Tribological Behaviour of Neem Oil with and without Graphene Nanoplatelets Using Four-Ball Tester

B. Suresha; G. Hemanth; Apurva Rakesh; K. M. Adarsh

doi:10.1155/2020/1984931

Tribological Behaviour of Neem Oil with and without Graphene Nanoplatelets Using Four-Ball Tester

Suresha, B.;Hemanth, G.;Rakesh, Apurva;Adarsh, K. M. 2020-01-25 00:00:00 Hindawi Advances in Tribology Volume 2020, Article ID 1984931, 11 pages https://doi.org/10.1155/2020/1984931 Research Article Tribological Behaviour of Neem Oil with and without Graphene Nanoplatelets Using Four-Ball Tester 1,2 1,2 1,2 1,2 B. Suresha , G. Hemanth , Apurva Rakesh, and K. M. Adarsh Department of Mechanical Engineering, e National Institute of Engineering, Mysore 570008, India Visvesvaraya Technological University, Belagavi, Karnataka, India Correspondence should be addressed to B. Suresha; sureshab2004@yahoo.co.in Received 12 May 2019; Revised 16 August 2019; Accepted 25 October 2019; Published 25 January 2020 Academic Editor: Patrick De Baets Copyright © 2020 B. Suresha et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e present work was aimed to study the friction and wear behaviour of graphene nanoplatelets (GNPs) under extreme pressure conditions as an anti-weld additive for neem oil. e eﬀect of neem oil, blended with various loading of GNPs on the friction and wear characteristics has been investigated. From the experimental results, it was found that 1 wt.% of GNPs in neem oil showed the least coeﬃcient of friction and smoother wear scar diameter. e extreme pressure test was performed on neem oil with and without GNPs as per ASTM standards. e extreme pressure test results indicated the improvement in seizure load of neem oil by 27.8% at 0.5 wt.% of GNPs as compared to pure neem oil. Optical microscopy of worn steel ball surface revealed the pit formation and the formation of wedge cutting edge in GNPs modiﬁed neem oil. with bio-based oils namely jatropha, spirulina, pongamia 1. Introduction [12–14]. Friction and wear of tribo-system depend on various e friction and wear characteristics of machine components tribo parameters like applied normal load, sliding velocity, is a signiﬁcant research area that is being thoroughly studied. sliding distance and type of lubrication. Hsu et al. concluded A lubricant, apart from being used in automotive engines, ﬁnds that the eﬀect of hydrodynamic condition of the lubricant does its necessity in pneumatic circuits, food processing machinery, not have a signiﬁcant eﬀect on surface wear. However, the airplanes, hydraulic press and hydraulic jacks [1–3]. e oper- interaction between lubricant and surfaces in contact inﬂuence ating conditions to which lubricants are exposed dictates its the tribological behaviour [15]. e bio-oils have a superior grade and shelf life. ere are many researchers who worked anti-corrosive property, high ﬂash and ﬁre point as well as to improve the properties of bio-based oils as lubricant and feeble aquatic toxicity. Lubricants extracted from edible oil reduced the wear loss of machine elements [4, 5]. Continuous seeds pose severe food versus fuel issues that can be overcome eﬀorts have been made to develop technology to avoid ill eﬀects by nonedible oils [16]. Many researchers have studied the fric- on the environment [6]. e rate of biodegradability of mineral tion and wear behaviour of bio-based oils [17–19]. e bio- oils is around 30–65% whereas, a bio-based oils is having oils comprise of triglycerol (molecular weight: 240.25 g/mol), almost 95% [7]. Erhan et al. studied the lubricant base stock and polar nature of the fatty acids allows it to form a bond potential of chemically modiﬁed vegetable oils and concluded with metallic surfaces and create a thin monolayer that is ben- that the pollution problem is so severe that nearly 50% of all eﬁcial in reducing wear and friction [18, 19]. e bio-based lubricants sold globally end up in the environment via volatil- oils have few shortcomings, like poor thermal-oxidative sta- ity, spills, or total loss applications [8]. bility, nonnegative pour point and gumming eﬀect [20–23]. Owing to the ill eﬀects of mineral and synthetic oils on Incorporation of nanoﬁllers into bio-oils has shown lower the environment and human health and increasing oil demand coeﬃcient of friction and smoother wear scar diameter and prices, the research objective was framed to pursue [24, 25]. e reduction in wear loss was attributed to an st research on bio resources in the late 90’s and early 21 century increase in the viscosity of the base oil [24]. e viscosity [9–11]. Regular eﬀorts were made to substitute mineral oils enhancement was associated with the number of particles 2 Advances in Tribology available per unit volume of oil. ere are lot of parameters that dictate the behaviour of nanoparticles in the lubricant, some of which are size, geometry and chemical and physical properties. Nanoparticles tend to diﬀuse between two mating components thereby avoiding metal contacts leading to wear reduction. Some nano-additives form a bond with metal sur- faces while some convert sliding into rolling friction [25–27]. Masuda et al. proved the incompatibility of metallic nanoﬁllers with lubricant and concluded that surface activity was respon- sible for this incompatibility [28]. Not only the particulate additives play an important role in enhancing the tribological properties, but blending bio-based oils into lubricants also showed multi-functional behaviour [29–32]. Li et al. have demonstrated the application of natural garlic oil as a high performance and extreme pressure additive for lubricants [33]. Ossia et al. have acknowledged the presence of eicosanoic and octadecanoic acids in castor and jojoba oil and enhancing their F 1: TEM image of GNPs [48]. oxidation stability and tribological properties [34]. Carbonaceous particles like soot, graphene, multiwalled car- bon nanotube showed very good lubricity [35–37]. Oil seeds Neem is a native tree to Indian-subcontinent and is widely crushing grown in Indian states namely, Uttar Pradesh, Tamil Nadu, Oil and Karnataka. Its applications are discussed in ayurvedic lit- Analysis extraction erature. Schmutterer has analyzed the eﬀect of neem derived products as pesticides [38]. ere are a lot of works available dealing with applications of neem and their derivatives [39– Oil coarse 45]. Chaudhari et al. have discussed a self-healing coating of Blended oil Work process chart ltering testing a polyurethane prepared from neem oil polyesteramides [46]. Muhammad et al. have discussed wear preventive character- istics of neem and Jatropha oil with antimony dialkyldithio carbonate [47]. Neem oil has promising beneﬁts in all ﬁelds. GNPs Oil ne blending ltering However, neem oil was less explored with tribological prop- erties as bio-lubricant. Hence, the present research work Pure oil explores neem oil and the role of graphene nanoplatelets testing (GNPs) in neem oil on viscosity, friction and wear as well as on seizure load which are important factors that are accounted F 2: Work process chart of the current experimental work. for the right selection of the appropriate lubricant in diﬀerent sliding components of food processing machines. Hence, neem oil was preferred for the further conscientious investi- with 50-micron mesh sieve to remove ﬁner impurities. Some gation with and without graphene nanoplatelets. of the particulate impurities were settled at the bottom of the container which was later discarded. 