thermal and tool wear characterization of graphene oxide ......turning flank wear a b s t r a c t...

Original Research Article

Thermal and tool wear characterization of grapheneoxide coated through magnetorheological fluids oncemented carbide tool inserts

M. Thiyagu a,b,*, L. Karunamoorthy b, N. Arunkumar c

aDepartment of Mechanical Engineering, Agni College of Technology, Chennai, IndiabDepartment of Mechanical Engineering, Anna University, Chennai, IndiacDepartment of Mechanical Engineering, St. Joseph's College of Engineering, Chennai, India

a r c h i v e s o f c i v i l a n d m e c h a n i c a l e n g i n e e r i n g 1 9 ( 2 0 1 9 ) 1 0 4 3 – 1 0 5 5

a r t i c l e i n f o

Article history:

Received 13 November 2018

Received in revised form

6 March 2019

Accepted 15 May 2019

Available online 20 June 2019

Keywords:

Graphene oxide

Tool texture

Magnetorheological fluid

Turning

Flank wear

a b s t r a c t

The proposed work is about the investigation of nano-textured tool insert with magnetor-

heological-based graphene coating process. The comparative study on nano-textured car-

bide insert with unpolished one for turning duplex stainless steel (S31803/2205) is made by

conducting number of experiments with Box–Behnken design using response surface

methodology. An array of sensor based on the conductive element of chromel and alumel

core integrated through DC magnetron sputtering on the rake surface of the tool insert. The

performance of the proposed sensor was evaluated from the obtained thermo-electromotive

force on tool chip contact interference and the temperature measurements taken at the

contours of multiple points with respect to the tool wear. Results obtained clarify that with

the rise in cutting tool temperature leads to the rise in tool wear based on the adhesion and

abrasion. It has been found that the graphene coated tool inserts provides high wearable

resistances with flank wear of 0.298 mm at 21st pass. The cutting tool temperature is found

to spread uniformly with a value of 202 8C for graphene coated inserts for cutting speed of

55 m/min. Microstructural images taken proved that the formation of cementite and

carbides with inter metallic compounds (IMCs) produced during the tool chip interface

leads to the strengthening of tool tip in reducing the tool-wear. Also the occurrence of

ultrafine grain boundaries on the tool tip occurs increasing the formation of covalent bonds

in providing the robust resistance against tool wears.

© 2019 Published by Elsevier B.V. on behalf of Politechnika Wroclawska.

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1. Introduction

The machining process with cutting tool operation inducesdynamic wear with the interference of tool chip contact on therake and flank side of the tool insert. The exhibited wear istedious to be analyzed, as it involves the chemo-mechanical

* Corresponding author at: Department of Mechanical Engineering, AgE-mail address: [email protected] (M. Thiyagu).

https://doi.org/10.1016/j.acme.2019.05.0051644-9665/© 2019 Published by Elsevier B.V. on behalf of Politechnika

reactions on the tool chip interface. It involves a transientdynamic behavior on the structural interactions of cuttingforces, cutting speed and chemical composition of the tool andthe work piece materials [1].

In dry machining conditions, the frictional contact betweenthe tool tip and the chip interface leads to the rise in cutting

ni College of Technology, Chennai, India.

Wroclawska.

