J Mater Sci(2007)42:763-771 a) fibre interface fibre Fig. 10 EDS analysis showing the composition of SiC/BMAS omposite interface after heat treatments at 700C and 1, 200C (NF: EDS analysis from near fibre, MID: Middle of interface. Fig9 TEM image of the sample heated (a)at 1, 100C and(b) AF: Away from fibre, U: Unidentified phase) semi-quantitative analysis. These results may give a oted by other workers [3, 20-23 and estimated general idea about the composition at the interface. theoretically [24]. Temperature changes during service Those clearly show that after the 700C heat treat- of a component can result in structural changes such as ment the carbon present at the interface is removed development of porosity or the formation of other leaving a silicon-rich layer whereas after the 1,200oC phases at the interface. The diffusivity sample thick heat treatment the carbon layer is not only still present ness was 2 mm so since the ply thickness was -0.2 mm but is even enhanced. Near the fibre and near the some interfaces were always normal to heat flow so any matrix are two regions which are carbon rich. Inter- gap at the interface would be expected to affect the estingly Ti, which can only have originated in the fibre thermal diffusivity of the composite. Significant effects is present in all the EDS spectra even that remote fre were observed particularly in the temperature range the fibre interface. The presence of Si, O, Mg, Al 700-900C. The diffusivity measurements were sup- Ti is attributed to diffusion of the matrix elements to ported by SEM and TEM studies. During the process- the interface. This has good agreement with previous ing of Sic fibre-reinforced composites in a glass findings [13, 14]. ceramic matrix a carbon layer is formed at the fibre/ matrix interface either by the reaction first mentioned orDer and Chyung [4(Eq. 1) Discussion SiC+O2→SiO2+C Clearly the fibre/matrix interface plays an important or that also suggested by Cooper and Chyung [4] role in the thermal properties of the composites. A Bemson et al. 5] and Le Strat et al. [ 27(Eq 2) discontinuity between fibres and matrix can result in decrease in thermal diffusivity, a feature that has been SiC 200- SiO2+ 3Csemi-quantitative analysis. These results may give a general idea about the composition at the interface. Those clearly show that after the 700 C heat treat￾ment the carbon present at the interface is removed leaving a silicon-rich layer whereas after the 1,200 C heat treatment the carbon layer is not only still present but is even enhanced. Near the fibre and near the matrix are two regions which are carbon rich. Inter￾estingly Ti, which can only have originated in the fibre is present in all the EDS spectra even that remote from the fibre interface. The presence of Si, O, Mg, Al and Ti is attributed to diffusion of the matrix elements to the interface. This has good agreement with previous findings [13, 14]. Discussion Clearly the fibre/matrix interface plays an important role in the thermal properties of the composites. A discontinuity between fibres and matrix can result in a decrease in thermal diffusivity, a feature that has been noted by other workers [3, 20–23] and estimated theoretically [24]. Temperature changes during service of a component can result in structural changes such as development of porosity or the formation of other phases at the interface. The diffusivity sample thick￾ness was 2 mm so since the ply thickness was ~0.2 mm some interfaces were always normal to heat flow so any gap at the interface would be expected to affect the thermal diffusivity of the composite. Significant effects were observed particularly in the temperature range 700–900 C. The diffusivity measurements were sup￾ported by SEM and TEM studies. During the process￾ing of SiC fibre-reinforced composites in a glass ceramic matrix a carbon layer is formed at the fibre/ matrix interface either by the reaction first mentioned by Cooper and Chyung [4] (Eq. 1) SiC þ O2 ! SiO2 þ C ð1Þ or that also suggested by Cooper and Chyung [4], Bemson et al. [5] and Le Strat et al. [27] (Eq. 2) SiC þ 2CO ! SiO2 þ 3C ð2Þ Fig. 10 EDS analysis showing the composition of SiC/BMAS composite interface after heat treatments at 700 C and 1,200 C (NF: EDS analysis from near fibre, MID: Middle of interface, Fig. 9 TEM image of the sample heated ( AF: Away from fibre, U: Unidentified phase) a) at 1,100 C and (b) at 1,200 C 123 J Mater Sci (2007) 42:763–771 769