Cutting properties of the Al2O3 + SiC(w) based tool ceramic reinforced

Journal of Materials Processing Technology 164–165 (2005) 924–929

Cutting properties of the Al2O3 + SiC(w) based tool ceramic reinforced with the PVD and CVD wear resistant coatings M. Sokovi´c a , J. Mikuła b , L.A. Dobrza´nski b,∗ , J. Kopaˇc a , L. Koseˇc c , P. Panjan d , J. Madejski b , A. Piech b b

a Faculty of Mechanical Engineering, University of Ljubljana, Aˇskerˇ ceva 6, SI-1000 Ljubljana, Slovenia Division of Materials Processing Technology and Computer Techniques in Materials Science, Institute of Engineering Materials and Biomaterials, Silesian University of Technology, ul. Konarskiego 18a, 44-100 Gliwice, Poland c NTF, Department of Materials and Metallurgy, University of Ljubljana, Aˇskerˇ ceva 12, SI-1000 Ljubljana, Slovenia d Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

Abstract The paper presents investigation results of tribological properties of the coatings deposited with the PVD and CVD techniques on cutting inserts made from the Al2 O3 + SiC(w) oxide tool ceramic. Tests were carried out on the multipoint inserts made from the Al2 O3 + SiC(w) oxide ceramics, uncoated and coated with gradient, mono-, multilayer and multicomponent hard wear resistant coatings composed of TiN, TiCN, TiAlN, TiAlSiN and Al2 O3 layers with PVD and CVD processes. Substrate hardness tests and microhardness tests of the deposited coatings were made on the ultra-micro-hardness tester. It was demonstrated, basing on the technological cutting tests of spheroidal cast iron, that putting down onto the tool ceramics the thin anti-wear coatings in the PVD and CVD processes increases their abrasion wear resistance, which has a direct effect on extending the tool edge life. Basing on the roughness parameter Ra of the machined cast iron surface after the cutting tests, improvement was revealed of the machined material properties, cut with coated oxide ceramics compared to material machined with the uncoated tools. © 2005 Elsevier B.V. All rights reserved. Keywords: Oxide ceramics; Al2 O3 ; SiC; Whiskers; Gradient coatings; Multilayer coating; Multicomponent coatings; PVD; CVD; TEM; SEM; Micro-hardness; Scratch test; Pin-on-disc

1. Introduction Machining productivity and quality of the machined workpiece depend, to a great extent, on the properties of tool materials. Ceramic materials with high hardness and high strength in the broad range of working temperatures and with low abrasion wear, with the Al2 O3 based ones among them, are used more and more often for cutting tools. The Al2 O3 oxide ceramics, as mentioned by the author of the reviewed thesis, is characteristic of high hardness, compression strength at the cutting temperature above 1000 ◦ C, and the best – compared to other tool materials – chemical wear resistance; however having high brittleness and low thermal shock resistance. These drawbacks are compensated in part by using the TiC ∗

Corresponding author. Tel.: +48 32 2371420; fax: +48 32 2371430. E-mail address: [email protected] (L.A. Dobrza´nski).

0924-0136/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jmatprotec.2005.02.071

additions and the SiC whiskers. Whiskers with the following parameters: thickness d = 0.1–0.5 ␮m and slenderness ratio l = (5–10)d, are introduced into the tool ceramics. Ceramics with whiskers are obtained mostly by the isostatic hot sintering and by the uniaxial hot pressing. The increase of the whiskers portion to 15–20% causes increase of the ceramics strength. Further increase of the SiC whiskers portion deteriorates the mechanical properties because of the increased probability of the development of whiskers agglomerates, featuring the cracking propagation source. A factor affecting the selection of the optimum portion of the SiC phase in the sinter is the decrease of the sinter density along with the growth of the whiskers portion leading to material hardness deterioration, which in case of the material used for cutting tools, is a significant limitation of possibility of its application. Introducing whisker to the oxide ceramics results in their hardness increase, improvement of their crack resistance and

