H. Li et al. /Ceramics International 35 (2009) 2277-2282 2. Experimental procedure CH4, and H2 were used as precursors. The deposition temperature was controlled in the 1300-1400C range [15]. 2.1. Fabrication of 2D C/LrC-SiC composites For the preparation of the other two kinds of coating structures, the same heat-treatment on the composites at 1400C The whole process for sample preparation is shown in Fig. 1. for 2 h was firstly conducted. A SiC powder(1I um, Beijing T-300 carbon fiber (Toray, Japan) was employed to fabricate Mountain Technical Development Center, China) layer was then fiber preforms. The preform with fiber content of 40 vol% was pasted on the composite, followed by depositing a ZrC coating shaped by lamination of 2D-carbon cloth. A thin pyrolytic (#2). In this process, CVD ZrC will penetrate in the gaps between carbon layer was deposited on surface of the carbon fiber as the Sic powders and form a mixture of Sic-ZrC coating with a layer interfacial layer by chemical vapor infiltration(CVD) with C3H6 of dense ZrC on the top. Likewise, ZrB2 powder(1 um, Beijing at 960C. The sample was then pretreated for graphitization at Mountain Technical Development Center, China)was pasted on 1800C for 2 h. The C/Sic composite was prepared by the composite followed by depositing a Sic layer on its top(#3) chemical vapor infiltration of SiC at 1000C of the prepared reform Methyltrichlorosilane (MTS, CH SiCl3)was used for 2.3. Oxidation tests the Sic precursor. After CVI, the composites were machined and polished to obtain 40 mm x 20 mm x 3.5 mm substrates The oxidation tests were carried out in a Ch, combustion wind The liquid highly branched polycarbosilane with allyl tunnel(Fig. 2). The wind tunnel possesses a controlled groups was synthesized in the Advanced Materials Laboratory environment chamber [16] providing various kinds and con- at Xiamen University [13, 14]. 20 wt% ZrC powder with an centrations of oxidizing gas. For each kind of coating structure, average grain size of I um(Beijing Mountain Technical the oxidation test was repeated at least three times. During the test, Development Center, China)was mixed into HBPCS by the specimen was vertically exposed to the flame for 30 min A magnetic stirring. The slurry was vacuum infiltrated into the mixture of O2 and CHa was charged into the combustion chamber substrates and pyrolysized at 900C for two cycles to realize and spark ignited. The gas-flow velocity was about 20 m/s. The further densification flame temperature at the center was 1800+ 30C, which was stabilized by controlling the flux of each component gas(mass 2. 2. Coating systems preparation flow controller was 58501 series of BROOKS, Japan). The calculated combustion gas composition is listed in Table 1 ZrB,/ZrC/SiC coatings were used in order to increase the oxidation resistance. The first kind of coating structure(#1)was 2.4. Measurement and characterization prepared as follows: two more cycles of polymer slurry infiltration and pyrolysis(Plp)process were conducted on the composite. Microstructures of the specimens were observed by subsequently, aheat-treatmentin flowing argon at 1400Cfor 2 h scanning electron microscope(SEM, JSM-6700F)and the a ZrC layer was deposited on the surface of this specimen by spectroscopy (EDS). X-ray diffraction (XRD) investigation chemical vapor deposition. As for the CVD ZrC process, ZrCL, were carried out by using a Rigaku D/max-2400 diffractompe. n (Tokyo, Japan) with copper Ko radiation Data were digitally recorded in a continuous scan in the range of angle(20) from Carbon fiber preform PyC 15°to75° with a scanning rate of0.087s CVI+PIP 3. Results and discussion C/ZrC-SiC composite 3.1. Microstructure of the 2D C/LrC-SiC composite Fig 3 shows the cross-sections of as-produced C/ZrC-Sic Machined and treated omposite. Between fibers and the Zrc-Sic matrix, SiC matrix Coating preparation CVD Zrc SiC particle ZrB2 particle +CVD Zrc +CVD SiC #1 I. holder 2. norzle 3 chamber 4. oil pip 5. entrance 6. spary 7. igniter 8, substrates different coating structures. Fig. 2. Schematic of the combustion wind