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Evaluation of the Adhesion of Ultrananocrystalline Diamond Coatings on WC-Co Substrates
Available online at www.sciencedirect.com
ScienceDirect Materials Today: Proceedings 4 (2017) 11538–11543
www.materialstoday.com/proceedings
ANM2016 Evaluation of the Adhesion of Ultrananocrystalline Diamond Coatings on WC-Co Substrates M. A. Fragaa *, A. Contina, J. Vieiraa, D. Barbosaa, R. Camposb, E. Corata, V. J. Trava Airoldia a
Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brasil b Universidade Federal do Sul e Sudeste do Pará, Marabá, Brasil
Abstract In order to improve the cutting performance and lifetime of WC-Co hard metal tools, the issues related to synthesis and adherence of micro- and nanocrystalline CVD diamond coatings on these tools has been frequently discussed in the literature. However, there are few studies focused on ultrananocrystalline diamond (UNCD) coatings. In this study, we report the results of the characterization of UNCD coatings with different thicknesses with the purpose of evaluating their adhesion to WC-9%Co substrates. The structure and morphology of the UNCD coatings as a function of their thicknesses were investigated by Raman spectroscopy, atomic force microscopy (AFM) and field emission gun scanning electron microscope (FEG-SEM) analysis. The UNCD coating-substrate adhesion was evaluated by means of indentation tests with a load of 1000N. © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 7th International Conference on Advanced Nanomaterials. Keywords: ultrananocrystalline diamond, coating, morphology, adhesion, cemented carbide
1. Introduction CVD diamond coatings have shown great potential to improve lifetime and service performance of hard metal cutting tools. Several studies have discussed the diamond coating adhesion on cemented carbide (WC-Co) tools [1-3]. Most of these works are focused on microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) [4,
* Corresponding author. Tel.: +551232086558 E-mail address: [email protected] 2214-7853 © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 7th International Conference on Advanced Nanomaterials.
M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
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5]. Here we investigate the adhesion of ultrananocrystalline diamond (UNCD) coatings of varying thicknesses grown by hot-filament chemical vapor deposition (HFCVD) on pretreated WC-9%Co substrates. The interest in UNCD coatings is because of their unique microstructure comprised of nanometer-sized diamond grains that provide remarkable material properties such as high hardness, extreme fracture toughness, low coefficient of friction, chemical inertia and low surface roughness [6]. 2. Experimental UNCD coatings were deposited on WC–Co disks (91% WC and 9% Co composition, 9 mm in diameter and 3 mm thick) by the conventional hot-filament technique using a gas mixture of methane (9%) and hydrogen (91%). Prior to deposition, the substrates were pretreated as follows: (i) first they were etched by Murakami solution (10 g K3[Fe(CN)6]+10g KOH+100ml H2O) for 10 min in an ultrasonic bath, (ii) the surface Co was etched in aqua regia solution (HNO3/HCl = 1:3) for 5 min and (iii) the etched substrates were seeded in water slurry containing 4 nm diamond nanoparticles dispersed by PSS (sodium4-styrenesulfonate) polymer [4]. This pretreatment plays a fundamental role because removes the cobalt from the substrate surface, which is crucial to achieve a high adhesion coating. In all depositions, the pretreated WC-Co substrate was placed at 5 mm from five tungsten filaments (0.125 mm in diameter and 100 mm long). The UNCD samples were grown at a temperature of 600ºC measured by a thermocouple fixed at the bottom of the substrate. Deposition parameters were kept as follows: CH4 flow rate (9 sccm), H2 flow rate (91 sccm), pressure (30 Torr) and deposition time was varied from 2 to 6 h. The UNCD coatings were characterized by Raman spectroscopy, atomic force microscope (AFM) and scanning electron microscopy (FESEM, Tescan Mira 3 FEG). Raman spectroscopy was carried out using a Horiba Jobin Yvon LabRAM HREvolution Raman microscope with 3 laser wavelengths. The spectra shown in this work were acquired using an Ar laser at 514 nm. Surface roughness studies were performed by atomic force microscope (AFM) Veeco multimode. The analyses were performed in intermittent mode over a 2.0 µm x 2.0 µm area. In order to evaluate the adhesion level of the CVD diamond coating, indentation tests using a diamond stylus Rockwell C with a conical diamond indenter (120º cone angle and 0.2 mm tip radius) were performed. 3. Results and discussion 3.1. Morphology and growth rate FEG-SEM images at 100,000X magnification on the surface of UNCD coatings grown for 2, 4 and 6 h are shown in Fig. 1. It is clear the morphological change with varying thicknesses. As the increases in the thickness of the UNCD coating, a more uniform and compact surface morphology is obtained. Still in Fig. 1, it can be observed the 2D and 3D AFM images of the coatings. The roughness of the UNCD coatings measured by AFM was found to be 68.6, 41.3 and 24.6 nm for deposition time from 2, 4 and 6 h, respectively.