2. Materials and Methods 2.2. Blending Oil with Graphene Nanoplatelets. e neem Neem oil (NO) was procured from NIE-Center for Renewable oil obtained was thoroughly mixed with GNPs following Energy and Sustained Technology, Mysore, India. e Graphene ultrasonication. e loading of nanoﬁllers has a great eﬀect nanoplatelets (GNPs) were procured from Sigma Aldrich, on the functionality of bio-oils as lubricants with about Bangalore, India. e speciﬁcations of GNPs are, surface area 0.1–1.5 wt.% stated as the optimum loading for nanoﬁllers 750 m /g, the GNPs considered is structured out of 3–6 layers in majority research works carried out [49–51]. erefore, in of <50 nm thick. e density of the material is 0.2–0.4 g/cm . the present work, for the purpose of evaluating the eﬀect of Figure 1 shows the Transmission Electron Microscopic image GNPs loading on the tribological properties of neem oil, nano- of GNPs obtained from product data sheet [48]. It can be lubricants have been made at four diﬀerent loadings viz., 0.25, observed from the TEM image that the GNPs are semi-trans- 0.5, 0.75, and 1.0 wt.% by incorporating GNPs to neem oil. parent and they are in order of few nanometres. e ultrasonication was performed for 15 min at a frequency of 22 kHz using Johnson Ultrasonicator. Figure 2 shows the 2.1. Extraction of Neem Oil. e neem oil was produced from process chart of the current research. its seeds. e neem seeds were cleaned and crushed to extract oil out of it. e oil so obtained was ﬁltered in two stages. 2.3. Measurement of Kinematic Viscosity. e viscosity of Firstly, with a coarse ﬁlter of 180-micron mesh sieve and later the blended oils was tested along with bio-based oils. e Advances in Tribology 3 ermometer Operating handle Inner cylinder Outer cylinder Oil level indicator Stirrer wall Stirrer vane Heating coil Ball valve Capillary tube Outlet valve Mark Conical ask containing 50 cc of oil F 3: Sectional front view of the Redwood viscometer. F 4: Schematic diagram of the four-ball tester. F 5: Assembly of four-ball tester with ball holder cup. viscosity test was carried on the redwood viscometer whose test procedure is governed by IP 70/62. 50 cm of oil is allowed to ﬂow down and corresponding ﬂow time () in seconds and 64–66 HRC with mirror polished surface was used for the was recorded for further calculations. e oriﬁce diameter investigation. e test duration was 60 min, the temperature of of viscometer is 1.62 mm. e test was initiated at 30°C and the oil was 75°C and the rotation speed was kept 1200 ± 1 rpm. for every 5°C rise in temperature, the consecutive reading e test load was maintained to be constant, which was was noted. Five trials were done to aﬃrm the values. Figure 3 40 ± 0.1 kg. e coeﬃcient of friction and wear scar diameter shows the schematic representation of Redwood viscometer. were obtained. Figures 4 and 5 depict the four-ball tester setup. Equation (1) was used to evaluate kinematic viscosity (). Seizure load is the lowest applied load at which the rotating ball weld to the stationery balls indicating extreme pressure level of the lubricants. e extreme pressure test was performed 0.65 (1) 휈 = 0.00247 × 푡 − . according to ASTM D2783 standard [53]. e test conditions were as follows, the load was varied from 400 N till the seizure 2.4. Friction and Wear Test. e wear preventive characteristics load with an increment of 100 N, speed was maintained to be of the NO-GNPs based lubricant were examined under four- 1760 ± 30 rpm, oil temperature was 25°C and the duration of ball tribometer. e test procedure was governed by ASTM the test was 10 s. Once the seizure occurs, to ﬁnd the seizure D 4172 [52]. e chromium steel balls of 12.7 mm diameter load precisely, the load was decreased by 10 N for each trial 4 Advances in Tribology T 1: Kinematic viscosity of various wt.% of GNPs-neem nano-lubricants. Nano-lubricant Kinematic viscosity Designation formulations at 40°C (mm /s) Pure neem oil NO 53.3 ± 0.35 Neem oil mixed with 0.25% GNPs-NO 55.5 ± 0.61 0.25 wt.% GNPs Neem oil mixed with 0. 50% GNPs-NO 58.7 ± 0.19 0.50 wt.% GNPs Neem oil mixed with 0.75% GNPs-NO 62.3 ± 0.53 0.75 wt.% GNPs Neem oil mixed with 1.0% GNPs-NO 67.193 ± 0.4 1.0 wt.% GNPs 30 35 40 45 50 55 until the seizure load was obtained. Five trials were performed Temperature as mentioned above to aﬃrm the values. NO NO+0.25 GNPs NO+0.5% GNPs 3. Results and Discussion NO+0.75% GNPs NO+1.0% GNPs 3.1. Eﬀect of GNPs Loading on Viscosity of Neem Oil. e rate F 6: Kinematic viscosity of GNPs-neem nano-lubricants. of ﬂuid resistance against its ﬂow is called viscosity, which is one of the vital factors for selecting proper lubricating oil for moving components in machinery. Since, one of the important properties of a lubricant is the viscosity, in the 0.12 present research work; the focus is on the eﬀect of loading of GNPs into the neem oil which results in change of viscosity. 0.10 For this reason, the viscosity of the lubricating oil which did not contain nanoparticles was considered as a base ﬂuid (neem 0.08 oil) and also the viscosity of the bio-lubricants which contain GNPs at four loadings 0.25, 0.5. 0.75, and 1.0 wt.% and with an 0.06 increase in temperature from 30°C to 55°C was measured. e experimental results are summarized in Table 1 and are also 0.04 shown in Figure 6. It can be seen, the viscosity of GNPs-NO nano-lubricants the temperatures had increased from 30°C to 0.02 55°C by increasing the loading of GNPs, although the rate of change in viscosity at lower loadings was much smaller than 0.00 that at higher loadings. e stimulating point related to the ampliﬁed viscosity of GNPs-NO nano-lubricants with 1.0 wt.% loading is that, for Blended neem oil increasing temperatures, the viscosity of neem oil without Mean CoF GNPs had a substantial decrease. When GNPs were incorpo- rated to the neem oil, they were positioned between the neem F 7: Mean coeﬃcient of friction of GNPs-neem nano-lubricants. oil layers and escort to ease the ﬂuid layer movement on each other. As a result, the viscosity decreased slightly and the decreasing trend can be seen for 0.25% and 0.5% GNPs-NO on pure NO and then followed by blended oils of NO. ere are nano-lubricants as shown in Figure 6. As GNPs loading many factors that inﬂuence lubricant properties. In this regard, increases, nanoﬁllers agglomerate and create bigger and asym- the coeﬃcient of friction versus oil combinations plot is as metric particles, which prevent movement of ﬂuid layers on shown in Figure 7. It was seen that the coeﬃcient of friction each other; hence the viscosity increased for higher loadings was reduced by 7.5% on incorporation of 0.25% GNPs-NO, (0.75 and 1.0 wt.