M. Sokovi´c et al. / Journal of Materials Processing Technology 164–165 (2005) 924–929

bending strength. Tools containing the SiC whiskers have the life exceeding other tool materials even by 300%, allowing at the same time very high cutting speeds. One of the disadvantages of the reinforced ceramics is decay of whiskers in case of machining alloys containing iron, which significantly limits its use. In connection with the unsatisfactory attempts to introduce the SiC whiskers to oxide ceramics and serious limitations in its use, the research is conducted on the possibility of improvement of properties of these materials by employment of the surface layers [1–24]. Due to employment of the physical deposition from the gas phase PVD and chemical deposition from the gas phase processes one can obtain further improvement of properties, including higher surface hardness of the cutting tools made from the ceramic tool materials, as the effective thermal and diffusion barrier is developed on their surface, chip carry away parameters are improved, which makes it possible to use higher cutting parameters, with the resulting productivity improvement and product quality, which results in the reduction of machining time and cost [1–24]. The goal of this paper has been investigation of properties of the Al2 O3 + SiC(w) based oxide tool ceramics coated with the anti-wear gradient, mono-, multilayers and multicomponent of the TiN, TiAIN, TiN + TiAlSiN + TiN, TiN + multiAiAlSiN + TiN and TiN + TiAlSiN + AlSiTiN types in the cathode arc evaporation CAE-PVD and with the multilayers of the TiCN + TiN and TiN + Al2 O3 types obtained in the chemical deposition from the gas phase CVD process.

2. Experimental procedure The investigations were carried out on the multipoint inserts made from the Al2 O3 + SiC(w) oxide ceramics uncoated, coated in the PVD and CVD processes with thin coatings. The inserts made from Al2 O3 + TiC were gradient, mono-, multilayer and multicomponent coated in the PVD process—cathodic arc evaporation (CAE) and CVD process. Specifications of the investigated materials are presented in Table 1. Table 1 Specifications of the PVD and CVD coatings put down on the Al2 O3 + SiC(w) oxide ceramics Type

Composition

Coating thickness (␮m)

Process type

Monolayer Gradient /multilayer Multilayer

TiN TiN + TiAlSiN + TiN

0.9 2.5

PVD PVD

TiN + multiTiAlSiN + TiN TiN + TiAlSiN + AlSiTiN TiAlN TiCN + TiN Al2 O3 + TiN

2.8

PVD

2.5

PVD

2.8 2.6 7.9

PVD CVD CVD

Gradient Multicomponent Two layers Two layers

925

Examinations of coatings’ thicknesses were made using the “kalotest” method, consisting in the measurement of the characteristic dimensions of craters developed on the examined specimen surface with a coating. The measurements were made on the device developed in house. In addition, to verify the obtained results, measurements of the coatings were made also on the scanning electron microscope on the fractures perpendicular to their free surfaces. The microhardness tests of coatings were made on the SHIMADZU DUH 202 ultra microhardness tester. Test conditions were selected so that the required and comparable test results would be obtained for all analyzed coatings. Measurements were made at 0.07 N load, eliminating influence of the substrate on the measurement results. Adhesion evaluation of the coatings on the investigated inserts was made using the scratch test on the CSEM REVETEST device, by moving the diamond penetrator along the examined specimen’s surface with the gradually increasing load. The tests were made with the following parameters: load range 0–100 N, load increase rate (dL/dt) 100 N/min, penetrator’s travel speed (dx/dt) 10 mm/min, acoustic emission detector’s sensitivity AE 1. The critical load Lc , at which coatings’ adhesion is lost, was determined basing on the registered values of the acoustic emission AE. Cutting ability of the investigated materials was determined basing on the technological continuous cutting tests of the KGR-Nl-400 spheroidal cast iron with the hardness of about 165 HV. The VB = 0.30 mm width of the wear band on the surface of the tool used for machining was the criterion of the cutting edge consumption evaluation. Cutting tests of the investigated Al2 O3 + SiC(w) based tool oxide ceramics – uncoated and coated – were carried out as the continuous turning without the use of cutting fluids on the numerically controlled MORI SEIKI model Sl 153 machine tool. The following parameters were used in the machining capability experiments: feed rate f = 0.20 mm/rev, depth of cut ap = 2 mm, cutting speed vc = 250 m/min. The character of the developed failure was evaluated basing on observations on the light microscope and on the scanning electron microscope. In case of the uncoated tools the test was continued until the wear criterion was reached; however, the test period for the coated tools was never shorter than in case of the uncoated tools, which makes it possible to compare the wear band width VB after reaching the wear criterion by the uncoated test piece. Measurements of the VB values with the accuracy of up to 0.01 mm were carried out using the Carl Zeiss Jena light microscope at the magnification of 14×. Photos of the cutting inserts’ flank and face at various wear stages were made on LEICA MEF4A light microscope at the magnification of 10×, and on the JEOL JSM-5610 scanning electron microscope using magnifications of 95–1100×. The examination results were presented as plots of the relationship of the wear band VB on tool flank versus test duration, at the particular experiment conditions. Investigations of surface roughness of KGR-Nl-