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M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
Fig. 1. FEG-SEM and AFM images of the UNCD films grown on pretreated WC-Co substrates for varying deposition times: (a) 2 h, (b) 4 h and (c) 6 h.
Figure 2 shows the FEG-SEM analysis of cross-section of the thicker UNCD coated WC-Co sample (grown for 6 h), which allowed us to determine the coating thickness (~1.2 µm), and consequently the UNCD growth rate (0.2 µm/h). Thus, the thinnest UNCD sample has around 400 nm.
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Fig. 2. An electron micrograph cross-section of the UNCD coating grown on pretreated WC-Co for 6 h.
3.2. Raman Analysis Raman spectra and their deconvolution for UNCD films of varying thicknesses are shown in Fig. 3. The spectra from all samples show the presence of C-H bonds as well the graphite G and D bands. The following peaks can be identified: (i) 1150 and 1450 cm-1 which has been assigned to transpolyacetylene segments at grain boundaries and surface [7]. However, most recent reports [8] show that 1150 cm-1 peak has to be reassigned to a deformation mode of C-H bonds present in diamond nanoparticles, (ii) 1350 cm-1 the graphite D band, and (iii) 1580 cm-1 the graphite G band. In addition, we can observe that the D band is so intense that masks the diamond peak (1332 cm-1). This indicates that a partial graphitization of the system took place favoring structures associated with the D and G band, which can be considered as fingerprints for the fine diamond grained structure related to UNCD [9].
Fig. 3. Raman spectra (514 nm excitation) of UNCD films grown on pretreated WC-Co substrates for varying deposition times.
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M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
3.3. Adhesion analysis In order to evaluate the coating–substrate adhesion, Rockwell indentation tests with a load of 1000N were performed on the UNCD coated WC-Co substrates. Figure 4 shows FEG-SEM images of the samples after indentation tests. It can be seen that the best adhesion was achieved for UNCD coating grown for 2 h. In this sample, there is only substrate crack and no coating delamination was observed. On the other hand, samples of UNCD coatings grown for 4 and 6 h exhibited delamination visible. It was also observed that with the thickness increases the size of delamination area increases. This result may be explained by assuming that with the increases in the thickness, the residual stress in coating increases.
Fig. 4. FEG-SEM images of the indentation crack morphology of UNCD coatings for varying deposition times: (a), (b) and (c) 2 h; (d), (e) and (f) 4 h; (g) and (h) 6 h.
M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
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4. Conclusions We have evaluated the adhesion between UNCD coating and pretreated WC-Co substrate. A set of UNCD samples with different thicknesses were prepared varying the deposition time: 2, 4 and 6 h. It was produced thick (around 1.2 μm) and thin (400 nm) UNCD coatings. The indentation tests under a load of 1000 N showed that there is no delamination of the UNCD coating deposited at 2h, which indicates a good adhesion. However, for thicker coatings a poor adhesion was observed. Acknowledgements We would like to thank FAPESP (processes number: 14/18139-8, 13/25939-8 and 12/15857-1) for the financial support.