%) of GNPs-NO nano-lubricants. e same 25.2% with 0.5% GNPs-NO, 28.9% with 0.75% GNPs-NO and behaviour was observed by other researchers with diﬀerent the highest reduction was found with 1.0% GNPs-NO which liquids and nano additives [54–57]. Wang et al. observed about was around 41.4% with the base NO. A signiﬁcant reduction of 86% improvement in the viscosity of distilled water on incor- 23% was observed in wear scar diameter with 1.0% GNPs-NO poration of Al O [54]. in relation to unblended NO. is reduction can be associated 2 3 with an increment in the viscosity of the oil which helped in 3.2. Wear Preventive Characteristics GNPs Modiﬁed Neem the formation of thin-ﬁlm owing to the decrease in wear scar Oil. e wear preventive characteristics were ﬁrst conducted diameter as well. NO 0.25% GNPs 0.5% GNPs 0.75% GNPs 1.0% GNPs Variation of viscosity (mm /s) Mean CoF Advances in Tribology 5 (a) (b) (c) (d) (e) F 8: Optical micrographs of wear scar diameter: (a) pure neem oil, (b) 0.25% GNPs-NO, (c) 0.50% GNPs-NO, (d) 0.75% GNPs-NO, and (e) 1.0% GNPs-NO. From Figure 8, it can be observed that GNPs modiﬁed oil with lower percentages of GNPs showed darker concentric grooves which depict abrasive wear whereas in higher per- centages of GNPs it showed smoother wear track depicting reduced contact between steel balls. e darker grooves are deeper whereas brighter grooves are shallow. A similar obser- vation was found by Suresha et al. [58]. It is these grooves that are responsible for holding GNPs back on the wear surface causing reduction in wear, the same phenomenon was dis- cussed by Huang et al. where they have incorporated graphite sheets [59]. Hernandez et al. have proved experimentally that nanoparticle will accumulate in the wear scar region [60]. e load is the primary characteristics that aﬀect wear. Ing et al. proved that variations in the load largely dictates the wear on the surface of the steel balls [61]. e chemical composition of the lubricant oil aﬀects the wear preventive characteristics. Blended neem oil Stachowiak and Batchelor have discussed that synthetically Seizure load produced lubricants have compounds containing phosphides and sulphide ions that have a tendency to react with the surface F 9: Seizure load of various wt.% of GNPs-neem nano- of the steel balls which prevent the metallic contact to a certain lubricants. extent and reduce the wear [62]. However, the sulphide and phosphide compounds are not present in bio-based resources which makes the bio-based resources to have higher wear scar GNPs blended into oil helps to sustain the failure by enhancing than mineral or synthetic oils [61]. e reason for improvement the seizure load. It was observed in Figure 9 that the seizure in anti-frictional properties was the enhancement in viscosity load was found to be increased with all combinations of GNPs whereas, improvement in anti-wear property was due to the blend. Among all combinations of oils 0.5% GNPs-NO has uniformity in the dispersion of GNPs. e quintessential proof portrayed the outstanding improvement in seizure load of for the latter condition can be found in the work of Hu et al. [63]. 2300 N owing to 27.7% increment in seizure load in accordance with NO. However, the higher percentages of GNPs modiﬁed 3.3. Eﬀect of GNPs Modiﬁed Neem Oil on Extreme Pressure NO did not show further increment in seizure load. Characteristics. e extreme pressure test was started with NO e reason that can be attributed to this increment in seizure to seek for their seizure load followed by the blended oils. e load is the viscosity of the unblended and blended neem oil. Binu 0.75 wt.% GNPs 0.25 wt.% GNPs 1.0 wt.% GNPs 0 wt.% GNPs 0.5 wt. % GNPs Seizure load (N) 6 Advances in Tribology to reduce in the surface area of the mating when compared to the apparent area. is reduction in the area causes a very high bearing pressure that tends to form strain hardening [68]. is was avoided by the formation of the thin ﬁlm that avoided the steel balls getting in contact with each other and prevented them from getting worn out. in-ﬁlm formation just before seizure load with 0.5% GNPs-NO and 1.0% GNPs-NO are shown in Figures 11(b) and 11(c). e ﬁlm thickness was shown varied because of exposure to the oil ﬁlm to the same load. Viscosity plays a major role leading to the formation of the thin ﬁlm. e wear mechanism aer blending GNPs with NO is unlike to the condition without GNPs. Upon increase in viscosity, lubricant ﬁlm formed will have a higher thickness that will avoid the steel balls getting into contact with each other, if the ﬁlm thickness increases, the gap between friction surfaces increases eventually reducing the wear. To get steel balls in contact with each other, lubricant ﬁlm destruction is necessary. To destroy lubricant ﬁlm requires more load. ereby, it increases the seizure load. Just before the seizure, the ﬁlm thickness was very less, then the minuscule GNPs will diﬀuse between the balls and some GNPs were stopped by the wear scar formed. Hence, they settle in the wear scar region, over which the balls slide. GNPs being multi- layered, experiences a shear force and avoids the metallic contact thereby further increasing the seizure load by a small amount. Aer certain loading, the thin ﬁlm fails to form leading F 10: Steel balls aer extreme pressure test at the seizure load. the metal surfaces to contact. is contact region was the high thermal zone leading to the melting of steel at the point of et al. have discussed the relation between the viscosity and load- contact. Syahrullail et al. found that during extreme pressure on vegetable oils the wedge cutting edges will be formed due carrying capacity by using diﬀerent models and experimental validation [64]. ere is a correlation between the minimum oil to high load [69]. In the present study, the wear scar was observed under an optical microscope and abrasive wear was ﬁlm thickness and viscosity [65]. e viscosity improves load carrying capacity [66]. Hence, it can be said that the thickness predominantly noticed. Xu et al. proved that the graphene adheres to the wear scar which acts as a solid lubricant and of oil ﬁlm generated controls maximum load on the component. ough the increment in viscosity was high with 1.0% GNPs-NO sustains the high load up to a certain level [70]. Figure 12 shows shearing of GNPs when exposed to a very the seizure load was lesser than 0.5% GNPs-NO. Kozma had worked and concluded about the relation high load and high speed of operation. e amount of GNPs (0.25% and 0.5%) present in the neem oil was better in reduc- between the scuﬃng load and viscosity, continuing and further noticed that with increment in viscosity, scuﬃng load ing coeﬃcient of friction and wear resistance, similar to that described by Xu et al. [70]. Abrasive wear occurs because of increased up to a certain extent and then remained constant with an increase in viscosity [67]. However, there is a limita- the presence of more amount of GNPs in a unit volume of oil considered. Hence, this abrasive action of GNPs removed the tion to the extent to which nanoparticles can be blended with liquid, beyond which the improved performance ceases to material from steel balls. e material removal was associated with high-temperature generation due to the metallic contact, prevail [49–51]. Figure 10 shows the steel balls aer the extreme pressure test. At the seizure load, the thickness of the which in turn causes the seizure by joining the steel balls. Zhang et al. investigated with oleic acid-modiﬁed graphene, ﬁlm reduces making the lubrication fall in thin-ﬁlm lubrica- tion regime. is thin ﬁlm gets the surfaces in contact leading at 5 wt.