J.Am. Ceran.Sor.,9[3969-972(2007) DOl:10.1l11551-29162006.01480.x c 2006 The American Ceramic Society journal Fabricating 2.5D SiC/SiC Composite Using Polycarbosilane/SiC/Al Mixture for matrix derivation Yunzhou Zhu, * T Zhengren Huang, Shaoming Dong, Ming Yuan, and Dongliang Jian Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China 2. 5D SiC/SiC col es were produced by a modified polymer fabrication of unidirectional Cr/Sic composite, and fine me- infiltration and pyrolysis process. Fine Al and Sic powders were chanical properties were achieved. In the pyrolysis process, the irst infiltrated into large inter-bundle pores. During pyrolytic ctive- filler phase will react with the nitrogen atmosphere or decomposition of the polymer, the active Al filler reacts with n products of the po When the atmosphere to form new phases of carbide or nitride The volume the volume expansion will compensate for the polymer shrink- ge to a certain extent. To our knowledge, few reports on degree. The microstructural evolution and mechanical perfor- addition of reactive fillers to ceramic fiber-reinforced ceramic mances were characterized. The result indicates that the addi atrix composites(CFCCs)are found in the literature tion of al fillers has significant influence on the mechanical The aim of the present study is to characterize the micro properties of the composites. For the composite with Al loading. tructural evolution and mechanical properties of 2.5D SiCr/Sic rtional-limit stress of 380 MPa and a maximum stress of composites by a modified PIP process, using micron SiC powder 441 MPa are achieved as inert filler and al powder as active filler to reduce the matrix shrinkage caused by the polymer pyrolysis. Al powder with low . Introduction room temperature and it can be nitridized and carburized at relatively lower temperature. P MER infiltration and pyrolysis(PIP) process has become attractive alternative to traditional chemical vapor infil- (CVI) for continuous-fiber- reinforced ceramic matrix composites, as it provides the feasibility of large-dimensional component manufacturing with complex shapes, microstruc- IL. Experimental Procedure tural control, and low-fabrication cost. The predesigned KD-I SiC fiber(from National University of Defense Technol- with ceramic matrix by repeatedly pyrolyzing the preceramic ogy, Changsha, China) with 800 filaments in each yarn was that of Nicalon SiC fiber (Nippon Carbon Co., Tokyo, Japan) However, PIP is not efficient in filling the large inter-bundle voids and completely densifying fibrous preforms. Further. Typical properties of the KD-I fiber are listed in Table I.The 2.5D SiC fiber preforms were braided by two-step processing more, the volume shrinkage of preceramic polymer is up to and supplied by Nanjing Fiberglass Research and Desi Po and ce result in microcracks and high-porosity formation in the matrix Institute(Nanjing, China). The fiber volume fraction of the preform was about 43% and thus decrease the mechanical properties of the final compo- Before the slurry infiltration process, some of the p sites. Seven to 14 PIP cycles are usually needed to decrease the were pyrocarbon(PyC) and then SiC coated. Methane(CHA) pyrolysis-left residual porosity, which is a quite time-consuming was used as C precursor under a pressure of 10 KPa with Ar as process. A considerable amount of work has been performed to dilute gas by isothermal chemical vapor infiltration (ICVD). The enhance ceramic yield and reduce matrix shrinkage durin pyrolysis process by adding micrometer- or nano-scale Sic flow rates of CHa and Ar were 20 and 100 mL/min, respectivel The thickness of Pyc coating was controlled at 400 nm. powder to the preceramic polymer solution to form a slurry for the first infiltration process of the fibrous preforms. In fact, deposition of Sic coating with H, as the dilute and carrying gas introduction of some reactive fillers to the slurry may result in increase of the bonding strength between the powder grains after the thickness of the een the fiber and the infiltrates fltration To avoid reaction bet pyrolysis, meanwhile the bonding strength between the powder Two kinds of slurries were prepared for the first grains and the pyrolyzed products can also be increased by process. One consisted of 20 wt% SiC powder and 20 wt% Al chemical reaction The addition of active boron into the powder mixed in polycarbosilane(PCS: National University of preceramic polymer has been performed by Suttor was for Defense Technology). This slurry was infiltrated into the pre- form with interphase deposited by ICvI. The other slurry for R. Naslain-contributing editor infiltration of the preform without interphase consisted of 40 wt% SiC powder. The average grain size of Sic powder(Norton FCP-15c: Saint Gobain Ceramic Materials As Lillesand. No Manuscript No. 22311. Received September 30. 2006: approved October 26, 2006. way) was 0.5 um and that of Al powder (FLQT5: Angang c schogy of Sangha. China nader e ead cirano s 04Dz1-402 Key Project of Science and Group Aluminium Powder Co, Ltd, Anshan, China)was 4 um The slurry infiltration process was first performed in a vacuum, es. Beijing, China. en a pressure of 2 MPa was applied by nitrogen gas to SIcac cn facilitate the infiltration process. After drying. the infiltratedFabricating 2.5D SiCf/SiC Composite Using Polycarbosilane/SiC/Al Mixture for Matrix Derivation Yunzhou Zhu,
,w Zhengren Huang, Shaoming Dong, Ming Yuan,
