Dongmei Pu,Pengju Chen,Peng Xiao,Zhuan Li,Pingyi Deng,Liang Pang,Jinwei Li,Yang Li
A dense and uniform c -AlPO 4 and SiC whisker co-modified mullite coating was successfully prepared on SiC-coated C/SiC composites with a thickness of about 70 μm by hydrothermal electrophoretic deposition . The thermal cycling performance of the coating samples was evaluated by thermally cycling between 1773 K and room temperature in a corundum tube furnace. Results show that the addition of SiC whisker (SiC w -mullite coating) significantly improved the thermal cycling resistance of single mullite outer layer on account of the toughening mechanism of SiC whiskers, such as whisker bridging and crack deflection. Then, the addition of c -AlPO 4 ( c -AlPO 4 -SiC w -mullite coating, termed ASM coating) further improved the thermal cycling resistance on account of the healing and bonding performances of c -AlPO 4 at high temperature. After 40 thermal cycles, the weight loss of ASM coating on SiC-coated C/SiC composites was 4.5% compared to 5.24% for the SiC w -mullite coating. The retention rate of compressive strength of ASM coating on SiC-coated C/SiC matrix was 80.66% compared to 73.65% for the SiC w -mullite coating.
Dongmei Pu,Pengju Chen,Peng Xiao,Zhuan Li,Zeyan Liu,Yang Li
An oxidation protective c -AlPO 4 and SiC whisker co-modified mullite coating ( c -AlPO 4 -SiC w -mullite) on SiC coated C/SiC composites were manufactured by hydrothermal electrophoretic deposition accompanied by magnetic stirring. Phase composition of c -AlPO 4 -SiC w -mullite coatings on SiC coated C/SiC composites with different deposition time was detected by X-ray Diffraction (XRD), element distribution and microstructure were investigated by electron probe microanalysis (EPMA) and scanning electron microscopy (SEM). Results show that a crack-free, dense and homogeneous coating was prepared by hydrothermal electrophoretic deposition method. The thickness, homogeneity and antioxidant properties of c -AlPO 4 -SiC w -mullite coating were improved with the extension of deposition time from 10 min to 30 min. The coating manufactured after deposition of 30 min showed smoothest surface and highest density, which can effectively protect C/SiC composites from oxidation for 160 h at 1773 K in air with a weight loss of 10.02 mg cm −2 . Microstructural characterization after oxidation indicated that the failure of the c -AlPO 4 -SiC w -mullite coating was due to the consecutive formation of penetrative micro-cracks and micro-holes.
Pengju Chen,Peng Xiao,Zhuan Li,Zeyan Liu,Dongmei Pu,Yang Li
A novel cristobalite aluminum phosphate particle ( c -AlPO 4 ) modified SiC whisker toughened mullite coating ( c -AlPO 4 -SiC w -mullite) was prepared on SiC coated carbon fiber reinforced SiC composites (C/SiC) by a new sol-gel method combined with air spraying to improve the oxidation resistance of SiC w -mullite coating. Results show that c -AlPO 4 -SiC w -mullite coatings with 10 and 20 wt.% of c -AlPO 4 exhibited obviously improved oxidation resistance at 1773 K in ambient air for 100 h than SiC w -mullite coating. Moreover, the oxidation resistance of c -AlPO 4 -SiC w -mullite coatings were rapidly declined when the c -AlPO 4 in c -AlPO 4 -SiC w -mullite coating were set to 30 and 40 wt.%. The c -AlPO 4 -SiC w -mullite coating with 20 wt.% of c -AlPO 4 showed most pronounced oxidation resistance, the weight loss rate after the oxidation in ambient air for 210 h was merely 3.00 × 10 −5 g·cm −2 h −1 . The failure of c -AlPO 4 -SiC w -mullite coating with 20 wt.% of c -AlPO 4 was due to the generation of penetrative micro-cracks and micro-holes in the coating, which cannot be self-healed by the silicate glass layer after long time oxidation at 1773 K.
Pengju Chen,Peng Xiao,Zhuan Li,Ling Pan,Jinwei Li,Zeyan Liu,Dongmei Pu,Yang Li
Mullite coating, SiC whiskers toughened mullite coating (SiC w -mullite), and cristobalite aluminum phosphate ( c -AlPO 4 ) particle modified SiC w -mullite coating ( c -AlPO 4 -SiC w -mullite) were prepared on SiC coated C/SiC composites using a novel sol-gel method combined with air spraying. Results show that molten SiO 2 formed by the oxidation of SiC whiskers and molten c -AlPO 4 improved the bonding strength between mullite outer coating and SiC–C/SiC composites due to their high-temperature bonding properties. The bonding strength between mullite, SiC w -mullite, c -AlPO 4 -SiC w -mullite outer coatings and SiC–C/SiC composites were 2.41, 4.31, and 7.38 MPa, respectively. After 48 thermal cycles between 1773 K and room temperature, the weight loss of mullite/SiC coating coated C/SiC composites was up to 11.61%, while the weight losses of SiC w -mullite/SiC and c -AlPO 4 -SiC w -mullite/SiC coatings coated C/SiC composites were reduced to 7.40% and 5.12%, respectively. The addition of appropriate SiC whiskers can considerably improve the thermal shock resistance of mullite coating owing to their excellent mechanical properties at high temperature. In addition, c -AlPO 4 particles can further improve the thermal shock resistance of SiC w -mullite coating due to their high-temperature bonding and sealing properties. No obvious micro-pores and cracks were observed on the surface of c -AlPO 4 -SiC w -mullite coating after 48 thermal cycles due to timely healing effect by formation of secondary mullite.
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