% showed abrasive wear behaviour [71]. Hernandez et al. have also discussed that the concentration of nanoparticles to abrasion. During abrasion, cooling eﬀect of lubricant failed which led to a rise in temperature to higher value. Melting the accumulated at wear scar region will vary and will be more than the concentration of nanoparticles in the lubricant [60]. steel balls and joining them. Metal squeeze out can also be observed at the interface. ere is one more reason which also has some critical inﬂu- ence on seizure load that is aggregates of GNPs bigger than 3.4. Wear Mechanism in Extreme Pressure Characteristics. e thin ﬁlm formed by the liquid which can not diﬀuse in between wear behaviour under extreme loading conditions was the steel balls paving a way to more wear and instant weld [72]. studied. e formation of a thin ﬁlm between two balls was responsible for high seizure load of NO at higher loads as 3.5. Metallurgical Aspects Involved in Welding of Balls. It was shown in Figure 11(a). Blok has discussed that there will the required to focus the eﬀect of the high load abrasive wear on surface irregularities which form an interlocking, that tends the metallurgical parameters and metallurgical modiﬁcations Advances in Tribology 7 (a) (b) (c) F 11: Illustration of formation of thin-ﬁlm between balls just before the weld: (a) 0.25 wt.% GNPs-NO, (b) 0.50% GNPs-NO, and (c) 1.0% GNPs-NO. At high loads Van der Waals force F 12: Illustration of shearing of GNPs at high load (2300 N) for 1.0% GNPs-NO. that occur in steel balls. In this regard, Ming Feng has discussed is suﬃcient to melt the steel balls at the contact point and stick that the metallic surface in contact and in relative motion it to one of the mating surfaces [73]. with each other forms grooves and the ridges. Consequently, Similar to the conditions discussed by Syahrullail et al., this formation is followed by strain hardening. It was also Figure 13(a) shows the wedge cutting edges found in case of mentioned that there will be debris formation or shear that neem oil [69]. e wedge cutting edge was formed due to the takes place that raises the temperature to such an extent that high load and high speed of operation which further led to 8 Advances in Tribology (b) (a) (a) (b) (d) (c) (c) (d) F 13: Optical micrographs showing wedge cutting edge and pit formation: (a) wedge cutting edge in NO, (b) Pit in Pure NO, (c) 0.25% GNPs-NO, and (d) 0.5% GNPs-NO. In this study, the above-mentioned case can be clearly observed in Figures 13(b)–13(d). Wear phenomenon forms a pit on the ball surface while examining. As evidence, pits were observed in optical microscope image taken from the optical microscope coupled with the Four-ball tribometer. Zulkiﬂi et al. have dis- cussed that the steel balls form a micro joint with each other and this micro joint when ruptured forms a pit [74]. In Figure 13, when compared to NO and 0.25% GNPs-NO, wear pit observed with 0.5% GNPs-NO was lesser as observed in Figure 13(d) because at such a high load the metal will squeeze out to the edges forming the wedge cutting edge rather than adhering on to the rotating ball surface. is phenomenon can be visu- alized in Figure 13(a). However, the formation of pits seem to be more signiﬁcant in the NO and 0.25% GNPs-NO. Figure 14 depicts the bulk matter squeezed out from the edges due to melting of balls operated under high load of 2300 N. e noteworthy reason is that due to very high load, F 14: Metal squeeze out due to high load (2300 N) 0.5% GNPs-NO. a temperature gradient was observed in steel balls at the point of contact and this temperature gradient decreases the hard- high temperature and caused the metal to melt. However, the ness value, in turn causing metal to melt. e squeeze-out in the case of 0.5% GNPs-NO is shown in Figure 14. edges were exposed to the very high thermal atmosphere caused a partial seizure that indicated the approaching weld point. At the point of contact due to the abrasion eﬀect, the temperature was increased and eventually seized the balls. 4. Conclusions It was observed that the balls were exposed to a very high load of order 2.3 kN and high operational speed the balls e current investigation presented the possible enhancement started welding and de-welding which in turn caused the of the viscosity, wear preventive and extreme pressure char- -joining of steel balls. Abrasion wear action further leads to the acteristics of neem oil via the inclusion of 0.25–1.0% GNPs-NO. micro joint of the metal from stationery balls to its counterpart. GNPs were around <50 nm, ﬂake form and very much Advances in Tribology 9 scattered, utilizing ultrasonication in the neem oil as a base Acknowledgments lubricant. On the basis of results presented in the preceding is work was funded by e National Institute of Engineering, section, the following conclusions can be drawn: Centre for Research & Development (NIE-CRD) and TEQIP- (i) e viscosity of pure neem oil curtailed as for tem- III, NPIU. e authors would like to acknowledge the support perature and augmented with respect to the GNPs of the Board of Management, NIE, Principal Dr. G. Ravi, and loading (0.25–1.0 wt.%) for the temperature range TEQIP-III Coordinator Dr. B.N. Yuvaraju. e tribometer was of 30°C–55°C of the examination. procured from Magnum Engineers, Bangalore, India we would like to extend our sincere gratitude to Magnum Engineers. We (ii) e tribological examination of neem oil with low ﬁller loading of graphene nanoplatelets (GNPs) as are also grateful to Ms. Chaitra Ramesh, Assistant Professor, NIE, who moderated this paper and in that line improved the additives particularly 1.0% GNPs-NO indicated a huge decrease in the friction coeﬃcient and wear manuscript signiﬁcantly. anks go to the following Centre for Composite Materials Research (CCMR), NIE, technical staﬀ scar diameter. is could be because of the better dispersibility of GNPs in neem oil as these nano- Mr. Byresh and Mr. M. Madhusudhan for the help rendered in conducting experiments. particles oﬀer better anti-wear ability. (iii) Tribological testing demonstrates that the utiliza- tion of GNPs is eﬀective for the decrease of coeﬃ- cient of friction and wear with expanding loading References of GNPs. e utilization of higher loaded GNPs (1.0 [1] M. R. Hilton and P. D. 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Publisher: Hindawi Publishing Corporation
Copyright: Copyright © 2020 B. Suresha et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ISSN: 1687-5915
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DOI: 10.1155/2020/1984931
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Abstract

