machinability of ti-al-n coated cermet tool with the ti[c, n]...

Machinability of Ti-Al-N Coated Cermet Tool with the Ti[C, N] ...F F

Journal of Metallurgical Engineering, 1(1-2) January-December 2011 63

Machinability of Ti-Al-N Coated CermetTool with the Ti[C, N] Mixed AluminaCeramic Cutting Tool and the UncoatedCermet Cutting Tool While Machining AISID2 Steel

A. Poomari, B. Mohan, A. Rajadurai1, A. Senthil Kumarand M. Adam Khan2

1MIT Campus, Anna University, Chennai, Tamil Nadu, India.2Sethu Institute of Technology, Virudhunagar, Tamil Nadu, India.

Abstract: Machining studies on AISI D2 die steel was performedwith Ti-Al-N coated cermet cutting tool (tool 2) with Ti[C, N]mixed alumina ceramic cutting tool (tool 3) and uncoated cermetcutting tool (tool 1). The purpose of the experimental work isto compare the tool wear of Ti-Al-N coated cermet cutting toolwith Ti[C, N] mixed alumina ceramic based ceramic cuttingtool and uncoated cermet cutting tool. Tool performanceevaluation was based on flank wear and surface finish. Cuttingtool flank wear was measured with the help of Metzer toolmaker’fs microscope. Ti-Al-N coated cermet cutting tool hasslightly higher tool wear than Ti[C, N] based alumina ceramiccutting tool whereas lower tool wear than that of uncoatedcermet cutting tool. From SEM observation, Ti-Al-N coatedcermet cutting tool has smooth wear land compared to uncoatedcermet cutting tool. Surface roughness of machined AISI D2die steel Ti-Al-N coated cermet cutting tool is slightly higherthan Ti[C, N] based alumina ceramic cutting tool, howeveruncoated cermet cutting tool produce more rough surface atminimum speed. Ti-Al-N coated cermet cutting tool hascomparable performance with that of Ti[C, N] mixed aluminaceramic cutting tool.

Keywords: coating; wear resistance; roughness; machining

A. Poomari, B. Mohan, A. Rajadurai, A. Senthil Kumar and M. Adam khanF F

64 Journal of Metallurgical Engineering, 1(1-2) January-December 2011

1. INTRODUCTIONThe development of machine tools and cutting tool materialsachieved over a past few decades have shown the way to use highercutting speed associated with conventional machine tools. Finalfinishing operation is reduced in these combinations or some timeit might be eliminated. The main draw back in the anatomy of thecutting tool is the tool wear caused due to high temperaturegenerated in cutting zone while machining at higher cutting speed.Paulo Davim et al (2007) statistically proved that cutting velocityplays a major role on machining AISI D2 steel with alumina basedceramic cutting tool. Alumina (Al2O3) based cutting tools are suitablefor high speed cutting operation. It is due to high hot hardness,wear resistance and chemical inertness of Al2O3 based cutting tool[Camuscu (2006)]. Consequently, machining studies on ceramiccutting tool is considered to be one of the most important areas forresearch. These alumina ceramic cutting tools are widely used tomachine hard to machine materials.

While machining hard materials, tool wear of alumina ceramiccutting tool are caused due to the interaction of abrasive wear,adhesive wear and micro chipping [Li et al (2002)]. Tool wearmechanisms are based on the stress and temperature on the rakeface of the cutting tool. It is generally attributed to rubbing of toolwith work materials. Tool wear also increase in case of hard inclusionor when there is debris in work piece materials [Senthil Kumaret al (2006)].

In the field of machining science a novel cutting tool namelycermet was developed in the combination of ceramic and metal.Cermet cutting insert represents the most common and importantcutting tool in this field. Compared to cemented carbide cutting tool,cermet has high temperature hardness, resistance to oxidation andbetter chemical stability [Ning Liu (2005), Won Tae Kwon (2005)].Because of these characteristics, cermet cutting tools are used forhigh cutting speed machining operations. The most importantapplication of cermet cutting tool is for finish machining process.



Cermets composed of hard phase, namely TiC and TiN orTi[C,N] bonded in the soft phase metallic binders. The metallicbinders represents a tough, ductility and conductivity phase whichhelps in mitigating in inherent brittleness of the ceramic and suppliesthe liquid phase that is necessary for sintering [Errico (1998)]. Whileevaluating the performance of ceramic tool materials, minimum inproduction cost, best for high speed finishing operation and it isoutperformed to other cutting tool materials like CBN and PCD.However ceramic performs better than the cermets [Errico (2001)].