References [1] R. Haubner, W. Kalss Int. J. Refract. Met. Hard Mater. 28 (2010) 475-483. [2] Y. Yuan, J. Li, W. Sun, Adhesion of diamond film on functionally gradient WC-10wt. %Co hardmetal, International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) 222-229. [3] A.Veillere, T. Guillemet, Z. Q. Xie, C. A. Zuhlke, D. R. Alexander, J. Silvain, J.Heintz, N. Chandra, Y. F. Lu. ACS Appl. Mater. Interfaces 3, (2011) 1134–1139. [4] M. A. Fraga, A. Contin, L. A. A. Rodríguez, J. Vieira, R. A. Campos, E. J. Corat, V. J. Trava Airoldi, Mater. Res. Express 3 (2016) 025601. [5] J. Zhang, X. Wang, B. Shen, F. Sun, T. Nonferr. Metal. SoC. 24 (2014) 3181-3188. [6] O. A. Williams, M. Daenen, J. D’Haenen, J. Maesc, V. V. Moshcalkov, M. Nesládek, D. M. Gruen, Diam. Relat. Mater. 15 (2006) 654-658. [7] A.C. Ferrari, J. Robertson. Phys. Rev. B, 63 (2001) 121405. [8] V. Mortet, L. Zhang, M. Eckert, J. D’Haen, A. Soltani, M. Moreau, D. Troadec, E. Neyts, J. Jaeger, J. Verbeeck, A. Bogaerts, G.V. Tendeloo, K. Haenen, P. Wagner, Phys. Status Solidi A. 9 (2012) 1675–1682. [9] D.C. Barbosa, M.R. Baldan, V.J. TravaAiroldi, E.J. Corat, Mater. Sci.Forum 802 (2014) 168-173.
ScienceDirect Materials Today: Proceedings 4 (2017) 11538–11543
www.materialstoday.com/proceedings
ANM2016 Evaluation of the Adhesion of Ultrananocrystalline Diamond Coatings on WC-Co Substrates M. A. Fragaa *, A. Contina, J. Vieiraa, D. Barbosaa, R. Camposb, E. Corata, V. J. Trava Airoldia a
Instituto Nacional de Pesquisas Espaciais, São José dos Campos, Brasil b Universidade Federal do Sul e Sudeste do Pará, Marabá, Brasil
Abstract In order to improve the cutting performance and lifetime of WC-Co hard metal tools, the issues related to synthesis and adherence of micro- and nanocrystalline CVD diamond coatings on these tools has been frequently discussed in the literature. However, there are few studies focused on ultrananocrystalline diamond (UNCD) coatings. In this study, we report the results of the characterization of UNCD coatings with different thicknesses with the purpose of evaluating their adhesion to WC-9%Co substrates. The structure and morphology of the UNCD coatings as a function of their thicknesses were investigated by Raman spectroscopy, atomic force microscopy (AFM) and field emission gun scanning electron microscope (FEG-SEM) analysis. The UNCD coating-substrate adhesion was evaluated by means of indentation tests with a load of 1000N. © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 7th International Conference on Advanced Nanomaterials. Keywords: ultrananocrystalline diamond, coating, morphology, adhesion, cemented carbide
1. Introduction CVD diamond coatings have shown great potential to improve lifetime and service performance of hard metal cutting tools. Several studies have discussed the diamond coating adhesion on cemented carbide (WC-Co) tools [1-3]. Most of these works are focused on microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) [4,
* Corresponding author. Tel.: +551232086558 E-mail address: [email protected] 2214-7853 © 2016 Elsevier Ltd. All rights reserved. Selection and Peer-review under responsibility of 7th International Conference on Advanced Nanomaterials.