Hindawi Advances in Tribology Volume 2020, Article ID 1984931, 11 pages https://doi.org/10.1155/2020/1984931 Research Article Tribological Behaviour of Neem Oil with and without Graphene Nanoplatelets Using Four-Ball Tester 1,2 1,2 1,2 1,2 B. Suresha , G. Hemanth , Apurva Rakesh, and K. M. Adarsh Department of Mechanical Engineering, e National Institute of Engineering, Mysore 570008, India Visvesvaraya Technological University, Belagavi, Karnataka, India Correspondence should be addressed to B. Suresha; sureshab2004@yahoo.co.in Received 12 May 2019; Revised 16 August 2019; Accepted 25 October 2019; Published 25 January 2020 Academic Editor: Patrick De Baets Copyright © 2020 B. Suresha et al. is is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. e present work was aimed to study the friction and wear behaviour of graphene nanoplatelets (GNPs) under extreme pressure conditions as an anti-weld additive for neem oil. e eﬀect of neem oil, blended with various loading of GNPs on the friction and wear characteristics has been investigated. From the experimental results, it was found that 1 wt.% of GNPs in neem oil showed the least coeﬃcient of friction and smoother wear scar diameter. e extreme pressure test was performed on neem oil with and without GNPs as per ASTM standards. e extreme pressure test results indicated the improvement in seizure load of neem oil by 27.8% at 0.5 wt.% of GNPs as compared to pure neem oil. Optical microscopy of worn steel ball surface revealed the pit formation and the formation of wedge cutting edge in GNPs modiﬁed neem oil. with bio-based oils namely jatropha, spirulina, pongamia 1. Introduction [12–14]. Friction and wear of tribo-system depend on various e friction and wear characteristics of machine components tribo parameters like applied normal load, sliding velocity, is a signiﬁcant research area that is being thoroughly studied. sliding distance and type of lubrication. Hsu et al. concluded A lubricant, apart from being used in automotive engines, ﬁnds that the eﬀect of hydrodynamic condition of the lubricant does its necessity in pneumatic circuits, food processing machinery, not have a signiﬁcant eﬀect on surface wear. However, the airplanes, hydraulic press and hydraulic jacks [1–3]. e oper- interaction between lubricant and surfaces in contact inﬂuence ating conditions to which lubricants are exposed dictates its the tribological behaviour [15]. e bio-oils have a superior grade and shelf life. ere are many researchers who worked anti-corrosive property, high ﬂash and ﬁre point as well as to improve the properties of bio-based oils as lubricant and feeble aquatic toxicity. Lubricants extracted from edible oil reduced the wear loss of machine elements [4, 5]. Continuous seeds pose severe food versus fuel issues that can be overcome eﬀorts have been made to develop technology to avoid ill eﬀects by nonedible oils [16]. Many researchers have studied the fric- on the environment [6]. e rate of biodegradability of mineral tion and wear behaviour of bio-based oils [17–19]. e bio- oils is around 30–65% whereas, a bio-based oils is having oils comprise of triglycerol (molecular weight: 240.25 g/mol), almost 95% [7]. Erhan et al. studied the lubricant base stock and polar nature of the fatty acids allows it to form a bond potential of chemically modiﬁed vegetable oils and concluded with metallic surfaces and create a thin monolayer that is ben- that the pollution problem is so severe that nearly 50% of all eﬁcial in reducing wear and friction [18, 19]. e bio-based lubricants sold globally end up in the environment via volatil- oils have few shortcomings, like poor thermal-oxidative sta- ity, spills, or total loss applications [8]. bility, nonnegative pour point and gumming eﬀect [20–23]. Owing to the ill eﬀects of mineral and synthetic oils on Incorporation of nanoﬁllers into bio-oils has shown lower the environment and human health and increasing oil demand coeﬃcient of friction and smoother wear scar diameter and prices, the research objective was framed to pursue [24, 25]. e reduction in wear loss was attributed to an st research on bio resources in the late 90’s and early 21 century increase in the viscosity of the base oil [24]. e viscosity [9–11]. Regular eﬀorts were made to substitute mineral oils enhancement was associated with the number of particles 2 Advances in Tribology available per unit volume of oil. ere are lot of parameters that dictate the behaviour of nanoparticles in the lubricant, some of which are size, geometry and chemical and physical properties. Nanoparticles tend to diﬀuse between two mating components thereby avoiding metal contacts leading to wear reduction. Some nano-additives form a bond with metal sur- faces while some convert sliding into rolling friction [25–27]. Masuda et al. proved the incompatibility of metallic nanoﬁllers with lubricant and concluded that surface activity was respon- sible for this incompatibility [28]. Not only the particulate additives play an important role in enhancing the tribological properties, but blending bio-based oils into lubricants also showed multi-functional behaviour [29–32]. Li et al. have demonstrated the application of natural garlic oil as a high performance and extreme pressure additive for lubricants [33]. Ossia et al. have acknowledged the presence of eicosanoic and octadecanoic acids in castor and jojoba oil and enhancing their F 1: TEM image of GNPs [48]. oxidation stability and tribological properties [34]. Carbonaceous particles like soot, graphene, multiwalled car- bon nanotube showed very good lubricity [35–37]. Oil seeds Neem is a native tree to Indian-subcontinent and is widely crushing grown in Indian states namely, Uttar Pradesh, Tamil Nadu, Oil and Karnataka. Its applications are discussed in ayurvedic lit- Analysis extraction erature. Schmutterer has analyzed the eﬀect of neem derived products as pesticides [38]. ere are a lot of works available dealing with applications of neem and their derivatives [39– Oil coarse 45]. Chaudhari et al. have discussed a self-healing coating of Blended oil Work process chart ltering testing a polyurethane prepared from neem oil polyesteramides [46]. Muhammad et al. have discussed wear preventive character- istics of neem and Jatropha oil with antimony dialkyldithio carbonate [47]. Neem oil has promising beneﬁts in all ﬁelds. GNPs Oil ne blending ltering However, neem oil was less explored with tribological prop- erties as bio-lubricant. Hence, the present research work Pure oil explores neem oil and the role of graphene nanoplatelets testing (GNPs) in neem oil on viscosity, friction and wear as well as on seizure load which are important factors that are accounted F 2: Work process chart of the current experimental work. for the right selection of the appropriate lubricant in diﬀerent sliding components of food processing machines. Hence, neem oil was preferred for the further conscientious investi- with 50-micron mesh sieve to remove ﬁner impurities. Some gation with and without graphene nanoplatelets. of the particulate impurities were settled at the bottom of the container which was later discarded. 