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tool temperature with high adhesion and abrasion wearoccurrence. This deteriorates the tool life consequently. Thisinitiates the pavement for the researchers to innovate a self-lubrication technology on the cutting tools for the reduction ofthermal impact on tool tip in achieving uniform heatdissipation on the substrate by reducing the friction coefficient[2]. The development of self-lubrication inserts with variousmethods has been attempted. Ze et al. [3] concluded hisfindings with the use of CaF2 as solid lubricant reduces thefriction coefficient at the tool tip with the reduction in thermalcontact conductance in comparison with the dry cuttingoperation using ceramic inserts. Other research developmentshave been found with the use of coating of these solidlubricities on the tool substrates that could improve thetribological properties. In case of drilling operation at lowcutting speeds, abrupt wear rates could be formed. Recentstudies in the use of nano coatings with MoS2 or MoS2/Ti ontool substrate could reduce and normalize the wear rates. Thenoted factor in the use of self-lubricated tools in the rapidformation of wear resistance film acting as frictionless nanobearings between the tool tip and work piece interferenceduring the dry cutting process [4]. Jianxin et al. [5], Xing et al. [6]and Lian et al. [7] defined their conclusions on the effectiveminimization of machining forces through micro groovesengraved on the rake and flank faces filled with nano fillers likeMoS2, multiwall carbon nanotube (MWCNT) and graphene thatpossess higher lubrication property and tool chip interferencein machining of hardened alloy. They also stated that theformation of thin lubricating film on the rake face of thesubstrate and chip serration for the reduction in contactstresses. The micro groove reduces the contact area betweenthe tool chip interference, which promotes the lubricationregime in reducing the cutting forces adequately [5–7].

The cutting tool with improved geometry based on surfacecoating and finishing with extremely low friction tools in drymachining process of ductile materials with high adhesivenature which gets laid on the cutting tool insert. It could bereduced with the flooding of cutting fluid to reduce adherenceof ductile materials on the tool inserts. The creep in tool insertoccurs frequently in the cutting operations without the properflow of cutting fluid on the tool chip interface. This muddlesthe thermodynamic flow of temperature gradient on the rakesurface of the cutting tool insert [8]. The robustness of toolinserts is mainly impacted on the micro relief and microstruc-ture/phase composition of tool inserts. These attributes definethe surface hardness of each layer that involves the erraticstresses that occurs during operation life [9].

The contacting area of the tool insert undergoes fatigueloads with concatenated transient loads that weaken thethermally affected zones leading to insert breakage [10]. Tooltexturing using coating methods have been studied for pastfour decades that improves the tool life and machiningcharacteristics. This enhances tribological nature of theworking substrates in manufacturing technology [11].

Frictionless contact at the tool chip contact zone to promotethe sliding chip formation on the rake face is a propitiousfactor to thwart the cutting tool temperature and wear rate. Ithas been recorded that surface texturing of rake and flankfaces in cutting tool inserts boosts the tribological character-istics; with the slithers on the rake face improving the chip

compression ratio and tool life [12]. Magnetic abrasivefinishing (MAF) profiles up the uniformity in surface roughnessof the peaks in work piece using flexible chains of carbonyl ironparticles (CIP) holding the abrasive particles at intermittency[13]. This work proposes the nano coating of carbide insertswith minimal wear on the cutting edges. In this paper, anexperimental procedure is adopted to determine the tribologi-cal and thermal characterization in the tool–chip contact areain the plain turning operation. To investigate the effects of theduplex stainless steel material characteristics on the tool–chipcontact conductance in turning experiments.

2. Materials and methods

2.1. Preparation of graphene nano platelets based onmagnetorheological coating fluid

The graphene nano platelets were extracted from the graphitepowder using Hummer's method. Icy H2SO4 (98%), KMnO andNaNO were added to the graphite powder. The solution ismixed using magnetic stirrer for 2 h and 30% HnO solution wasadded slowly into the slurry until the color turned to brilliantbrown with oxidation of graphite oxide. The graphite oxideslurry was serrated as foils using ultrasonic generator for 6 h.The final graphene nano platelets were collected usingcentrifugation process and washed with 5% HCl and finallywashed with distilled water. Fig. 1 shows the SEM and EDAX ofthe prepared graphene nano platelets.

The magnetorheological fluid was prepared using carbonyliron particles mixed with silicone oil with added surfactants asethylene glycol. The influence of graphene particles onmagnetorheological fluid improves the viscous nature duringthe influence of magnetic field. The ration of CIP weremaintained constant to be 65% and the variation of graphenenanoplatelets were adjusted between 0.1, 0.5, and 1.0 wt.%based on the specific gravity of the suspended particles insilicone oil. The rheological properties of the graphene inducedmagnetorheological fluid are shown in Table 1.

