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Adhesion strength of diamond films on heat-treated WC–Co cutting tools
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Diamond & Related Materials 16 (2007) 1992 – 1995 www.elsevier.com/locate/diamond
Adhesion strength of diamond films on heat-treated WC–Co cutting tools Ki-Woong Chae a,⁎, Jong-Keuk Park b , Wook-Seong Lee b a
b
Department of Materials Engineering, Hoseo University, Asan 336-795, Republic of Korea Thin Film Technology Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea Received 15 September 2006; received in revised form 21 March 2007; accepted 12 September 2007 Available online 19 September 2007
Abstract The adhesion strength and deposition behavior of diamond films with different grain size onto heat-treated WC–Co cutting tool inserts were investigated. The diamond film was deposited on WC–6%Co cutting tool inserts by the hot-filament chemical vapor deposition method, with H2/ 3% CH4 mixed gas. The N2 gas was incorporated in the mixed gas to refine the grain size of the deposited diamond film (nanocrystalline diamond: NCD). Pores were observed in the interface region between the micrometer-size diamond film (MCD) and the WC–Co cutting tool insert. This suggested that the growth of diamond grains on top of elongated WC grains, which was induced by heat treatment to improve the adhesion strength of the deposited film, hindered the deposition of diamond in the valley area between the elongated WC grains. By contrast, in the case of the NCD film with a grain size of less than 50 nm obtained by addition of N2 gas, no pores were observed, due to the fact that the refined diamond grains filled the interface region regardless of the existence of the elongated WC grains. The adhesion strength of the NCD film was likely to be greater than that of the MCD film on the heat-treated WC–Co cutting tool insert, which was explained by the full coverage with small diamond grains at the rough interface region. © 2007 Elsevier B.V. All rights reserved. Keywords: Adhesion; Refinement; Heat treatment; Pore; Interface
1. Introduction By comparison with micrometer-size diamond films (MCD), the new type of diamond film with refined grain size (nanocrystalline diamond: NCD) is considered to have overcome the surface roughness problem that resulted from the large crystalline facet of diamond grain, and to have improved the surface finish of the workpiece during the machining process. However, without strong bonding to the substrate, the diamond film with refined grain size will not survive the mechanical stress developed during cutting applications, and it becomes the main cause of an unpredictable and unreliable lifetime-tool. A lot of techniques on WC–Co cutting tools such as substrate pretreatment and buffer layer deposition have been investigated to improve the adhesion of deposited diamond film [1–9]. Among them, heat-treatment of WC–Co substrate prior to coating has ⁎ Corresponding author. Tel.: +82 41 540 5765; fax: +82 41 548 3502. E-mail address: [email protected] (K.-W. Chae). 0925-9635/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2007.09.003
been shown as an effective method for improving the adhesion by reducing surface Co content and increasing surface rough due to WC grain growth [7–9]. The diamond grain size could be reduced by controlling process parameters such as temperature, methane concentration and addition of N2 gas during the deposition of diamond [10– 13]. However, the effect of NCD on the microstructure and adhesion of the heat-treated WC–Co cutting tool insert has not been determined in detail. The aim of this work is to investigate the adhesion property and deposition behavior of diamond films with different grain sizes on the heat-treated WC–Co cutting tool inserts. The effect of N2 addition on the refinement of diamond grain by hot-filament chemical vapor deposition (HFCVD) was re-examined. 2. Experimental Commercially available WC–6%Co cutting tool inserts were used as substrate for diamond coating. The insert was heat-
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
1993
The HF-CVD technique was employed to deposit diamond film on WC–Co cutting tool inserts. The reactant gases were 3% CH4 in H2 and the gas pressure was 60 torr. The insert temperature was fixed at 900 °C during the deposition of diamond. For deposition of the refined diamond grains, N2 gas was incorporated with 3% CH4 in the ratio of 0.1. The surface morphology and the grain size of deposited films were characterized by scanning electron microscopy and the adhesion strength was estimated by the Rockwell indentation method. 3. Results and discussion
Fig. 1. Surface morphology of the heat-treated WC–Co cutting tool insert.
treated to improve adhesion of the deposited film by increasing surface roughness due to growth of the WC grain on the surface of the insert [7]. The heat treatment was performed in a H2 atmosphere at 1450 °C for 20 min and then in a CH4 atmosphere for 20 min. The inserts to be coated with diamond film were pretreated by ultrasonic vibration with diamond powder of 0.5 μm average size.
