Analysis of coating performances in machining titanium alloys for aerospace applications

Transcription

1 158 Int. J. Machining and Machinability of Materials, Vol. 13, Nos. 2/3, 2013 Analysis of coating performances in machining titanium alloys for aerospace applications M. Nouari* Laboratoire d Energétique et de Mécanique Théorique et Appliquée (LEMTA-CNRS UMR 7563), Ecole des Mines de Nancy, GIP-InSIC 27 rue d Hellieule 88100, Saint-Dié-Des-Vosges, France Fax: mohammed.nouari@univ-lorraine.fr *Corresponding author Madalina Calamaz Arts et Métiers Paris Tech, I2M, Université Bordeaux 1, Esplanade des Arts et Métiers, Talence Cedex, France madalina.calamaz@ensam.eu B. Haddag Laboratoire d Energétique et de Mécanique Théorique et Appliquée (LEMTA-CNRS UMR 7563), Ecole des Mines de Nancy, GIP-InSIC 27 rue d Hellieule 88100, Saint-Dié-Des-Vosges, France badis.haddag@univ-lorraine.fr Franck Girot Ikerbasque, Basque Foundation for Science, Bilbao, Spain and I2M, Arts et Métiers ParisTech, Université de Bordeaux. Esplanade des Arts et Métiers, Talence Cedex, France franck.girot@ensam.eu Abstract: The current study emphasises the role of coating materials in enhancing the wear resistance of the cutting tool and improving the tool-chip contact. The wear mechanisms have been investigated through a series of cutting experiments performed on an instrumented planer machine. Machining tests were conducted on the usual Ti-6Al-4V alloy (workpiece) and cemented carbide tools. Four new coatings were especially designed for the study: Copyright 2013 Inderscience Enterprises Ltd.

2 Analysis of coating performances in machining titanium alloys 159 1) diamond (thin layer, about 2 to 3 μm); 2) diamond+tib2+crn/dlc (diamond like carbon, about 3, 5 μm); 3) diamond (thick layer, 6 μm); 4) TiB2+CrN/DLC (3 μm). The performance of each coating material was analysed and compared in one hand to the uncoated carbide tools and on the other hand to the CBN reinforced carbide tools in terms of cutting forces and tool wear mechanisms. Keywords: Ti-6Al-4V; coatings; CBN reinforced tools; DLC; tool-chip contact; wear mechanisms. Reference to this paper should be made as follows: Nouari, M., Calamaz, M., Haddag, B. and Girot, F. (2013) Analysis of coating performances in machining titanium alloys for aerospace applications, Int. J. Machining and Machinability of Materials, Vol. 13, Nos. 2/3, pp Biographical notes: M. Nouari received his PhD from the University of Metz (France) in December 2000 and the Habilitation à Diriger des Recherche HDR degrees in Mechanics of Materials from the University of Bordeaux, France in In September 2007, he joined the Ecole Nationale Supérieure des Mines at Nancy France as a Full Professor with many responsibilities such as the Director of Research of the InSIC Institute, and Research Group Leader of the Equipe de Recherche en Mécanique et Plasturgie team (ERMeP). His research interests include development of behaviour laws of materials under extreme contact loading (large deformation, high pressure and strain rate), modelling and numerical simulations of manufacturing processes as machining and metal forming, numerical techniques, (FEA, DEM and SPH) applied to the analysis heterogeneous materials, and damage evolution and failure of nanostructures under a wide range of temperatures and loading rates. Madalina Calamaz received her PhD from Bordeaux and she is working as a Lecturer at Arts et Métiers ParisTech, I2M, Université Bordeaux. B. Haddag obtained his PhD from the University of Metz, he is working as a Lecturer at InsSIC Institute. He obtained his MEng from ENSAM. His research is in machining process, in particular, machining of aeronautic materials. He has contributed in some international journals and conferences. He has research collaboration with Prof. M. Nouari. Franck Girot is a Professor in Materials and Process Science from the University of Bordeaux (1987). His research lines are optimisation and simulation of manufacturing processes and application of nano-technologies to manufacturing processes. He has joined the Department of Mechanics at the Escuela Técnica Superior of Engineering in Bilbao, UPV-EHU. He was the Head of Department of Processes and Materials at Arts et Métiers ParisTech (ENSAM campus in Bordeaux). 1 Introduction Various machining processes in aerospace applications such as turning, milling are characterised by intense thermomechanical loading, especially at the tool-chip interface. The coupling between thermal and mechanical loads leads to a premature tool failure when machining refractory materials as titanium alloys. Within such environments the efficiency of the coating material plays an important role in preserving the structural

