Figure 8(b)(c) highlighted clear scratches and plow furrows on the worn surfaces with mix(4:1) and mix(2:1) lubrication. These surfaces exhibited more debris and relatively rougher surface quality compared to other experimental groups. The surface roughness (Ra) of the wear marks was measured and presented in Table 6. It was apparent that the surface roughness aligned with the surface quality observed in the SEM images. Specifically, the mix(1:1) and mix(1:2) demonstrated the best surface roughness values of 0.692 \u0026micro;m and 0.723 \u0026micro;m, respectively, while the mix(4:1) exhibited relatively poorer surface roughness (1.037 \u0026micro;m). Due to the limited heat transfer capabilities of titanium alloys, adhesive wear often occurs during frictional processes. Previous studies have explored oil-based lubricants for titanium alloys, but achieving satisfactory machined surface quality has proven challenging with surface roughness ranging from 1.14 \u0026micro;m to 1.328 \u0026micro;m \u003csup\u003e[28-29]\u003c/sup\u003e. In this experiment, the surfaces after frictional tests appeared smooth and flat, with fewer adhesive wear scars, indicating that the hybrid aqueous nanofluid exhibited superior lubricating and anti-friction effects compared to pure nanofluids for titanium alloys.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e6\u003c/strong\u003e\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003eAverage\u0026nbsp;surface roughness\u0026nbsp;of the worn surfaces.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"524\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003eLubricant\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(4:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(2:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(1:4)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eMix(0:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003eCSS Solution\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"11.954459203036054%\"\u003e\n \u003cp\u003eSurface roughness (Ra/\u0026micro;m\u003cstrong\u003e)\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.712\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e1.037\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.825\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.692\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.723\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e0.905\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e1.199\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.005692599620494%\"\u003e\n \u003cp\u003e1.359\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eCompared to pure graphene nanofluids, the use of hybrid nanofluids can achieve similar or even superior coefficients of friction and wear volume. The mix(1:1) and mix(1:2) demonstrated the lowest friction coefficients. Considering the high price of graphene, the addition of graphite reduces the cost of lubricant greatly. As a result, nanofluid with graphene and spherical graphite in a ratio of 1:2 achieves a balance between lubricating performance and price, making it the optimal choice of cutting fluid for titanium alloys.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e3.4. Lubrication Mechanisms\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo further characterize the frictional properties of different carbon nanoparticles, the wettability of the nanofluids on titanium alloys were tested. The contact angles of the four types of nanofluids (circular graphite, flake graphite, graphene, and multi-walled carbon nanotube) on titanium alloy substrates were shown in Figure 9. The contact angle of 10wt% CSS aqueous solution without any nanoparticles was 10.03. The addition of spherical graphite and flake graphite could increase the contact angle to 10.93 and 12.43 separately. The contact angle of MWCNTs nanofluid reached to 22.61, which was more than that of pure CSS solution. The wettability of MWCNTs was the worst among the four kinds of nanofluids. While the graphene nanofluid with the smallest contact angle 8.66 showed the best wettability. Combining the lubricating performance of the four types of nanofluids shown in Figure 3, it can be summarized that graphene with the smallest contact angle had the best lubricating ability. MWCNTs with the largest contact angle had the worst lubricating performance. The lubricants which could spread on titanium alloy surface more easily can form lubricating film more effectively.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;In order to clarify how the nanoparticles acting with titanium surface and reveal the lubricating mechanism,\u0026nbsp;XPS analysis was used to investigate the elemental states and binding modes of the worn titanium surface. Detailed high resolution XPS scans of C1s and Ti2p were recorded and shown in Figure 10. The binding energy peaks of C1s appeared at approximately 284.8 eV, 285.8 eV indicating the presence of C-C, C-O. The peaks at 454.3 eV, 458.8 eV, and 464.6 eV corresponded to Ti and TiO2.\u0026nbsp;The peak with a binding energy of 288.8 eV indicated O-C=O. By contrast, there were no significant differences between the peaks of the four kinds of nanofluids. Furthermore, no C-Ti peak at 281.7 eV was observed in Figure 10 (a1), (b1), (c1), and (d1), indicating that carbon-based nanoparticles do not directly undergo frictional chemical reactions with titanium which was very different with ferrous metals. The interfacial C-Fe bonds could passivate the surface of ferrous metals during friction which played a significant role in friction reduction and anti-wear ability\u003csup\u003e\u0026nbsp;[30][31]\u003c/sup\u003e. On the contrary, no chemical reaction film formed on titanium alloy surface and the main wear was a combination of abrasive wear and adhesive wear. The accumulated debris generated during friction process caused surface damage of titanium alloys \u003csup\u003e[32]\u003c/sup\u003e. It can be suggested that the differences in the lubricating performance are not primarily caused by frictional chemical reactions but their inherent low shear strength. As seen in the Ti2p spectrum, a large amount of TiO2 was generated during friction for the heat effect. If the debris cannot be smoothly removed, adhesive wear is more likely to occur.