Deposition of Diamond-like Carbon Films and Metal-DLC thin films on PCBN Substrates by RF Magnetron Sputtering Method

Transcription

1 Deposition of Diamond-like Carbon Films and Metal-DLC thin films on PCBN Substrates by RF Magnetron Sputtering Method Authors & affiliations: Chii-Ruey Lin a,*, Chun-Hsi Su a, Chien-Kuo Chang b, Da-Hua Wei a a Department of Mechanical Engineering, National Taipei University of Technology, Taipei, 106 Taiwan b Graduate Institute of Mechanical and Electrical Engineering, National Taipei University of Technology, Taipei, 106 Taiwan Abstract The application of Poly-crystalline cubic Boron Nitride (PCBN) and Diamond-like Carbon (DLC) film in cutting tool material recently has processed many remarkable developments. Specially with high hardness (~19 GPa), high thermal conductivity (3~ W cm 1 K 1 ), and low friction coefficient (0.15~ 0.22), DLC film has various applications as the cutting tool material in metal cutting process. By now, many studies has been done to improve the adhesion, wear resistance as well as reduce the interfacial stress of the coated films, because of their importance to the properties of cutting tool. In this research, DLC and Metal-DLC films are deposited onto PCBN as substrate material using Radio Frequency (RF) Magnetron sputtering method. Several analytical techniques, including scanning electron microscopy and Raman spectroscopy, were used to test the properties of these thin films. The results show the very good adhesion. The cutting tests were conducted on the CNC lathe with a PCBN cutting tool with feed rate and cutting speed of 0.2 m/min and 600 m/min, respectively. The cutting distance of PCBN without coating DLC is m. The cutting distance of coating DLC films is m, which prepared under an inlet Argon of 16 SCCM and RF power of 300 watts. The adhesive strength of Metal-DLC thin films is testified by Micro-hardness tester with the load of 50 g. The adhesion test indicated that the Cr is an excellent buffer layer between DLC films and PCBN compared with Ta and Nb due to the Cr intermediate layer can reduce the internal stress. Keywords : PCBN(Poly-crystalline cubic Boron Nitride), DLC (Diamond-Like Carbon), Intermediate layer 1

2 1. Introduction Diamond-Like Carbon ( DLC ) has extreme properties similar to diamond. It can have a high mechanical and chemical inertness, such as a high mechanical hardness, low coefficient of friction, and a high heat-conduction[1-2]. DLC films have wide-spreading applications as protective coatings in field cutting tool for example. Poly-crystalline cubic Boron Nitride (CBN) sintered body means polycrystalline CBN. PCBN illustration is as Fig.1. The development of tool material- PCBN, has made it possible to use turning. PCBN is used an accurate cutting tool for removing material from a workpiece. The machining accuracy of the cutter can be less than 1μm, and the surface roughness of its processing can be less than 0.2μm. However, its high costs and low toughness limit its use[3]. Diamond-like carbon film has better hardness, thermal conductivity, and lowest friction coefficient. Studies of chromium, tantalum, and niobium as interlayer between DLC films and PCBN, to improve adhesion ability and reduce interlay stress. In particular it relates to a coated PCBN cutting tool improved in wear-resistance and hardness. Fig.1 Schematic of a Poly-crystalline cubic Boron Nitride (PCBN). 2. Experiments In this study, Diamond-like Carbon (DLC) and Me-DLC films were prepared on PCBN surface by RF magnetron sputtering system with a diamond powder target. RF magnetron sputtering system show as Fig.2. The main parts of the system are Power control, the chamber, and vacuum system. The flow chart indicate as Fig. 3. Experiments are conducted with various coating conditions. This research is based on RF Magnetron Sputtering process gradient layer deposition of DLC and Me-DLC films onto PCBN, then to discuss the film structure under different parameters by SEM, XRD and Raman Spectrum. Using AFM, NIP and wear test to analyzing the mechanical behavior. The experiment parameter design table is as table 1. Fig.2 Schematic diagram of the RF magnetron sputtering system. 2

3 Fig.3 Schematic of DLC and Me-DLC films were prepared on PCBN surface by RF magnetron sputtering system. Table 1 Coating parameters of PVD used in experiments 3. Results and Discussion 3.1 Microstructure Analysis of DLC and Cr-DLC films The surface and components of the as-deposited DLC and Cr-DLC films were observed by SEM and EDS. Fig. 4(a) shown a typical SEM picture of DLC film with RF Power of 200W and Ar of 20 sccm. The as-deposited amorphous DLC film shows a smooth morphology. Fig. 4 is the components (C peak). Fig. 4(c) shows the Cr/DLC film on PCBN cutter surface, and Fig. 4(d) is the components (C peak and Cr peak). (a) 3

