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Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel

Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after... Hindawi Publishing Corporation Advances in Tribology Volume 2013, Article ID 519686, 10 pages http://dx.doi.org/10.1155/2013/519686 Research Article Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel 1 1 2 Johannes Kümmel, Katja Poser, Frederik Zanger, 2 1,2 Jürgen Michna, and Volker Schulze Institute of Applied Materials (IAM-WK), Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germany Institute of Production Science (wbk), Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germany Correspondence should be addressed to Johannes Kummel; ¨ johannes.kuemmel@kit.edu Received 21 May 2012; Accepted 20 December 2012 Academic Editor: Meng Hua Copyright © 2013 Johannes Kummel ¨ 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. Analyzing wear mechanisms and developments of surface layers in WC/Co-cemented carbide cutting inserts is of great importance for metal-cutting manufacturing. By knowing relevant processes within the surface layers of cutting tools during machining the choice of machining parameters can be influenced to get less wear and high tool life of the cutting tool. Tool wear obviously influences tool life and surface integrity of the workpiece (residual stresses, surface quality, work hardening, etc.), so the choice of optimised process parameters is of great relevance. Vapour-deposited coatings on WC/Co-cemented carbide cutting inserts are known to improve machining performance and tool life, but the mechanisms behind these improvements are not fully understood. The interaction between commercial TiN-coated and uncoated WC/Co-cemented carbide cutting inserts and a normalised SAE 1045 steel workpiece was investigated during a dry plain turning operation with constant material removal under varied machining parameters. Tool wear was assessed by light-optical microscopy, scanning electron microscopy (SEM), and EDX analysis. eTh state of surface layer was investigated by metallographic sectioning. Microstructural changes and material transfer due to tribological processes in the cutting zone were examined by SEM and EDX analyses. 1. Introduction maps [3]. Here the most important aspects of wear (seizure, delamination wear, mild wear, severe wear, etc.) are displayed At machining metals it is important to know about the wear with respect to the parameters varied in the wear tests behaviour of the cutting tool. This importance arises due to (sliding velocity, pressure, etc.). eTh wear map approach is the fact that the surface integrity of the machined workpiece also applied to metal machining, and therefore the wear is is influenced by tool wear [ 1, 2]. In this case surface integrity displayed as a function of cutting speed𝑣 and feed rate𝑓 [4, is described by three main parameters: the surface roughness, 5]. In this work the aim is to develop a better understanding the residual stress state, and the work hardening in the surface of the wear characteristics for different cutting parameters zone [1]. For further improvement in the knowledge of wear and different tool materials and to get therefore a deeper behaviour of cutting tools the surface layer states of the worn knowledge of the wear processes acting in the cutting zone. tools are important to distinguish between different wear The surface layer states in the uncoated and in the TiN- mechanisms acting in the cutting zone. One possibility at coated cutting tool generated during the metal machining investigating wear with respect to the applied cutting para- operation are mainly addressed. These surface layer states meters (e.g., cutting speed, feed rate, and depth of cut) is the are important for the wear mechanisms that will lead to the idea proposed by Lim and Ashby with the wear mechanism degradation of the cutting tool. By knowing these surface 2 Advances in Tribology Table 1: Chemical composition of workpiece material (SAE 1045) in weight %. CSi Mn P S Cr Ni Mo 0.420 0.285 0.663 0.021 0.035 0.153 0.107 0.021 Table 2: Cutting parameter combinations used in cutting experiments for the uncoated tool (all values) and for the TiN coated tool (values marked with symbol ). ∗ ∗ ∗ ∗ Cutting speed (m/min) 50 100 125 150 100 100 100 100 100 ∗ ∗ ∗ ∗ Feed rate (mm/rev) 0.2 0.2 0.2 0.2 0.1 0.15 0.25 0.3 0.5 layer states a knowledge based-metal cutting operation can be 3. Results achieved. Nowadays some more complex coatings than TiN 3.1. Wear Examination of Uncoated Cutting Tools for Dier ff ent coatings are also used in the metal cutting of plain carbon Cutting Parameters. The wear was documented aeft r different steels (e.g., TiAlCN, AlCrN + TiAlCN coatings, etc.). For cutting lengths for the different cutting parameter combi- this examination the TiN-coating was used to have a better nations used, which were mentioned in Table 2.In Figure 1 possibility of surface layer state characterisation by metallo- there is a display of the wear evolution for the parameters graphic methods and the SEM examination [6]. 𝑣 = 100 m/min,𝑓 = 0.25 mm/rev, and𝑎 = 0.1 mm. The 𝑐 𝑝 reason for the detailed examination of wear measurement is the proper determination of tool wear curves [8, 9]and to 2. Experimental Setup get the possibility to relate the wear of the cutting tool to the For the experiments the chosen workpiece material was SAE surface layer state in the resulting workpiece surface. 1045 plain carbon steel in a normalised state. eTh workpiece With an increasing cutting length the tool has an increas- material had a ferritic-pearlitic microstructure with a mean ing crater wear depth and an increase in flank and notch wear. grain size of ferrite and pearlite of 16𝜇 m. The hardness of the Another wear characteristic is the good adhesion between steel was 194 HV1 measured by the Vickers hardness testing the workpiece material and the cutting tool. In Figure 1 the method. eTh chemical composition of the workpiece material formation of built-up edges is visible and some built-up layer is given in Table 1. zones are shown. Those are present due to good adhesion tendency between steel and cemented carbide. Fragments of The workpieces were cylinders with length 100 mm and these built-up edges (or dead zones) which are described diameter 58 mm. The machining was done by dry plain turn- fundamentally in [10, 11]are visiblealsoonthe chip surface ing down to a diameter of 24 mm. The dry plain turning was andonthe workpiecesurface.Theselayerscause relatively performed with a machining centre Heller MC 16. The cutting rough surfaces on the workpiece with a severely deformed tool used for the experiments was industrial ne-g fi rained microstructure. For the constant cutting speed of 100 m/min (grain size of WC is 0.5𝜇 m) cemented carbide (K10) with a the feed rate was varied according to Table 2.Theresults