2.2. Magnetorheological coating process

The working mechanism of the magnetorheological basedtexturing process is studied based on the following assump-tions. The magnetic force F acting on the fluid can becalculated as shown in Eq. (1)

F ¼ VxH:grad H (1)

where V is the volume of the magnetic particle, x is thesusceptibility, H and grad H are the field intensity and sheargradient of the magnetic field, respectively. The initial surfaceroughness of the tool substrate is measured, using an opticalprofilometer and it is found to be less than 140 nm. Themechanism of magnetorheological coating process is shownin Fig. 2.

Magnetorheological coating is one of the promisingunconventional finishing processes, which uses a smart fluidcalled magnetorheological fluid (MR fluid). The MR fluid is

Fig. 1 – SEM and EDAX image of graphene nano platelets.

Table 1 – Rheological properties of proposed grapheneinduced magnetorheological fluid.

Properties Value Units

Graphene particle size 10 nmSilicone oil 150 cpCIP 10 mmSurfactant Ethylene glycol –

Kinematic viscosity 600–10,000 cpMagnetic field strength 250 kA/mYield stress 2800 Pa

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slurry with rheological properties, which obeys Bingham'splastic law. Its constituents mainly depend on the concentra-tion of carbonyl iron particles in binder oil but are not limitedto the specific compositions. The proposed fluid contains thelubricative substances like graphene nano platelets with thesuitable surfactant like oleic acid to bind the platelets with theoil. Graphene nanoparticles were used for coating of microvoid substrates to promote the lubrication between tool chipand contact surface and also its thermal resistance toward thedistribution of heat flow over the substrates reduces the toolwear. The MR fluid is introduced through nozzle of the newlydeveloped rotary magnetic tool to the target tool insert surface.In the presence of magnetic field MR fluid particles getstiffened and form columns or brush like appearance along thelines of magnetic flux. The visco-plastic nature of the fluiddevelops shear force, which is used for surface finishing of tool

inserts in nano-level. The yielding nature of the viscousmagnetorheological fluid increases as the magnetic fieldstrength increases. The increase in shear viscosity nature ofthe fluid is based on the ferromagnetic particles present in thefluid obtains a chain like structure to hold the grapheneplatelets with the weak Vander wall forces. In the presence ofmagnetic field, graphene particles get aligned in between thetwo carbonyl iron particles like a chain structure and normalpolishing force pushes the graphene particles inside the microvoids of the tool substrate which acts as lubrication medium.The experimental setup as shown in Fig. 3 consists of arotating electromagnetic tool which holds the carrier fluid atits tip. The carrier fluid which contains the graphene particlesis agitated and pumped using a peristaltic pump connected toa feedback loop controller. The injection of MR fluid into thetool tip is controlled by the force sensor with the measurementof Coriolis forces of the MR fluid on the substrate of the toolinsert. Experiments were carried out based on the inputvariable parameters such as working voltage, coating time, basevoltage and % of graphene concentration. The parameters wereinvestigated experimentally using the Box–Benkhen model ofresponse surface design as shown in Table 2. The outputresponses such of surface roughness (Ra), and % of graphenedispersion were obtained for the variable input parameters.

The contours of three dimensional responses usinggraphical optimization through response surface methodolo-gy is developed for analyzing the maximum impact of inputparameters that define the output responses as shown in Fig. 4is obtained.

Fig. 2 – Mechanism of the proposed magnetorheological coating process.

Fig. 3 – Photographic view of the magnetorheological process for coating the cutting tool insert.


Fig. 4 – Three-dimensional responses for (a) surfaceroughness, (b) % of graphene dispersion onmagnetorheological coating of graphene oxide.

Table 3 – Embedded thermocouple engraving.

Properties Value

Average wavelength 780 nmOutput power 80 mWFrequency 210 fsScanning speed 0.150 mm/sPitch 3 mmGroove width/depth 5 mmSintered compound for chromel Cr3C2

Sintered compound for alumel Al2O3

Laser engraving width 100 mm

Table 2 – Magnetorheological coating conditions.

