Availableonlineatwww.sciencedirect.com Transactions of ScienceDirect Nonferrous Metals x)e Science Society of China ELSEVIER Press Trans. Nonferrous Met. Soc. China 19(2009)61-64 www.tnmsc.cn Oxidation behavior of oxidation protective coatings for C/C-SiC composites at 1 500 C YAN Zhi-qiao(闫志巧2, XIONG Xiang(熊翔), XIAO Peng(肖鹏) CHEN Feng(陈峰}, ZHANG Hong-bo(张红波), HUANG Bai-yun(黄伯云 1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; 2. Guangzhou Research Institute of Nonferrous Metals, Quangzhou 510650, China Received 16 January 2008; accepted 28 April 2008 Abstract: Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and Sic/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD)alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 C was compared. The results show that the C/C-sic substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of nany bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense Sic layer and porous Si-Mo layer. Dense Sic layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating. Key words: C/C-SiC composites; oxidation protective coating, slurry painting; chemical vapor deposition composites in particular(4-7. Unfortunately, the process 1 Introduction has to be carried out above 1 800 C and residual silicon may escape from the C/C-SiC substrate causing substrate Molten silicon infiltration(MSI) is a major to become loose and the mechanical strength to decrease manufacturing process of C/C-Sic composites. In this regard, pack cementation is not suitable for MSI Compared with chemical vapor infiltration(CVI) and C/C-SiC composites polymer impregnation and pyrolysis(PIP), MsI has many In this work, three-layer Si-Mo coating prepared by advantages such as lower component fabrication time to slurry painting, and SiC/Si-Mo multilayer coating reduce costs significantly[l]. It is generally thought that prepared by CVd alternated with slurry painting, were C/C-SiC composites exhibit better oxidation resistance applied on MSI C/C-SiC composites, respectively. The than C/C composites because SiC and residual Si are oxidation of substrate and two coated samples at 1 500 contained. However. our research found that the initial C was investigated oxidation temperature of C/C-SiC composites is about 100 C lower than that of C/C composites. The mass loss 2 Experiment rate below 1 000 C was much higher[2]. Consequently MSI C/C-SiC composites need oxidation protection 2.1 Specimen preparation when exposed to oxidizing environment at hig The 2.5D bulk needled carbon fiber felts(bulk density of 0.56 g/cm) from Tianniao Yixing High Currently, three primary methods are used to apply Technology Co, Ltd, China, were used as preforms. A oxidation protection coating on the surface of carbon CVd process was used to deposit pyrocarbon in the felts materials:pack cementation, chemical vapor deposition and MSI was adopted to infiltrate the porous carbon/ (CVD)and slurry method(3]. Among these methods, carbon preforms to form C/C-SiC composites. The pack cementation is widely used to form coatings on C/c details were reported in Ref[2] oject(2006CB600908)supported by the National Basic Research Program of China Corresponding author: XIONG Xiang, Tel: +86-731-8836079; E-mail: xiong228@sinac DOI:10.10l6S1003-6326(0860229-0Oxidation behavior of oxidation protective coatings for C/C-SiC composites at 1 500 ć YAN Zhi-qiao(䮿ᖫᎻ) 1, 2, XIONG Xiang(❞ 㖨) 1 , XIAO Peng(㙪 吣) 1 , CHEN Feng(䰜 ዄ) 1 , ZHANG Hong-bo(ᓴ㑶⊶) 1 , HUANG Bai-yun(咘ԃѥ) 1 1. State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China; 2. Guangzhou Research Institute of Nonferrous Metals, Quangzhou 510650, China Received 16 January 2008; accepted 28 April 2008 Abstract: Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD) alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 ć was compared. The results show that the C/C-SiC substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of many bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense SiC layer and porous Si-Mo layer. Dense SiC layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating. Key words: C/C-SiC composites; oxidation protective coating; slurry painting; chemical vapor deposition 1 Introduction Molten silicon infiltration(MSI) is a major manufacturing process of C/C-SiC composites. Compared with chemical vapor infiltration(CVI) and polymer impregnation and pyrolysis(PIP), MSI has many advantages such as lower component fabrication time to reduce costs significantly[1]. It is generally thought that C/C-SiC composites exhibit better oxidation resistance than C/C composites because SiC and residual Si are contained. However, our research found that the initial oxidation temperature of C/C-SiC composites is about 100 ć lower than that of C/C composites. The mass loss rate below 1 000 ć was much higher[2]. Consequently, MSI C/C-SiC composites need oxidation protection when exposed to oxidizing environment at high temperatures. Currently, three primary methods are used to apply oxidation protection coating on the surface of carbon materials: pack cementation, chemical vapor deposition (CVD) and slurry method[3]. Among these methods, pack cementation is widely used to form coatings on C/C composites in particular[4í7]. Unfortunately, the process has to be carried out above 1 800 ć and residual silicon may escape from the C/C-SiC substrate causing substrate to become loose and the mechanical strength to decrease. In this regard, pack cementation is not suitable for MSI C/C-SiC composites. In this work, three-layer Si-Mo coating prepared by slurry painting, and SiC/Si-Mo multilayer coating prepared by CVD alternated with slurry painting, were applied on MSI C/C-SiC composites, respectively. The oxidation of substrate and two coated samples at 1 500 ć was investigated. 2 Experimental 2.1 Specimen preparation The 2.5D bulk needled carbon fiber felts (bulk density of 0.56 g/cm3 ) from Tianniao Yixing High Technology Co., Ltd., China, were used as preforms. A CVD process was used to deposit pyrocarbon in the felts and MSI was adopted to infiltrate the porous carbon/ carbon preforms to form C/C-SiC composites. The details were reported in Ref.[2]. Foundation item: Project(2006CB600908) supported by the National Basic Research Program of China Corresponding author: XIONG Xiang; Tel: +86-731-8836079; E-mail: xiong228@sina.com DOI: 10.1016/S1003-6326(08)60229-0