2. Materials and Methods 2.2. Blending Oil with Graphene Nanoplatelets. e neem Neem oil (NO) was procured from NIE-Center for Renewable oil obtained was thoroughly mixed with GNPs following Energy and Sustained Technology, Mysore, India. e Graphene ultrasonication. e loading of nanoﬁllers has a great eﬀect nanoplatelets (GNPs) were procured from Sigma Aldrich, on the functionality of bio-oils as lubricants with about Bangalore, India. e speciﬁcations of GNPs are, surface area 0.1–1.5 wt.% stated as the optimum loading for nanoﬁllers 750 m /g, the GNPs considered is structured out of 3–6 layers in majority research works carried out [49–51]. erefore, in of <50 nm thick. e density of the material is 0.2–0.4 g/cm . the present work, for the purpose of evaluating the eﬀect of Figure 1 shows the Transmission Electron Microscopic image GNPs loading on the tribological properties of neem oil, nano- of GNPs obtained from product data sheet [48]. It can be lubricants have been made at four diﬀerent loadings viz., 0.25, observed from the TEM image that the GNPs are semi-trans- 0.5, 0.75, and 1.0 wt.% by incorporating GNPs to neem oil. parent and they are in order of few nanometres. e ultrasonication was performed for 15 min at a frequency of 22 kHz using Johnson Ultrasonicator. Figure 2 shows the 2.1. Extraction of Neem Oil. e neem oil was produced from process chart of the current research. its seeds. e neem seeds were cleaned and crushed to extract oil out of it. e oil so obtained was ﬁltered in two stages. 2.3. Measurement of Kinematic Viscosity. e viscosity of Firstly, with a coarse ﬁlter of 180-micron mesh sieve and later the blended oils was tested along with bio-based oils. e Advances in Tribology 3 ermometer Operating handle Inner cylinder Outer cylinder Oil level indicator Stirrer wall Stirrer vane Heating coil Ball valve Capillary tube Outlet valve Mark Conical ask containing 50 cc of oil F 3: Sectional front view of the Redwood viscometer. F 4: Schematic diagram of the four-ball tester. F 5: Assembly of four-ball tester with ball holder cup. viscosity test was carried on the redwood viscometer whose test procedure is governed by IP 70/62. 50 cm of oil is allowed to ﬂow down and corresponding ﬂow time () in seconds and 64–66 HRC with mirror polished surface was used for the was recorded for further calculations. e oriﬁce diameter investigation. e test duration was 60 min, the temperature of of viscometer is 1.62 mm. e test was initiated at 30°C and the oil was 75°C and the rotation speed was kept 1200 ± 1 rpm. for every 5°C rise in temperature, the consecutive reading e test load was maintained to be constant, which was was noted. Five trials were done to aﬃrm the values. Figure 3 40 ± 0.1 kg. e coeﬃcient of friction and wear scar diameter shows the schematic representation of Redwood viscometer. were obtained. Figures 4 and 5 depict the four-ball tester setup. Equation (1) was used to evaluate kinematic viscosity (). Seizure load is the lowest applied load at which the rotating ball weld to the stationery balls indicating extreme pressure level of the lubricants. e extreme pressure test was performed 0.65 (1) 휈 = 0.00247 × 푡 − . according to ASTM D2783 standard [53]. e test conditions were as follows, the load was varied from 400 N till the seizure 2.4. Friction and Wear Test. e wear preventive characteristics load with an increment of 100 N, speed was maintained to be of the NO-GNPs based lubricant were examined under four- 1760 ± 30 rpm, oil temperature was 25°C and the duration of ball tribometer. e test procedure was governed by ASTM the test was 10 s. Once the seizure occurs, to ﬁnd the seizure D 4172 [52]. e chromium steel balls of 12.7 mm diameter load precisely, the load was decreased by 10 N for each trial 4 Advances in Tribology T 1: Kinematic viscosity of various wt.% of GNPs-neem nano-lubricants. Nano-lubricant Kinematic viscosity Designation formulations at 40°C (mm /s) Pure neem oil NO 53.3 ± 0.35 Neem oil mixed with 0.25% GNPs-NO 55.5 ± 0.61 0.25 wt.% GNPs Neem oil mixed with 0. 50% GNPs-NO 58.7 ± 0.19 0.50 wt.% GNPs Neem oil mixed with 0.75% GNPs-NO 62.3 ± 0.53 0.75 wt.% GNPs Neem oil mixed with 1.0% GNPs-NO 67.193 ± 0.4 1.0 wt.% GNPs 30 35 40 45 50 55 until the seizure load was obtained. Five trials were performed Temperature as mentioned above to aﬃrm the values. NO NO+0.25 GNPs NO+0.5% GNPs 3. Results and Discussion NO+0.75% GNPs NO+1.0% GNPs 3.1. Eﬀect of GNPs Loading on Viscosity of Neem Oil. e rate F 6: Kinematic viscosity of GNPs-neem nano-lubricants. of ﬂuid resistance against its ﬂow is called viscosity, which is one of the vital factors for selecting proper lubricating oil for moving components in machinery. Since, one of the important properties of a lubricant is the viscosity, in the 0.12 present research work; the focus is on the eﬀect of loading of GNPs into the neem oil which results in change of viscosity. 0.10 For this reason, the viscosity of the lubricating oil which did not contain nanoparticles was considered as a base ﬂuid (neem 0.08 oil) and also the viscosity of the bio-lubricants which contain GNPs at four loadings 0.25, 0.5. 0.75, and 1.0 wt.% and with an 0.06 increase in temperature from 30°C to 55°C was measured. e experimental results are summarized in Table 1 and are also 0.04 shown in Figure 6. It can be seen, the viscosity of GNPs-NO nano-lubricants the temperatures had increased from 30°C to 0.02 55°C by increasing the loading of GNPs, although the rate of change in viscosity at lower loadings was much smaller than 0.00 that at higher loadings. e stimulating point related to the ampliﬁed viscosity of GNPs-NO nano-lubricants with 1.0 wt.% loading is that, for Blended neem oil increasing temperatures, the viscosity of neem oil without Mean CoF GNPs had a substantial decrease. When GNPs were incorpo- rated to the neem oil, they were positioned between the neem F 7: Mean coeﬃcient of friction of GNPs-neem nano-lubricants. oil layers and escort to ease the ﬂuid layer movement on each other. As a result, the viscosity decreased slightly and the decreasing trend can be seen for 0.25% and 0.5% GNPs-NO on pure NO and then followed by blended oils of NO. ere are nano-lubricants as shown in Figure 6. As GNPs loading many factors that inﬂuence lubricant properties. In this regard, increases, nanoﬁllers agglomerate and create bigger and asym- the coeﬃcient of friction versus oil combinations plot is as metric particles, which prevent movement of ﬂuid layers on shown in Figure 7. It was seen that the coeﬃcient of friction each other; hence the viscosity increased for higher loadings was reduced by 7.5% on incorporation of 0.25% GNPs-NO, (0.75 and 1.0 wt.