Conditions Range

Coating time 15, 20, 25 minSpindle speed 300 rpmWorking gap 0.5, 0.75, 1 mmWorking voltage 12–36 VBase line voltage 24–48 VCoating rate 120 s/cycleMR fluid flow rate 3–5 ml/min


A statistical model was developed to fit the data significancewith the interaction of factors by linear regression analysisusing Design-Expert software. A second order quadratic modelis developed and multi-response optimization function used for

the prediction of the best output responses of the coated insertwith the given input parameters. The regression model for thetool substrate surface roughness (Ra) and % of graphenedispersion is obtained and are considered valid after analyzingANOVA. This regression equation given in coded terms of theactual factors of the input parameters can be used to makepredictions of the response in the given levels of each factor. Thequadratic regression model developed using RSM for magne-torheological coating process output responses is given below.

Surface roughnessðRaÞ ¼ þ51:83 þ 1:92 � A þ 0:5000 � B

þ 0:2500 � C þ 0:1667 � D

þ AB�0:7500 � AC þ AD þ 0:2500

� BC�0:2500 � BD�0:2500

� CD�0:3750 � A2 þ B2�0:1250

� C2 þ D2 (2)

Graphene dispersionð%Þ ¼ þ31:75 þ 3:25 � A�0:5833 � B

þ 0:3333 � C þ D�0:5000 � AB

þ AC�1:25 � AD�0:7500 � BC

þ 0:5000 � BD�0:2500

� CD�0:6250 � A2�0:125B2 þ C2

þ D2 (3)

where A – working voltage (V), B – graphene concentration (%),C – coating time (min), D – base voltage (V)

2.3. Proposal of thermocouple array on cutting tool insert

Uncoated cutting insert blanks P30 supplied by ISCARMetalworking Company were used as substrates for sensorfabrication. Before sensor fabrication, the substrates werecleaned by micro-fabrication cleaning procedure using ace-tone, isopropyl alcohol and de-ionized water. Moisture contenton the substrate removed using furnace treatment at 125 8C. K-type thermocouple is arranged on rake face of the toolsubstrate in a face-centered structure. The process parametersfor thermocouple engraving are shown in Table 3.

Laser engraving technique is used in this process to groovethe thermocouple layers over the tool inserts. The engravedspecimen is coated with Cr3C2 (chrome carbide) on one side ofthe engraved junction line by masking the other side withsilicone gel. The other junction is coated with the Al2O3 in

Table 4 – Calibration results.

Properties Results Units

Thermocouple range �100 to 800 8CSensitivity 41–65 mV/8CError rate 0.4% –

Resolution 2.2 8CSampling frequency 20 kHzData rate 32 bit


masking the Cr3C2 junction. Then the rake face of the insert ispolished and grinded using magnetic polishing machine toexcavate the unwanted burs laid over the rake surface apartfrom the grooves. The end of the junction line is soldered withchromel and alumel wires for signal transmission. This arrayformation paves a way to define the contours of thermaldistribution on the rake face of the cutting tool insert.

2.4. Prototyping of online condition monitoring system fortemperature measurement

The proposed system consists of signal amplifier for K-typethermocouple as shown in Fig. 5. The experimental setupconsists of the thermal condition monitoring of tungstencarbide tool insert engraved using laser engraving for 200 mmdepth. The data was recorded using HANTEK digital oscillo-scope with 20 MHz sampling rate.