Fig. 2. Microstructures of the diamond film deposited on the heat-treated WC–Co cutting tool insert for 15 h with (a) 3% CH4 and (b) 3% CH4 and 0.3% N2 in H2.
Heat treatment of WC–Co cutting tool inserts prior to coating is well known to improve the adhesion strength of a diamond film in cutting application, because large WC grains can play an effective role in mechanical interlocking [7–9]. A typical microstructure of the heat-treated WC–Co insert is shown in Fig. 1. Note that elongated WC grains with an average size of 10 μm are observed on the tool surface. The surface roughness change (Rz) of the WC–Co insert was from 2.98 to 9.73 μm, which was measured by Surface Roughness Tester (Model: SJ-301, Mitutoyo) before and after the heat treatment. Fig. 2a and b show the surface microstructures of the diamond film deposited on the WC–Co insert shown in Fig. 1 for 15 h with (a) 3% CH4 and (b) 3% CH4 and 0.3% N2 in H2, respectively. The diamond film grown without nitrogen (Fig. 2a) shows large, well-defined crystalline facets that are indicative of high purity diamond. In contrast, the diamond film grown with the addition of N2 gas (Fig. 2b) exhibits an agglomerated appearance with round nodules of approximately 10 μm, which is similar in size to the elongated WC grains on the surface of insert. It seems that the surface morphology of the deposited NCD films is influenced by the substrate morphology. The agglomerated grains consist of diamond grains with sizes of 30 ∼ 50 nm as shown in Fig. 3. This shows clearly that the addition of N2 is a very effective for deposition of NCD films. Fig. 4a and b show the cross-sectional microstructures of diamond films as shown in Fig. 2a and b, respectively. They form a continuous film and show the change of grain size from
Fig. 3. High magnification microstructure of the diamond film shown in Fig. 2b.
1994
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
which is considered that the diamond crystals early deposited on WC–Co substrate prefer to grow and can constrain secondary formation of nuclei. Thus, the diamond grains columnar grown on the top of the elongated WC grains seem to obstruct the path for deposition of diamond, which resulted in the microstructure shown in Fig. 4a. By contrast, in the case of the NCD film (Fig. 4b) with a grain size of less than 50 nm, there are no large diamond grains on top of WC grains to obstruct the deposition path. This result seems to be caused by the NCD film maintaining the diamond grains refined, regardless of the deposition time, by a re-nucleation process. The refined diamond grains fill the valley area at the interface region and no pores were observed, which were indicated by circles in Fig. 4b. For the past few years, the adhesion of diamond coated tools has been improved enough to survive a turning operation [4,6]. However, the application for milling is not yet solved. For milling, the diamond coated tools need sufficient toughness to endure the interrupted cutting. If there is a pore at the interface between the diamond film and the cutting tool insert, it could be the origin for a stress concentration fracture. From this observation in Fig. 4, the NCD film will be more advantageous and more practical in terms of machine milling than the MCD film. In order to estimate the adhesion strength between the deposited film and the WC–Co insert, the diamond coated
Fig. 4. Cross-sectional microstructures of the diamond films as shown in (a) Fig. 2a and (b) Fig. 2b. Large WC grains on the surface of heat-treated WC–Co insert are indicated by arrows and circles show the valley area at the interface.