tunnel2. Experimental procedure 2.1. Fabrication of 2D C/ZrC–SiC composites The whole process for sample preparation is shown in Fig. 1. T-300TM carbon fiber (Toray, Japan) was employed to fabricate fiber preforms. The preform with fiber content of 40 vol% was shaped by lamination of 2D-carbon cloth. A thin pyrolytic carbon layer was deposited on surface of the carbon fiber as the interfacial layer by chemical vapor infiltration (CVI) with C3H6 at 960 8C. The sample was then pretreated for graphitization at 1800 8C for 2 h. The C/SiC composite was prepared by chemical vapor infiltration of SiC at 1000 8C of the prepared preform. Methyltrichlorosilane (MTS, CH3SiCl3) was used for the SiC precursor. After CVI, the composites were machined and polished to obtain 40 mm 20 mm 3.5 mm substrates. The liquid highly branched polycarbosilane with allyl groups was synthesized in the Advanced Materials Laboratory at Xiamen University [13,14]. 20 wt% ZrC powder with an average grain size of 1 mm (Beijing Mountain Technical Development Center, China) was mixed into HBPCS by magnetic stirring. The slurry was vacuum infiltrated into the substrates and pyrolysized at 900 8C for two cycles to realize further densification. 2.2. Coating systems preparation ZrB2/ZrC/SiC coatings were used in order to increase the oxidation resistance. The first kind of coating structure (#1) was preparedasfollows: two morecycles ofpolymer slurryinfiltration and pyrolysis (PIP) process were conducted on the composite. Subsequently, a heat-treatmentinflowing argon at 1400 8C for 2 h was carried out in order to stabilize the composite matrix. Finally, a ZrC layer was deposited on the surface of this specimen by chemical vapor deposition. As for the CVD ZrC process, ZrCl4, CH4, and H2 were used as precursors. The deposition temperature was controlled in the 1300–1400 8C range [15]. For the preparation of the other two kinds of coating structures, the same heat-treatment on the composites at 1400 8C for 2 h was firstly conducted. A SiC powder (1 mm, Beijing Mountain Technical Development Center, China) layer was then pasted on the composite, followed by depositing a ZrC coating (#2). In this process, CVD ZrC will penetrate in the gaps between SiC powders and form a mixture of SiC–ZrC coating with a layer of dense ZrC on the top. Likewise, ZrB2 powder (1 mm, Beijing Mountain Technical Development Center, China) was pasted on the composite followed by depositing a SiC layer on its top (#3). 2.3. Oxidation tests The oxidation tests were carried out in a CH4 combustion wind tunnel (Fig. 2). The wind tunnel possesses a controlled environment chamber [16] providing various kinds and con￾centrations of oxidizing gas. For each kind of coating structure, the oxidation test was repeated at least three times. During the test, the specimen was vertically exposed to the flame for 30 min. A mixture of O2 and CH4 was charged into the combustion chamber and spark ignited. The gas-flow velocity was about 20 m/s. The flame temperature at the center was 1800 30 8C, which was stabilized by controlling the flux of each component gas (mass flow controller was 5850i series of BROOKS, Japan). The calculated combustion gas composition is listed in Table 1. 2.4. Measurement and characterization Microstructures of the specimens were observed by scanning electron microscope (SEM, JSM-6700F) and the elemental analysis was conducted by energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) investigations were carried out by using a Rigaku D/max-2400 diffractometer (Tokyo, Japan) with copper Ka radiation. Data were digitally recorded in a continuous scan in the range of angle (2u) from 158 to 758 with a scanning rate of 0.088/s. 3. Results and discussion 3.1. Microstructure of the 2D C/ZrC–SiC composite Fig. 3 shows the cross-sections of as-produced C/ZrC–SiC composite. Between fibers and the ZrC–SiC matrix, SiC matrix Fig. 1. Experimental procedure for preparation of C/ZrC–SiC composites with different coating structures. Fig. 2. Schematic of the combustion wind tunnel. 2278 H. Li et al. / Ceramics International 35 (2009) 2277–2282