3 160 M. Nouari et al. integrity of the cutting tool surface. The chip formation and tool wear processes are strongly controlled by tribological phenomena that occur at the tool-chip interface (Abukhshim, 2006; Komanduri and Turkovich, 1981; Ackroyd et al., 2003). When the sliding chip velocity is increased (by increasing the cutting speed) the tool rake face temperature reaches its high values (about 800 to 900ºC) (Shaw et al., 1954; Stephenson et al., 1997). The temperature can be more important when machining refractory titanium alloys due to the intense deformation work associated with large shear strains and to the dynamic friction along the tool-chip interface (Moufki et al., 1997, 1998). The application of protective layer on the tool surface is still the solution widely employed by manufacturers. Typical materials used for coatings are titanium carbides TiC, titanium nitrides TiN, and aluminium oxides Al 2 O 3. Nowadays, new coatings are used in machining applications, such as diamond like carbon (DLC) or cubic boron nitride (CBN) (Bhowmick and Alpas, 2008; Minaki et al., 2008; Wada, 2010). Application of the coating to the cemented carbide inserts in machining is performed of one or multilayer of the protective material using physical or chemical vapour deposition techniques (PVD or CVD). In machining of steels, it is well known that the CVD-coated carbide provides a better result comparing to the uncoated one (Che-Haron et al., 2001). In the case of refractory titanium alloys such as Ti-6Al-4V or Ti-6242, Jawaid et al. (2000) have been reported that the CVD-coated carbide WC-(Ti, W, Ta, Nb) C-Co with (TiCN/Al 2 O 3 ) coating show a good performance when face milling Ti-6Al-4V under wet cutting conditions. The implementation of hard coating materials such as CBN (PCBN) and diamond (PCD) in machining titanium alloys have been done by several authors (Kuljanic et al., 1998; Zoya and Krishnamurthy, 2000; Nabhani, 2001a, 2001b). It could be concluded from theses studies that hard coating materials show a good performance at high cutting speeds in terms of tool life and surface finish. Therefore, the current work concerns the performance of multilayer coatings and their effect on the tool wear behaviour. Different kinds of new coatings tools have been tested in machining the aeronautical titanium alloy Ti-6Al-4V. The analysis is focused on the correlation between the effect of coating material on cutting forces and wear mechanisms. 2 Experimental set up and machining tests The orthogonal cutting tests have been carried out using a planer machine. For the purpose of cutting force measurements (cutting force Fc and feed force Ff); the machine was instrumented by a KISTLER dynamometer with four piezoelectric sensors. The workpiece is a block with dimension of (1, ) mm; see Figure 1(a). Prior to the orthogonal cutting tests, all six surfaces of workpiece were trued by face milling process and followed by end milling process to produce grooves as shown in the inset of Figure 1(a). The width of the groove is equal to the width of cutting w (about 4 mm). Note that the width of the cutting tool edge is about 4.5 mm. The cutting tool made of tungsten carbide (WC-Co class K20) was chosen for this study. The insert was mounted on a special purpose tool holder to have different rake angles (α) of 0, 15 and 30 and clearance angle (β) of 12 [Figure 2(a)]. The cutting conditions were set at cutting speeds

4 Analysis of coating performances in machining titanium alloys 161 (V) of 15, 30 and 60 m/min and feed rate (f) of 0.1 mm. All machining tests were carried out without lubrication (dry machining). Figure 1 Geometry and microstructure of the titanium alloy workpiece, (a) workpiece geometry. (b) microstructure of the selected titanium alloy Ti-6Al-4V (see online version for colours) (a) (b) 2.1 Properties and microstructure of the machined material The aeronautical refractory titanium alloy Ti-6Al-4V has been selected for machining experiments. This alloy is characterised by a duplex structure α + β with average grain size around 10 μm (range from 5 μm to 20 μm), and micro-hardness HV Figure 1 depicts the microstructure before machining tests, and data in Table 2 gives the chemical composition with a comparison between of two different titanium alloys: Ti-6Al-4V with α + β structure and Ti-555 with only β structure.