the micrometer scale (Fig. 4a) to the nanometer scale (Fig. 4b), depending on the addition of N2 gas. It can be observed that both films have about 15 μm thickness, which means that the deposition rate is independent of adding N2 gas. As indicated by the arrows in Fig. 4, the elongated and protruded WC grains are formed on the surface of the WC–Co cutting tool insert by the heat treatment. They are expected to allow mechanical interlocking with diamond films, and result in an increase of adhesion strength. A careful examination of Fig. 4a reveals that with a dense and uniform diamond film deposited at the upper part, the interfaces between the protruded WC grains formed the pores. The large irregular shaped pores with size of ∼ 10 μm (shown by circles in Fig. 4a) are found and they are surrounded by elongated WC grains. The observed pores are assumed to result from the fact that the growth of the diamond film may hinder the deposition of diamond in the valley area between the elongated WC grains on the WC–Co cutting tool insert, and thus the space between the elongated WC grains is left empty. In the early stage of deposition, the refined diamond grains are deposited uniformly on the rough substrate surface. As the deposition time increases, the diamond grain becomes bigger enough to bridge across the top of the elongated WC grains without filling in between them. The columnar structure in films can be observed from Fig. 4a,
Fig. 5. Surface morphologies of the Rockwell indentation with load of 100 kgf on the (a) NCD, and (b) MCD diamond films deposited for 30 h on the heattreated WC–Co cutting tool inserts.
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
inserts were examined by the Rockwell method, with a load of 60 kgf. For both of the insert with film thickness of ∼ 15 μm shown in Fig. 4, peeling off or cracking of the deposited films was not observed, indicating that the adhesion strength of MCD and NCD was enough to withstand the load of 60 kgf due to the mechanical interlocking between the elongated WC grain and the diamond film. It could confirm that the heat-treatment technique is very effective in enhancing the adhesion strength of diamond film on WC–Co cutting tools. With increasing the deposited film thickness, the adhesion strength between diamond film and substrate decreases due to the increase with compressive residual stress in the film. To test the adhesion property of NCD and MCD films in severe condition, the indentation measurement have been performed with a thicker diamond films and increasing indentation load. In the case of the film thickness of 30 μm, delamination occurred in both NCD and MCD with the load of 100 kgf. However, they showed the difference in the percentages of the delamination. The NCD films was observed to be delaminated about 20%: 2 times of 10 indentation tests, while the MCD films was about 40%: 4 of 10 indentations. Fig. 5 shows examples of the microstructures resulted from the Rockwell indentation test with load of 100 kgf on the (a) NCD, and (b) MCD film deposited for 30 h, respectively. The film thickness of both was about 30 um. According as the deposition time increased, the diamond grain size of MCD film increased to 18 um. On the contrary, NCD showed the same grain size of 30 ∼ 50 nm, regardless of deposition time, by a re-nucleation process. Scotch tape was used to clean the damaged area after indentation test. As shown in Fig. 5a, there is no delamination of the NCD diamond film in the indentation region. On the contrary, the MCD film (Fig. 5b) of the same thickness shows a heavy damage in the indented area. The delamination in the MCD film, once occurred, was not restricted to the indented region but took place in much wider area with diameter between 200 and 600 μm, and it is considered to be caused by large residual compressive stress in this film. Although the adhesion strength using the indentation method is not determined quantitatively in detail, the results shown in Figs. 4 and 5 suggest strongly that the adhesion property of the NCD film is greater than that of the MCD film on WC–Co cutting tool insert.