The calibration of the embedded thermocouple is validatedwith the thermometer to hold the reference temperature. Thethermocouple embedded cutting tool insert is placed on thesilicone oil. The temperature was plotted using four channeldata acquisition system (Hantek USB 400) with a samplingfrequency 1 s, and a resolution of 10 mV. The temperature wasmeasured between 100 8C and 30 8C. The chromel wire wasused for extension with (ø 0.1 mm) in connecting the Cr3C2

sputtered line, which transfer the thermoelectric voltage. TheSeebeck voltage generated at each location in the substratevalidates in linearity. The calibration was made with the basiceffectiveness value of the sensor in finding the sensitivity anddata accuracy. The data interpolation was analyzed for themelting of ice around ambient temperature. The error rateswere found to be with an approximation of �5 8C. Thecalibrated result of the proposed thermocouple sensor is

Fig. 5 – Proposal of cutting tool temperature c

shown in Table 4. Hence the calibration shows trends in goodlinearity for the prediction of cutting tool temperature.

2.5. Evaluation procedure

The photographic view of the online condition monitoredtemperature measurement system is shown in Fig. 6. Turningoperation includes the orthogonal cutting of duplex stainlesssteel on a turret lathe. The process is carried out using plainand graphene coated inserts. The process parameters such ascutting speed, feed rate and depth of cut were used to evaluatethe machinability characteristics such as tool wear and cuttingtemperature.

The cutting conditions for the turning of duplex stainlesssteel are shown in Table 5. The cutting tool temperature atembedded locations was recorded using data acquisitionsystem with 20 MHz sampling rate. The contours of thetemperature were processed using image-processing software(MATLAB). The tool wear is examined using USB digitalmicroscope 1000� and their structural morphologies werecharacterized as shown in Fig. 10. The worn inserts undervariable machining conditions is tested for Micro Vickers

ontour measurement with sensor array.

Fig. 6 – Photographic view of the online condition temperature measurement of cutting tool insert.

Table 5 – Cutting conditions.

Parameters Range Units

Cutting speed, Vc 55, 102, 131 m/minFeed rate, fd 0.145, 0.205, 0.245 mm/revDepth of cut, ap 1.5, 2.0, 2.5 mmTool Tungsten carbide (P30) –

Designation SCMT 12 04 08 –

Type SquareWork piece Duplex stainless steel –

Grade S31803Cutting length 300 mmDiameter 100 mmMachining type Dry turning


hardness with the diamond indent positioned near the tool tipfor load 887 kg/mm2. The durability of tool insert in formationof carbonaceous IMCs such as cementite and graphite obtainan average hardness value of 450 HV.

2.6. Statistical validation

The prediction of non-linear responses in the measurement offlank wear is evaluated using response surface methodology(RSM). The statistical response with mean, standard deviationand confidence interval describes the data significance of thefitted model. The central composite design has been used forthe experimental trials with the process parameters cutting

Table 6 – Response surface methodology – CCD design.

Std. order A: Cutting speed (m/min) B: Feed rate (mm/rev) C: Depth of cut (mm) Average flank wear (mm)

1 55 0.145 1.5 0.2432 131 0.145 1.5 0.2763 55 0.245 1.5 0.2454 131 0.245 1.5 0.2845 55 0.145 2.5 0.2536 131 0.145 2.5 0.2877 55 0.245 2.5 0.2428 131 0.245 2.5 0.2989 29.0919 0.205 2 0.23210 156.908 0.205 2 0.30611 102 0.11091 2 0.27612 102 0.27909 2 0.26713 102 0.205 1.1591 0.28314 102 0.205 2.8409 0.28115 102 0.205 2 0.28316 102 0.205 2 0.27817 102 0.205 2 0.27918 102 0.205 2 0.27319 102 0.205 2 0.283

Table 7 – ANOVA for flank wear.