4 (c) (d) Fig.4 The surface and components of the as-deposited DLC and Cr-DLC films were observed by SEM and EDS. Fig. (a) shows the amorphous DLC film on PCBN cutter surface, and Fig. is the components (C peak). Fig. (c) shows the Cr/DLC film on PCBN cutter surface, and Fig. (d) is the components (C peak and Cr peak). 3.2 Raman spectrum analysis Raman spectroscopy is to indicate a high strength of DLC bonding in deposited hardened carbon films. The single Raman peak at 1580 cm -1 coincides with that of the highly crystalline graphite. A peak located at 1350 cm -1 is attributed to micro-crystalline, disordered sp 3 sites graphite[4]. A D (Disorder) band peak near 1351 cm -1 has appeared to shift a bit right. And, a G (Graphite) band peak near 1577 cm -1 has appeared to shift to the left because distorted atom bonds, as shown in Fig.5. The Raman spectra of Cr/DLC films and Ta/DLC films is shown in Fig.6. When the intermediate layer design, it is Cr, Ta and Nb that are taken as the main body, compared with Raman which deposits spectrum I D /I G ratio. By RF Power of 300 W, Ar of 16 sccm and the heating temperatures are 200 Cr/DLC membranes for highest, I D /I G approximately is Fig.5 The Raman spectra of specimen No.2(RF Power of 200 Wand Ar of 20 sccm). 4

5 (a) Fig.6 The Raman spectra of specimen Fig.(a) Cr/DLC films and Fig. Ta/DLC films. 3.3 Mechanical properties analysis and Cutting Test Mechanical properties of DLC film were analyzed by nano-indentation test. Fig.7(a) and show the surface of DLC film after NIP test, and its hardness is GPa. The cutting tests were conducted on the CNC lathe with a PCBN cutting tool with feed rate and cutting speed of 0.2 m/min and 600 m/min, respectively. The cutting distance of PCBN without coating DLC is m. The cutting distance of coating DLC films is m, which prepared under an inlet Argon of 16 SCCM and RF power of 300 watts, as show in Fig.8. The adhesive strength of Metal-DLC thin films is testified by Micro-hardness tester with the load of 50 g. The adhesion test indicated that the Cr is an excellent buffer layer between DLC films and PCBN compared with Ta and Nb due to the Cr intermediate layer can reduce the internal stress, as shown in Fig.9. (a) Fig.7 Nano-indenter of RF Power of 200 W and Ar of 20 sccm. (Loading:500μN, Er:250.5 Gpa, and Hardness:33.38 Gpa) 5

6 (a) Fig.8 The surface of PCBN cutter after the cutting test. Fig. (a) shows the non-coated PCBN cutter, and Fig. shows DLC film on PCBN cutter surface. (a) Fig.9 The adhesive strength of Cr-DLC and Ta-DLC films on PCBN cutter surface is testified by Micro-hardness tester with the load of 50 g. Fig. (a) shows the Cr-DLC films, and Fig. shows the Ta-DLC films. 4. Conclusion The cutting tests were conducted on the CNC lathe with a PCBN cutting tool with feed rate and cutting speed of 0.2 m/min and 600 m/min, respectively. The cutting distance of PCBN without coating DLC is m. The cutting distance of coating DLC films is m, which prepared under an inlet Argon of 16 SCCM and RF power of 300 watts.the adhesive strength of Metal-DLC thin films is testified by Micro-hardness tester with the load of 50 g. The adhesion test indicated that the Cr is an excellent buffer layer between DLC films and PCBN compared with Ta and Nb due to the Cr intermediate layer can reduce the internal stress. References [1] J.C. Angus and C.C. Hayman, "Low-pressure,metastable growth of diamond and diamond-like phase, " Science, 241, 1988, p.913. [2] Demichelis, F., Rong, X.F., "Deposition and characterization of amorphous carbon nitride thin ilms, " Diamond and Related Materials, 3, 1994, p.361. [3] Adilson Jose de Oliveira,, et. al.,, Hard turning in continuous and interrupted cut with PCBN and whisker-reinforced cutting tools, Journal of Materials Processing Technology, 209 (2009) pp [4] V. J. Morris., A. R. Kirbv., A. P. Gunning., Atomic Force Microscopy for Biologists, Imperial College Press, London,