1995
4. Conclusions Under normal diamond coating condition (MCD), pores were observed in the interface between the WC–Co cutting tool insert having large, elongated grains on the surface and the deposited films. The diamond grains grown on top of elongated WC grains seems to obstruct the path for deposition of diamond, causing inhibition of the deposition of diamond in the valley area between the large elongated grains, and thus pores were formed. By contrast, the diamond film with a grain size of less than 50 nm obtained by the addition of N2 showed a dense diamond film-substrate interface, and no pores were observed. The refined diamond grains filled the space effectively without any gaps and are thus more practical than MCD film for machine milling application, which require sufficient toughness to overcome interrupted cutting. Acknowledgement This work was supported by the academic research fund of Hoseo University. References [1] R. Haubner, B. Lux, Int. J. Refract. Met. Hard Mater. 14 (1996) 111. [2] N. Dilawar, R. Kapil, Brahamprakash, V.D. Vankar, D.K. Avasthi, D. Kabiraj, G.K. Meha, Thin Solid Films 3213 (1998) 163. [3] S. Silva, V.P. Mammana, M.C. Salvadori, O.R. Monteiro, I.G. Brown, Diamond Relat. Mater. 8 (1999) 1913. [4] C.R. Lin, C.T. Kuo, R.M. Chang, Diamond Relat. Mater. 7 (1998) 1628. [5] F.H. Sun, Z.M. Zhang, M. Chen, H.S. Shen, Diamond Relat. Mater. 12 (2003) 711. [6] W. Tang, Q. Wang, S. Wang, F. Lu, Diamond Relat. Mater. 10 (2001) 1700. [7] S.H. Yeo, W.S. Lee, Y.J. Baik, K.W. Chae, D.S. Lim, J. Korean Ceram. Soc. 38 (1) (2001) 28. [8] A. Inspektor, C.E. Bauer, E.J. Oles, Surf. Coat. Technol. 68/69 (1994) 359. [9] E.J. Oles, A. Inspektor, C.E. Bauer, Diamond Relat. Mater. 5 (1996) 617. [10] L.C. Chen, T.Y. Wang, W.F. Pong, Diamond Relat. Mater. 9 (2000) 877. [11] Shane A. Catledge, Yogesh K. Vohra, J. Appl. Phys. 86 (1) (1999) 698. [12] J.W. Zimmer, US patent No. 6,319,610. 2001 [13] R. Ikeda, M. Hayashi, A. Yonezu, T. Ogawa, M. Takemoto, Diamond Relat. Mater. 13 (2004) 2024.
Diamond & Related Materials 16 (2007) 1992 – 1995 www.elsevier.com/locate/diamond
Adhesion strength of diamond films on heat-treated WC–Co cutting tools Ki-Woong Chae a,⁎, Jong-Keuk Park b , Wook-Seong Lee b a
b
Department of Materials Engineering, Hoseo University, Asan 336-795, Republic of Korea Thin Film Technology Research Center, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, Republic of Korea Received 15 September 2006; received in revised form 21 March 2007; accepted 12 September 2007 Available online 19 September 2007
Abstract The adhesion strength and deposition behavior of diamond films with different grain size onto heat-treated WC–Co cutting tool inserts were investigated. The diamond film was deposited on WC–6%Co cutting tool inserts by the hot-filament chemical vapor deposition method, with H2/ 3% CH4 mixed gas. The N2 gas was incorporated in the mixed gas to refine the grain size of the deposited diamond film (nanocrystalline diamond: NCD). Pores were observed in the interface region between the micrometer-size diamond film (MCD) and the WC–Co cutting tool insert. This suggested that the growth of diamond grains on top of elongated WC grains, which was induced by heat treatment to improve the adhesion strength of the deposited film, hindered the deposition of diamond in the valley area between the elongated WC grains. By contrast, in the case of the NCD film with a grain size of less than 50 nm obtained by addition of N2 gas, no pores were observed, due to the fact that the refined diamond grains filled the interface region regardless of the existence of the elongated WC grains. The adhesion strength of the NCD film was likely to be greater than that of the MCD film on the heat-treated WC–Co cutting tool insert, which was explained by the full coverage with small diamond grains at the rough interface region. © 2007 Elsevier B.V. All rights reserved. Keywords: Adhesion; Refinement; Heat treatment; Pore; Interface