Source Sum of squares DOF Mean square F-value p-Value Inference

Model 0.0052 9 0.0006 4.16 0.0226 SignificantA – Cutting speed 0.0023 1 0.0023 16.63 0.0028 SignificantB – Feed rate 0.0003 1 0.0003 2.40 0.1560C – Depth of cut 0.0001 1 0.0001 0.5319 0.4843AB 0.0000 1 0.0000 0.1292 0.7276AC 0.0009 1 0.0009 6.63 0.0299 SignificantBC 0.0000 1 0.0000 0.3588 0.5639A2 0.0011 1 0.0011 7.95 0.0201 SignificantB2 0.0001 1 0.0001 0.8794 0.3728C2 0.0006 1 0.0006 4.18 0.0713Residual 0.0013 9 0.0001Lack of fit 0.0009 5 0.0002 1.78 0.2985 Not significantPure error 0.0004 4 0.0001Cor total 0.0065 18

Std. dev. 0.0118 R2 0.9362Mean 0.2685 Adjusted R2 0.8943C.V. % 4.40 Predicted R2 0.8764

Adeq precision 6.1239


speed (Vc), feed rate ( f) and depth of cut (ap). The experimentaldesign with 19 runs is shown in Table 6. The average flank wearobtained after three repetitions is tabulated as shown in Table 6.

ANOVA was conducted to determine the significance levelof the process parameters as shown in Table 7. The proposedquadratic polynomial model for the input parameters cuttingspeed (Vc), feed rate ( f) and depth of cut (ap) is validated withthe p-value 0.0226 less than 0.05 significance level and F-value4.16 is higher than the tabulated value of F-table for 95%confidence interval to determine the data adequacy of themodel.

The coefficient of determination (R2) for the predictedmodel is 0.9362 is in good agreement with the experimental

data. The response surface plots for the influence of inputprocess parameters on flank wear is shown in Fig. 7(a–c). It isobserved that the flank wear increases with the highervalues of cutting speed and show less impact with increasein federate. In the interaction plot between cutting speedand depth of cut, the impact is randomized with the highervalues of flank wear. From Fig. 7(c) the flank wear is minimalin the limits of federate 0.185 mm/rev and depth of cut2.15 mm.

Three confirmation tests were conducted at optimumcombinations of process parameters to validate the accuracyof the developed quadratic model. The % of error withinallowable limits is shown in Table 8.

Fig. 7 – (a–c) Effect of input factors interaction of flank wear.

Table 8 – Confirmation test trial.

Optimum input parameter levels Output response Predict

A – Cutting speed = 93 m/min Flank wear (mm) 0.B – Feed rate = 0.185 mm/revC – Depth of cut = 2.15 mm


3. Results and discussions

3.1. Effect of nano coating on the cutting temperature onrake-face of the tool substrate

The cutting temperature for the tool inserts were measuredusing the embedded thermocouple as shown in Fig. 8(a–f). Therecorded contours of temperature distribution for variouscutting speed, feed rate and depth of cut were analyzed todefine the influence of cutting stresses on duplex stainlesssteel and the tool chip interference.

At high cutting speed Vc = 131 m/min, when turningwith plain insert the cutting temperature is more concen-trated at tool main cutting edge, tool tip. The maximumtemperature observed around 405 8C. In graphene coatedinsert the temperature is evenly distributed on the rakeface and flank zone with maximum temperature observedis 322 8C. At Vc = 102 m/min, when turning with plain insertthe maximum temperature observed around 366 8C. Ingraphene coated insert the maximum temperature ob-served is 284 8C. At Vc = 55 m/min, when turning with plaininsert the maximum temperature observed around 304 8C.In graphene coated insert the maximum temperatureobserved is 290 8C.

From Fig. 8(a–f); it is clear that the identification of thermalimpact of contours of the rake face to the initiation from tooltip found to be reduced for nano coated inserts. Graphenenano foils resist the conduction of heat over the rake surfaceby acting as thermal barrier in maintaining the uniform spreadof heat dissipation rate. The differential scanning calorimetry(DSC) of the coated inserts with exothermic peaks at 47.1 8Cand 41.2 8C for the crystallization process of carbonaceousmaterial due to the existence of the metastable solid phasetransition.

It can be seen that with an increase in the volumetricdispersion of graphene oxide (GO) over the insert substrate, thecrystallization peak temperature shifts toward a lower temper-ature. This is due to the encapsulated structural characteristicsand the strong interactions between the GO and tungstencarbide that confine the rearrangement and diffusion ofmolecular chains during the phase change. This phenomenaloccurrence with the addition of graphene to carbide bonds inthe insert substrate results in decrease of crystallizationtemperature and increase in hardness of the surface layerwith increased wear resistance [14].

ed value Experimental values Error (%)

Trial-1 Trial-2 Trial-3 Avg.