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Table 2 Comparison of mechanical and functional properties of uncoated and coated Al2 O3 + SiC(w) tool ceramics Coating

Process type

Microhardness HV0.07 (MPa)

Critical load Lc (N)

– TiN TiN + TiAlSiN + TiN TiN + multiTiAlSiN + TiN TiN + TiAlSiN + AlSiTiN TiAlN TiCN + TiN Al2 O3 + TiN

– PVD PVD PVD

1870 2780 2480 4020

– 38opt 70 58

PVD

2380

80opt

PVD CVD CVD

3370 2270 3670

99opt 40 18

400 spheroidal cast iron in machinability test were made on device SURTRONIC 10 TAYLOR-HOBSON. 3. Discussion of investigation results The Al2 O3 + SiC(w) ceramics microhardness is 1870 MPa and grows significantly after deposition of the PVD and CVD coatings, except the TiCN + TiN coating. The maximum microhardness of HV0.07 = 40.2 GPa was observed in case of the TiN + multiTiAlSiN + TiN PVD coating deposited onto the Al2 O3 + SiC(w) . ceramics substrate. Over 80% increasing of microhardness value is also observed after depositing of TiAlN PVD coating and TiN + Al2 O3 CVD coating (Table 2). No relationship was found out between the substrate hardness and hardness of the deposited coating, which confirms the proper selection of the maximum load Fmax = 0.07 N to eliminate the influence of the substrate hardness on the measurement result. The TiN + TiAlSiN + TiN coating demonstrates the highest critical load value Lc = 70 N measured by the acoustic emission registration (Fig. 1, Table 2). No sudden increase of the acoustic emission was registered in case of the TiAlN coating; however, the metallographic observations make it possible to determine optically the critical load of Lc(opt) = 99 N. A very high acoustic emission level was registered for the TiN + TiAlSiN + AlSiTiN coating nearly from the very beginning of the test. It was found out, basing on the

metallographic observations that the high acoustic emission levels registered for the TiN + TiAlSiN + AlSiTiN coating may result from the specific structure of the AlSiTiN layer, having many micro-particles on its surface. In that case Lc was determined optically. In case of TiN + multiTiAlSiN + TiN coating the first coating failure symptoms are the conformal cracks resulting from tension, turning into single spallings located at the bottom of the developing crevice and in the coating-crevice contact zone. Chipping and spalling failures develop in the central zones of the crevices and at their edges in the form of the fine arc-shaped craters. Similar effects can be observed at the edges in the ending part of the crevice. Single failures are often connected forming bands of the local coating delamination, not more. Semicircles connected with the conformal cracking occur at the crevice bottom at the big load force, attesting the fragmentation, local delamination, and consequent relocation of the torn coating fragments along with the plastic strain of the substrate by the traveling indenter. In case of other PVD coating damages they gave the abrasive wear character, consisting in abrasion of the particular layers, with no delamination and significant spalling or one- or double-side chipping, and peeling, which attests (especially in case of the first damage type) to very good adhesion of the particular layers to themselves and to the very good adhesion to the substrate. In case of the CVD coatings deposited onto the Al2 O3 + SiC(w) substrate, the delamination was observed at the scratch edge and single-sided chipping (Fig. 2). It was found out, basing on the repeated technological turning test of grey cast iron with the Al2 O3 + SiC(w) ceramics, that the tool reaches the VB = 0.30 mm wear criterion after t = 7.8 min cutting time. Time of t = 7.8 min was assumed as the comparative criterion for measurement of the wear band width for all specimens with the Al2 O3 + SiC(w) substrate After the assumed machining test duration the smallest cutting tool flank wear band width of VB = 0.13 mm was revealed in case of the TiN + Al2 O3 CVD coating (Fig. 3), and the biggest cutting tool flank wear band width of VB = 0.28 mm was revealed in case of the TiN PVD coating. It was found out, thanks to the metallographic analysis carried out on the scanning electron microscope, that the tribological defect types occurring most often, identified

Fig. 1. (a) Indenter trace with the optical Lc load, and (b) scratch test results of the TiN + TiAlSiN + TiN coating surface deposited on Al2 O3 + SiC(w) substrate.

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Fig. 2. (a) Character of wear of the Al2 O3 + SiC(w) sample with TiN + TiAlSiN + AlSiTiN coating, investigated with SEM after cutting test, and (b) the detail of (a).