of composition of 94 volume-% WC and 6 volume-% Co in an the wear measurement are shown in Figure 2.Anincreasein uncoated state and in a TiN coated state. eTh TiN-coating (thickness 3𝜇 m) was deposited directly on the cemented the wear intensity with increasing feed rate can be seen. The same measurements were done for constant feed rate carbide substrate. eTh designation of the tool is SNMA 120408 of 0.2 mm/rev and varying cutting speed. eTh results are according to the standard DIN ISO 1832 without any chip shown in Figure 3. breakers to provide better wear measurement. eTh cutting For varying cutting speed there is also a strong tendency tool has a square geometry and a wedge angle𝛽 of 90 .The to increase wear intensity with increasing cutting speed. For corner radius𝑟 is 0.8 mm and the cutting edge radius𝑟 of 𝜀 𝛽 the cutting speed of 100 m/min there is a slight minimum, the cutting tools is 30𝜇 m. The entering angle between the considering the final state of the worn cutting tool after the main cutting edge and feed direction𝜅 is 45 ,and theused ∘ ∘ same amount of material removal. clearance angle𝛼 was 7 with a rake angle𝛾 of−7 .Thevaried cutting parameters (cutting speed and feed rate) used in the experiments are shown in Table 2. 3.2. Wear Examination of TiN-Coated Cutting Tools. For the The wear measurements were conducted aeft r different comparison of the uncoated and TiN-coated cutting tools cutting lengths by light optical microscopy and according to four sets of parameters (feed rate and cutting speed) were the standard ISO Norm 3685 [7]. eTh examination of surface chosen. es Th e sets of parameters are also shown in Table 2 layer states was done by scanning electron microscopy (SEM) marked with the symbol . andchemicalanalysisbyEDX.For furtherexamination the In Figure 4 a comparison of the wear of uncoated cutting cutting tools were sectioned in the worn zone by using a tools and TiN-coated cutting tools is shown for one of the diamond wire saw for acquiring a metallographic section. four parametersets. It canbeseenthatthe TiNcoating is These specimens were also examined by SEM and EDX highly improving the wear behaviour of the cemented carbide analyses. cutting tools. During the cutting process there is no built-up Advances in Tribology 3 Cutting length 719 3312 5894 8340 (m) Minor cutting Crater wear edge 1 mm 1 mm 1 mm 1 mm Main cutting edge Minor cutting Flank wear and edge notch wear 1 mm 1 mm 1 mm 1 mm Main cutting edge Figure 1: Overview of wear evolution for the cutting parameters 𝑣 =100 m/min, 𝑓=0.25 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 V = 200 cm removal v = 100 m/min 100 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0 5000 10000 15000 20000 Feed rate (mm/rev) Cutting length (m) f = 0.1 mm/rev Flank wear land width VB f = 0.25 mm/rev f = 0.15 mm/rev f = 0.3 mm/rev f = 0.2 mm/rev f = 0.5 mm/rev (b) (a) Figure 2: Flank wear land width VB measurement with respect to the cutting length for different feed rates (0.1 mm/rev–0.5 mm/rev) and comparison of the final state of tool wear after material removal of 200 cm . edge formation on the TiN-coated cutting tool, and the wear Figure 5 one can clearly see that the TiN coating is highly intensity is much smaller than for the uncoated cutting tool. improving the wear resistance for the cutting tool in dry plain For the TiN-coated tool there is only little wear visible in turning application. Especially in the higher cutting speed Figure 4. regime (150 m/min) for the own chosen cutting parameters eTh wear wasalsomeasuredinthe case of theTiN-coated the TiN coating improves wear behaviour to a great extent. cutting tool and is displayed in Figure 5 with respect to the The dashed line “linear tfi TiN” in Figure 5 is a linear cutting length, and the n fi al wear states are also matched regression line for the TiN-coated cutting tool used with in a 3D-view of flank wear land width VB with regard to the parameters𝑣 = 150 m/min and𝑓 = 0.2 mm/rev. The the cutting parameters: cutting speed and feed rate. From solid line “linear tfi WC/Co” in Figure 5 is a linear regression μm) Flank wear land width VB ( μm) Flank wear land width VB ( 4 Advances in Tribology 2000 2000 V = 200 cm removal f = 0.2 mm/rev 1500 1500 1000 1000 500 500 0 0 0 2000 4000 6000 8000 10000 50 75 100 125 150 Cutting length (m) Cutting speed (m/min) v = 125 m/min v = 50 m/min c Flank wear land width VB v = 100 m/min v = 150 m/min c c (b) (a) Figure 3: Flank wear land width VB with respect to cutting length (for varying cutting speed 50 m/min–150 m/min) and constant feed rate and comparison of the final state of tool wear aeft r material removal of 200 cm . Cutting length 898 3405 5630 8155 (m) Minor cutting edge Flank and notch wear (uncoated) 1 mm 1 mm 1 mm 1 mm Main cutting edge Minor cutting edge Flank wear and notch wear (TiN coated) 1 mm 1 mm 1 mm 1 mm Main cutting edge Figure 4: Comparison of wear of uncoated and TiN-coated cutting tools for set of parameter: 𝑣 = 100 m/min,𝑓 = 0.20 mm/rev, and 𝑎 =0.1 mm. line for the linear wear regime up to a cutting length of speed applied during the metal cutting process leads to a 8000 mfortheuncoatedcuttingtoolusedwiththesamepara- smoother worn surface in the crater wear region which is seen meters. in a higher magnification in Figure 6(b). eTh examination of wear in the n fi al state of the cutting The rake face of the TiN-coated cutting tool that is shown process was also done by SEM. Two different states, one for a in Figure 7 is less worn than for the uncoated cutting tool. lower (100 m/min) and one for a higher (150 m/min) cutting Only in the region next to the cutting edge, where the speed, were examined. highest intensity of chip flow is assumed, there are some areas In Figure 6 the surface structure of the worn rake face of without the TiN coating. In these parts of the rake face the the uncoated cutting tool is shown. In the crater wear region cemented carbide substrate is visible. Further examination the most important wear mechanisms are the adhesion of by energy dispersive X-ray spectroscopy (EDX) on the rake workpiece material adhering to the rake face and tungsten face gives some chemical information of the worn surface. carbide grain pullouts. This is due to the strong adhesion In Figure 8 there is a picture shown from the rake face with tendency of steel to the cemented carbide. This strong a delaminated TiN-coating structure and an EDX line scan adhesive effect is also responsible for the formation of built- showing the chemical analysis across the worn surface. In the up edges. In comparison with Figure 6(a) the higher cutting brighter region of the worn tool (WC/Co substrate) there is Flank wear land width VB (μm) Flank wear width VB (μm) Cutting speed (m/min) Advances in Tribology 5 0.5 0 2000 4000 6000 8000 10000 12000 0.4 Cutting length (m) 0.3 0.2 WC/Co v = 50 m/min; f = 0.2 mm/rev WC/Co v = 100 