Silicon Nitride Tools Coated with TiC Or TiN Composite Diamond Structures
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Fig.1 SEM micrographs of Si3N 4 substrates coated with the diamond layer (a), the diamond TiC /diamond layer (b), the diamond/TiN/diamond layer layer (c), and the TiN/diamond (d) were performed at elongation rate of 0.05 in/min. The surface of the diamond film was examined by SEM after each wear test. Quantitative metallographic analysis was carried out to determine the percentage diamond retained on the surface coatings. RESULTS AND DISCUSSIONS The SEM micrographs of single and composite diamond films are shown in Figs. l(a)-(d). The average size of diamond crystallites in Figs. l(a)-(c) is 3-5 tm. Multiple facets of diamond particles are seen in all these films. Fig. l(d) shows the Si 3N 4 substrate coated with the first discontinuous layer of diamond and conformal coating of TiN. In this film, the size of diamond particles is about 0.5 Atm. Raman spectra of the continuous diamond films are shown in Fig. 2. The characteristic diamond peak at 1332 cm-1 is found in composite diamond films. The diamond peak is shifted to 1331 cm- 1 in the single layer of diamond. This shift indicates the single layer of diamond is subjected to tensile stresses [7]. All these films have not exhibited diamondlike or graphite phases. SEM micrographs of three specimens after polishing test for four hours are shown in Figs. 3(a), (b), and (c), respectively. After wear test, only 30% diamond film is retained on the Si 3 N4 substrate coated with the single layer of diamond, 50% with the TiC composite diamond layer, and 80% with the TiN composite layer. After 4 hrs wear against the Al-Si alloy, the
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Fig. 2. Raman spectra of single diamond and composite diamond coatings on Silicon nitride
Ug C
1100
1500
1300
1700
Raman shift (/cm)
Fig.3 SEM micrographs of polished Si 3 N 4 substrates coated with the diamond layer (a), the diamond /TiC /diamond layer (b), and the diamond /TiN /diamond layer layer (c)
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Diamond
Diamond
Silicon nitride
Silicon nitride
Silicon nitride
Silicon nitride
(a)
(b)
(c)
(d)
Fig. 4 Four samples used for pull tests Table 1. Strength of adhesion of diamond, TiC, and TiN on Silicon notride Samples
TiC/SiN
Strength of adhesion (107) Pa 3.5 Broken place
D/TiC/SiN
TiN/SiN
D/TiN/SiN
2.4
2.9
2.8
Rod-TiC TiC-SiN
Rod-TiN TiC-TiN
Fig. 5 SEM micrographs of two broken surfaces of the Si 3N4 substrate coated with diamond and TiN films.
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surfaces are covered with a continuous layer of diamond, which indicates good adhesion in all these samples. Four samples were prepared for pull-test, as shown in Figs. 4(a)-(d). Table 1 shows the results of adhesion strength. In samples a and b, the separation took place at the interface between the rods and TiC or TiN, which shows the epoxy is not strong enough to hold the TiC and TiN films. The adhesion strength of TiC or TiN on the Si 3N4 substrate is better than 3.5x10 7 Pascal or 2.9x10 7 Pascal. The adhesion strength for the substrates coated with TiC composite diamond films or TiN composite diamond films, is 2.4x107 Pascal or 2.8x107 Pascal, respective
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