M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
11539
5]. Here we investigate the adhesion of ultrananocrystalline diamond (UNCD) coatings of varying thicknesses grown by hot-filament chemical vapor deposition (HFCVD) on pretreated WC-9%Co substrates. The interest in UNCD coatings is because of their unique microstructure comprised of nanometer-sized diamond grains that provide remarkable material properties such as high hardness, extreme fracture toughness, low coefficient of friction, chemical inertia and low surface roughness [6]. 2. Experimental UNCD coatings were deposited on WC–Co disks (91% WC and 9% Co composition, 9 mm in diameter and 3 mm thick) by the conventional hot-filament technique using a gas mixture of methane (9%) and hydrogen (91%). Prior to deposition, the substrates were pretreated as follows: (i) first they were etched by Murakami solution (10 g K3[Fe(CN)6]+10g KOH+100ml H2O) for 10 min in an ultrasonic bath, (ii) the surface Co was etched in aqua regia solution (HNO3/HCl = 1:3) for 5 min and (iii) the etched substrates were seeded in water slurry containing 4 nm diamond nanoparticles dispersed by PSS (sodium4-styrenesulfonate) polymer [4]. This pretreatment plays a fundamental role because removes the cobalt from the substrate surface, which is crucial to achieve a high adhesion coating. In all depositions, the pretreated WC-Co substrate was placed at 5 mm from five tungsten filaments (0.125 mm in diameter and 100 mm long). The UNCD samples were grown at a temperature of 600ºC measured by a thermocouple fixed at the bottom of the substrate. Deposition parameters were kept as follows: CH4 flow rate (9 sccm), H2 flow rate (91 sccm), pressure (30 Torr) and deposition time was varied from 2 to 6 h. The UNCD coatings were characterized by Raman spectroscopy, atomic force microscope (AFM) and scanning electron microscopy (FESEM, Tescan Mira 3 FEG). Raman spectroscopy was carried out using a Horiba Jobin Yvon LabRAM HREvolution Raman microscope with 3 laser wavelengths. The spectra shown in this work were acquired using an Ar laser at 514 nm. Surface roughness studies were performed by atomic force microscope (AFM) Veeco multimode. The analyses were performed in intermittent mode over a 2.0 µm x 2.0 µm area. In order to evaluate the adhesion level of the CVD diamond coating, indentation tests using a diamond stylus Rockwell C with a conical diamond indenter (120º cone angle and 0.2 mm tip radius) were performed. 3. Results and discussion 3.1. Morphology and growth rate FEG-SEM images at 100,000X magnification on the surface of UNCD coatings grown for 2, 4 and 6 h are shown in Fig. 1. It is clear the morphological change with varying thicknesses. As the increases in the thickness of the UNCD coating, a more uniform and compact surface morphology is obtained. Still in Fig. 1, it can be observed the 2D and 3D AFM images of the coatings. The roughness of the UNCD coatings measured by AFM was found to be 68.6, 41.3 and 24.6 nm for deposition time from 2, 4 and 6 h, respectively.
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M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
Fig. 1. FEG-SEM and AFM images of the UNCD films grown on pretreated WC-Co substrates for varying deposition times: (a) 2 h, (b) 4 h and (c) 6 h.
Figure 2 shows the FEG-SEM analysis of cross-section of the thicker UNCD coated WC-Co sample (grown for 6 h), which allowed us to determine the coating thickness (~1.2 µm), and consequently the UNCD growth rate (0.2 µm/h). Thus, the thinnest UNCD sample has around 400 nm.
M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
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Fig. 2. An electron micrograph cross-section of the UNCD coating grown on pretreated WC-Co for 6 h.