m/min; f = 0.2 mm/rev WC/Co v = 150 m/min; f = 0.2 mm/rev Uncoated tool WC/Co v = 100 m/min; f = 0.5 mm/rev TiN-coated tool TiN v = 50 m/min; f = 0.2 mm/rev TiN v = 100 m/min; f = 0.2 mm/rev TiN v = 150 m/min; f = 0.2 mm/rev TiN v = 100 m/min; f = 0.5 mm/rev Linear fit WC/Co Linear fit TiN (b) (a) Figure 5: Comparison of flank wear land width VB with respect to the cutting length for the uncoated (black closed symbols) and TiN-coated (open symbols) cutting tool. eTh diagram on the right side shows a comparison (uncoated versus coated cutting tool) of the flank wear land width VB in the final state of the cutting tool with respect to cutting speed and feed rate. 200µm 200µm 50 µm 2 µm 50 µm 2 µm (a) (b) Figure 6: SEM examination of worn rake face of uncoated cutting tools. In (a) the crater wear is visible for the cutting parameters 𝑣 = 100 m/min,𝑓 = 0.25 mm/rev, and𝑎 =0.1 mm. In the highest magnification there is a WC-grain pullout visible on the rake face. On the 𝑐 𝑝 right (b) there is a SEM examination of worn rake face of uncoated cutting tool with𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 a strong tendency of Fe adhesion from the workpiece (peaks In Figure 8(b) two important intensity curves obtained of high intensity of Fe). eTh TiN-coated areas (darker parts from an EDX line scan are shown. The black closed symbols in Figure 8(a))shownosuchintensive Fe peaksinthe EDX denote the titanium peak intensity and the open symbols spectrum. er Th efore, the adhesion of iron to the TiN coating denote the intensity of Fe. In the region without TiN coating is less strong. there are high intensities from Fe, showing strong adhesion Feed rate (mm/rev) Flank wear land width VB (μm) Flank wear land width VB (μm) 6 Advances in Tribology 200 µm 40µm µm Figure 7: SEM examination of worn rake face of TiN-coated cutting tool: 𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 50 μm 0 1020304050 Measuring length (μm) Ti Fe (a) (b) Figure 8: (a) SEM image worn rake face of TiN-coated cutting tool: 𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. The arrow depicts 𝑐 𝑝 the path of the EDX line scan shown in (b). Intensity (counts) Advances in Tribology 7 10 μm 200 μm (a) (b) Figure 9: SEM picture of worn uncoated cutting tool in final state (aeft r cutting length of 7084 m) with cutting parameters as follows: 𝑣 = 100 m/min,𝑓 = 0.30 mm/rev, and𝑎 = 0.1 mm. Due to the high temperatures acting in the cutting zone some evidence is seen for 𝑐 𝑝 plastic lowering of the cutting edge [9]. 40 μm 2 μm (a) (b) Figure 10: SEM picture of worn uncoated cutting tool in final state (aer ft cutting length of 14669 m) with cutting parameters as follows: 𝑣 = 100 m/min,𝑓=0.15 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 of workpiece material on the rake face, because of the worn the wear mechanisms acting for the uncoated cutting tool, TiN coating. microcracking of WC grains is found. es Th e small particles cause abrasive wear due to their hardness. This abrasive wear is caused by the small wear debris in the interfacial area. 3.3. Examination of Surface Layer States in Uncoated and eTh same procedure for the examination of cutting tool TiN-Coated Cutting Tool. For the examination of the surface surface layer states of TiN-coated cutting tools was applied for layer states in the cutting tool metallographic sectioning was the cutting parameter set𝑣 =100 m/min,𝑓=0.5 mm/rev, done [6], where the worn tool is carefully cut by the use and𝑎 =0.1 mm. of a diamond wire saw and is prepared by metallographic In Figure 9(a) the flank wear and crater wear are both methods. The sectioned worn cutting tool was embedded in visible. On the right side in Figure 9(b) there is a detailed a thermoset resin for metallographic grinding and polishing. pictureshowing thebuilt-upedgeinahigher magnicfi ation. Some examples of metallographic sections prepared this way In Figure 10(a) thecraterwearisvisible with alarge are shown in Figures 9 and 10. In Figure 9 an overview of a worn WC-Co cemented built-up layer of work material. In Figure 10(b) the interface carbide cutting tool in uncoated state is shown with a built-up between the cemented carbide substrate and the etched SAE 1045 built-up layer is shown (etching agent: Nital). edge on the cutting edge. In the metallographic sections the crater wear, flank wear and material transfer from the work In Figure 11 it is shown that the TiN coating has a protective eect ff on the wear behaviour of the cutting tool. piece can be detected. Only locally there are some workpiece fragments adhering on In Figure 10 thewornsurface stateisshown,and with the aid of the back scatter electron detector (BSE) some little the cutting tool substrate, where the TiN coating is worn, and the cemented carbide substrate is exposed to the workpiece WC-grain fragments are visible in the interface between the built-up layer and the uncoated cutting tool. Concerning material. 8 Advances in Tribology Fe TiN WC/Co 5 μm 20 μm Figure 11: SEM picture of slightly worn TiN-coated cutting tool in final state with cutting parameters as follows: 𝑣 = 100 m/min, 𝑓 = 0.5 mm/rev, and𝑎 = 0.1 mm. The cutting edge is shown, and on the right hand side the detail is shown, with a piece of workpiece material adhering to the WC/Co substrate. 1500 Ti C O Ti Al NFe Si Ti Mn Mn Fe 0 2468 10 keV (b) (a) Figure 12: EDX spectrum on rake face of a worn TiN-coated cutting tool for point 2 near the cutting edge. Some elements from the workpiece material were found (cutting conditions:𝑣 =150 m/min,𝑓=0.2 mm/rev, and𝑎 =0.1 mm). 𝑐 𝑝 4. Discussion speed regime by a factor of 20 due to the TiN coating for the comparison of the highest cutting speed of 150 m/min in the The examination of surface layer states of uncoated WC/Co- linear wear regime in Figure 5 (the wear intensities as flank cutting tools is one important aim of this paper. eTh main wear land width VB per cutting length were calculated by wear mechanisms for all chosen parameters in Table 2 linear regression of the flank wear distribution in Figure 5). areadhesivewearand athree-bodyabrasivewearfor the This can be explained by different reasons. TiN has got a uncoated cutting tool. The adhesive and three-body abrasive higher hardness (2300 HV0.05 [15]) than cemented carbide wear was also shown in further studies [12]. Other wear (fine-grained cemented carbide 94 volume-% WC, 6 volume- mechanisms like diffusion are also possible [ 13, 14]. The %Co(1850 HV30)[16]). eTh thermal conductivity of TiN −1 −1 morphology of crater wear on therakefacefor lowercutting is lower (29 Wm K [16]) than that of cemented carbide −1 −1 speeds and feed rates, as seen in Figure 6, can be explained (68.9 Wm K [16]). er Th efore, more heat will be conducted by the chip side flow because of small cutting depth chosen through the chip and the work piece material, and the TiN- in the experiments. eTh chips show a curled structure, so