and Dongliang Jiang Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, China 2.5D SiCf/SiC composites were produced by a modified polymer infiltration and pyrolysis process. Fine Al and SiC powders were first infiltrated into large inter-bundle pores. During pyrolytic decomposition of the polymer, the active Al filler reacts with small carbon-bearing polymer fragments, and reactive nitrogen atmosphere to form new phases of carbide or nitride. The volume expansion compensates for polymer shrinkage to a certain degree. The microstructural evolution and mechanical perfor￾mances were characterized. The result indicates that the addi￾tion of Al fillers has significant influence on the mechanical properties of the composites. For the composite with Al loading, a proportional-limit stress of 380 MPa and a maximum stress of 441 MPa are achieved. I. Introduction POLYMER infiltration and pyrolysis (PIP) process has become an attractive alternative to traditional chemical vapor infil￾tration (CVI) for continuous-fiber-reinforced ceramic matrix composites, as it provides the feasibility of large-dimensional component manufacturing with complex shapes, microstruc￾tural control, and low-fabrication cost.1–3 The predesigned fibrous preforms with 2D, 2.5D, or 3D fiber texture are filled with ceramic matrix by repeatedly pyrolyzing the preceramic polymer infiltrated into the interior pores in the preforms. However, PIP is not efficient in filling the large inter-bundle voids and completely densifying fibrous preforms.4 Further￾more, the volume shrinkage of preceramic polymer is up to 60% and ceramic yield is usually lower than 70 wt%,5 which will result in microcracks and high-porosity formation in the matrix and thus decrease the mechanical properties of the final compo￾sites. Seven to 14 PIP cycles are usually needed to decrease the pyrolysis-left residual porosity,6 which is a quite time-consuming process. A considerable amount of work has been performed to enhance ceramic yield and reduce matrix shrinkage during pyrolysis process by adding micrometer- or nano-scale SiC powder to the preceramic polymer solution to form a slurry for the first infiltration process of the fibrous preforms.7,8 In fact, introduction of some reactive fillers to the slurry may result in increase of the bonding strength between the powder grains after pyrolysis, meanwhile the bonding strength between the powder grains and the pyrolyzed products can also be increased by chemical reaction.9 The addition of active boron into the preceramic polymer has been performed by Suttor et al. 5 for fabrication of unidirectional Cf/SiC composite, and fine me￾chanical properties were achieved. In the pyrolysis process, the active-filler phase will react with the nitrogen atmosphere or decomposition products of the polymer. When the specific volume of product phase is larger than that of the starting filler, the volume expansion will compensate for the polymer shrink￾age to a certain extent. To our knowledge, few reports on addition of reactive fillers to ceramic fiber-reinforced ceramic matrix composites (CFCCs) are found in the literature. The aim of the present study is to characterize the micro￾structural evolution and mechanical properties of 2.5D SiCf/SiC composites by a modified PIP process, using micron SiC powder as inert filler and Al powder as active filler to reduce the matrix shrinkage caused by the polymer pyrolysis. Al powder with low density can meet the demand of lightweight components at room temperature and it can be nitridized and carburized at relatively lower temperature. II. Experimental Procedure KD-I SiC fiber (from National University of Defense Technol￾ogy, Changsha, China) with 800 filaments in each yarn was employed. The properties of this kind of SiC fiber are similar to that of Nicalon SiC fiber (Nippon Carbon Co., Tokyo, Japan). Typical properties of the KD-I fiber are listed in Table I. The 2.5D SiC fiber preforms were braided by two-step processing and supplied by Nanjing Fiberglass Research and Design Institute (Nanjing, China). The fiber volume fraction of the preform was about 43%. Before the slurry infiltration process, some of the preforms were pyrocarbon (PyC) and then SiC coated. Methane (CH4) was used as C precursor under a pressure of 10 KPa with Ar as dilute gas by isothermal chemical vapor infiltration (ICVI). The flow rates of CH4 and Ar were 20 and 100 mL/min, respectively. The thickness of PyC coating was controlled at 400 nm. Hexamethyldisilazane (HMDS) was selected as a precursor for deposition of SiC coating with H2 as the dilute and carrying gas. To avoid reaction between the fiber and the infiltrated Al fillers, the thickness of the deposited SiC coating was about 2–3 mm. Two kinds of slurries were prepared for the first infiltration process. One consisted of 20 wt% SiC powder and 20 wt% Al powder mixed in polycarbosilane (PCS; National University of Defense Technology). This slurry was infiltrated into the pre￾form with interphase deposited by ICVI. The other slurry for infiltration of the preform without interphase consisted of 40 wt% SiC powder. The average grain size of SiC powder (Norton FCP-15c; Saint Gobain Ceramic Materials AS, Lillesand, Nor￾way) was 0.5 mm and that of Al powder (FLQT5; Angang Group Aluminium Powder Co., Ltd, Anshan, China) was 4 mm. The slurry infiltration process was first performed in a vacuum, then a pressure of 2 MPa was applied by nitrogen gas to facilitate the infiltration process. After drying, the infiltrated R. Naslain—contributing editor This study was financially supported by 973 program and the Key Project of Science and Technology of Shanghai, China, under Grant no. 04DZ14002.
School of Graduate, Chinese Academy of Sciences, Beijing, China. w Author to whom correspondence should be addressed. e-mail: yunzhouzhu@mail. sic.ac.cn Manuscript No. 22311. Received September 30, 2006; approved October 26, 2006. Journal J. Am. Ceram. Soc., 90 [3] 969–972 (2007) DOI: 10.1111/j.1551-2916.2006.01480.x r 2006 The American Ceramic Society 969