1. Introduction By comparison with micrometer-size diamond films (MCD), the new type of diamond film with refined grain size (nanocrystalline diamond: NCD) is considered to have overcome the surface roughness problem that resulted from the large crystalline facet of diamond grain, and to have improved the surface finish of the workpiece during the machining process. However, without strong bonding to the substrate, the diamond film with refined grain size will not survive the mechanical stress developed during cutting applications, and it becomes the main cause of an unpredictable and unreliable lifetime-tool. A lot of techniques on WC–Co cutting tools such as substrate pretreatment and buffer layer deposition have been investigated to improve the adhesion of deposited diamond film [1–9]. Among them, heat-treatment of WC–Co substrate prior to coating has ⁎ Corresponding author. Tel.: +82 41 540 5765; fax: +82 41 548 3502. E-mail address: [email protected] (K.-W. Chae). 0925-9635/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.diamond.2007.09.003
been shown as an effective method for improving the adhesion by reducing surface Co content and increasing surface rough due to WC grain growth [7–9]. The diamond grain size could be reduced by controlling process parameters such as temperature, methane concentration and addition of N2 gas during the deposition of diamond [10– 13]. However, the effect of NCD on the microstructure and adhesion of the heat-treated WC–Co cutting tool insert has not been determined in detail. The aim of this work is to investigate the adhesion property and deposition behavior of diamond films with different grain sizes on the heat-treated WC–Co cutting tool inserts. The effect of N2 addition on the refinement of diamond grain by hot-filament chemical vapor deposition (HFCVD) was re-examined. 2. Experimental Commercially available WC–6%Co cutting tool inserts were used as substrate for diamond coating. The insert was heat-
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
1993
The HF-CVD technique was employed to deposit diamond film on WC–Co cutting tool inserts. The reactant gases were 3% CH4 in H2 and the gas pressure was 60 torr. The insert temperature was fixed at 900 °C during the deposition of diamond. For deposition of the refined diamond grains, N2 gas was incorporated with 3% CH4 in the ratio of 0.1. The surface morphology and the grain size of deposited films were characterized by scanning electron microscopy and the adhesion strength was estimated by the Rockwell indentation method. 3. Results and discussion
Fig. 1. Surface morphology of the heat-treated WC–Co cutting tool insert.
treated to improve adhesion of the deposited film by increasing surface roughness due to growth of the WC grain on the surface of the insert [7]. The heat treatment was performed in a H2 atmosphere at 1450 °C for 20 min and then in a CH4 atmosphere for 20 min. The inserts to be coated with diamond film were pretreated by ultrasonic vibration with diamond powder of 0.5 μm average size.
Fig. 2. Microstructures of the diamond film deposited on the heat-treated WC–Co cutting tool insert for 15 h with (a) 3% CH4 and (b) 3% CH4 and 0.3% N2 in H2.
Heat treatment of WC–Co cutting tool inserts prior to coating is well known to improve the adhesion strength of a diamond film in cutting application, because large WC grains can play an effective role in mechanical interlocking [7–9]. A typical microstructure of the heat-treated WC–Co insert is shown in Fig. 1. Note that elongated WC grains with an average size of 10 μm are observed on the tool surface. The surface roughness change (Rz) of the WC–Co insert was from 2.98 to 9.73 μm, which was measured by Surface Roughness Tester (Model: SJ-301, Mitutoyo) before and after the heat treatment. Fig. 2a and b show the surface microstructures of the diamond film deposited on the WC–Co insert shown in Fig. 1 for 15 h with (a) 3% CH4 and (b) 3% CH4 and 0.3% N2 in H2, respectively. The diamond film grown without nitrogen (Fig. 2a) shows large, well-defined crystalline facets that are indicative of high purity diamond. In contrast, the diamond film grown with the addition of N2 gas (Fig. 2b) exhibits an agglomerated appearance with round nodules of approximately 10 μm, which is similar in size to the elongated WC grains on the surface of insert. It seems that the surface morphology of the deposited NCD films is influenced by the substrate morphology. The agglomerated grains consist of diamond grains with sizes of 30 ∼ 50 nm as shown in Fig. 3. This shows clearly that the addition of N2 is a very effective for deposition of NCD films. Fig. 4a and b show the cross-sectional microstructures of diamond films as shown in Fig. 2a and b, respectively. They form a continuous film and show the change of grain size from
Fig. 3. High magnification microstructure of the diamond film shown in Fig. 2b.