255 0.263 0.269 0.258 0.263 3.04

Fig. 8 – (a–f) Effect of contours on cutting tool temperature for plain and coated inserts at feed rate f = 0.205 mm/rev and depthof cut ap = 2.0 mm with variable cutting speed Vc.


The cutting tool temperature is reduced to the presence ofgraphene particles as nano ball bearings between the tungstencarbide grids. This provides self-lubrication regime betweenthe tool tip and chip interference. From the experimentconducted through the study of machinability characteriza-tion of duplex stainless steel with turning process variable likeincrease in cutting speed creates a high thermal impact on toolchip interference due abrupt changes occurring in cuttingforces. This could be found reduced in case nano-texturedinserts with the higher melting point of graphene particles ofabout 3000 8C [15].

Instead of depositing a coating on a cutting tool, the nanofluid additive enables the coolant to coat a tool. According tonano synthesis, research it conducted with Drexel Universityfound that the nanoparticles shot peen the surface of a cuttingtool, smoothing it and filling surface micro pores. Therepeated shot peening under the cutting process highpressure and high temperature impinges the lubriciousnanoparticles in to the tool surface thereby reducing frictionduring cutting [16].

The coated graphene platelets are pollution free and canhold itself on the base substrate voids for eventual period oftime due to the reorientation nature graphene particles as foilsduring the tool chip interference with abrasion wear providinglow coefficient of friction in acting as an aqua slider thatprovides a lubrication effect. Nanoparticles do not provide aholding period for serration from the coated surface, as theypossess high resistive temperature for anti-adhesion from thesubstrate unlike micro particles [17]. The machinabilityperformance on turning of duplex stainless steel shows theeffect of changes in contact spot size area. The thermaladhesive wear is mainly influenced by the heat dissipationrate and thermodynamic flow on the surface of the tool

substrate. The resistivity and uniformity in thermal contactconductance is based on the effective dissipation of steadystate in heat flow over the headers of the tool substrate inmachining duplex stainless steel. As the presence of grapheneparticles improves the thermal resistance in contact spotswith their higher thermal conductivity in machining duplexstainless steel. The carbonaceous core leads to the formationof cementite at tool tip with the formation of intermetalliccompounds. The graphene particles lead to the formation ofgraphite with the thermal alloying at tool tip interference,which could be observed in Fig. 10.

3.2. Effect of nano coating on tool wear inside the rake-faceof the tool substrate

The tool wear of the coated and uncoated inserts, whichwere recorded for variation in cutting speed, feed rate anddepth of cut, are shown in Fig. 9(a–c). In steady state wearzone, after 20 min of machining at cutting speed of 55 m/min, the flank wear of graphene coated insert was found tobe 15% reduced than plain insert. Whereas at cutting speedof 102 m/min reduction in VB noticed is 5% and at cuttingspeed of 131 m/min reduction in flank wear is 9% as shown inFig. 9(a). With the machining at feed rate of 0.142 mm/rev,the flank wear land of graphene coated insert was found tobe 50% reduced than plain insert. Whereas at feed rate of0.205 mm/rev reduction in flank wear noticed is 5% and atfeed rate of 0.245 mm/rev reduction in flank wear is 8%.Graphene coated insert performed better at lower feed rateas shown in Fig. 9(b).

After 21st pass of turning using graphene coated insert theflank wear land observed was 0.298 mm when compared withtitanium aluminum nitride (TiAlN) PVD coated insert, which is

Fig. 9 – Effect of flank wear on (a) cutting speed, (b) feed rateand (c) no. of passes.


0.403 mm. There is 26% reduction in flank wear land observedusing graphene coated insert as shown in Fig. 9(c).

