Diamond/β-SiC film as adhesion-enhanced interlayer for top diamond coatings on cemented tungsten carbide substrate

doi:10.1016/j.jmst.2017.06.005

Abstract

Abstract:

In present work, diamond/β-SiC composite interlayers were deposited on cemented tungsten carbide (WC-6%Co) substrates by microwave plasma enhanced chemical vapor deposition (MPCVD) using H₂, CH₄ and tetramethylsilane (TMS) gas mixtures. The microstructure, chemical bonding, element distribution and crystalline quality of the composite interlayers were systematically characterized by means of field-emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD), X-ray photoelectron spectrometer (XPS), electron probe microanalysis (EPMA), Raman spectroscopy and transmission electron microscropy (TEM). The influences of varying TMS flow rates on the diamond/β-SiC composite interlayers were investigated. Through changing the TMS flow rates in the reaction gas, the volume fraction of β-SiC in the composite interlayers were tunable in the range of 12.0%-68.1%. XPS and EPMA analysis reveal that the composite interlayers are composed of C, Si element with little cobalt distribution. The better crystallinity of the diamond in the composite is characterized based on the Raman spectroscopy, which are helpful to deposit top diamond coatings with high quality. Then, the adhesion of top diamond coatings were estimated using Rockwell C indentation analysis, revealing that the adhesion of top diamond coatings on the WC-6%Co substrates can be improved by the interlayers with the diamond/β-SiC composite structures. Comprehensive TEM interfacial analysis exhibits that the cobalt diffusion is weak from WC-6%Co substrate to the composite interlayer. The homogeneous microcrystalline diamond coatings with the most excellent adhesion can be fabricated on the substrates with the composite interlayer with the β-SiC/diamond ratio of about 45%. The composite structures are appropriate for the application in high-efficiency mechanical tool as a buffer layer for the deposition of the diamond coating.

Key words: Diamond/β-SiC, Interlayer, Microstructure, Adhesion, MPCVD

Tian Qingquan, Huang Nan, Yang Bing, Zhuang Hao, Wang Chun, Zhai Zhaofeng, Li Junhao, Jia Xinyi, Liu Lusheng, Jiang Xin. Diamond/β-SiC film as adhesion-enhanced interlayer for top diamond coatings on cemented tungsten carbide substrate[J]. J. Mater. Sci. Technol., 2017, 33(10): 1097-1106.

Figures/Tables 13

Fig. 1. FE-SEM micrographs of diamond/β-SiC composite interlayers deposited with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm. The flow rates of H2 and CH4 were kept at 400 sccm and 4 sccm, respectively.

Fig. 2. Plot of β-SiC volume fractions in composite interlayers as a function of TMS flow rates.

Fig. 3. XRD patterns of composite interlayers deposited with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm.

Fig. 4. C1s XPS spectra of composite interlayers with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm. The fitting of the composite interlayers C1s peaks was carried out by using Lorentzian peaks at binding energies of 283.0 eV, 284.2 eV and 285.1 eV, which are attributed to the sp3 C ─Si, sp2 C═C and sp3 C─C chemical bond, respectively.

Fig. 5. (a) EPMA images of composite interlayers with different TMS flow rates in backscattered electron mode; element mapping of C (b), Si (c) and Co (d) corresponding to the specimen in the same area. The colour spectrum maps represent levels of X-ray counts. Red and blue colours show the highest and lowest counts, respectively.

Fig. 6. Raman spectra of composite interlayers deposited with different TMS flow rates. A He-Cd laser with 325 nm wavelength was ultilized as the excitation source.

Fig. 7. Fitting curves of Raman spectrum of composite interlayers deposited with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm. The peaks marked by different colour lines obtained are listed as: I: 1246.1 cm-1; II 1334.3 cm-1; III: 1390.1 cm-1; IV: 1535.6 cm-1; V: 1596.9 cm-1. The positions at 1334.3 cm-1 correspond to diamond while G bands (1535.6 cm-1 and 1596.9 cm-1) represent the non-diamond carbon. The peaks at 1246.1 cm-1 is probally considered to be trans-poly acetylene [35]. The peak at 1390 cm-1 may be corresponding to vibration density of states (VDOS) of a sp2 network [36].

Table 1 Positions and FWHM of Raman peaks of diamond composite interlayers with different TMS flow rates.

Flow rate (sccm)	5	10	20	30
sp³ carbon position (cm^-1)	1336.0	1335.4	1334.3	1333.8
FWHM (cm^-1)	9.8	12.0	12.7	7.8

Fig. 8. FE-SEM cross-sectional micrographs of top diamond coatings on composite interlayers with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm.

Fig. 9. Backscattered electron images of cross-section of diamond films deposited on composite interlayers with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm.

Fig. 10. FE-SEM micrographs after Rockwell C indentations with a load of 60 kgf on composite interlayers with different TMS flow rates: (a) 5 sccm; (b) 10 sccm; (c) 20 sccm; (d) 30 sccm.

Fig. 11. Plain-view TEM micrographs of diamond/β-SiC composite interlayer deposited at TMS flow rate of 20 sccm: (a) STEM image; (b) high-magnification image at bright field; (c) and (d) are the EDS analysis of the points corresponding to marked zones with white circle and black circles, respectively; (e) SAED of the composite interlayer; (f) and (g) are HR-TEM images of the diamond and β-SiC, respectively in the composite interlayer.

Fig. 12. (a) Cross-sectional STEM micrograph of diamond/β-SiC composite interlayer between composite films and WC-6%Co substrate deposited with TMS flow rate of 20 sccm; element mapping of Co (b), Si (c), W (d) and C (e) at the interfaces correspondding to the enlarged view of the rectangle area.

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