1994
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
which is considered that the diamond crystals early deposited on WC–Co substrate prefer to grow and can constrain secondary formation of nuclei. Thus, the diamond grains columnar grown on the top of the elongated WC grains seem to obstruct the path for deposition of diamond, which resulted in the microstructure shown in Fig. 4a. By contrast, in the case of the NCD film (Fig. 4b) with a grain size of less than 50 nm, there are no large diamond grains on top of WC grains to obstruct the deposition path. This result seems to be caused by the NCD film maintaining the diamond grains refined, regardless of the deposition time, by a re-nucleation process. The refined diamond grains fill the valley area at the interface region and no pores were observed, which were indicated by circles in Fig. 4b. For the past few years, the adhesion of diamond coated tools has been improved enough to survive a turning operation [4,6]. However, the application for milling is not yet solved. For milling, the diamond coated tools need sufficient toughness to endure the interrupted cutting. If there is a pore at the interface between the diamond film and the cutting tool insert, it could be the origin for a stress concentration fracture. From this observation in Fig. 4, the NCD film will be more advantageous and more practical in terms of machine milling than the MCD film. In order to estimate the adhesion strength between the deposited film and the WC–Co insert, the diamond coated
Fig. 4. Cross-sectional microstructures of the diamond films as shown in (a) Fig. 2a and (b) Fig. 2b. Large WC grains on the surface of heat-treated WC–Co insert are indicated by arrows and circles show the valley area at the interface.
the micrometer scale (Fig. 4a) to the nanometer scale (Fig. 4b), depending on the addition of N2 gas. It can be observed that both films have about 15 μm thickness, which means that the deposition rate is independent of adding N2 gas. As indicated by the arrows in Fig. 4, the elongated and protruded WC grains are formed on the surface of the WC–Co cutting tool insert by the heat treatment. They are expected to allow mechanical interlocking with diamond films, and result in an increase of adhesion strength. A careful examination of Fig. 4a reveals that with a dense and uniform diamond film deposited at the upper part, the interfaces between the protruded WC grains formed the pores. The large irregular shaped pores with size of ∼ 10 μm (shown by circles in Fig. 4a) are found and they are surrounded by elongated WC grains. The observed pores are assumed to result from the fact that the growth of the diamond film may hinder the deposition of diamond in the valley area between the elongated WC grains on the WC–Co cutting tool insert, and thus the space between the elongated WC grains is left empty. In the early stage of deposition, the refined diamond grains are deposited uniformly on the rough substrate surface. As the deposition time increases, the diamond grain becomes bigger enough to bridge across the top of the elongated WC grains without filling in between them. The columnar structure in films can be observed from Fig. 4a,
Fig. 5. Surface morphologies of the Rockwell indentation with load of 100 kgf on the (a) NCD, and (b) MCD diamond films deposited for 30 h on the heattreated WC–Co cutting tool inserts.