%) of GNPs-NO nano-lubricants. e same 25.2% with 0.5% GNPs-NO, 28.9% with 0.75% GNPs-NO and behaviour was observed by other researchers with diﬀerent the highest reduction was found with 1.0% GNPs-NO which liquids and nano additives [54–57]. Wang et al. observed about was around 41.4% with the base NO. A signiﬁcant reduction of 86% improvement in the viscosity of distilled water on incor- 23% was observed in wear scar diameter with 1.0% GNPs-NO poration of Al O [54]. in relation to unblended NO. is reduction can be associated 2 3 with an increment in the viscosity of the oil which helped in 3.2. Wear Preventive Characteristics GNPs Modiﬁed Neem the formation of thin-ﬁlm owing to the decrease in wear scar Oil. e wear preventive characteristics were ﬁrst conducted diameter as well. NO 0.25% GNPs 0.5% GNPs 0.75% GNPs 1.0% GNPs Variation of viscosity (mm /s) Mean CoF Advances in Tribology 5 (a) (b) (c) (d) (e) F 8: Optical micrographs of wear scar diameter: (a) pure neem oil, (b) 0.25% GNPs-NO, (c) 0.50% GNPs-NO, (d) 0.75% GNPs-NO, and (e) 1.0% GNPs-NO. From Figure 8, it can be observed that GNPs modiﬁed oil with lower percentages of GNPs showed darker concentric grooves which depict abrasive wear whereas in higher per- centages of GNPs it showed smoother wear track depicting reduced contact between steel balls. e darker grooves are deeper whereas brighter grooves are shallow. A similar obser- vation was found by Suresha et al. [58]. It is these grooves that are responsible for holding GNPs back on the wear surface causing reduction in wear, the same phenomenon was dis- cussed by Huang et al. where they have incorporated graphite sheets [59]. Hernandez et al. have proved experimentally that nanoparticle will accumulate in the wear scar region [60]. e load is the primary characteristics that aﬀect wear. Ing et al. proved that variations in the load largely dictates the wear on the surface of the steel balls [61]. e chemical composition of the lubricant oil aﬀects the wear preventive characteristics. Blended neem oil Stachowiak and Batchelor have discussed that synthetically Seizure load produced lubricants have compounds containing phosphides and sulphide ions that have a tendency to react with the surface F 9: Seizure load of various wt.% of GNPs-neem nano- of the steel balls which prevent the metallic contact to a certain lubricants. extent and reduce the wear [62]. However, the sulphide and phosphide compounds are not present in bio-based resources which makes the bio-based resources to have higher wear scar GNPs blended into oil helps to sustain the failure by enhancing than mineral or synthetic oils [61]. e reason for improvement the seizure load. It was observed in Figure 9 that the seizure in anti-frictional properties was the enhancement in viscosity load was found to be increased with all combinations of GNPs whereas, improvement in anti-wear property was due to the blend. Among all combinations of oils 0.5% GNPs-NO has uniformity in the dispersion of GNPs. e quintessential proof portrayed the outstanding improvement in seizure load of for the latter condition can be found in the work of Hu et al. [63]. 2300 N owing to 27.7% increment in seizure load in accordance with NO. However, the higher percentages of GNPs modiﬁed 3.3. Eﬀect of GNPs Modiﬁed Neem Oil on Extreme Pressure NO did not show further increment in seizure load. Characteristics. e extreme pressure test was started with NO e reason that can be attributed to this increment in seizure to seek for their seizure load followed by the blended oils. e load is the viscosity of the unblended and blended neem oil. Binu 0.75 wt.% GNPs 0.25 wt.% GNPs 1.0 wt.% GNPs 0 wt.% GNPs 0.5 wt. % GNPs Seizure load (N) 6 Advances in Tribology to reduce in the surface area of the mating when compared to the apparent area. is reduction in the area causes a very high bearing pressure that tends to form strain hardening [68]. is was avoided by the formation of the thin ﬁlm that avoided the steel balls getting in contact with each other and prevented them from getting worn out. in-ﬁlm formation just before seizure load with 0.5% GNPs-NO and 1.0% GNPs-NO are shown in Figures 11(b) and 11(c). e ﬁlm thickness was shown varied because of exposure to the oil ﬁlm to the same load. Viscosity plays a major role leading to the formation of the thin ﬁlm. e wear mechanism aer blending GNPs with NO is unlike to the condition without GNPs. Upon increase in viscosity, lubricant ﬁlm formed will have a higher thickness that will avoid the steel balls getting into contact with each other, if the ﬁlm thickness increases, the gap between friction surfaces increases eventually reducing the wear. To get steel balls in contact with each other, lubricant ﬁlm destruction is necessary. To destroy lubricant ﬁlm requires more load. ereby, it increases the seizure load. Just before the seizure, the ﬁlm thickness was very less, then the minuscule GNPs will diﬀuse between the balls and some GNPs were stopped by the wear scar formed. Hence, they settle in the wear scar region, over which the balls slide. GNPs being multi- layered, experiences a shear force and avoids the metallic contact thereby further increasing the seizure load by a small amount. Aer certain loading, the thin ﬁlm fails to form leading F 10: Steel balls aer extreme pressure test at the seizure load. the metal surfaces to contact. is contact region was the high thermal zone leading to the melting of steel at the point of et al. have discussed the relation between the viscosity and load- contact. Syahrullail et al. found that during extreme pressure on vegetable oils the wedge cutting edges will be formed due carrying capacity by using diﬀerent models and experimental validation [64]. ere is a correlation between the minimum oil to high load [69]. In the present study, the wear scar was observed under an optical microscope and abrasive wear was ﬁlm thickness and viscosity [65]. e viscosity improves load carrying capacity [66]. Hence, it can be said that the thickness predominantly noticed. Xu et al. proved that the graphene adheres to the wear scar which acts as a solid lubricant and of oil ﬁlm generated controls maximum load on the component. ough the increment in viscosity was high with 1.0% GNPs-NO sustains the high load up to a certain level [70]. Figure 12 shows shearing of GNPs when exposed to a very the seizure load was lesser than 0.5% GNPs-NO. Kozma had worked and concluded about the relation high load and high speed of operation. e amount of GNPs (0.25% and 0.5%) present in the neem oil was better in reduc- between the scuﬃng load and viscosity, continuing and further noticed that with increment in viscosity, scuﬃng load ing coeﬃcient of friction and wear resistance, similar to that described by Xu et al. [70]. Abrasive wear occurs because of increased up to a certain extent and then remained constant with an increase in viscosity [67]. However, there is a limita- the presence of more amount of GNPs in a unit volume of oil considered. Hence, this abrasive action of GNPs removed the tion to the extent to which nanoparticles can be blended with liquid, beyond which the improved performance ceases to material from steel balls. e material removal was associated with high-temperature generation due to the metallic contact, prevail [49–51]. Figure 10 shows the steel balls aer the extreme pressure test. At the seizure load, the thickness of the which in turn causes the seizure by joining the steel balls. Zhang et al. investigated with oleic acid-modiﬁed graphene, ﬁlm reduces making the lubrication fall in thin-ﬁlm lubrica- tion regime. is thin ﬁlm gets the surfaces in contact leading at 5 wt.