5 162 M. Nouari et al. Table 1 Mechanical and thermal properties of uncoated carbide tools (WC-6%Co). Young modulus (GPa) Poisson coefficient Hardness (Knoop) (GPa) density (kg/m 3 ) Thermal conductivity (W/mK) Thermal expansion at room temperature (10 6 K 1 ) , Table 2 Chemical composition of the workpiece (Ti-6Al-4V) Element Ti-6Al-4V Ti-555 % weight % weight Al V Fe Max Mo Cr Nb Zr Properties and microstructure of tools and coating materials Coated and uncoated carbide tools made of tungsten carbide (WC) with cobalt (Co) as binder have been chosen. The microstructure of the tool substrate is presented in Figure 2(b), and all properties are given in Table 1. The chemical analysis on a polished surface inside the substrate gives a composition with 6 wt.% of cobalt and no mixed carbide has been detected (TiC, TaC). WC grains have sizes varying from 2 to 4 μm. As shown in Figure 2(b), the carbide insert rake face presents an inhomogeneous state regarding the chemical composition and morphology. All SEM observations show very concentrated areas with WC grains close to very Co binder rich areas. To analyse the effect of coating, four coating materials were chosen: Coating 1 diamond (thin layer, about 3 μm in thickness) Coating 2 diamond+tib2+crn/dlc (DLC) (about 3.5 µm) Coating 3 (by CVD) diamond (thick layer, about 6 μm) Coating 4 (by CVD) TiB2+CrN/DLC (DLC) (3 μm). Each inserts have single or multilayer coatings. Diamond coating (coating 1) has successfully been deposited by CVD under a temperature of 850ºC. Because of their high hardness, diamond coatings are well adapted for machining non-ferrous alloys and non-metal materials. The ferrous alloys cannot be machined with this kind of coating because of the high chemical affinity of carbon with respect to iron. Diamond is characterised by a polycrystalline structure with a microhardness between 8,000 and 10,000 (HV 0,05), and low roughness about 0.3 µm.

6 Analysis of coating performances in machining titanium alloys 163 Coating 2 is made up of a PVD multilayer coating: TiB2+CrN/DLC. With a microhardness about 3,000 HV, the coating 2 is characterised by a very low friction coefficient (about 0.15) and a total thickness of 3.5 µm. Coating 3 contains a fine layer of diamond and a layer of TiB2+CrN/DLC (DLC), the total thickness is about 6 µm. Figure 2 (a) Tool holder with three different rake angles: 0, 15 and 30 (b) SEM micrograph showing the microstructure of tungsten carbide tools (see online version for colours) (a) o WC grains (b) In addition, tungsten carbide tools have been reinforced by CBN material (CBN: WC/Co-CBN) and also have been tested and compared to coated and uncoated carbide tools. Figure 3 depicts the microstructure of these tools. Note that the WC/Co-CBN tool contains two layers; the first layer with 1,500 µm in thickness contains tungsten carbide material, 12% of Co and 15% of CBN. The second layer (substrate) contains only tungsten carbide WC with 6% of Co. In the first layer, the CBN grains are uniformly distributed and WC grains have sizes varying from 1 to 9 µm. The WC/Co-CBN tools have been tested under the same machining conditions than those for uncoated tools and coated tools with the four coatings described before.

7 164 M. Nouari et al. Figure 3 SEM micrographs of the CBN-reinforced carbide tool 2.3 Orthogonal cutting tests and cutting conditions During the cutting process, the tool removes a part of the workpiece by a process of intense plastic deformation at high strain rate within the primary and secondary shear zones, see Figure 4(a). Thus, the cutting tool is subjected to a high temperature and a great pressure. As shown by Figure 4(a) and Figure 4(b), the chip formation can be observed using a high speed camera under orthogonal cutting configuration. The later is characterised by the following parameters: Φ shear angle, Ff feed force, Fc cutting force, α rake angle, Fs shear force, Fns normal force, Ft and Fn tangential and normal friction forces, respectively. The cutting force Fc and feed force Ff are measured with KISTLER dynamometer for each machining test. The cutting conditions and tool geometry can be summarised as follow: the rake angle is about 0, feed = 0. 1 mm, and cutting speed V c = 15, 30, 60 m/min. As said before, a special tool holder was manufactured for the planer machine, offering a zero rake angle. The later was particularly chosen because it allows good cutting edge strength under dry machining of hard metals. To analyse tool wear and the effect of coatings on tool wear and cutting forces, all machining tests were carried out without using lubrication (dry condition). Clearance angle is obtained by grinding the flank face of the insert. It was kept constant (about 11 ) for all tested tools and all considered cutting conditions.