K.-W. Chae et al. / Diamond & Related Materials 16 (2007) 1992–1995
inserts were examined by the Rockwell method, with a load of 60 kgf. For both of the insert with film thickness of ∼ 15 μm shown in Fig. 4, peeling off or cracking of the deposited films was not observed, indicating that the adhesion strength of MCD and NCD was enough to withstand the load of 60 kgf due to the mechanical interlocking between the elongated WC grain and the diamond film. It could confirm that the heat-treatment technique is very effective in enhancing the adhesion strength of diamond film on WC–Co cutting tools. With increasing the deposited film thickness, the adhesion strength between diamond film and substrate decreases due to the increase with compressive residual stress in the film. To test the adhesion property of NCD and MCD films in severe condition, the indentation measurement have been performed with a thicker diamond films and increasing indentation load. In the case of the film thickness of 30 μm, delamination occurred in both NCD and MCD with the load of 100 kgf. However, they showed the difference in the percentages of the delamination. The NCD films was observed to be delaminated about 20%: 2 times of 10 indentation tests, while the MCD films was about 40%: 4 of 10 indentations. Fig. 5 shows examples of the microstructures resulted from the Rockwell indentation test with load of 100 kgf on the (a) NCD, and (b) MCD film deposited for 30 h, respectively. The film thickness of both was about 30 um. According as the deposition time increased, the diamond grain size of MCD film increased to 18 um. On the contrary, NCD showed the same grain size of 30 ∼ 50 nm, regardless of deposition time, by a re-nucleation process. Scotch tape was used to clean the damaged area after indentation test. As shown in Fig. 5a, there is no delamination of the NCD diamond film in the indentation region. On the contrary, the MCD film (Fig. 5b) of the same thickness shows a heavy damage in the indented area. The delamination in the MCD film, once occurred, was not restricted to the indented region but took place in much wider area with diameter between 200 and 600 μm, and it is considered to be caused by large residual compressive stress in this film. Although the adhesion strength using the indentation method is not determined quantitatively in detail, the results shown in Figs. 4 and 5 suggest strongly that the adhesion property of the NCD film is greater than that of the MCD film on WC–Co cutting tool insert.
1995
4. Conclusions Under normal diamond coating condition (MCD), pores were observed in the interface between the WC–Co cutting tool insert having large, elongated grains on the surface and the deposited films. The diamond grains grown on top of elongated WC grains seems to obstruct the path for deposition of diamond, causing inhibition of the deposition of diamond in the valley area between the large elongated grains, and thus pores were formed. By contrast, the diamond film with a grain size of less than 50 nm obtained by the addition of N2 showed a dense diamond film-substrate interface, and no pores were observed. The refined diamond grains filled the space effectively without any gaps and are thus more practical than MCD film for machine milling application, which require sufficient toughness to overcome interrupted cutting. Acknowledgement This work was supported by the academic research fund of Hoseo University. References [1] R. Haubner, B. Lux, Int. J. Refract. Met. Hard Mater. 14 (1996) 111. [2] N. Dilawar, R. Kapil, Brahamprakash, V.D. Vankar, D.K. Avasthi, D. Kabiraj, G.K. Meha, Thin Solid Films 3213 (1998) 163. [3] S. Silva, V.P. Mammana, M.C. Salvadori, O.R. Monteiro, I.G. Brown, Diamond Relat. Mater. 8 (1999) 1913. [4] C.R. Lin, C.T. Kuo, R.M. Chang, Diamond Relat. Mater. 7 (1998) 1628. [5] F.H. Sun, Z.M. Zhang, M. Chen, H.S. Shen, Diamond Relat. Mater. 12 (2003) 711. [6] W. Tang, Q. Wang, S. Wang, F. Lu, Diamond Relat. Mater. 10 (2001) 1700. [7] S.H. Yeo, W.S. Lee, Y.J. Baik, K.W. Chae, D.S. Lim, J. Korean Ceram. Soc. 38 (1) (2001) 28. [8] A. Inspektor, C.E. Bauer, E.J. Oles, Surf. Coat. Technol. 68/69 (1994) 359. [9] E.J. Oles, A. Inspektor, C.E. Bauer, Diamond Relat. Mater. 5 (1996) 617. [10] L.C. Chen, T.Y. Wang, W.F. Pong, Diamond Relat. Mater. 9 (2000) 877. [11] Shane A. Catledge, Yogesh K. Vohra, J. Appl. Phys. 86 (1) (1999) 698. [12] J.W. Zimmer, US patent No. 6,319,610. 2001 [13] R. Ikeda, M. Hayashi, A. Yonezu, T. Ogawa, M. Takemoto, Diamond Relat. Mater. 13 (2004) 2024.