that coated cutting tool will see lower temperatures. they can produce notch-like crater wear. The most important difference between the wear be- The examination of surface layer states in the TiN- haviour of uncoated and TiN-coated tools is, however, the coated cutting tool is another important aim of this paper. adhesion between workpiece and tool. In the case of steel From Figure 5 it can be seen that the TiN coating is highly workpieces, this adhesion to cemented carbide substrate is improving the wear behaviour of cemented carbide cutting much stronger than to TiN coating. eTh adhesive wear is tools. The wear intensity is reduced in the highest cutting correlated to the atomic bonding of the different materials Advances in Tribology 9 WC/Co Fe Worn TiN unworn TiN 200 μm 20 μm Figure 13: Small region of flank wear (resp. notch wear) of TiN-coated cutting tool, which was used under the cutting conditions of 𝑣 = 100 m/min,𝑓=0.5 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 between the different atoms of the workpiece material, and The formation of built-up edges, built-up layers, and the cutting tool material and a smooth surface is necessary dead zones is detected for the uncoated cemented carbide [17]. eTh different wear mechanisms acting in the cutting zone cutting tool. eTh reason for that is a strong adhesion of steel are abrasion and adhesion. (workpiece material) to the cemented carbide. The wear was examined by metallographic sectioning, As shown, there is less-adhesive effect of the work mate- and it was revealed that the wear mechanisms are adhesion rial on the TiN coating. The wear mechanisms acting, when and abrasion. turning with a TiN-coated tool, were not examined in detail. Improving wear behaviour of the TiN-coated cemented eTh re are some further possible reasons, why TiN has got a carbide cutting tools is due to the low adhesion of the selected better wear behaviour. Some protective adhesion layers were workpiece material (SAE 1045) to the TiN coating. Hence foundorassumedonTiN andAlCrNcoatings[6, 18]. On the there is no built-up edge or built-up layer formation on worn TiN-layers some elements (Al, Si, etc., see Table 1)from the TiN coating. On delaminated, respectively, fully worn the workpiece material were found (see Figure 12). These TiN coating there is again a strong adhesion detected to the could also form a protective tribolayer during the cutting cemented carbide substrate, and a local increase in wear rate process. is observed. eTh TiN coating changes its surface structure from a rougher surface to a smoother surface during the metal cutting process which can be attributed to the wear of Acknowledgment chip flow respectively, the tool-workpiece interaction (see The authors gratefully acknowledge the company OC Oer- Figure 13). In Figure 13 thewornregionofthe TiNcoating has got a smoother surface structure than the unworn TiN- likon Balzers for the deposition of the TiN coating. coating. In Figure 13, a small part of the flank face is shown where References some notch wear is detected via SEM. There are three main parts of the cutting tool region: the surrounding part is [1] I. S. Jawahir, E. Brinksmeier, R. M’Saoubi et al., “Surface consisting of unworn TiN coating. This as-deposited coating integrity in material removal processes: recent advances,” CIRP Annals—Manufacturing Technology,vol.60, no.2,pp. 603–626, has got a rougher surface structure than the worn part of the tool, where sliding between chip/workpiece and the tool occurs. Here the sliding process leads to a smoothening of the [2] Q. Xie, A. E. Bayoumi, and L. A. Kendall, “On tool wear and TiN coating. In the middle of the worn region, the coating is its eeff ct on machined surface integrity,” Journal of Materials Shaping Technology,vol.8,no. 4, pp.255–265,1990. fully worn. Cemented carbide substrate can be seen (brighter area in Figure 13), and adhering workpiece material (Fe) can [3]S.C.Lim andM.F.Ashby,“Wear-mechanism maps,” Acta be detected. This notch wear can be attributed to the high Metallurgica,vol.35, no.1,pp. 1–24,1987. wear intensity that is acting at the beginning of the cutting [4] S.C.Lim, Y. B. Liu, S. H. Lee, andK.H.W.Seah, “Mapping process, when the cutting edge enters the workpiece. thewearofsomecutting-toolmaterials,” Wear,vol.162-164,pp. 971–974, 1993. [5] S. C. Lim, “Recent developments in wear-mechanism maps,” 5. Conclusions/Summary Tribology International,vol.31, no.1–3,pp. 87–97, 1998. An increasing load (higher feed rate or higher cutting speed) [6] S. Karagoz ¨ and H. F. Fischmeister, “Metallographic observations subjected to the cutting tool results in an increasing wear rate on the wear process of TiN-coated cutting tools,” Surface and with respect to flank wear. Coatings Technology,vol.81, no.2-3,pp. 190–200, 1996. 10 Advances in Tribology [7] “ISO 3685: tool-life testing with single-point turning tools,” [8] V. P. Astakhov, Tribology of Metal Cutting,vol.52of Tribology and Interface Engineering Series, Elsevier, 2006. [9] V. P. Astakhov, “eTh assessment of cutting tool wear,” Interna- tional Journal of Machine Tools and Manufacture,vol.44, no.6, pp. 637–647, 2004. [10] S. Jacobson and P. Wallen, ´ “A new classification system for dead zones in metal cutting,” International Journal of Machine Tool Design and Research, vol. 28, no. 4, pp. 529–538, 1988. [11] P. K. Philip, “Built-up edge phenomenon in machining steel with carbide,” International Journal of Machine Tool Design and Research, vol. 11, no. 2, pp. 121–132, 1971. [12] H. Opitz and M. Gappisch, “Some recent research on the wear behaviour of carbide cutting tools,” International Journal of Machine Tool Design and Research,vol.2,no. 1, pp.43–73,1962. [13] J.A.Arsecularatne,L.C.Zhang,and C. Montross,“Wear and tool life of tungsten carbide, PCBN and PCD cutting tools,” International Journal of Machine Tools and Manufacture,vol.46, no. 5, pp. 482–491, 2006. [14] H. O. Gekonde and S. V. Subramanian, “Tribology of tool- chip interface and tool wear mechanisms,” Surface and Coatings Technology,vol.149,no. 2-3, pp.151–160,2002. [15] “Oerlikon Balzers product information BALINIT A,” 2011. [16] “Springer Materials: the Landolt Bor ¨ nstein database, the worlds largest resource for physical and chemical data,” 2009. [17] Valentin L. Popov, Kontaktmechanik und Reibung: Von der Nan- otribologie bis zur Erdbebendynamik, Springer, Berlin, Germany, [18] J. Gerth, M. Larsson, U. Wiklund, F. Riddar, and S. Hogmark, “On the wear of PVD-coated HSS hobs in dry gear cutting,” Wear,vol.266,no. 3-4, pp.444–452,2009. 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Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel

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Hindawi Publishing Corporation
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Copyright © 2013 Johannes Kümmel 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.
