Availableonlineatwww.sciencedirect.com Part A: applied science and manufacturing ELSEVIER Composites: Part A 37(2006)1396-1401 Corrosion of SiC/SiC composite in Na SO4 vapor environments from1000to1500°C Shoujun Wu, Aifei Cheng, Litong Zhang, Yongdong Xu, Xingang Luan, Hui mei National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, 547 Mailbox, Xian, Shaanxi 710072, People's Republic of china Received 21 December 2004: received in revised form 9 May 2005: accepted 9 July 2005 Abstract Corrosion of a three-dimensional SiC/SiC composite with a Cvd SiC coating was investigated in environments containing Na sO vapor, oxygen and water vapor at temperatures from 1000 to 1500C. The corrosion behavior was greatly related to temperature Below 1200C, the composite exhibited excellent resistance to corrosion, and then the residual flexural strength nearly kept the same value as the as-received strength. From 1200 to 1300C, the interaction of oxidation and corrosion led to a rapid weight gain. Above 1300C, weight loss due to volatilization and sublimation of si(oH)4 and Na,o. xSio on the surface increased continuously. At the same time, the gas release resulted in the formation of bubbles/corrosion pits and the maximum diameters of them increased with an increasing temperature Additionally, above 1200C, with an increasing temperature, the residual fexural strength of the composite decreased greatly 2005 Elsevier Ltd. All rights reserved Keywords: A. 3D SiC/SiC composite; B Corrosion; A Na2SO4 1. Introduction studied. However. the corrosion behaviors of SiC/SiC composite in environments contain- ites(SiC/SiC) are considered as the most promising ther- 1200C, have not been reported up to now. por above Silicon carbide fiber-reinforced silicon carbide compos- ing Na2SO4 vapor, oxygen and water vapor above mal structural materials due to their high toughness, The present investigation deals with the corrosion of a good resistance to thermal shock, good mechanical proper- 3D SiC/SiC composite with a CVD SiC coating in environ- ties at high temperature, especially improved iaw tolerance ments containing Na2 SO4 vapor, oxygen and water vapor and noncatastrophic mode of failure [1-3]. Besides oxida- at a range of temperature from 1000 to 1500C. Much of tion resistance, corrosion resistance is another important the analysis and discussion will then focus on the corrosion property of the composites that should be taken into con- mechanism of the composite assessed by the weight change sideration for long-time service, such as components for kinetics, residual flexural strength change and th e micro- high thrust/weight jet engines because the combustion gas structural analysis contains salts [4, 5]. The oxidation behavior of Sic-based composites in oxidizing environments containing water va- 2. Materials and experimental procedure por [6-8] and the corrosion behavior in Na2 SO4 [9]atmo- 2.1. Specimens preparation Corresponding author. Tel +86 29 8849 4616: fax: +86 29 8849 4620 Hi-Nicalon silicon carbide fiber from Japan Nippon E-inailaddress:shoujun_wu(@163.com(S.Wu) Carbon was employed. The fiber preformed was prepared 1359-835X/S- see front matter c 2005 Elsevier Ltd. All rights reservedCorrosion of SiC/SiC composite in Na2SO4 vapor environments from 1000 to 1500 C Shoujun Wu *, Laifei Cheng, Litong Zhang, Yongdong Xu, Xingang Luan, Hui Mei National Key Laboratory of Thermostructure Composite Materials, Northwestern Polytechnical University, 547 Mailbox, Xi’an, Shaanxi 710072, People’s Republic of China Received 21 December 2004; received in revised form 9 May 2005; accepted 9 July 2005 Abstract Corrosion of a three-dimensional SiC/SiC composite with a CVD SiC coating was investigated in environments containing Na2SO4 vapor, oxygen and water vapor at temperatures from 1000 to 1500 C. The corrosion behavior was greatly related to temperature. Below 1200 C, the composite exhibited excellent resistance to corrosion, and then the residual flexural strength nearly kept the same value as the as-received strength. From 1200 to 1300 C, the interaction of oxidation and corrosion led to a rapid weight gain. Above 1300 C, weight loss due to volatilization and sublimation of Si(OH)4 and Na2O Æ xSiO2 on the surface increased continuously. At the same time, the gas release resulted in the formation of bubbles/corrosion pits and the maximum diameters of them increased with an increasing temperature. Additionally, above 1200 C, with an increasing temperature, the residual flexural strength of the composite decreased greatly. 2005 Elsevier Ltd. All rights reserved. Keywords: A. 3D SiC/SiC composite; B. Corrosion; A. Na2SO4 1. Introduction Silicon carbide fiber-reinforced silicon carbide compos￾ites (SiC/SiC) are considered as the most promising ther￾mal structural materials due to their high toughness, good resistance to thermal shock, good mechanical proper￾ties at high temperature, especially improved flaw tolerance and noncatastrophic mode of failure [1–3]. Besides oxida￾tion resistance, corrosion resistance is another important property of the composites that should be taken into con￾sideration for long-time service, such as components for high thrust/weight jet engines because the combustion gas contains salts [4,5]. The oxidation behavior of SiC-based composites in oxidizing environments containing water va￾por [6–8] and the corrosion behavior in Na2SO4 [9] atmo￾sphere have been studied. However, the corrosion behaviors of SiC/SiC composite in environments contain￾ing Na2SO4 vapor, oxygen and water vapor above 1200 C, have not been reported up to now. The present investigation deals with the corrosion of a 3D SiC/SiC composite with a CVD SiC coating in environ￾ments containing Na2SO4 vapor, oxygen and water vapor at a range of temperature from 1000 to 1500 C. Much of the analysis and discussion will then focus on the corrosion mechanism of the composite assessed by the weight change kinetics, residual flexural strength change and the micro￾structural analysis. 2. Materials and experimental procedure 2.1. Specimens preparation Hi-Nicalone silicon carbide fiber from Japan Nippon Carbon was employed. The fiber preformed was prepared 1359-835X/$ - see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compositesa.2005.07.010 * Corresponding author. Tel.: +86 29 8849 4616; fax: +86 29 8849 4620. E-mail address: shoujun_wu@163.com (S. Wu). www.elsevier.com/locate/compositesa Composites: Part A 37 (2006) 1396–1401