% showed abrasive wear behaviour [71]. Hernandez et al. have also discussed that the concentration of nanoparticles to abrasion. During abrasion, cooling eﬀect of lubricant failed which led to a rise in temperature to higher value. Melting the accumulated at wear scar region will vary and will be more than the concentration of nanoparticles in the lubricant [60]. steel balls and joining them. Metal squeeze out can also be observed at the interface. ere is one more reason which also has some critical inﬂu- ence on seizure load that is aggregates of GNPs bigger than 3.4. Wear Mechanism in Extreme Pressure Characteristics. e thin ﬁlm formed by the liquid which can not diﬀuse in between wear behaviour under extreme loading conditions was the steel balls paving a way to more wear and instant weld [72]. studied. e formation of a thin ﬁlm between two balls was responsible for high seizure load of NO at higher loads as 3.5. Metallurgical Aspects Involved in Welding of Balls. It was shown in Figure 11(a). Blok has discussed that there will the required to focus the eﬀect of the high load abrasive wear on surface irregularities which form an interlocking, that tends the metallurgical parameters and metallurgical modiﬁcations Advances in Tribology 7 (a) (b) (c) F 11: Illustration of formation of thin-ﬁlm between balls just before the weld: (a) 0.25 wt.% GNPs-NO, (b) 0.50% GNPs-NO, and (c) 1.0% GNPs-NO. At high loads Van der Waals force F 12: Illustration of shearing of GNPs at high load (2300 N) for 1.0% GNPs-NO. that occur in steel balls. In this regard, Ming Feng has discussed is suﬃcient to melt the steel balls at the contact point and stick that the metallic surface in contact and in relative motion it to one of the mating surfaces [73]. with each other forms grooves and the ridges. Consequently, Similar to the conditions discussed by Syahrullail et al., this formation is followed by strain hardening. It was also Figure 13(a) shows the wedge cutting edges found in case of mentioned that there will be debris formation or shear that neem oil [69]. e wedge cutting edge was formed due to the takes place that raises the temperature to such an extent that high load and high speed of operation which further led to 8 Advances in Tribology (b) (a) (a) (b) (d) (c) (c) (d) F 13: Optical micrographs showing wedge cutting edge and pit formation: (a) wedge cutting edge in NO, (b) Pit in Pure NO, (c) 0.25% GNPs-NO, and (d) 0.5% GNPs-NO. In this study, the above-mentioned case can be clearly observed in Figures 13(b)–13(d). Wear phenomenon forms a pit on the ball surface while examining. As evidence, pits were observed in optical microscope image taken from the optical microscope coupled with the Four-ball tribometer. Zulkiﬂi et al. have dis- cussed that the steel balls form a micro joint with each other and this micro joint when ruptured forms a pit [74]. In Figure 13, when compared to NO and 0.25% GNPs-NO, wear pit observed with 0.5% GNPs-NO was lesser as observed in Figure 13(d) because at such a high load the metal will squeeze out to the edges forming the wedge cutting edge rather than adhering on to the rotating ball surface. is phenomenon can be visu- alized in Figure 13(a). However, the formation of pits seem to be more signiﬁcant in the NO and 0.25% GNPs-NO. Figure 14 depicts the bulk matter squeezed out from the edges due to melting of balls operated under high load of 2300 N. e noteworthy reason is that due to very high load, F 14: Metal squeeze out due to high load (2300 N) 0.5% GNPs-NO. a temperature gradient was observed in steel balls at the point of contact and this temperature gradient decreases the hard- high temperature and caused the metal to melt. However, the ness value, in turn causing metal to melt. e squeeze-out in the case of 0.5% GNPs-NO is shown in Figure 14. edges were exposed to the very high thermal atmosphere caused a partial seizure that indicated the approaching weld point. At the point of contact due to the abrasion eﬀect, the temperature was increased and eventually seized the balls. 4. Conclusions It was observed that the balls were exposed to a very high load of order 2.3 kN and high operational speed the balls e current investigation presented the possible enhancement started welding and de-welding which in turn caused the of the viscosity, wear preventive and extreme pressure char- -joining of steel balls. Abrasion wear action further leads to the acteristics of neem oil via the inclusion of 0.25–1.0% GNPs-NO. micro joint of the metal from stationery balls to its counterpart. GNPs were around <50 nm, ﬂake form and very much Advances in Tribology 9 scattered, utilizing ultrasonication in the neem oil as a base Acknowledgments lubricant. On the basis of results presented in the preceding is work was funded by e National Institute of Engineering, section, the following conclusions can be drawn: Centre for Research & Development (NIE-CRD) and TEQIP- (i) e viscosity of pure neem oil curtailed as for tem- III, NPIU. e authors would like to acknowledge the support perature and augmented with respect to the GNPs of the Board of Management, NIE, Principal Dr. G. Ravi, and loading (0.25–1.0 wt.%) for the temperature range TEQIP-III Coordinator Dr. B.N. Yuvaraju. e tribometer was of 30°C–55°C of the examination. procured from Magnum Engineers, Bangalore, India we would like to extend our sincere gratitude to Magnum Engineers. We (ii) e tribological examination of neem oil with low ﬁller loading of graphene nanoplatelets (GNPs) as are also grateful to Ms. Chaitra Ramesh, Assistant Professor, NIE, who moderated this paper and in that line improved the additives particularly 1.0% GNPs-NO indicated a huge decrease in the friction coeﬃcient and wear manuscript signiﬁcantly. anks go to the following Centre for Composite Materials Research (CCMR), NIE, technical staﬀ scar diameter. is could be because of the better dispersibility of GNPs in neem oil as these nano- Mr. Byresh and Mr. M. Madhusudhan for the help rendered in conducting experiments. particles oﬀer better anti-wear ability. (iii) Tribological testing demonstrates that the utiliza- tion of GNPs is eﬀective for the decrease of coeﬃ- cient of friction and wear with expanding loading References of GNPs. e utilization of higher loaded GNPs (1.0 [1] M. R. Hilton and P. D. 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Journal

Advances in Tribology – Hindawi Publishing Corporation

Published: Jan 25, 2020

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H. D. Huang, J. P. Tu, L. P. Gan, and C. Z. Li
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E. Hu, X. Hu, T. Liu, L. Fang, K. D. Dearn, and H. Xu
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Y. Xu, Y. Peng, K. D. Dearn, X. Zheng, L. Yao, and X. Hu
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W. Zhang, M. Zhou, H. Zhu et al.
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E. Omrani, P. L. Menezes, and P. K. Rohatgi
Metal transfer and wear,

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Wear prevention characteristics of a palm oil-based TMP (trimethylolpropane) ester as an engine lubricant,

N. W. Zulkifli, M. A. Kalam, H. H. Masjuki, M. Shahabuddin, and R. Yunus

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Tribological Behaviour of Neem Oil with and without Graphene Nanoplatelets Using Four-Ball Tester

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