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10.1155/2013/519686
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Abstract

Hindawi Publishing Corporation Advances in Tribology Volume 2013, Article ID 519686, 10 pages http://dx.doi.org/10.1155/2013/519686 Research Article Surface Layer States of Worn Uncoated and TiN-Coated WC/Co-Cemented Carbide Cutting Tools after Dry Plain Turning of Carbon Steel 1 1 2 Johannes Kümmel, Katja Poser, Frederik Zanger, 2 1,2 Jürgen Michna, and Volker Schulze Institute of Applied Materials (IAM-WK), Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germany Institute of Production Science (wbk), Karlsruhe Institute of Technology (KIT), Kaiserstraße 12, 76131 Karlsruhe, Germany Correspondence should be addressed to Johannes Kummel; ¨ johannes.kuemmel@kit.edu Received 21 May 2012; Accepted 20 December 2012 Academic Editor: Meng Hua Copyright © 2013 Johannes Kummel ¨ 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. Analyzing wear mechanisms and developments of surface layers in WC/Co-cemented carbide cutting inserts is of great importance for metal-cutting manufacturing. By knowing relevant processes within the surface layers of cutting tools during machining the choice of machining parameters can be influenced to get less wear and high tool life of the cutting tool. Tool wear obviously influences tool life and surface integrity of the workpiece (residual stresses, surface quality, work hardening, etc.), so the choice of optimised process parameters is of great relevance. Vapour-deposited coatings on WC/Co-cemented carbide cutting inserts are known to improve machining performance and tool life, but the mechanisms behind these improvements are not fully understood. The interaction between commercial TiN-coated and uncoated WC/Co-cemented carbide cutting inserts and a normalised SAE 1045 steel workpiece was investigated during a dry plain turning operation with constant material removal under varied machining parameters. Tool wear was assessed by light-optical microscopy, scanning electron microscopy (SEM), and EDX analysis. eTh state of surface layer was investigated by metallographic sectioning. Microstructural changes and material transfer due to tribological processes in the cutting zone were examined by SEM and EDX analyses. 1. Introduction maps [3]. Here the most important aspects of wear (seizure, delamination wear, mild wear, severe wear, etc.) are displayed At machining metals it is important to know about the wear with respect to the parameters varied in the wear tests behaviour of the cutting tool. This importance arises due to (sliding velocity, pressure, etc.). eTh wear map approach is the fact that the surface integrity of the machined workpiece also applied to metal machining, and therefore the wear is is influenced by tool wear [ 1, 2]. In this case surface integrity displayed as a function of cutting speed𝑣 and feed rate𝑓 [4, is described by three main parameters: the surface roughness, 5]. In this work the aim is to develop a better understanding the residual stress state, and the work hardening in the surface of the wear characteristics for different cutting parameters zone [1]. For further improvement in the knowledge of wear and different tool materials and to get therefore a deeper behaviour of cutting tools the surface layer states of the worn knowledge of the wear processes acting in the cutting zone. tools are important to distinguish between different wear The surface layer states in the uncoated and in the TiN- mechanisms acting in the cutting zone. One possibility at coated cutting tool generated during the metal machining investigating wear with respect to the applied cutting para- operation are mainly addressed. These surface layer states meters (e.g., cutting speed, feed rate, and depth of cut) is the are important for the wear mechanisms that will lead to the idea proposed by Lim and Ashby with the wear mechanism degradation of the cutting tool. By knowing these surface 2 Advances in Tribology Table 1: Chemical composition of workpiece material (SAE 1045) in weight %. CSi Mn P S Cr Ni Mo 0.420 0.285 0.663 0.021 0.035 0.153 0.107 0.021 Table 2: Cutting parameter combinations used in cutting experiments for the uncoated tool (all values) and for the TiN coated tool (values marked with symbol ). ∗ ∗ ∗ ∗ Cutting speed (m/min) 50 100 125 150 100 100 100 100 100 ∗ ∗ ∗ ∗ Feed rate (mm/rev) 0.2 0.2 0.2 0.2 0.1 0.15 0.25 0.3 0.5 layer states a knowledge based-metal cutting operation can be 3. Results achieved. Nowadays some more complex coatings than TiN 3.1. Wear Examination of Uncoated Cutting Tools for Dier ff ent coatings are also used in the metal cutting of plain carbon Cutting Parameters. The wear was documented aeft r different steels (e.g., TiAlCN, AlCrN + TiAlCN coatings, etc.). For cutting lengths for the different cutting parameter combi- this examination the TiN-coating was used to have a better nations used, which were mentioned in Table 2.In Figure 1 possibility of surface layer state characterisation by metallo- there is a display of the wear evolution for the parameters graphic methods and the SEM examination [6]. 𝑣 = 100 m/min,𝑓 = 0.25 mm/rev, and𝑎 = 0.1 mm. The 𝑐 𝑝 reason for the detailed examination of wear measurement is the proper determination of tool wear curves [8, 9]and to 2. Experimental Setup get the possibility to relate the wear of the cutting tool to the For the experiments the chosen workpiece material was SAE surface layer state in the resulting workpiece surface. 1045 plain carbon steel in a normalised state. eTh workpiece With an increasing cutting length the tool has an increas- material had a ferritic-pearlitic microstructure with a mean ing crater wear depth and an increase in flank and notch wear. grain size of ferrite and pearlite of 16𝜇 m. The hardness of the Another wear characteristic is the good adhesion between steel was 194 HV1 measured by the Vickers hardness testing the workpiece material and the cutting tool. In Figure 1 the method. eTh chemical composition of the workpiece material formation of built-up edges is visible and some built-up layer is given in Table 1. zones are shown. Those are present due to good adhesion tendency between steel and cemented carbide. Fragments of The workpieces were cylinders with length 100 mm and these built-up edges (or dead zones) which are described diameter 58 mm. The machining was done by dry plain turn- fundamentally in [10, 11]are visiblealsoonthe chip surface ing down to a diameter of 24 mm. The dry plain turning was andonthe workpiecesurface.Theselayerscause relatively performed with a machining centre Heller MC 16. The cutting rough surfaces on the workpiece with a severely deformed tool used for the experiments was industrial ne-g fi rained microstructure. For the constant cutting speed of 100 m/min (grain size of WC is 0.5𝜇 m) cemented carbide (K10) with a the feed rate was varied according to Table 2.Theresults of composition of 94 volume-% WC and 6 volume-% Co in an the wear measurement are shown in Figure 2.Anincreasein uncoated state and in a TiN coated state. eTh TiN-coating (thickness 3𝜇 m) was deposited directly on the cemented the wear intensity with increasing feed rate can be seen. The same measurements were done for constant feed rate carbide substrate. eTh designation of the tool is SNMA 120408 of 0.2 mm/rev and varying cutting speed. eTh results are according to the standard DIN ISO 1832 without any chip shown in Figure 3. breakers to provide better wear measurement. eTh cutting For varying cutting speed there is also a strong tendency tool has a square geometry and a wedge angle𝛽 of 90 .The to increase wear intensity with increasing cutting speed. For corner radius𝑟 is 0.8 mm and the cutting edge radius𝑟 of 𝜀 𝛽 the cutting speed of 100 m/min there is a slight minimum, the cutting tools is 30𝜇 m. The entering angle between the considering the final state of the worn cutting tool after the main cutting edge and feed direction𝜅 is 45 ,and theused ∘ ∘ same amount of material removal. clearance angle𝛼 was 7 with a rake angle𝛾 of−7 .Thevaried cutting parameters (cutting speed and feed rate) used in the experiments are shown in Table 2. 