8 Analysis of coating performances in machining titanium alloys 165 Figure 4 Orhtogonal cutting configuration and diagram of cutting forces, (a) high speed video showing the chip formation process under orthogonal cutting configuration (b) scheme of orthogonal machining (see online version for colours) Tool Chip Secondary shear zone Primary shear zone Workpiece (a) Chip α φ F s Tool F ns F c F t F f F n Workpiece (b) 3 Results 3.1 Cutting and feed forces Uncoated tools Data recorded from experiments on uncoated tools are presented in Figure 5. The value of the cutting force with error bar of each test is an average of forces recorded during

9 166 M. Nouari et al. several machining passes. It can be observed from Figure 5(a) that the cutting force is stable between 15 and 30 m/min and decreases (about 11%) when the cutting speed increases from 30 to 60 m/min. Müller et al. (2004) have been done a work on the same material and under the same cutting conditions. They show that the measured cutting temperature increases from 550ºC with a cutting speed V c =15 m/min to 700ºC with V c = 60 m/min. It means that the thermal softening of the material makes the cutting forces lower. Indeed, when machining titanium alloys, the tool-chip interface is controlled by the contact temperature which can attain large values and affects drastically the mechanical properties of the machined material, consequently the contact pressure and cutting forces decrease. In the same time, the high temperature (especially with low thermal conductivity of titanium alloys) affects significantly the wear behaviour of cutting tools. From Figure 5(b), it can be observed that the feed force increases with speed. This tendency shows the effect of tool wear on the flank face of the cutting tool. Figure 5 Evolution of cutting and feed forces vs. speed (see online version for colours) Note: The other cutting conditions are: rake angle α = 0º and feed f = 0.1 mm. The tool wear will cause a change in tool geometry during the machining process. The consequence of chipping and adhesion mechanisms for example is an increase in the force level, especially for feed forces as noticed in Figure 5(a). Therefore, the wear state of the tool surface affects the chip formation (in terms of segmentation frequency, shear band thickness, etc.) and also the cutting and feed forces, Figure 4(a) Coated tools The use of coatings is a strategy used by manufacturers to increase the cutting tool life and productivity. Coating often decreases cutting forces by improving the contact between tool, chip and workpiece. Figure 6(a) shows an average value of cutting forces recorded during machining process with uncoated tools, coated tools, and CBN reinforced carbide tools. It can also be observed from this figure that the coating 1 [diamond (3 µm)], and the coating 3 [diamond (6 µm)] give low cutting forces compared to those given by the coating 2 [diamond+tib2+crn/dlc (3.5 µm)] and the coating 4 (TiB2+CrN/DLC 3 µm). In the case of the CBN reinforced carbide tools, the cutting forces can be reduced by 20% to 40% compared to uncoated tools and the other coatings (1 4). In Figure 6(b), feed forces are not affected by coatings.

10 Analysis of coating performances in machining titanium alloys 167 Figure 6 Evolution of cutting and feed forces for different coatings and CBN reinforced cemented carbide tools, (a) cutting forces (b) feed forces (see online version for colours) Cutting force (N) 1,200 0 _60 m/min_0.1 mm 1, Uncoated WC-Co Coating 1 Coating 2 Coating 3 Coating 4 WC/Co+CBN Feed force (N) Uncoated WC-Co (a) 0 _60m/min_0.1mm Coating1 Coating 2 Coating 3 Coating 4 WC/Co+CBN (b) 3.2 Tool wear The various types of tool wear depend on the nature of the tool, the workpiece material, cutting conditions and the nature of machining operations (turning, milling, drilling, ). At low cutting speeds, the tool-chip interface temperature (cutting temperature) is relatively low and abrasion wear dominates when the tribological conditions are essentially sliding. At these low temperatures, there is not yet thermal softening and the cutting forces are important. Adhesion wear is then caused by the mechanical removal of the tool material when the adhesive junctions are broken. This attrition process can dramatically deteriorate the tool rake face. If the cutting speed is more important, the temperature will be higher and adhesion wear effect will be attenuated. A thin adhesive layer is then obtained by chemical diffusion process, see Figure 8. This will facilitate the chip sliding by decreasing the friction between tool and chip. But at very high temperature, chemical wear takes place and some chemical species can diffuse from the

