Effects of Al2O3 coating induced structural and mechanical changes of C/C composites

• Published in: Journal of alloys and compounds Vol. 818; p. 152847
• Main Authors: Jia, Jiangang, Zhang, Bo, Liu, Diqiang, Liu, Shunwei, Ji, Genshun, Ji, Ruifang
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 25.03.2020; Elsevier BV
• Subjects: Al2O3; Aluminum oxide; C/C composites; Carbon fibers; Chemical vapor infiltration; Coating; Composite materials; Fiber preforms; Flexural strength; Fracture toughness; Heat treating; Heat treatment; High temperature effects; Interface coating layer; Matrix texture; Mechanical properties; Organic chemistry; Texture; Interface coating layer; Matrix texture; C/C composites; Al2O3; Fracture toughness
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2019.152847

Different C/C composites, identified as Cf/C, CAl2O3/C, C1600/C and C1600-Al2O3/C, were fabricated by condensation of different treated 3D needle-punched carbon fiber preforms through a thermal gradient chemical vapor infiltration (TG-CVI) method. Effects of high temperature treatment and Al2O3 coating of the carbon fiber preforms on matrix texture and mechanical properties of C/C composites were investigated. SL PyC is obtained for Cf/C and C1600/C, which preforms are without Al2O3 coating. Whereas the texture of carbon matrix for CAl2O3/C, and C1600-Al2O3/C changes to RL under the same deposition conditions, indicating that Al2O3 coating layer significantly affects the texture of carbon matrix. Heat treatment of the carbon fiber preforms at 1600 °C for 4 h obviously increase the toughness of the C/C composites. The fracture toughness increased by 226% from 0.938 MPa/m2 for Cf/C to 3.061 MPa/m2 for C1600-Al2O3/C. The significant toughness increasing is attributed to the unique fracture mode for C1600-Al2O3/C, where a hollow “cylindrical” PyC matrix is pulled out and a corresponding big hole is left with a central fiber in it. The flexural strength, however, is mainly affected by the final density of the C/C composites. •Al2O3 coating on fiber surface of the preforms greatly influence the deposition mechanisms and the texture of carbon matrix.•SL is obtained for uncoated preforms whereas RL PyC is developed for the Al2O3 coated preforms.•High temperature treatment combined with Al2O3 coating of the preforms significantly increases the toughness of the C/C composites.