G. Brauer et al. /Applied Surface Science 252(2006)3342-3351 electron microscopy (TEM)) and sintering additives XRD clearly shows the existence of the 3C-SiC (Al2O3+Y2O3=12 wt %(Al2O3: Y2O3=60: 40)and polytype, and no indication of another Sic polytype is SiO2=3 wt %);(2) preparation of a matrix slurry observed. The cubic polytype has the highest 3C-SiC nano-powder and sintering additives in symmetry and, therefore, shows the lowest number ethylene solution);(3)infiltration of matrix slurry of diffraction lines. All lower symmetric SiC into the fabrics(fibre: 500 nm near-stoichiometric polytypes give diffraction lines near to and between SiC continuous Tyranno-SA Grade-3, Ube Indus- the positions of the 3C-SiC diffraction lines. However, tries Ltd, Ube, Japan, covered with pyrolytic carbon; no intensity is found at the""between position",e.g.at architecture: unidirectional cross-plies; fibre volume =342°,38.2°,658°and73.6°for6H-SiC.The fraction: 40%):(4) sintering(1.780C, Ar atmo- diameter of the Sic crystallites is M60 nm,as sphere, 20 MPA pressure, I h) calculated from the line width after deconvolution of the measured data with the instrumental resolution This indicates the size of regions showing coherent 3. Results and discussion scattering. As this value is about twice the diameter of the nano-particles availed for sintering, this is another 3.1. X-ray diffraction indication of the perfectness of the sintered body. In particular, no real grain boundaries are indicated but A standard phase analysis was performed by XRD just a disturbance of translational symmetry in one in Bragg-Brentano geometry using a D8-Advance crystal direction(here, the surface normal of the instrument(Bruker AXS). Fig. I shows the diffraction 10 mm x 10 mm sample face), whereas the other pattern measured with Cu Ko radiation crystal directions may keep translational symmetry (=0.154 nm). The positions of the diffraction lines Furthermore, only the most intense graphite line according to the powder diffraction database(PDF (002)was measured because other lines have a more with (hk)=(111),(200),(220),(31 1)and than one order less intensity in randomly oriented (222)are indicated for 3C-SiC(PDF 29-1129)and graphite: the intensity of the next intense( 0 1) line is graphite with (hk D=(002)(PDF 41-1487). Non- only 6% of the intensity of the(00 2) line indicated lines are formed by the sintering additive YAlO3(PDF 38-0222) 3. 2. Atomic force microscopy surface morphology of the SiC/SiC sample was nvestigated by AFM using a closed-loop scanner, -.-SiC sintered which allows high precision measurements on the nanometer scale. All measurements were recorded under ambient conditions in Tapping Mode[14, 15 品 typical tip radius smaller than 10 nm and an opening angle of less than 20 were applied. The scanner's large measurement range of 15 um in the vertical direction was in particular beneficial for this investigation since the sample exhibits-due to the manufacturing process-a gnificant root mean square(RMs) roughness of RMS N 300 nm and maximum height differences of Scattering angle2e(°) about 1.5 um on a 10 um x 10 um image The AFM results are summarized in Fig. 2 showing Fig. 1. Normalized scattering intensity from XRD of the SiC/Sic composite sample as a function of scattering angle 20 measured with representative images ranging from 10 um x 10 um Cu Ka radiation (=0.154 nm). The (1 11).(200),(220).(310 to I um x I um scan size. The large area scan and (222) peaks of 3C-SiC as well as the(002) peak of graphite (Fig. 2a) leaves the overall impression that the surface haracterized by two main morphological featureselectron microscopy (TEM)) and sintering additives (Al2O3 + Y2O3 = 12 wt.% (Al2O3:Y2O3 = 60:40) and SiO2 = 3 wt.%); (2) preparation of a matrix slurry (3C–SiC nano-powder and sintering additives in ethylene solution); (3) infiltration of matrix slurry into the fabrics (fibre: 500 nm near-stoichiometric SiC continuous TyrannoTM-SA Grade-3, Ube Indus￾tries Ltd., Ube, Japan, covered with pyrolytic carbon; architecture: unidirectional cross-plies; fibre volume fraction: 40%); (4) sintering (1.780 8C, Ar atmo￾sphere, 20 MPA pressure, 1 h). 3. Results and discussion 3.1. X-ray diffraction A standard phase analysis was performed by XRD in Bragg-Brentano geometry using a D8-Advance instrument (Bruker AXS). Fig. 1 shows the diffraction pattern measured with Cu Ka radiation (l = 0.154 nm). The positions of the diffraction lines according to the powder diffraction database (PDF) with (hkl) = (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) are indicated for 3C–SiC (PDF 29-1129) and graphite with (hkl) = (0 0 2) (PDF 41-1487). Non￾indicated lines are formed by the sintering additive YAlO3 (PDF 38-0222). XRD clearly shows the existence of the 3C–SiC polytype, and no indication of another SiC polytype is observed. The cubic polytype has the highest symmetry and, therefore, shows the lowest number of diffraction lines. All lower symmetric SiC polytypes give diffraction lines near to and between the positions of the 3C–SiC diffraction lines. However, no intensity is found at the ‘‘between position’’, e.g. at 2u = 34.28, 38.28, 65.88 and 73.68 for 6H–SiC. The diameter of the SiC crystallites is 60 nm, as calculated from the line width after deconvolution of the measured data with the instrumental resolution. This indicates the size of regions showing coherent scattering. As this value is about twice the diameter of the nano-particles availed for sintering, this is another indication of the perfectness of the sintered body. In particular, no real grain boundaries are indicated but just a disturbance of translational symmetry in one crystal direction (here, the surface normal of the 10 mm
10 mm sample face), whereas the other crystal directions may keep translational symmetry. Furthermore, only the most intense graphite line (0 0 2) was measured because other lines have a more than one order less intensity in randomly oriented graphite: the intensity of the next intense (1 0 1) line is only 6% of the intensity of the (0 0 2) line. 3.2. Atomic force microscopy The surface morphology of the SiC/SiC sample was investigated by AFM using a closed-loop scanner, which allows high precision measurements on the nanometer scale. All measurements were recorded under ambient conditions in ‘Tapping Mode’ [14,15]. Silicon-tips with a typical tip radius smaller than 10 nm and an opening angle of less than 208 were applied. The scanner’s large measurement range of 15 mm in the vertical direction was in particular beneficial for this investigation since the sample exhibits – due to the manufacturing process – a significant root mean square (RMS) roughness of RMS 300 nm and maximum height differences of about 1.5 mm on a 10 mm
10 mm image. The AFM results are summarized in Fig. 2 showing representative images ranging from 10 mm
10 mm to 1 mm
1 mm scan size. The large area scan (Fig. 2a) leaves the overall impression that the surface is characterized by two main morphological features: 3344 G. Brauer et al. / Applied Surface Science 252 (2006) 3342–3351 Fig. 1. Normalized scattering intensity from XRD of the SiC/SiC composite sample as a function of scattering angle 2u measured with Cu Ka radiation (l = 0.154 nm). The (1 1 1), (2 0 0), (2 2 0), (3 1 1) and (2 2 2) peaks of 3C–SiC as well as the (0 0 2) peak of graphite are indicated.