11 168 M. Nouari et al. tool surface towards the chip and vice versa. This chemical diffusion changes the contact conditions and facilitates the coating delamination process. A microanalysis using white light interferometer technique and scanning electron microscopy (SEM) coupled to both energy dispersive X-ray spectroscopy (EDS) and Auger electron spectroscopy (AES) were performed on worn tools (uncoated, coated, and CBN reinforced tools). Each specimen was analysed after obtaining stable cutting forces Uncoated tools Figure 7 shows micrographs of the cutting edge where the damage is located. A brittle fracture such as flaking and chipping can be noted. The obtained damage shows the severity of the contact conditions in terms of temperature and pressure. A cracking mechanism can clearly be observed for uncoated tools. From the high magnification images of the worn cutting edge in Figure 7, it is not easy to observe the plastic deformation phenomenon since the machining forces are not very important. For the cutting condition of Figure 7, the cutting force is about 800 N and the feed force not exceeds 600 N. Also, an important adhesion process has been observed on the surface of uncoated tools. The white light interferometry analysis shows that the height of these adhesion zones varies from 6 μm to 40 μm. Other SEM analyses coupled to Auger microanalysis of the cutting edge show that adhesion wear is the wear mechanism for all uncoated tools. Adhesion that occurs during machining titanium alloys results from a chemical diffusion process between tool and chip along the interface, see Figure 8. Figure 7 Micrographs of worn uncoated tool Note: The cutting conditions are: cutting speed V c = 60 m/min, feed f = 0.1 mm and rake angle α = 0º. Auger analysis shows that a thin built-up layer has been formed on uncoated cemented carbide tools. Other studies (Stephenson et al., 1997; Müller et al., 2004) reported that during machining refractory materials such as titanium based-alloys or nickel basedalloys, temperatures and pressures can attain large values. This supports the activation of diffusion process and particles move toward areas of low concentration. Diffusion phenomena were first reported by Loladze (1962, 1981) who showed that at low cutting speed, tool wear is mainly due to abrasion. When the cutting speeds increases, adhesion caused by diffusion process dominates.

12 Analysis of coating performances in machining titanium alloys 169 Other authors showed that in the case of machining titanium alloys with diamond tools (PCD tools), diffusion and dissolution processes can be exacerbated by high local temperature resulting from the poor thermal conductivity of the workpiece material (König and Neises, 1993). In our case, the results of EDS and Auger analyses show that some grains of cutting tools as W, C and Co are located in the chip medium and grains of the machined material as Ti, V and Al are located in the tool medium, see Figure 8. Atoms that diffuse from the chip into the cutting tool medium and vice versa (trough the interface) lead to adhesion process between tool and workpiece. As shown by Figure 7, this causes attrition wear by the mechanical removal of tool material when the adhesive junctions are broken as the chip flows over the tool. Consequently, the tool mechanical resistance and its efficiency are reduced. Figure 8 AUGER profile at the tool-chip interface along the line L1 showing the diffusion process between uncoated tool and Ti-6Al-4V chip (see online version for colours) Notes: A = tool medium, B = chip medium. V c = 60m/min, f = 0.1 mm.