3.2. Raman Analysis Raman spectra and their deconvolution for UNCD films of varying thicknesses are shown in Fig. 3. The spectra from all samples show the presence of C-H bonds as well the graphite G and D bands. The following peaks can be identified: (i) 1150 and 1450 cm-1 which has been assigned to transpolyacetylene segments at grain boundaries and surface [7]. However, most recent reports [8] show that 1150 cm-1 peak has to be reassigned to a deformation mode of C-H bonds present in diamond nanoparticles, (ii) 1350 cm-1 the graphite D band, and (iii) 1580 cm-1 the graphite G band. In addition, we can observe that the D band is so intense that masks the diamond peak (1332 cm-1). This indicates that a partial graphitization of the system took place favoring structures associated with the D and G band, which can be considered as fingerprints for the fine diamond grained structure related to UNCD [9].
Fig. 3. Raman spectra (514 nm excitation) of UNCD films grown on pretreated WC-Co substrates for varying deposition times.
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M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
3.3. Adhesion analysis In order to evaluate the coating–substrate adhesion, Rockwell indentation tests with a load of 1000N were performed on the UNCD coated WC-Co substrates. Figure 4 shows FEG-SEM images of the samples after indentation tests. It can be seen that the best adhesion was achieved for UNCD coating grown for 2 h. In this sample, there is only substrate crack and no coating delamination was observed. On the other hand, samples of UNCD coatings grown for 4 and 6 h exhibited delamination visible. It was also observed that with the thickness increases the size of delamination area increases. This result may be explained by assuming that with the increases in the thickness, the residual stress in coating increases.
Fig. 4. FEG-SEM images of the indentation crack morphology of UNCD coatings for varying deposition times: (a), (b) and (c) 2 h; (d), (e) and (f) 4 h; (g) and (h) 6 h.
M. A. Fraga/ Materials Today: Proceedings 4 (2017) 11538–11543
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4. Conclusions We have evaluated the adhesion between UNCD coating and pretreated WC-Co substrate. A set of UNCD samples with different thicknesses were prepared varying the deposition time: 2, 4 and 6 h. It was produced thick (around 1.2 μm) and thin (400 nm) UNCD coatings. The indentation tests under a load of 1000 N showed that there is no delamination of the UNCD coating deposited at 2h, which indicates a good adhesion. However, for thicker coatings a poor adhesion was observed. Acknowledgements We would like to thank FAPESP (processes number: 14/18139-8, 13/25939-8 and 12/15857-1) for the financial support.
References [1] R. Haubner, W. Kalss Int. J. Refract. Met. Hard Mater. 28 (2010) 475-483. [2] Y. Yuan, J. Li, W. Sun, Adhesion of diamond film on functionally gradient WC-10wt. %Co hardmetal, International Power, Electronics and Materials Engineering Conference (IPEMEC 2015) 222-229. [3] A.Veillere, T. Guillemet, Z. Q. Xie, C. A. Zuhlke, D. R. Alexander, J. Silvain, J.Heintz, N. Chandra, Y. F. Lu. ACS Appl. Mater. Interfaces 3, (2011) 1134–1139. [4] M. A. Fraga, A. Contin, L. A. A. Rodríguez, J. Vieira, R. A. Campos, E. J. Corat, V. J. Trava Airoldi, Mater. Res. Express 3 (2016) 025601. [5] J. Zhang, X. Wang, B. Shen, F. Sun, T. Nonferr. Metal. SoC. 24 (2014) 3181-3188. [6] O. A. Williams, M. Daenen, J. D’Haenen, J. Maesc, V. V. Moshcalkov, M. Nesládek, D. M. Gruen, Diam. Relat. Mater. 15 (2006) 654-658. [7] A.C. Ferrari, J. Robertson. Phys. Rev. B, 63 (2001) 121405. [8] V. Mortet, L. Zhang, M. Eckert, J. D’Haen, A. Soltani, M. Moreau, D. Troadec, E. Neyts, J. Jaeger, J. Verbeeck, A. Bogaerts, G.V. Tendeloo, K. Haenen, P. Wagner, Phys. Status Solidi A. 9 (2012) 1675–1682. [9] D.C. Barbosa, M.R. Baldan, V.J. TravaAiroldi, E.J. Corat, Mater. Sci.Forum 802 (2014) 168-173.