3.2. Wear Examination of TiN-Coated Cutting Tools. For the The wear measurements were conducted aeft r different comparison of the uncoated and TiN-coated cutting tools cutting lengths by light optical microscopy and according to four sets of parameters (feed rate and cutting speed) were the standard ISO Norm 3685 [7]. eTh examination of surface chosen. es Th e sets of parameters are also shown in Table 2 layer states was done by scanning electron microscopy (SEM) marked with the symbol . andchemicalanalysisbyEDX.For furtherexamination the In Figure 4 a comparison of the wear of uncoated cutting cutting tools were sectioned in the worn zone by using a tools and TiN-coated cutting tools is shown for one of the diamond wire saw for acquiring a metallographic section. four parametersets. It canbeseenthatthe TiNcoating is These specimens were also examined by SEM and EDX highly improving the wear behaviour of the cemented carbide analyses. cutting tools. During the cutting process there is no built-up Advances in Tribology 3 Cutting length 719 3312 5894 8340 (m) Minor cutting Crater wear edge 1 mm 1 mm 1 mm 1 mm Main cutting edge Minor cutting Flank wear and edge notch wear 1 mm 1 mm 1 mm 1 mm Main cutting edge Figure 1: Overview of wear evolution for the cutting parameters 𝑣 =100 m/min, 𝑓=0.25 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 V = 200 cm removal v = 100 m/min 100 100 0 0.1 0.2 0.3 0.4 0.5 0.6 0 5000 10000 15000 20000 Feed rate (mm/rev) Cutting length (m) f = 0.1 mm/rev Flank wear land width VB f = 0.25 mm/rev f = 0.15 mm/rev f = 0.3 mm/rev f = 0.2 mm/rev f = 0.5 mm/rev (b) (a) Figure 2: Flank wear land width VB measurement with respect to the cutting length for different feed rates (0.1 mm/rev–0.5 mm/rev) and comparison of the final state of tool wear after material removal of 200 cm . edge formation on the TiN-coated cutting tool, and the wear Figure 5 one can clearly see that the TiN coating is highly intensity is much smaller than for the uncoated cutting tool. improving the wear resistance for the cutting tool in dry plain For the TiN-coated tool there is only little wear visible in turning application. Especially in the higher cutting speed Figure 4. regime (150 m/min) for the own chosen cutting parameters eTh wear wasalsomeasuredinthe case of theTiN-coated the TiN coating improves wear behaviour to a great extent. cutting tool and is displayed in Figure 5 with respect to the The dashed line “linear tfi TiN” in Figure 5 is a linear cutting length, and the n fi al wear states are also matched regression line for the TiN-coated cutting tool used with in a 3D-view of flank wear land width VB with regard to the parameters𝑣 = 150 m/min and𝑓 = 0.2 mm/rev. The the cutting parameters: cutting speed and feed rate. From solid line “linear tfi WC/Co” in Figure 5 is a linear regression μm) Flank wear land width VB ( μm) Flank wear land width VB ( 4 Advances in Tribology 2000 2000 V = 200 cm removal f = 0.2 mm/rev 1500 1500 1000 1000 500 500 0 0 0 2000 4000 6000 8000 10000 50 75 100 125 150 Cutting length (m) Cutting speed (m/min) v = 125 m/min v = 50 m/min c Flank wear land width VB v = 100 m/min v = 150 m/min c c (b) (a) Figure 3: Flank wear land width VB with respect to cutting length (for varying cutting speed 50 m/min–150 m/min) and constant feed rate and comparison of the final state of tool wear aeft r material removal of 200 cm . Cutting length 898 3405 5630 8155 (m) Minor cutting edge Flank and notch wear (uncoated) 1 mm 1 mm 1 mm 1 mm Main cutting edge Minor cutting edge Flank wear and notch wear (TiN coated) 1 mm 1 mm 1 mm 1 mm Main cutting edge Figure 4: Comparison of wear of uncoated and TiN-coated cutting tools for set of parameter: 𝑣 = 100 m/min,𝑓 = 0.20 mm/rev, and 𝑎 =0.1 mm. line for the linear wear regime up to a cutting length of speed applied during the metal cutting process leads to a 8000 mfortheuncoatedcuttingtoolusedwiththesamepara- smoother worn surface in the crater wear region which is seen meters. in a higher magnification in Figure 6(b). eTh examination of wear in the n fi al state of the cutting The rake face of the TiN-coated cutting tool that is shown process was also done by SEM. Two different states, one for a in Figure 7 is less worn than for the uncoated cutting tool. lower (100 m/min) and one for a higher (150 m/min) cutting Only in the region next to the cutting edge, where the speed, were examined. highest intensity of chip flow is assumed, there are some areas In Figure 6 the surface structure of the worn rake face of without the TiN coating. In these parts of the rake face the the uncoated cutting tool is shown. In the crater wear region cemented carbide substrate is visible. Further examination the most important wear mechanisms are the adhesion of by energy dispersive X-ray spectroscopy (EDX) on the rake workpiece material adhering to the rake face and tungsten face gives some chemical information of the worn surface. carbide grain pullouts. This is due to the strong adhesion In Figure 8 there is a picture shown from the rake face with tendency of steel to the cemented carbide. This strong a delaminated TiN-coating structure and an EDX line scan adhesive effect is also responsible for the formation of built- showing the chemical analysis across the worn surface. In the up edges. In comparison with Figure 6(a) the higher cutting brighter region of the worn tool (WC/Co substrate) there is Flank wear land width VB (μm) Flank wear width VB (μm) Cutting speed (m/min) Advances in Tribology 5 0.5 0 2000 4000 6000 8000 10000 12000 0.4 Cutting length (m) 0.3 0.2 WC/Co v = 50 m/min; f = 0.2 mm/rev WC/Co v = 100 m/min; f = 0.2 mm/rev WC/Co v = 150 m/min; f = 0.2 mm/rev Uncoated tool WC/Co v = 100 m/min; f = 0.5 mm/rev TiN-coated tool TiN v = 50 m/min; f = 0.2 mm/rev TiN v = 100 m/min; f = 0.2 mm/rev TiN v = 150 m/min; f = 0.2 mm/rev TiN v = 100 m/min; f = 0.5 mm/rev Linear fit WC/Co Linear fit TiN (b) (a) Figure 5: Comparison of flank wear land width VB with respect to the cutting length for the uncoated (black closed symbols) and TiN-coated (open symbols) cutting tool. eTh diagram on the right side shows a comparison (uncoated versus coated cutting tool) of the flank wear land width VB in the final state of the cutting tool with respect to cutting speed and feed rate. 200µm 200µm 50 µm 2 µm 50 µm 2 µm (a) (b) Figure 6: SEM examination of worn rake face of uncoated cutting tools. In (a) the crater wear is visible for the cutting parameters 𝑣 = 100 m/min,𝑓 = 0.25 mm/rev, and𝑎 =0.1 mm. In the highest magnification there is a WC-grain pullout visible on the rake face. On the 𝑐 𝑝 right (b) there is a SEM examination of worn rake face of uncoated cutting tool with𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 a strong tendency of Fe adhesion from the workpiece (peaks In Figure 8(b) two important intensity curves obtained of high intensity of Fe). eTh TiN-coated areas (darker parts from an EDX line scan are shown. The black closed symbols in Figure 8(a))shownosuchintensive Fe peaksinthe EDX denote the titanium peak intensity and the open symbols spectrum. er Th efore, the adhesion of iron to the TiN coating denote the intensity of Fe. In the region without TiN coating is less strong. there are high intensities from Fe, showing strong adhesion Feed rate (mm/rev) Flank wear land width VB (μm) Flank wear land width VB (μm) 6 Advances in Tribology 200 µm 40µm µm Figure 7: SEM examination of worn rake face of TiN-coated cutting tool: 𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 50 μm 0 1020304050 Measuring length (μm) Ti Fe (a) (b) Figure 8: (a) SEM image worn rake face of TiN-coated cutting tool: 𝑣 =150 m/min,𝑓=0.20 mm/rev, and𝑎 =0.1 mm. The arrow depicts 𝑐 𝑝 the path of the EDX line scan shown in (b). Intensity (counts) Advances in Tribology 7 10 μm 200 μm (a) (b) Figure 9: SEM picture of worn uncoated cutting tool in final state (aeft r cutting length of 7084 m) with cutting parameters as follows: 𝑣 = 100 m/min,𝑓 = 0.30 mm/rev, and𝑎 = 0.1 mm. Due to the high temperatures acting in the cutting zone some evidence is seen for 𝑐 𝑝 plastic lowering of the cutting edge [9]. 40 μm 2 μm (a) (b) Figure 10: SEM picture of worn uncoated cutting tool in final state (aer ft cutting length of 14669 m) with cutting parameters as follows: 𝑣 = 100 m/min,𝑓=0.15 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 of workpiece material on the rake face, because of the worn the wear mechanisms acting for the uncoated cutting tool, TiN coating. microcracking of WC grains is found. es Th e small particles cause abrasive wear due to their hardness. This abrasive wear is caused by the small wear debris in the interfacial area. 3.3. Examination of Surface Layer States in Uncoated and eTh same procedure for the examination of cutting tool TiN-Coated Cutting Tool. For the examination of the surface surface layer states of TiN-coated cutting tools was applied for layer states in the cutting tool metallographic sectioning was the cutting parameter set𝑣 =100 m/min,𝑓=0.5 mm/rev, done [6], where the worn tool is carefully cut by the use and𝑎 =0.1 mm. of a diamond wire saw and is prepared by metallographic In Figure 9(a) the flank wear and crater wear are both methods. The sectioned worn cutting tool was embedded in visible. On the right side in Figure 9(b) there is a detailed a thermoset resin for metallographic grinding and polishing. pictureshowing thebuilt-upedgeinahigher magnicfi ation. Some examples of metallographic sections prepared this way In Figure 10(a) thecraterwearisvisible with alarge are shown in Figures 9 and 10. In Figure 9 an overview of a worn WC-Co cemented built-up layer of work material. In Figure 10(b) the interface carbide cutting tool in uncoated state is shown with a built-up between the cemented carbide substrate and the etched SAE 1045 built-up layer is shown (etching agent: Nital). edge on the cutting edge. In the metallographic sections the crater wear, flank wear and material transfer from the work In Figure 11 it is shown that the TiN coating has a protective eect ff on the wear behaviour of the cutting tool. piece can be detected. Only locally there are some workpiece fragments adhering on In Figure 10 thewornsurface stateisshown,and with the aid of the back scatter electron detector (BSE) some little the cutting tool substrate, where the TiN coating is worn, and the cemented carbide substrate is exposed to the workpiece WC-grain fragments are visible in the interface between the built-up layer and the uncoated cutting tool. Concerning material. 8 Advances in Tribology Fe TiN WC/Co 5 μm 20 μm Figure 11: SEM picture of slightly worn TiN-coated cutting tool in final state with cutting parameters as follows: 𝑣 = 100 m/min, 𝑓 = 0.5 mm/rev, and𝑎 = 0.1 mm. The cutting edge is shown, and on the right hand side the detail is shown, with a piece of workpiece material adhering to the WC/Co substrate. 1500 Ti C O Ti Al NFe Si Ti Mn Mn Fe 0 2468 10 keV (b) (a) Figure 12: EDX spectrum on rake face of a worn TiN-coated cutting tool for point 2 near the cutting edge. Some elements from the workpiece material were found (cutting conditions:𝑣 =150 m/min,𝑓=0.2 mm/rev, and𝑎 =0.1 mm). 𝑐 𝑝 4. Discussion speed regime by a factor of 20 due to the TiN coating for the comparison of the highest cutting speed of 150 m/min in the The examination of surface layer states of uncoated WC/Co- linear wear regime in Figure 5 (the wear intensities as flank cutting tools is one important aim of this paper. eTh main wear land width VB per cutting length were calculated by wear mechanisms for all chosen parameters in Table 2 linear regression of the flank wear distribution in Figure 5). areadhesivewearand athree-bodyabrasivewearfor the This can be explained by different reasons. TiN has got a uncoated cutting tool. The adhesive and three-body abrasive higher hardness (2300 HV0.05 [15]) than cemented carbide wear was also shown in further studies [12]. Other wear (fine-grained cemented carbide 94 volume-% WC, 6 volume- mechanisms like diffusion are also possible [ 13, 14]. The %Co(1850 HV30)[16]). eTh thermal conductivity of TiN −1 −1 morphology of crater wear on therakefacefor lowercutting is lower (29 Wm K [16]) than that of cemented carbide −1 −1 speeds and feed rates, as seen in Figure 6, can be explained (68.9 Wm K [16]). er Th efore, more heat will be conducted by the chip side flow because of small cutting depth chosen through the chip and the work piece material, and the TiN- in the experiments. eTh chips show a curled structure, so that coated cutting tool will see lower temperatures. they can produce notch-like crater wear. The most important difference between the wear be- The examination of surface layer states in the TiN- haviour of uncoated and TiN-coated tools is, however, the coated cutting tool is another important aim of this paper. adhesion between workpiece and tool. In the case of steel From Figure 5 it can be seen that the TiN coating is highly workpieces, this adhesion to cemented carbide substrate is improving the wear behaviour of cemented carbide cutting much stronger than to TiN coating. eTh adhesive wear is tools. The wear intensity is reduced in the highest cutting correlated to the atomic bonding of the different materials Advances in Tribology 9 WC/Co Fe Worn TiN unworn TiN 200 μm 20 μm Figure 13: Small region of flank wear (resp. notch wear) of TiN-coated cutting tool, which was used under the cutting conditions of 𝑣 = 100 m/min,𝑓=0.5 mm/rev, and𝑎 =0.1 mm. 