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The friction coefficient of spherical graphite is similar to that of flake graphite nanoparticles, but the wear volume and surface quality are significantly different. It can be attributed to the shape of the nanoparticles. As shown in Figure 11(a), the contact area between spherical graphite nanoparticles and frictional debris is small, making it difficult to adhere to the debris. The spherical nanoparticles do not affect the motion of the debris during the friction process but act as bearings to reduce friction. This is reflected in the SEM image (Figure 4a), where the titanium alloy surface lubricated with spherical graphite nanoparticles showed few debris and slight adhesive wear. Compared with spherical nanoparticles, flake nanoparticles were more favorable for forming a lubricating film in the early stages due to their structure. As friction progresses, the flake nanoparticles were more prone to aggregation and ultimately adhered to the friction pair (Figure 11b). The contact area between the layered nanoparticles and the frictional debris was large, hindering the flow of debris. The accumulated debris on the contact surface prevented the formation of effective lubricating film and eventually lead to adhesive wear on the contact surface which was demonstrated in Figure 4(b). Graphene has a large specific surface area and ultrahigh thermal conductivity. Even if graphene adheres to the surface of debris, it is difficult to impede the flow of debris for the extremely thin thickness, excellent thermal conductivity, and outstanding ductility. Moreover, it is easy to spread and form a lubricating film due to the layered structure. When lubricated with graphene nanofluid, almost no adhesive wear was observed (Figure 4c). Graphene exhibited the best lubrication performance. As to MWCNTs, when passing through titanium alloy surface, they may wrap and adhere onto the debris which promoted grain fracture and made debris difficult to go out. So adhesive wear and spalling can be observed in Figure 6. This action is similar to a non-slip chain. With the increasing of length, the interaction of the particles with the debris became stronger, resulting in higher friction coefficient and wear volume.\u0026nbsp;\u003c/p\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThe lubrication performance of different forms of carbon nanoparticles in water-based lubrication for titanium alloys was investigated, and several conclusions were drawn as follows:\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eThe lubricating performance of four kinds of carbon-based nanofluids on titanium alloys were tested and the results showed that single-layer graphene had the smallest COF and wear volume, which reduce by 34.3% and 44.8% compared with the solution without any nanoparticles.\u003c/li\u003e\n \u003cli\u003eThe interaction between nanoparticles and debris is an important factor that influences the lubrication performance of nanoparticles for titanium alloy. The surface of the titanium alloy lubricated by sheet-like nanoparticles is more prone to adhesion and aggregation, resulting in significant differences in surface quality between spherical and sheet-like graphite.\u003c/li\u003e\n \u003cli\u003eThe effect of length on the lubricating property of MWCNTs was investigated. It was found that the shorter the length of the MWCNTs, the lower their friction coefficient and wear volume. Smaller nanoparticles usually had better lubrication performance.\u003c/li\u003e\n \u003cli\u003eFor graphene/spherical graphite hybrid nanofluids, mix(1:1) and mix(1:2) showed the most significant anti-friction effect on titanium alloy. The hybrid nanofluid with graphene and spherical graphite in a ratio of 1:2 achieved a balance between lubricating performance and price, making it the optimal choice.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eCarbon nanoparticles play a crucial role in the field of nanofluid lubrication, and their morphology has a profound impact on lubrication performance. This article provides insight into the application of water-based nanofluids for difficult-to-machine materials to improve cutting efficiency and surface quality. It is expected to be used in cutting fluid development in the future.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe work is financially supported by the National Key Research and Development Program of China (Grant No. 2022YFB3403801), National Natural Science Foundation of China (Grant No. 52005010), the Project of Cultivation for Young Top-motch Talents of Beijing Municipal Institutions (Grant No. BPHR202203035).\u0026nbsp;\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eLeyens C., Peters M. Titanium and Titanium Alloys; Wiley Online Library; Wiley-VCH Verlag: Weinheim, Germany, 2003.\u003c/li\u003e\n \u003cli\u003eYang Y., Zhang C.H., Dai Y.J., Tribological properties of titanium alloys under lubrication of SEE oil and aqueous solutions. Tribol. 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Carbon, 2016, 106, 118\u0026ndash;124.\u003c/li\u003e\n \u003cli\u003eSong Z., Fanyue M., Bingli F., Yu D., Jibo W., Xiaowen Q., Evaluation of wear mechanism between TC4 titanium alloys and self-lubricating fabrics, Wear. 2023, 512\u0026ndash;513.\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"carbon nanofluids, water-based lubrication, titanium alloy, hybrid nanofluids","lastPublishedDoi":"10.21203/rs.3.rs-4001746/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4001746/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Titanium alloys are difficult to machine and have poor tribological properties. This paper investigated the lubricating performance of different carbon nanoparticles in water-based lubrication for titanium alloys. The lubricating performance of four kinds of carbon nanofluids on titanium alloys were tested and the results showed that single-layer graphene had the smallest COF and wear volume. The interaction between nanoparticles and debris was an important factor that influenced the lubrication performance of nanoparticles for titanium alloy. The effect of length on the lubricating property of multi-walled carbon nanotubes (MWCNTs) was investigated. It was found that the shorter the length of the MWCNTs, the lower their friction coefficient and wear volume. Moreover, the hybrid nanofluid with graphene and spherical graphite in a ratio of 1:2 achieved a balance between lubricating performance and price, making it the optimal choice. The mechanisms of these nanoparticles were analyzed and the interaction between nanoparticles and debris was evaluated.","manuscriptTitle":"Investigation on the lubrication performance of different carbon nanofluids for titanium alloy","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-03-06 20:11:50","doi":"10.21203/rs.3.rs-4001746/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"c3565094-d831-4bbb-88e8-71dbe4d1f9ae","owner":[],"postedDate":"March 6th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[],"tags":[],"updatedAt":"2024-03-12T06:01:26+00:00","versionOfRecord":[],"versionCreatedAt":"2024-03-06 20:11:50","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-4001746","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4001746","identity":"rs-4001746","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}