13 170 M. Nouari et al Coated and CBN reinforced tools For all coated tools, little cracking and chipping have been observed on the cutting tool surface (see Figure 9). However, a phenomenon of coating delamination has been clearly distinguished, especially for tools with the coatings 1 [diamond (3 μm)], 2 [diamond+tib2+crn/dlc (3.5 μm)] and 4 (TiB2+CrN/DLC 3 μm). As for uncoated tools, the results of the chemical analyses EDS and AES confirm that adhesion is the dominant wear mechanism of coated tools. Compared to the uncoated one, the chemical analysis of coated tools shows that micro-cracks take place in the coating layer and they are immediately followed by the removal of the coating material. These micro-cracks propagate not only in the horizontal direction but also in the vertical one through the interface between the tool substrate and the coating materials. This causes delamination of the coating layer. All specimens with the coatings 1 [diamond (3 μm)], 2 [diamond+tib2+crn/dlc (3.5 μm)] and 3 [diamond (6 μm)] show that the coating delamination phenomenon is the initial wear mode. However, tools with the coating 4 (TiB2+CrN/DLC 3 μm) show a good performance. Only little adhesion has been observed on the tool surface at the contact zone Lc. Note that this coating contains a very thin layer of TiB2+CrN/DLC. The total thickness of the coating 4 (TiB2+CrN/DLC) is about 3 μm, its high performance is essentially due the DLC which generates a very low friction coefficient between 0.03 and 0.15 (Dongcan et al., (2010). The DLC coating has a beneficial effect on tool resistance and reduces drastically tool wear. This amazing property makes this coating the only choice for industrially relevant extreme tribological applications as machining process. Kuljanic et al. (1998) inferred from the thermo-chemical data and stability of TiC that titanium has a greater affinity to carbon. They explain that the formation of a titanium carbide film results from a reaction between the work material and tool material on the diamond surface. This film can protect the tool and consequently extend the tool life during the machining process. Figure 9 Wear of cutting tools with coating 1 (diamond 3 μm) Notes: SEM images of the tool surface showing coating delamination process. Wear obtained after 2 m of machining with V c = 60 m/min and f = 0.1 mm. The rake angle α = 0º.

14 Analysis of coating performances in machining titanium alloys 171 In spite of the low cutting forces obtained in machining Ti-6Al-4V alloy, CBN reinforced tools exhibit chipping failure. Figure 10 shows severe abrasion wear located at a distance of a few tens of microns from the tool cutting edge. It means that the cutting edge is much weakened. A previous work (Ginting and Nouari, 2006) showed that the localisation of abrasion at the intimate contact between tool and chip provides an ideal environment for wear progression and catastrophic failure. It can be concluded from this last result that the reinforcement of CBN did not improve the performance of carbide tools. This is due to the fact that in machining applications, the cutting edge is a point where the maximum cutting load is concentrated during the process of chip formation. Figure 10 Wear of CBN reinforced cutting tools Notes: SEM images of the tool surface showing a local abrasion wear mechanism. Wear obtained after 2 m of machining with V c = 60 m/min and f = 0.1mm. The rake angle α = 0º. 4 Conclusions The analysis of coating performances in machining the refractory titanium alloy Ti-6Al-4V has been conducted in this study. Observations of uncoated tools based on the SEM and Auger techniques suggest that adhesion of the work piece material is the main wear mechanism of the cutting tool when dry machining Ti-6Al-4V. The material flow leads to adhesion of chips on the tool surface. The adhesive chips are partially removed from the contact and constantly renewed. This generates the formation of cracks and notches on the cutting edge (chipping).