It is observed that the graphene coated inserts could resistthe rake wear with the value of when compared with theuncoated inserts. The variation in cutting speed increases thetool wear abruptly as the increase in concentration of cuttingtool temperature at the tool tip. In case of the observation ofgraphene coated inserts which provides a thermal barrier at thetool chip contact conductance thereby by smoothening the rakesurface in sliding the chips produced [18]. This reduces the rakewear in the coated inserts. Another attribute with the presenceof graphene nano platelets on the peripheral zone of the toolinsert absorbs the cutting temperature and resist it intransferring to the surface of the tungsten carbide zone. Itprovides uniformity in transferring the temperature over the

rake surface thereby reducing the contact spot temperatureconcentration [19]. This reduces the tool wear to a greaterextent.

As studied earlier with the use of carbide inserts to machineductile materials resist built up edge formation with the non-metallic interaction of the carbide materials in resisting theadhesion between chip and tool tip. The presence of grapheneon the nano voids of the rake surface acts as nano bearings inpromoting the lubrication at tool chip contact interference inreducing the tool wear from the rake surface.

3.3. Microstructural analysis on coated inserts onmachining of duplex stainless steel

From Fig. 10(a–c), it could be observed that during thermalinterference during tool tip and chip contact leads to thecrystallization of coated inserts, which are in contact tomechanical and thermal shocks. This alters the structuralgrains and morphology of eutectic cells, which are formed asIMCs at the tool chip interface zone. The presence ofgraphene occurs in the form dendrite and vermicularstructures. Fig. 10(a) shows the uniform of spread ofgraphene particles on the rake face of the tool insert at 20-mm scale in range. The presence of uniformity in grapheneparticles leads to the resistance in stagnation of temperatureat a particular point thereby reducing the tool wear due tothermal impact. From Fig. 10(b) shows the wear location atthe rake face. It is observed that the formation of wear crackson the crater zone due to the presence of uncoated zone. Alsothe observation of accumulated graphene particles near thewear scar zone.

The vermicular strands of the graphene particles over therake face provide efficient wear resistance as chip breakers andpromote lubrication. From Fig. 10(c) shows the wear location atflank face with the formation of IMCs such as graphite andcementite. Also the serration of coated surfaces occurs insmaller zones. This proves the consistency of graphenecoating in resistance to the thermo mechanical shocks.

4. Conclusions

From the above study in turning duplex stainless steel with thegraphene oxide coated cemented inserts, the followingconclusions could be drawn

� Nano texturing with graphene nano platelets acts as a nano-ball bearings on the rake surface of the tool insert in reducingthe tool wear at tool chip interface.

� The effect of carbonaceous particles on tool chip contactzone under thermal condition leads rise to the formation ofintermetallic compounds like cementite and graphite whichacts as a strengthening element with refractory properties ofhardness up to 450 HV.

� The initial tool wear in the graphene coated inserts iscontrolled through superficial plastic deformation of thegraphene sheets rolled as filaments in resisting the microabrasion with the reduction discrete chipping of coatedlayers. The latter chipping leads to the removal of thegraphene layer in increasing the wear rate.

Fig. 10 – Microstructural images of tool wear on (a) rake face of coated insert, (b) wear location at rake face, (c) wear location attool tip.


� The graphene oxide coated inserts could reduce the tool tiptemperature up to 322 8C at higher cutting speed value of131 m/min in contrast with the plain insert with 405 8C. Thisis due to the higher thermal resistivity of graphene ascarbonaceous material.

� The tool wear for the coated graphene insert could beobserved to be 0.298 mm for 21st pass, which is minimalwhen compared with the plain insert with the wear of0.367 mm.

� At lower cutting speed the graphene coated insert yielded areduced flank wear as compared with the higher cuttingspeed.

� It could be concluded that the tool life was increased by 26%for the graphene coated insert when compared with the PVDcoated TiAlN inserts.

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thermal and tool wear characterization of graphene oxide ......turning flank wear a b s t r a c t...

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