A question of recent interest is to review whether the resistanceof cermet cutting tools to wear has improved by the use ofappropriate hard coatings. Research in this area is concentrated onnew composite gradient coating, multi component and multilayercoating and adding new elements to coating combination like siliconor vanadium to Ti-Al-N [Dobrzanski (2005)].

In this paper, it is attempted to compare the performance of toolwear of Ti-Al-N coated cermet cutting tool with Ti[C,N] mixedalumina based ceramic cutting tool and uncoated cermet cuttingtool.

2. EXPERIMENTAL PROCEDURE2.1 MaterialsThe investigation on continuous machining study was performedon AISI D2 die steel (52 HRC). In order to calculate and assure thatthe chuck / work material / cutting tool, it should have requiredstrength with respect to Length to Diameter (L/D) ratio (Lima etal., 2005). Geometry of AISI D2 steel is 50 mm in diameter andmachining length of 300 mm and it has L/D ratio of 6. At the end ofmachining studies, the L/D ratio will be approximately 8 whichensure that the required stiffness can be attained in chuck /workmaterial / cutting tool system.

Ti[C,N] based alumina ceramic cutting tool and TiC based cermetof uncoated and Ti-Al-N coated wear resisting cutting tool were



used to machine the work material. Details of cutting tool are givenin Table 1 and Table 2. The property detail of Ti-Al-N coating madeon cermet cutting tool was presented in Table 3.

Table 1Details of Cutting Tools

Details of Tool Composition Density Hardness Young’sMaterial (g/cm3) Modulus (GPa)

Ti[C,N] mixed Al2O3 70%alumina ceramic TiN 22.5% 4.26% 1800 400

TiC 7.5% (Hv10)

TiC 56%TiC based VC 10%Cermet Ni 20% 4.9 1680 439.4

Co 14% (HV18)

Table 2Details of Tool Geometry of the Cutting Tools

Cutting tools rake clearance inclination plan included noseangle angle angle approach angle radius

angle( ) ( ) ( ) ( ) (er) (re)

Tool 1, Tool 2 –6° 6° –6° 95° 80° 0.8 mmand Tool 3

Table 3Properties of BALINIT® Ti-Al-N Coating

Properties Units BALINIT® FUTURA NANO

Coating material Ti-Al-NMicro hardness (HV 0.05) 3300Coefficient of friction against steel (dry) 0.30 . 0.35Coating thickness ( m) 4Residual compressive stress (GPa) -2.0Maximum service temperature (°C) 900Coating temperature (°C) < 500Coating colour violet-greyCoating structure Nano - structured



2.2 Machining StudiesMachining studies were carried out to machine AISI D2 Die steelmaterial in precision lathe using uncoated cermet cutting tool (Tool1) and Ti-Al-N coated cermet cutting tool (Tool 2) along with Ti[C,N] mixed alumina ceramic cutting tool (Tool 3). Machining processwas performed by varying cutting speeds at constant feed rate (0.06mm/rev) and depth of cut (0.2 mm). Flank wear of the cutting toolsand surface finish were observed while machining AISI D2 die steel.Flank wear is measured using Metzer Toolmakers microscope. Andthe tool wear of each cutting tool was interpreted to compare theperformance of each machining process. Surface roughness ofmachined AISI D2 die steel was measured using TR200 Seriesroughness meter with respect to machining time and cutting velocity.

3. RESULTS AND DISCUSSIONS3.1 Tool Wear MechanismThe classic definition of wear, regardless of the cause but herereferring specifically to cutting tools, is: “the loss or dislocation ofmass of a material caused by some kind of tribological pheno-menon”. Wear on tools can appear in the form of a crater on therake face, flank wear on the flank face or a notch that may appear ateither the nose or the end of the cutting depth, normally on the flankface. The wear on cutting tools because of they undergo severerubbing process and they are subjected to extreme stress andtemperature during machining. Moreover due to various types ofwear mechanisms like abrasion, adhesion, diffusion, plasticdeformation etc. It is considered that during the machining, the mainwear mechanisms are as follows: (1) granule abrasion, (2) adhesiveabrasion, (3) diffusion abrasion, and (4) oxidation abrasion [XiaoSG (1990)]. Wear on the flank (relief) face is called flank wear andresults in the formation of a wear land. Wear land formation is notalways uniform along the major and minor cutting edges of the tool.Flank wear can be measured as the average and the maximum ofthe wear land, known as VB and VBmax respectively. Nose grooving



is a common form of wear during high speed machining operations,whilst notching occurs when machining hardened materials likestainless steel, nickel base alloys and cobalt base alloys. Crater wearoccurs due to the flow of chips across the rake face, and the depth ofthe crater formed on the rake face is measured as crater wear depth‘KT’. Crater wear in the cutting tool occurs due to the erosion of toolmaterial by the impingement of solid particles of work materials[D. Erricco et al (1997)].