15 172 M. Nouari et al. The analysis of the coated tools shows that the coatings 2 [diamond+tib2+crn/dlc (3.5 μm)] and the coating 4 (TiB2+CrN/DLC 3 μm) give higher cutting forces than the coatings 1 [diamond (3 μm)], and 3 [diamond (6 μm)]. The high performance of the coatings 2 and 4 is essentially due to the presence of DLC. The later generates low friction coefficient (between 0.03 and 0.15), and consequently low friction heat. The DLC coating film acts as a lubricant and has beneficial effects on tool wear resistance and wear reduction. Tools coated with DLC films can then be applied to the machining of difficult-to-cut materials (Ti-6Al-4V) for which the cutting temperature increases rapidly and heavy adhesion occurs. Diffusion profiles obtained with CBN specimens confirm a solid-adhesion mechanism after a chemical diffusion at the tool-chip interface. Chipping of the CBN reinforced cutting edge can be attributed to the hard abrasive nature of the CBN microstructure. References Abukhshim, N.A. (2006) Fifth International Conference on High Speed Machining (HSM), p.129, Metz, France. Ackroyd, B., Chandrasekar, S. and Compton, W.D. (2003) A model for the contact conditions at the chip-tool interface in machining, Journal of Tribology, Vol. 125, No. 3, p.649, 12p. Bhowmick, S. and Alpas, A.T. (2008) Minimum quantity lubrication drilling of aluminium-silicon alloys in water using diamond-like carbon coated drills, International Journal of Machine Tools and Manufacture, Vol. 48, Nos , pp Che Haron, C.H., Ginting, A. and Goh, J.H. (2001) Wear of coated and uncoated carbides in turning tool steel, Journal of Materials Processing Technology, Vol. 116, No. 1, pp Dongcan, Z., Bin, S. and Fanghong, S. (2010) Study on tribological behavior and cutting performance of CVD diamond and DLC films on co-cemented tungsten carbide substrates, Applied Surface Science, Vol. 256, No. 8, pp Ginting, A. and Nouari, M. (2006) Experimental and numerical studies on the performance of alloyed carbide tool in dry milling of aerospace material, International Journal of Machine Tools and Manufacture, Vol. 46, Nos. 7 8, pp Jawaid, A., Sharif, S. and Koksal, S. (2000) Evaluation of wear mechanisms of coated carbide tools when face milling titanium alloy, Journal of Materials Processing Technology, Vol. 99, Nos. 1 3, pp Komanduri, R. and Turkovich, B.F. (1981) New observations on the mechanism of chip formation when machining titanium alloys, Wear, Vol. 69, No. 2, pp König, W. and Neises, A. (1993) Turning Ti6Al4V with PCD, Industrial Diamond Review (IDR), Vol. 2, pp Kuljanic, E., Fioretti, M., Beltrame, L. and Miani, F. (1998) Milling titanium compressor blades with PCD cutter, CIRP Annals Manufacturing Technology, Vol. 47, No. 1, pp Loladze, T.N. (1962) Mechanical engineering division, Proceedings of the 42nd Annual Convention, p.108, Calcutta, West Bengal. Loladze, T.N. (1981) Of the theory of diffusion wear, CIRP Annals Manufacturing Technology, Vol. 30, No. 1, pp Minaki, K., Kitajima, K., Nakahira, Y., Ohnishi, M., Sugimoto, T. and Kaminomura, S. (2008) Development of DLC coated tool for cutting of aluminum alloy influence of deposition condition on cutting characteristic, Key Engineering Materials, Vols , pp Moufki, A., Molinari, A. and Dudzinski, D. (1997) Modelling of orthogonal cutting, First French and German Conference on High Speed Machining, p.8.

16 Analysis of coating performances in machining titanium alloys 173 Moufki, A., Molinari, A. and Dudzinski, D. (1998) Modelling of orthogonal cutting with a temperature dependent friction law, Journal of the Mechanics and Physics of Solids, Vol. 46, No. 10, pp Müller, B., Renz, U., Hoppe, S. and Klocke, F. (2004) Radiation thermometry at a high-speed turning process, Journal of Manufacturing Science and Engineering, Vol. 126, No. 3, p.488, 8p. Nabhani, F. (2001a) Machining of aerospace titanium alloys, Robotics and Computer-Integrated Manufacturing, Vol. 17, Nos. 1 2, pp Nabhani, F. (2001b) Wear mechanisms of ultra-hard cutting tools materials, Journal of Materials Processing Technology, Vol. 115, No. 3, pp Shaw, M.C., Dirke, S.O., Smith, P.A., Cook, N.H., Loewen, E.G. and Yang, C.T. (1954) Machining titanium, MIT Rep., Massachusetts Institute of Technology, Cambridge, MA, Contract AF 22(600) Stephenson, D.A., Jen, T-C. and Lavine, A.S. (1997) Cutting tool temperatures in contour turning: transient analysis and experimental verification, Journal of Manufacturing Science and Engineering, Vol. 119, No. 4A, p.494, 8p. Wada, T. (2010) Cutting performance of diamond-like carbon coated tool in cutting of aluminium alloys, Materials Science Forum, Vols , pp Zoya, Z.A. and Krishnamurthy, R. (2000) The performance of CBN tools in the machining of titanium alloys, Journal of Materials Processing Technology, Vol. 100, Nos. 1 3, pp