F. Qian-Gang et al /Ceramics Intemational 36(2010)1463-1466 65 b Fig. 4. SEM images of the cross-section of the samples with SiC coatings prepared by PRS(a) and HPRS (b) and the coating materials are existent at the edges of the holes in oxidation resistance, and the mass loss of the C/C sample 'C composites near the coating. At the processing tempera- with this coating is only 1. 84 wt. after 15-time thermal ture, the silicon powders in the original pack mixtures melted cycles. The Sic coating obtained by HPRS has a dense and and possessed strong infiltration ability. The liquid Si would crack-free structure, so it has a better oxidation protective nfiltrate deeply to the inside of the C/C composites through the ability for C/C composites holes and cracks in these composites and react with C/C, which The flexural property parameters of C/C and coated C/C is advantageous to the bonding between coating and C/c composites are shown in Table 1. The flexural strength of C/C, PRS-SiC coated C/C and HPRS-SiC coated C/C are 89+7 Fig 5 shows the percent mass losses of the samples Bare Dare C/C composites, the Sic coated C/C composites have hermal cycling between 1773 K and room temperature. C/C composite specimen has a poor oxidation resistance, and higher strength and modulus for the reason that SiC coating can its mass loss percentage is up to 70 wt. after thermal cycling eliminate some defects in C/C composites near their surface for only 10 times. With a SiC coating prepared by PRS, the These defects consist of microcracks resulted from the sample loses mass for about 17.6 wt. after 15-time thermal machining of C/C and holes left in C/C substrate during their cycles. Compared with the SiC coating by PRS, the SiC coating preparation. More defects will be eliminated by the stronger prepared by HPRS exhibits a better thermal shock and infiltration ability of Si under pressure. So, the sample with a HPRS-SiC coating exhibits higher mechanical property than that with a PRS-SiC coating Fig. 6 shows the load-displacement curves of the samples. It can be seen that the bare C/C sample exhibited a bit pseudo- C+PRS-SIC C+HPRS-SiC plastic fracture behavior. With a PRS-SiC coating, the toughness of the sample was reduced evidently. While the HPRS-SiC coated sample experienced a bit of brittle fracture Fig. 7 shows the fracture surface of the samples after flexural tests. From Fig. 7(a), carbon fibers were pulled out from C/C+HPRS-SiC 0246810121416 Thermal shock time/time →CC+ PRS SIC Fig. 5. Percent mass losses of samples during thermal cycling between 1773 K Table Flexural properties of the as-tested samples. Strength/MPa Modulus/GPa 89±7 11±1 C/C + PRS-Sic 105±10 12±1 Displacement/mm C/C+ HPRS-SiC 140±12 27士3 Fig. 6. The load-displacement curves of the samplesand the coating materials are existent at the edges of the holes in C/C composites near the coating. At the processing tempera￾ture, the silicon powders in the original pack mixtures melted and possessed strong infiltration ability. The liquid Si would infiltrate deeply to the inside of the C/C composites through the holes and cracks in these composites and react with C/C, which is advantageous to the bonding between coating and C/C composites. Fig. 5 shows the percent mass losses of the samples during thermal cycling between 1773 K and room temperature. Bare C/C composite specimen has a poor oxidation resistance, and its mass loss percentage is up to 70 wt.% after thermal cycling for only 10 times. With a SiC coating prepared by PRS, the sample loses mass for about 17.6 wt.% after 15-time thermal cycles. Compared with the SiC coating by PRS, the SiC coating prepared by HPRS exhibits a better thermal shock and oxidation resistance, and the mass loss of the C/C sample with this coating is only 1.84 wt.% after 15-time thermal cycles. The SiC coating obtained by HPRS has a dense and crack-free structure, so it has a better oxidation protective ability for C/C composites. The flexural property parameters of C/C and coated C/C composites are shown in Table 1. The flexural strength of C/C, PRS-SiC coated C/C and HPRS-SiC coated C/C are 89 7, 105 10 and 140 12 MPa, respectively. Compared to the bare C/C composites, the SiC coated C/C composites have higher strength and modulus for the reason that SiC coating can eliminate some defects in C/C composites near their surface. These defects consist of microcracks resulted from the machining of C/C and holes left in C/C substrate during their preparation. More defects will be eliminated by the stronger infiltration ability of Si under pressure. So, the sample with a HPRS-SiC coating exhibits higher mechanical property than that with a PRS-SiC coating. Fig. 6 shows the load-displacement curves of the samples. It can be seen that the bare C/C sample exhibited a bit pseudo￾plastic fracture behavior. With a PRS-SiC coating, the toughness of the sample was reduced evidently. While the HPRS-SiC coated sample experienced a bit of brittle fracture mode. Fig. 7 shows the fracture surface of the samples after flexural tests. From Fig. 7(a), carbon fibers were pulled out from Table 1 Flexural properties of the as-tested samples. Samples Strength/MPa Modulus/GPa C/C 89 7 11 1 C/C + PRS-SiC 105 10 12 1 C/C + HPRS-SiC 140 12 27 3 Fig. 4. SEM images of the cross-section of the samples with SiC coatings prepared by PRS (a) and HPRS (b). Fig. 5. Percent mass losses of samples during thermal cycling between 1773 K and room temperature. Fig. 6. The load-displacement curves of the samples. F. Qian-Gang et al. / Ceramics International 36 (2010) 1463–1466 1465