3.2 Flank WearFlank wear of cutting tool are set based on the finish machiningwith a maximum flank wear of 0.3 mm. Tool wear observed whilemachining AISI D2 die steel using cermet cutting tool and alumnaceramic cutting are plotted in Figure 1 and Figure 2. As the cuttingspeed increase the tool wear also gradually increase with respect tomachining time. Flank wear of Ti-Al-N coated cermet cutting toolhas comparable tool wear to that of the Ti[C,N] mixed aluminaceramic cutting tool material. At the same cutting condition toolwear of uncoated cermet cutting tool has rapid increase than Ti-Al-N coated cermet and alumina ceramic cutting tool. Cutting tool wearof 0.29 mm was observed on Ti-Al-N coated cermet cutting toolwhich is slightly elevated to 0.26 mm tool wear of Ti[C,N] mixedalumina ceramic cutting tool. However, 0.35 mm tool wear wasobserved on uncoated cermet cutting tool at 6 minutes.

Fig. 1: Flank Wear of Uncoated Cermet Cutting Tool (tool 1), Ti-Al-N CoatedCermet Cutting Tool (tool 2) and Ti[C,N] Mixed Alumina Cutting Tool (tool 3)

with Respect to Cutting Speed (m/min)



With respect to machining time, the tool wear of Ti-Al-N coatedcermet cutting tool is 0.29mm at 6 minutes and 0.33mm at 9 minutesat a cutting velocity of 118 m/min which is drastic in changes, atthe same cutting condition tool wear of uncoated cermet cuttingtool fails at 6 minutes with more tool wear. Tool wear of Ti-Al-Ncoated cermet cutting tool compared with Ti[C,N] mixed aluminaceramic cutting tool is very similar and both the tool produced betterresults at minimum cutting velocity. This is due the hard coating(of Titanium – aluminum – nickel coatings) made over the titaniumcarbide based cermet cutting tool. Ti-Al-N coated cermet cuttingtool has very low tool wear than that of uncoated cermetcutting tool.

3.3 Uncoated Cermet Cutting ToolWhile cutting, the cutting tool edge undergoes many changes fromits original shape until its failure criterion. It is the gradual loss ofits materials that is measured to determine the tool wear. The endof tool life fails after reaching the failure criterion. Morphology ofuncoated cermet cutting tool edge was presented in the Figure 3.During high temperature application of the cutting tool, the

Fig. 2: Flank Wear of Uncoated Cermet Cutting Tool (tool 1), Ti-Al-N CoatedCermet Cutting Tool (tool 2) and Ti[C,N] Mixed Alumina Cutting Tool (tool 3)

with Respect to Machining Time (m/min)



deformation of the cutting tool edge undergoes catastrophic failure,along with the thermal fatigue. This is caused due to the cyclic changein temperature variation with cutting tool edge and atmosphere.Thermal fatigue leads to tool fracture at minimum cutting speeditself and leading to lower tool life. At the same cutting conditionthe cutting tool wear appears with ridge and seam on uncoatedcermet insert edge.

Fig. 3: SEM Micrograph of Uncoated Cermet Cutting Tool Wear

Along with the thermal fatigue, a deep camber was observedon the relief face (flank face) of the cutting tool which is termed ascrater wear. Hard metal chip formed while machining die steelmakes to plug the surface of the cutting tool to damage. It leads tohigh wear trend as shown in wear rating observation. High wearrate was observed at very less cutting speed and meets the tool failurecriterion soon. Thus these uncoated cermet cutting tool does nottends to withstand at minimum cutting tool speed and failures atvery less machining time. . In uncoated cermet cutting tool, the weartracks in worn blocks suggest the abrasive wear mechanism withplastic deformation is responsible for tool wear.