Fig. 3. Comparison of the approximated values of the VB wear of the Al2 O3 + SiC(w) based ceramics: uncoated and coated with the CVD TiN + Al2 O3 coating, depending on machining time.

in the investigated materials are as follows: mechanical defects and abrasive wear of the tool flank, development of the crater on tool face, thermal cracks on tool flank, spalling of the cutting edge, and build-up edge from the chip fragments (Fig. 4) Comparison of the approximated values of the VB wear of the Al2 O3 + SiC(w) based ceramics: uncoated and coated with the PVD and CVD coatings, depending on machining time is shown in Table 3. Basing on the roughness tests of the machined material, depending on the cutting period, it was found out that depositing the PVD and CVD coatings (except TiN, TiAlN and TiN + Al2 O3 coatings) onto the Al2 O3 + SiC(w) oxide

Table 3 Comparison of calculated with the least squares method curves of the VB wear for Al2 O3 + SiC(w) based ceramics: uncoated and coated with the PVD and CVD coatings, depending on machining time Coating

Regression curve

R2

Uncoated TiN TiN + TiAlSiN + TiN TiN + multiTiAlSiN + TiN TiN + TiAlSiN + AlSiTiN TiAlN TiCN + TiN TiN + Al2 O3

y = 0.0007x3 − 0.0090x2 + 0.0649x y = 0.0002x3 − 0.0035x2 + 0.0421x y = 0.00005x3 − 0.0013x2 + 0.0357x y = 0.0001x3 − 0.0024x2 + 0.0369x

0.9982 0.9957 0.9995 0.9943

y = 0.00008x3 − 0.0009x2 + 0.0287x

0.9989

y = −0.00005x3 + 0.00091x2 + 0.0225x y = 0.0002x3 − 0.0030x2 + 0.0455x y = 0.00005x3 − 0.0005x2 + 0.0184x

0.9944 0.9964 0.9779

Fig. 4. (a) Character of wear of the Al2 O3 + SiC(w) sample with TiN + Al2 O3 coating, investigated with SEM after cutting test, and (b) the detail of (a).

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Table 4 Comparison of the Ra roughness parameter values of the grey cast iron surface machined with the Al2 O3 + SiC(w) based tools: uncoated and coated with the PVD and CVD coatings, depending on machining time Coating Time

–

TiN

TiN +TiAlSiN + TiN

TiN + multi TiAlSiN + TiN

TiN +TiAlSiN +AlSiTiN

TiAlN

TiCN + TiN

TiN + Al2 O3

1 min 00 s 3 min 15 s 4 min 30 s 5 min 45 s 6 min 00 s 7 min 15 s

1.73 1.83 1.73 1.70 1.60 1.60 1.53

2.10 2.17 2.33 2.13 2.20 1.97 1.93

1.47 1.37 1.40 1.33 1.43 1.57 1.37

1.83 1.83 1.73 1.60 1.37 1.33 1.13

1.47 1.47 1.23 1.50 1.73 1.53 1.40

2.00 2.10 2.10 2.30 2.70 2.70 2.43

2.10 1.97 1.67 1.70 1.73 1.73 1.80

1.50 1.40 1.47 1.50 1.57 1.63 2.20

tool ceramics results in decrease of the machined material roughness and – the same – improvement of its quality, especially at the final machining process stage. From all the investigated materials, the minimum roughness of Ra = 1.13 ␮m at the final machining stage was revealed in case of the TiN + multiTiAlSiN + TiN coating deposited onto the Al2 O3 + SiC(w) ceramics substrate (Table 4). In case of all coatings the roughness of Ra parameter at the final machining stage is below 2.5 ␮m so the quality of machined material can be described as high.

Project “COAT-CUT” entitled “New generation PVD coatings on tools for dry on high speed cutting processes” between the Government of the Republic of Poland and the Government of the Republic of Slovenia headed by Prof. L.A. Dobrza´nski and Prof. J. Kopaˇc. Researches were financed partially within the framework of the Polish State Committe for Scientific Research Project KBN Nr 3 T08C 04726, headed by Dr. K. Lukaszkowicz and PBZ-100/4/2004 headed by Prof. L.A. Dobrza´nski.

References 4. Summary The Al2 O3 + SiC(w) ceramics microhardness grows significantly after deposition of the PVD and CVD coatings. Over 110% increasing of microhardness value is also observed after depositing of TiN + multiTiAlSiN + TiN PVD coating, over 80% increasing of microhardness value is observed after depositing of TiAlN PVD coating and TiN + Al2 O3 CVD coatings. The TiN + TiAlSiN + TiN coating demonstrates the highest critical load value Lc = 70 N measured by the acoustic emission registration but in case of TiAlN coating Lc value was determined optically and achieved 99 N. All the coatings put down demonstrate good adhesion to the substrate. The tribological defect types occurring most often, identified in the investigated materials during the technological cutting tests are the mechanical defects and abrasive wear of the tool flank, development of the crater on tool face, thermal cracks on tool flank, spalling of the cutting edge, and build-up edge from the chip fragments. Depositing the PVD and CVD coatings onto the Al2 O3 + SiC(w) oxide tool ceramics results in the significant increase of the tool life and in lowering the roughness parameter value for the machined material, and finally in improvement of its quality, especially at the final machining process stage.