𝑐 𝑝 between the different atoms of the workpiece material, and The formation of built-up edges, built-up layers, and the cutting tool material and a smooth surface is necessary dead zones is detected for the uncoated cemented carbide [17]. eTh different wear mechanisms acting in the cutting zone cutting tool. eTh reason for that is a strong adhesion of steel are abrasion and adhesion. (workpiece material) to the cemented carbide. The wear was examined by metallographic sectioning, As shown, there is less-adhesive effect of the work mate- and it was revealed that the wear mechanisms are adhesion rial on the TiN coating. The wear mechanisms acting, when and abrasion. turning with a TiN-coated tool, were not examined in detail. Improving wear behaviour of the TiN-coated cemented eTh re are some further possible reasons, why TiN has got a carbide cutting tools is due to the low adhesion of the selected better wear behaviour. Some protective adhesion layers were workpiece material (SAE 1045) to the TiN coating. Hence foundorassumedonTiN andAlCrNcoatings[6, 18]. On the there is no built-up edge or built-up layer formation on worn TiN-layers some elements (Al, Si, etc., see Table 1)from the TiN coating. On delaminated, respectively, fully worn the workpiece material were found (see Figure 12). These TiN coating there is again a strong adhesion detected to the could also form a protective tribolayer during the cutting cemented carbide substrate, and a local increase in wear rate process. is observed. eTh TiN coating changes its surface structure from a rougher surface to a smoother surface during the metal cutting process which can be attributed to the wear of Acknowledgment chip flow respectively, the tool-workpiece interaction (see The authors gratefully acknowledge the company OC Oer- Figure 13). In Figure 13 thewornregionofthe TiNcoating has got a smoother surface structure than the unworn TiN- likon Balzers for the deposition of the TiN coating. coating. In Figure 13, a small part of the flank face is shown where References some notch wear is detected via SEM. There are three main parts of the cutting tool region: the surrounding part is [1] I. S. Jawahir, E. Brinksmeier, R. M’Saoubi et al., “Surface consisting of unworn TiN coating. This as-deposited coating integrity in material removal processes: recent advances,” CIRP Annals—Manufacturing Technology,vol.60, no.2,pp. 603–626, has got a rougher surface structure than the worn part of the tool, where sliding between chip/workpiece and the tool occurs. Here the sliding process leads to a smoothening of the [2] Q. Xie, A. E. Bayoumi, and L. A. Kendall, “On tool wear and TiN coating. In the middle of the worn region, the coating is its eeff ct on machined surface integrity,” Journal of Materials Shaping Technology,vol.8,no. 4, pp.255–265,1990. fully worn. Cemented carbide substrate can be seen (brighter area in Figure 13), and adhering workpiece material (Fe) can [3]S.C.Lim andM.F.Ashby,“Wear-mechanism maps,” Acta be detected. This notch wear can be attributed to the high Metallurgica,vol.35, no.1,pp. 1–24,1987. wear intensity that is acting at the beginning of the cutting [4] S.C.Lim, Y. B. Liu, S. H. Lee, andK.H.W.Seah, “Mapping process, when the cutting edge enters the workpiece. thewearofsomecutting-toolmaterials,” Wear,vol.162-164,pp. 971–974, 1993. [5] S. C. Lim, “Recent developments in wear-mechanism maps,” 5. Conclusions/Summary Tribology International,vol.31, no.1–3,pp. 87–97, 1998. An increasing load (higher feed rate or higher cutting speed) [6] S. Karagoz ¨ and H. F. Fischmeister, “Metallographic observations subjected to the cutting tool results in an increasing wear rate on the wear process of TiN-coated cutting tools,” Surface and with respect to flank wear. Coatings Technology,vol.81, no.2-3,pp. 190–200, 1996. 10 Advances in Tribology [7] “ISO 3685: tool-life testing with single-point turning tools,” [8] V. P. Astakhov, Tribology of Metal Cutting,vol.52of Tribology and Interface Engineering Series, Elsevier, 2006. [9] V. P. Astakhov, “eTh assessment of cutting tool wear,” Interna- tional Journal of Machine Tools and Manufacture,vol.44, no.6, pp. 637–647, 2004. [10] S. Jacobson and P. Wallen, ´ “A new classification system for dead zones in metal cutting,” International Journal of Machine Tool Design and Research, vol. 28, no. 4, pp. 529–538, 1988. [11] P. K. Philip, “Built-up edge phenomenon in machining steel with carbide,” International Journal of Machine Tool Design and Research, vol. 11, no. 2, pp. 121–132, 1971. [12] H. Opitz and M. Gappisch, “Some recent research on the wear behaviour of carbide cutting tools,” International Journal of Machine Tool Design and Research,vol.2,no. 1, pp.43–73,1962. [13] J.A.Arsecularatne,L.C.Zhang,and C. Montross,“Wear and tool life of tungsten carbide, PCBN and PCD cutting tools,” International Journal of Machine Tools and Manufacture,vol.46, no. 5, pp. 482–491, 2006. [14] H. O. Gekonde and S. V. Subramanian, “Tribology of tool- chip interface and tool wear mechanisms,” Surface and Coatings Technology,vol.149,no. 2-3, pp.151–160,2002. [15] “Oerlikon Balzers product information BALINIT A,” 2011. [16] “Springer Materials: the Landolt Bor ¨ nstein database, the worlds largest resource for physical and chemical data,” 2009. [17] Valentin L. Popov, Kontaktmechanik und Reibung: Von der Nan- otribologie bis zur Erdbebendynamik, Springer, Berlin, Germany, [18] J. Gerth, M. Larsson, U. Wiklund, F. Riddar, and S. Hogmark, “On the wear of PVD-coated HSS hobs in dry gear cutting,” Wear,vol.266,no. 3-4, pp.444–452,2009. 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Advances in Tribology – Hindawi Publishing Corporation

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References

  • Surface integrity in material removal processes: recent advances,
    I. S. Jawahir, E. Brinksmeier, R. M’Saoubi et al.
  • On tool wear and its effect on machined surface integrity,
    Q. Xie, A. E. Bayoumi, and L. A. Kendall
  • Wear-mechanism maps,
    S. C. Lim and M. F. Ashby
  • Mapping the wear of some cutting-tool materials,
    S. C. Lim, Y. B. Liu, S. H. Lee, and K. H. W. Seah
  • Recent developments in wear-mechanism maps,
    S. C. Lim
  • Metallographic observations on the wear process of TiN-coated cutting tools,
    S. Karagöz and H. F. Fischmeister
  • The assessment of cutting tool wear,
    V. P. Astakhov
  • A new classification system for dead zones in metal cutting,
    S. Jacobson and P. Wallén
  • Built-up edge phenomenon in machining steel with carbide,
    P. K. Philip
  • Some recent research on the wear behaviour of carbide cutting tools,
    H. Opitz and M. Gappisch
  • Wear and tool life of tungsten carbide, PCBN and PCD cutting tools,
    J. A. Arsecularatne, L. C. Zhang, and C. Montross
  • Tribology of tool-chip interface and tool wear mechanisms,
    H. O. Gekonde and S. V. Subramanian
  • On the wear of PVD-coated HSS hobs in dry gear cutting,
    J. Gerth, M. Larsson, U. Wiklund, F. Riddar, and S. Hogmark