3.4 Ti-Al-N Coated ToolTo retain maximum tool life of the cutting tool, some of the processesare take in consideration. In recent machining studies the cuttingtools have dealt with titanium based nitride coatings. Ti-Al-Ncoatings were composed of the Titanium – Aluminum – Nitrogenelements [Zheng et al (2009)]. SEM Micrograph of Ti-Al-N coatedlayer of cermet cutting tool was shown in Figure 4. This is best onproducing better wear resistance. The coating has densehomogeneous microstructure of approximately 4 microns and itseffective adhesiveness with the substrate. Ti-Al-N coating providesexcellent wear and oxidation resistance which enables the improvedmachinability at dry cutting conditions. Titanium based coating hasless affinity to metal machining process. This created a strong layerwhile machining hard metals. The coated cutting tool was able towithstand the thermal fatigue and there was no appearance ofthermal crack as shown in Figure 5. From the SEM micrograph(Figure 5), it is clear to observe that while machining die steel, thetool wear land is very smooth and gradual wear. The deformationof tool edge is very less and smooth wear land than that of uncoatedcermet cutting tool. Thermal fatigue and crater in relief edge is alsogone due to the coating of Ti-Al-N coated cermet cutting tool. Duringthe wear process, the Ti-al-N coated cermet tool and AISI D2 steel,the wear mechanism was adhesive wear combined with abrasivewear at maximum cutting velocity.

Fig. 4: SEM Micrograph of Ti-Al-N Coating on Cermet Cutting Tool



3.5 Ti[C, N] Mixed Alumina Ceramic Cutting ToolTi[C,N] based alumina ceramic cutting tool has high affinity tomachining die steel. While machining at lower cutting speed, thetool wear of cutting tool is rapid in nature. Hard metal chips tend toplug the tool edge material and lead to tool to deform whilemachining die steel. It leads to form ridges and groves on the edgesurface [Senthil Kumar et al (1997)]. On comparing the tool wearland with cermet cutting tool, ridges are more in Ti[C,N] mixedalumina cutting tool and less than that of uncoated cermet cuttingtool. However, tool edge failure with thermal crack are not foundin Ti[C,N] mixed alumina ceramic cutting tool. Ti[C,N] mixedalumina ceramic cutting can able to machine hard materials at highcutting velocity with better performance.

3.6 Surface RoughnessSurface roughness of machined AISI D2 die steel using uncoatedcermet cutting tool (tool 1), Ti-Al-N coated cermet cutting tool (tool2) and Ti[C,N] based alumina ceramic cutting tool (tool 3) wasplotted in figure 6. Ti-Al-N coated cermet cutting tool has producedcomparable surface finish than that of Ti[C,N] based alumina ceramic

Fig. 5: SEM Micrograph of Ti-Al-N Coated Cermet Cutting Tool Wear



cutting tool. This is due to the high resistive coating of Ti-Al-Ncoating on cermet cutting tool which leads in less spalling on cuttingtool edge. At higher cutting velocity (118 m/min), surface finish ofunworn cutting tools are very less; at the same cutting conditionrapid increase in roughness was observed. Uncoated cermet cuttingtool produce poor surface finish on machined surface after prolongedmachining due to increased tool-workpiece contact area, withincreased flank wear. However, plastic deformation of the cuttingtool edge of the coated cermet tool tends to reduce the machiningoperation. Ti-Al-N coated cermet cutting tool has undergone veryless deformation and produced better surface finish than that of theuncoated cermet cutting tool. Ti-Al-N coated cermet cutting toolprovides better cutting performance than uncoated cermet cuttingtool and it is comparable to that of Ti[C, N] mixed alumina ceramiccutting tool.

Fig. 6: Surface Roughness µm of Cutting Tools with Respect to Cutting Velocityat 9 Minutes)

4. CONCLUSIONOn machining AISI D2 die steel, Ti-Al-N coated cermet cutting toolperformed satisfactorily than that of uncoated cermet cutting tooland produced comparable performance with Ti[C,N] based alumina



ceramic cutting tool. Ti-Al-N coated cermet cutting tool has less edgedeformation than uncoated cermet cutting tool. Wear land was alsofound to be very smooth in TiAlN coated cermet tool than that ofothers. Fine surface finish was also found in alumina ceramic andTi-Al-N coated cermet cutting tool, however at the worn out stage,surface finish of uncoated cermet cutting tool has poor finish.

In conclusion, Ti-Al-N coated cermet tool can also be used tomachine AISI D2 die steel it produces comparable performance withTi[C,N] mixed alumina ceramic cutting tool and shows betterperformance than uncoated cermet cutting tool.

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[5] Ning Liu, Chengliang Han, Haidong Yang, Yudong Xu, Min Shi, Sheng Chao,Feng Xie, (2005). “The Milling Performances of TiC-based Cermet Tools withTiN Nanopowders Addition Against Normalized Medium Carbon SteelAISI1045”, Wear, Vol. 258, pp. 1688-1695.

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machinability of ti-al-n coated cermet tool with the ti[c, n]...

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