Acknowledgements Investigations were partially realized within the framework of the Scientific and Technology Cooperation Joint

[1] L.A. Dobrza´nski, Fundamentals of Materials Science and Physical Metallurgy. Engineering Materials with the Fundamentals of Materials Design, WNT, Warszawa, 2002 (in Polish). [2] L.A. Dobrza´nski, E. Hajduczek, J. Marciniak, R. Nowosielski, Physical Metallurgy and Heat Treatment of Tool Materials, WNT, Warszawa, 1990 (in Polish). [3] M. Sokovi´c, K. Mijanoviˇc, J. Mater. Process. Technol. 109 (2001) 181–189. [4] J. Kopaˇc, M. Bahor, M. Sokovi´c, Int. J. Mach. Tools Manuf. 42 (2002) 707–716. [5] J. Mikuła, Structure and properties of Al2O3 based on tool oxide ceramics with wear resistant PVD and CVD coatings, PhD Thesis, Silesian University of Technology, Faculty of Mechanical Engineering, Gliwice, 2004 (in Polish). [6] S. Novak, M. Sokovi´c, M. Komaˇc, B. Pracek, Vacuum 48 (1997) 107–112. [7] P. Holubar, M. Jilek, M. Sima, Surf. Coat. Technol. 133–134 (2000) 145–151. [8] P. Holubar, M. Jilek, M. Sima, P. Holubar, Surf. Coat. Technol. 120–121 (1999) 184–188. [9] B. Navinsek, P. Panjan, M. Cekada, Surf. Coat. Technol. 154 (2002) 194–203. [10] Grzesik, S. Brol, J. Mater. Process. Technol. 134 (2003) 265–272. [11] W. Grzesik, Int. J. Mach. Tools Manuf. 43 (2003) 145–150. [12] J. Barry, G. Byrne, Wear 247 (2001) 139–151. [13] J.D. Bressan, R. Hesse, E.M. Silva Jr., Wear 250 (2001) 561–568. [14] J. Deng, X. Ai, Tribol. Int. 30 (1997) 807–813. [15] L.A. Dobrza´nski, D. Pakuła, E. Hajduczek, J. Mater. Process. Technol. 157–158 (2004) 331–340. [16] D. Pakuła, L.A. Dobrza´nski, K. Goł˛abek, M. Pancielejko, A. Kriz, J. Mater. Process. Technol. 157–158 (2004) 388–393. [17] A.K. Ghani, I.A. Choudhury, Husni, J. Mater. Process. Technol. 127 (2002) 17–22. [18] L.A. Dobrza´nski, K. Gołombek, J. Kopaˇc, M. Sokovi´c, Mater. Sci. Forum 437–438 (2003) 41–44.

M. Sokovi´c et al. / Journal of Materials Processing Technology 164–165 (2005) 924–929 [19] L.A. Dobrza´nski, J. Mikuła, The Worldwide Congress of Materials and Manufacturing Engineering and Technology COMMENT, Wisła, 2005 (the same issue). [20] L.A. Dobrza´nski, J. Mikuła, The 13th International Conference on Processing and Fabrication of Advanced Materials, Singapore, December 6–8, 2004. [21] L.A. Dobrza´nski, D. Pakuła, K. Gołombek, J. Mikuła, Proceedings of the 11th Scientific International Conference AMME’02, GliwiceZakopane, 2002, pp. 131–134 (in Polish).

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[22] L.A. Dobrza´nski, J. Mikuła, D. Pakuła, J. Kopaˇc, M. Sokovi´c, Proceedings of the 11th Scientific International Conference AMME’03, Gliwice-Zakopane, 2003, pp. 249–252. [23] L.A. Dobrza´nski, J. Mikuła, D. Pakuła, A. Kriz, Proceedings of the 12th Scientific International Conference AMME’03, GliwiceZakopane, 2003, pp. 249–252. [24] L.A. Dobrza´nski, J. Mikuła, Proceedings of the 11th International Conference on Composites/NanoEngineering (ICCE-11), South Carolina, 2004, pp. 137–138.